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ADDING SHORT SPRINTS TO EXERCISE AT FATMAX:

IMPLICATIONS FOR ACUTE ENERGY BALANCE AND

ENJOYMENT IN OVERFAT BOYS

Nicole Annette Crisp

Bachelor of Science (Honours)

This thesis is presented for the degree of Doctor of Philosophy at

The University of Western Australia

School of Sport Science, Exercise and Health

2012

This thesis is dedicated to Aaron Paul Crisp (06.12.1988 – 04.05.2011)

Fly he did, above the limitless sky...

Little brother, you are always in my heart.

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EXECUTIVE SUMMARY

It is well established that exercise plays an important role in the prevention and

management of obesity in children, but the optimal type of exercise to achieve this is

not known. Recent research suggests that training at a specific low-moderate exercise

intensity that maximises fat oxidation (Fatmax) may be favourable for fat loss and easily

adhered to. However, higher intensity exercise results in increased energy expenditure

per unit of time which is more likely to invoke a negative energy balance with a lower

time investment. One of the major concerns with prescribing continuous high intensity

exercise to individuals carrying excess body fat is that they may not adhere to a long-

term training program, due to feelings of discomfort and displeasure. Interestingly,

when children are observed during spontaneous physical activity or free-play, they most

commonly engage in unstructured games or sports that require multiple short sprint

efforts of 3-4 sec in duration, interspersed with longer duration low-moderate intensity

exercise. This nature of exercise may be simulated by sprint interval exercise to provide

a means of increasing the intensity of exercise whilst keeping the exercise enjoyable, in

order to maximise the energy expenditure of paediatric-specific exercise training

protocols. The research presented in this thesis explores the acute influence of adding

short, maximal sprint efforts to continuous exercise at Fatmax on energy expenditure and

fat oxidation (during and post-exercise), post-exercise energy intake and enjoyment in

boys. A preliminary aim was to determine whether there is potential for a single graded

exercise protocol with 3-min stages to be utilised for the estimation of Fatmax in boys

carrying excess body fat (overfat).

A single graded exercise test is the most commonly utilised technique for estimating

Fatmax in adults and children, but no research has validated its use in an overfat

paediatric population. Therefore, the purpose of the first study of this thesis was to

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determine whether Fatmax remains stable across 30 min of constant load exercise (i.e.

whether the duration of exercise affects fat oxidation rates and ultimately, the Fatmax

estimate) in overfat boys. A secondary aim was to compare the Fatmax estimated from a

single graded exercise test with 3-min stages against 30-min bouts of prolonged

exercise, to determine whether the cumulative duration of a graded exercise test affects

Fatmax. Ten overfat boys aged 8-12 years completed a continuous, submaximal graded

exercise protocol with seven 3-min stages (GRAD) at 35, 40, 45, 50, 55, 60 and 65%

O2peak and five 30-min bouts of prolonged exercise (PROL) conducted on separate

days at 40, 45, 50, 55 and 60% O2peak. In response to PROL, the rate of fat oxidation

was stable across 30 min of steady-state exercise, irrespective of the exercise intensity.

Furthermore, Fatmax was similar at 3, 10, 20 and 30 min of PROL, suggesting that for

exercise lasting 30 min or less, exercise duration does not affect Fatmax in overfat boys.

However, although GRAD and PROL provided a similar estimate of Fatmax at the group

level, the Fatmax

The second study of this thesis explored whether the addition of multiple short sprint

efforts to continuous exercise at Fatmax enhanced enjoyment and energy expenditure,

without prompting increased acute post-exercise energy intake in boys. Nine overfat

boys and nine boys carrying normal levels of body fat (control) aged 8-12 years

completed 30 min of either continuous cycling at Fatmax (MOD) or sprint interval

exercise (SI) consisting of continuous cycling at Fatmax interspersed with 4-sec maximal

sprint efforts every 2 min. Energy expenditure and substrate oxidation were measured

during exercise and for 30 min post-exercise, at which time participants completed a

modified Physical Activity Enjoyment Scale (PACES). Following this, a buffet-type

breakfast was provided from which participants could consume ad libitum to measure

acute post-exercise energy intake. It was observed that the addition of short sprint

identified using GRAD may need to be interpreted with caution given

the considerable variation observed between the two protocols at the individual level.

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efforts to continuous exercise at Fatmax increased energy expenditure without

compromising fat oxidation rates or stimulating an acute increase in post-exercise

energy intake. In addition, although there was no significant difference in the PACES

between the two protocols, the boys indicated that they preferred SI and did not

perceive it to be harder than MOD.

Given the finding that overfat boys prefer participating in SI over MOD, the final study

of this thesis explored the extent to which the frequency of sprints could be increased to

maximise the amount of energy expenditure during the exercise bout, before the

enjoyment and preference for this type of sprint interval exercise started to decline.

Eleven overfat boys completed 30 min of MOD and three sprint interval protocols

consisting of continuous cycling at Fatmax interspersed with 4-sec maximal sprint efforts

every 2 min (SI120), every 1 min (SI60) and every 30 sec (SI30). Energy expenditure and

substrate oxidation were measured during exercise, after which participants completed

the PACES to assess enjoyment. This was followed by a buffet-type breakfast from

which participants could consume ad libitum to measure acute post-exercise energy

intake. It was found that overall energy expenditure progressively increased with

increasing sprint frequency, although the difference between SI60 and SI30 did not reach

significance. This was likely the result of a combination of reduced sprint quality and

the participants’ inability to maintain the required intensity between sprints when they

were performed every 30 sec. As described in Study 2, there was no acute increase in

post-exercise energy intake to compensate for the extra energy expended during the

sprint interval protocols. In fact, post-exercise energy intake was significantly less for

SI60 compared with MOD. Finally, the overfat boys preferred participating in SI60,

followed by SI120, despite perceiving the exercise to be harder than MOD. However,

their levels of enjoyment declined when too many sprints were introduced (i.e. SI30), as

indicated by the PACES.

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The findings from the research presented in this thesis have important implications for

prescribing exercise for the prevention and management of obesity in children.

Specifically, the sprint interval exercise protocols adopted in these studies (particularly

SI60) promote increased energy expenditure, when compared with moderate intensity

continuous exercise at Fatmax, without prompting an increase in acute post-exercise

energy intake or compromising enjoyment in overfat boys, provided the sprint

frequency is not too high (i.e. SI30). This increased energy expenditure without a

compensatory increase in energy intake may be more effective in contributing to the

negative energy balance required for fat loss. Furthermore, the increased preference for

SI60 and SI120 over MOD may help to promote greater adherence to regular exercise in

the long-term.

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STATEMENT OF CANDIDATE CONTRIBUTION

The work involved in designing and conducting the studies described in this thesis has

been conducted primarily by Nicole Crisp (the candidate). The thesis outline and

experimental design of the studies was developed and planned in consultation with Dr

Kym Guelfi, Dr Melissa Licari, Dr Rebecca Braham and Dr Paul Fournier (the

candidate’s supervisors). All participant recruitment and management was carried out

entirely by the candidate, along with the organisation, implementation and collection of

data for the experiments. In addition, the candidate was responsible for all data analysis,

and original drafting of the thesis and the peer-reviewed publications. Dr Kym Guelfi,

Dr Melissa Licari, Dr Rebecca Braham and Dr Paul Fournier have provided feedback

for further drafts and polishing of the thesis and manuscripts.

This thesis contains published work and work prepared for publication, some of which

has been co-authored. Permission has been granted by Dr Kym Guelfi, Dr Melissa

Licari, Dr Rebecca Braham and Dr Paul Fournier for the published work listed on page

xix to be included in this thesis.

Signed: __________________ __________________

Nicole Crisp Dr Kym Guelfi

(Candidate) (Coordinating Supervisor)

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TABLE OF CONTENTS

EXECUTIVE SUMMARY i

STATEMENT OF CANDIDATE CONTRIBUTION v

TABLE OF CONTENTS vi

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xv

ACKNOWLEDGEMENTS xvii

PUBLICATIONS ARISING FROM THIS THESIS xix

CHAPTER 1: LITERATURE REVIEW 1

1.1 THE PROBLEM OF OBESITY 1

1.2 DEFINING OBESITY 2

1.3 THE CAUSES OF OBESITY 4

1.3.1 The Role of Genetics 6

1.3.2 The Role of Energy Balance (Intake versus Expenditure) 7

1.3.2a Energy Intake 7

1.3.2b Energy Expenditure 9

1.4 CURRENT APPROACHES FOR MANAGING OBESITY IN CHILDREN 12

1.5 OPTIMISING EXERCISE FOR THE OVERWEIGHT OR OBESE CHILD 15

1.5.1 The Relationship between Exercise Intensity and Fat Oxidation 16

1.5.2 The Benefits of Exercise at Fatmax 18

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1.5.2a Methodological Issues with the Estimation of Fatmax 19

1.5.2b Estimating Fatmax in Paediatric Populations 22

1.5.3 The Benefits of High Intensity Exercise 26

1.5.4 Interval Exercise as an Alternative to Continuous High Intensity

Exercise 28

1.5.4a Sprint Interval Exercise 30

1.6 OTHER CONSIDERATIONS WHEN PRESCRIBING EXERCISE FOR OVERWEIGHT

CHILDREN 33

1.6.1 Appetite and Post-exercise Energy Intake 33

1.6.2 Enjoyment and Adherence 36

1.7 SUMMARY 40

1.7.1 Statement of the Problem 40

1.7.2 Aims 41

1.7.3 Research Hypotheses 42

1.7.4 Organisation and Structure of this Thesis 43

CHAPTER 2: STUDY 1

DOES EXERCISE DURATION AFFECT FATMAX 44 IN OVERFAT BOYS?

2.1 ABSTRACT 45

2.2 INTRODUCTION 45

2.3 METHODS 48

2.3.1 Participants 48

2.3.2 Research Design 49

2.3.3 Anthropometry and Body Composition 50

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2.3.4 Determination of Peak Aerobic Capacity 51

2.3.5 Fatmax Determination Using a 3-min Graded Exercise Test 52

2.3.6 Fatmax Determination Using 30-min Constant Load Protocols 53

2.3.7 Statistical Analysis 54

2.4 RESULTS 55

2.4.1 Effect of Exercise Duration and Intensity on Fat and

Carbohydrate Oxidation 55

2.4.2 Effect of Exercise Duration on Fatmax 55

2.4.3 Fatmax Estimated from a Single Graded Exercise Test 58

2.4.4 Heart Rate and Lactate Measurements 60

2.5 DISCUSSION 60

CHAPTER 3: STUDY 2

ADDING SPRINTS TO EXERCISE AT FATMAX

65

: IMPLICATIONS FOR ACUTE ENERGY

BALANCE AND ENJOYMENT IN BOYS

3.1 ABSTRACT 66

3.2 INTRODUCTION 67

3.3 METHODS 69



3.3.3 Baseline Measurements 71

3.3.3a Anthropometry and Body Composition 71

3.3.3b Determination of Peak Aerobic Capacity and Fatmax 71

3.3.4 Experimental Sessions 73

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3.3.4a Resting Metabolic Rate and Substrate Oxidation 73

3.3.4b Exercise Protocols 74

3.3.4c Post-exercise Recovery 75

3.3.4d Enjoyment 75

3.3.4e Post-exercise Energy Intake and Perceived Hunger and Satiety 75


3.4 RESULTS 77

3.4.1 Participant Characteristics 77

3.4.2 Protocol Characteristics 78

3.4.3 Energy Expenditure 79

3.4.4 Fat and Carbohydrate Oxidation 79

3.4.5 Enjoyment 83

3.4.6 Perceived Exertion 84

3.4.7 Perceived Hunger, Satiety and Post-exercise Energy Intake 85

3.4.8 Energy Balance 87

3.5 DISCUSSION 88

CHAPTER 4: STUDY 3

OPTIMISING SPRINT INTERVAL EXERCISE TO MAXIMISE ENERGY

EXPENDITURE AND ENJOYMENT IN OVERFAT BOYS 94

4.1 ABSTRACT 95

4.2 INTRODUCTION 96

4.3 METHODS 98

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4.3.3 Baseline Measurements 100

4.3.3a Anthropometry and Body Composition 100

4.3.3b Determination of Peak Aerobic Capacity and Fatmax 101

4.3.4 Experimental Sessions 102

4.3.4a Exercise Protocols 102

4.3.4b Perceived Hunger and Satiety, Enjoyment and Post-exercise

Energy Intake 104


4.4 RESULTS 105

4.4.1 Dietary Standardisation Prior to the Experimental Sessions 105

4.4.2 Protocol Characteristics 105

4.4.3 Energy Expenditure, and Fat and Carbohydrate Oxidation 109

4.4.4 Hunger, Satiety and Post-exercise Energy Intake 109

4.4.5 Enjoyment 113

4.4.6 Perceived Exertion 114

4.5 DISCUSSION 115

CHAPTER 5: GENERAL DISCUSSION 121

5.1 SUMMARY 121

5.2 CONCLUSIONS 125

5.3 IMPLICATIONS 126

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5.4 LIMITATIONS 127

5.5 DIRECTIONS FOR FUTURE RESEARCH 128

REFERENCES 131

CHAPTER 6: APPENDICES 152

xii

LIST OF TABLES

1.1 Studies that have estimated Fatmax in paediatric populations 24

2.1 Participant Characteristics 49

2.2 Absolute amount of energy expenditure, and fat and carbohydrate

oxidation during PROL 57


3.2 Protocol Characteristics for MOD and SI for the overfat and control

groups 78

3.3 Post-exercise VAS scores for hunger and satiety following MOD and SI 85


4.2 Protocol Characteristics for MOD, SI120, SI60 and SI30 107

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LIST OF FIGURES

1.1 Body fat maintenance is achieved when energy expenditure is balanced

with energy intake 5

1.2 (a) Positive energy balance (i.e. energy intake exceeds energy

expenditure) resulting in fat gain, and (b) negative energy balance (i.e.

energy expenditure exceeds energy intake) resulting in fat loss 13

1.3 Effect of exercise intensity on the (a) relative contribution of fat and

carbohydrate oxidation to energy expenditure, and (b) absolute rate of

fat and carbohydrate oxidation 17

1.4 Fat oxidation rate relative to exercise intensity and Fatmax estimation

using the technique developed by (a) Zakrzewski and Tolfrey (2011a)

and (b) Achten et al. (2002) 25

1.5 Excess post-exercise oxygen consumption following submaximal

exercise 27

2.1 Example scatterplot of fat oxidation rate vs. exercise intensity during a

submaximal graded exercise test with 3-min stages used to visually

estimate Fatmax 53

2.2 Mean energy expenditure and contributions of fat and carbohydrate

oxidation at 10, 20 and 30 min of the 30-min steady-state exercise

sessions at 40, 45, 50, 55 and 60% O2peak 56

2.3 Mean Fatmax at 3, 10, 20 and 30 min of the 30-min steady state exercise

bouts at 40, 45, 50, 55 and 60% O2peak 58

2.4 (a) Individual variability, and (b) Bland-Altman plot for average

difference in Fatmax, determined using GRAD and PROL 59

3.1 Example scatterplot of fat oxidation rate and lactate concentration vs.

exercise intensity during a graded exercise test with 3-min stages used

for the visual determination of Fatmax for one participant 73

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3.2 Energy expenditure before, during and after MOD and SI in the (a)

overfat and (b) control groups 80

3.3 Rate of fat oxidation before, during and after MOD and SI in the (a)

overfat and (b) control groups 81

3.4 Rate of carbohydrate oxidation before, during and after MOD and SI in

the (a) overfat and (b) control groups 82

3.5 Ratings of enjoyment using the PACES in the overfat and control

groups for 30 min MOD and SI 83

3.6 Ratings of perceived exertion for the overfat and control groups at 10,

20 and 30 min of MOD and SI 84

3.7 Post-exercise energy intake in the overfat and control groups following

MOD and SI 86

3.8 Energy balance (intake - expenditure) in the overfat and control groups

for MOD and SI 87

4.1 Contributions of carbohydrate, fat and protein to total energy intake (kJ)

in the 24 hours prior MOD, SI120, SI60 and SI30 106

4.2 Cyclemax data for (a) mean power and (b) peak power during MOD,

SI120, SI60 and SI30 108

4.3 Contributions of fat and carbohydrate oxidation to total energy

expenditure for MOD, SI120, SI60 and SI30 110

4.4 Fat oxidation rate at 10, 20 and 30 min of MOD, SI120, SI60 and SI30 111

4.5 Post-exercise energy intake for MOD, SI120, SI60 and SI30 112

4.6 Ratings of enjoyment using the PACES for MOD, SI120, SI60 and SI30 113

4.7 RPE at 10, 20 and 30 min of MOD, SI120, SI60 and SI30 114

xv

LIST OF ABBREVIATIONS

% O2peak Percentage of peak rate of oxygen consumption

ANOVA Analysis of variance

BMI Body mass index

bpm Beats per minute

CO2 Carbon dioxide

control Boys carrying normal levels of body fat

DEXA Dual Energy X-ray Absorptiometry

EPOC Excess post-exercise oxygen consumption

ES Effect size

Fatmax Exercise intensity that maximises fat oxidation (% O2peak)

FFM Fat free mass

GRAD Graded exercise test with 3-min stages

HIIE High intensity interval exercise

hr Hour

HRmax Maximum heart rate

HRres Heart rate reserve

kg Kilograms

kJ Kilojoules

LoA Limits of agreement

m Metres

MFO Maximal rate of fat oxidation

min Minutes

MOD Moderate intensity continuous exercise at Fatmax

O2 Oxygen

overfat Boys carrying excess body fat

PACES Physical Activity Enjoyment Scale

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PCERT Pictorial Children’s Effort Rating Scale

PROL 30-min bouts of prolonged exercise

RE Residual error

RMR Resting metabolic rate

RPE Rate of perceived exertion

SB Systematic bias

SD Standard deviation

sec Seconds

SI/SI120 Continuous exercise at Fatmax interspersed with a 4-sec maximal sprint effort every 2 min

SI30 Continuous exercise at Fatmax interspersed with a 4-sec maximal sprint effort every 30 sec

SI60 Continuous exercise at Fatmax interspersed with a 4-sec maximal sprint effort every 1 min

wk Week

Wmaxth Theoretical maximal power

Wmax Maximal power output

W Watts

VAS Visual Analogue Scale

O2max Maximal rate of oxygen consumption

O2peak Peak rate of oxygen consumption

xvii

ACKNOWLEDGEMENTS

There are so many people that I would like to thank on what has been such a tough, but

rewarding (especially now!) process.

First and foremost, words could never do justice to describe the motivation and support

that my coordinating supervisor Dr Kym Guelfi has provided me with on this journey.

There were so many occasions that I would walk into her office for a meeting feeling

slightly defeated, but would always walk out feeling like I could take on the world.

Kym, you are one of the most wonderful, genuine and caring people that I have ever

met.

I could always count on Dr Melissa Licari to give me statistical advice and ‘quick and

efficient’ feedback, usually on the ‘flow’ of my thesis. Isn’t that right Mel?!

Dr Rebecca Braham, you are my little shining light that provided support through the

tough times.

Dr Paul Fournier, you were never short of enthusiasm, knowledge and ability to think

outside the square!

A massive Thank You to all of my study participants who gave up their mornings to

participate in my research, despite the fact that I asked them to starve... And then sprint!

Without you, this research would not have been possible. I would like to make a very

special mention of Zach and Kate Hevron who enthusiastically participated in every

single one of my research studies (including my Honours)!

Thank you to John Connell, Tim Lyons, Suzette Felton and Natalie Bennet-Bremner

who assisted with the biggest challenge of participant recruitment!

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Thanks to the reception ladies and technical staff who assisted with the ‘behind the

scenes’.

To fellow students at the School of Sports Science, Exercise and Health who helped to

brighten up my days. Even if it was just a simple “hello” in the corridor!

Dom, I thought that you would be the easiest

person to write about... All I can say is that I

am so grateful for your ongoing support and

I’m blessed to have been able to share this

journey with you. We’re a perfect team!

Finally to my family... I was working, I swear! And

here’s the proof!

Thanks for watching over

me, my Guardian Angel.

xix

PUBLICATIONS ARISING FROM THIS THESIS

Peer-Reviewed Publications

Crisp NA, Guelfi KJ, Licari MK, Braham R, Fournier PA (2012) Does exercise duration

affect Fatmax

Crisp NA, Fournier PA, Licari MK, Braham R, Guelfi KJ (2012) Adding sprints to

continuous exercise at the intensity that maximises fat oxidation: Implications for acute

energy balance and enjoyment in boys. Metabolism DOI:

10.1016/j.metabol.2012.02.009 (Chapter 3)

in overweight boys? European Journal of Applied Physiology 112(7):

2557-2564 (Chapter 2)

Crisp NA, Guelfi KJ, Licari M, Braham R, Fournier P (in press) Optimising sprint

interval exercise to maximise energy expenditure and enjoyment in overweight boys.

Applied Physiology, Nutrition and Metabolism (Chapter 4)

Conference Proceedings

Crisp NA, Fournier PA, Licari MK, Braham R, Guelfi KJ. Impact of exercise modality

on energy balance and enjoyment in overweight boys: Comparison of moderate

intensity continuous and sprint interval exercise. The Australian Society for Medical

Research WA Scientific Symposium, 3rd June 2011, Curtin University of Technology,

Bentley, Western Australia, Australia.

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Crisp NA, Licari MK, Fournier PA, Braham R, Guelfi KJ. Comparison of Moderate

Intensity Continuous and Sprint Interval Exercise on Energy Balance and Enjoyment in

Overweight Boys. 5th Exercise and Sports Science Australia Conference: Research to

Practice. 19-21st April 2012, Jupiters Casino, Gold Coast, Queensland, Australia.

Crisp NA, Guelfi KJ, Licari MK, Braham R, Fournier PA. Optimising Sprint Interval

Exercise to Maximise Energy Expenditure and Enjoyment in Overweight Boys. The

Australian Society for Medical Research WA Scientific Symposium, 7th June 2012, Edith

Cowan University, Mount Lawley, Western Australia, Australia.

1

1 LITERATURE REVIEW

1.1 THE PROBLEM OF OBESITY

Obesity is characterised by an excess accumulation of body fat to an extent that it starts

to negatively affect an individuals’ health. This condition is associated with an

increased risk of developing numerous health complications such as heart disease,

hypertension, high blood cholesterol, stroke, insulin resistance and diabetes, respiratory

problems, osteoarthritis, sleeping disorders and some cancers which, in the long term,

may lead to reduced life expectancy (Daniels, 2006; Lobstein et al., 2004; Must et al.,

1999; Reilly, 2005; Reilly & Kelly, 2011). In addition to its direct impact on physical

health, carrying excessive body fat may also affect psychological well-being by

increasing the risk of depression, low self-esteem, poor self-confidence and self-worth,

impaired quality of life and relationship issues (Daniels, 2006; Lobstein et al., 2004;

Reilly, 2005; Schwimmer et al., 2003). As a result, obesity is fast becoming a forefront

issue for many developed countries and places a considerable economic burden on

society. In 2008, it was estimated that obesity and its associated health consequences for

2

both adults and children cost Australian society and governments more than $58 billion

(Access Economics, 2008).

Despite such severe health and economic consequences associated with overweight and

obesity, the prevalence continues to rise and presently accounts for approximately 61%

of Australian adults and 25% of Australian children (Australian Bureau of Statistics,

2009; Olds et al., 2010). Childhood obesity is of particular concern given not only the

early detrimental health implications associated with this condition, but also the

increased likelihood of such children becoming overweight and obese adults (Lee et al.,

2010; Lobstein et al., 2004; Maffeis, 2000; Margarey et al., 2001), with an increased

risk of physical morbidity and premature mortality (Reilly & Kelly, 2011). It is

estimated that once an obese child surpasses six years of age, the likelihood of their

obesity carrying on to adulthood is greater than 50%, compared to only a 10% risk for a

child within the healthy weight range (Whitaker et al., 1997). Despite increased

publicity through the media in an attempt to make Australian’s more aware of the

condition, the prevalence of childhood obesity is continuing to increase. Between 1985

and 1997, the combined prevalence of overweight and obesity in young Australians

doubled, and that of obesity alone trebled (Booth et al., 2003). More recent statistics

continue to note this trend in the rate of child overweight and obesity, with an increase

in prevalence from 21% in 1995 to 25% in 2007-08. Of this 4% increase, the proportion

of overweight children remained stable at 17%, but the obesity rate alone increased

from 5% in 1995 to 8% in 2007-08 (Australian Bureau of Statistics, 2009).

1.2 DEFINING OBESITY

Although obesity affects such a large proportion of the population, there is a general

lack of consensus as to the most accurate criteria for defining obesity, particularly in

3

children. Body composition is made up of differing proportions of bone, fat, muscle and

water, and there are a number of techniques available to measure some or all of these

constituents to classify an individual as normal weight, overweight or obese.

Body Mass Index (BMI) is the most convenient method of classification and is adopted

by the majority of researchers as it is quick, easy and inexpensive (Dencker et al.,

2007). It is calculated by dividing an individual’s body mass (kg) by their height (m)

squared (mass/height2). This method is useful when examining large cohorts due to its

ease of administration and standard definitions of overweight and obesity using BMI

have been developed for use across different ethnic groups and age categories (Cole et

al., 2000; Appendix A1). However, a major issue with the use of BMI is that it fails to

distinguish between fat mass, muscle mass or bone, and may incorrectly classify

individuals with high muscularity as overweight or obese (Crisp et al., 2011; McCarthy

et al., 2006). In an attempt to overcome this problem, subcutaneous body fat has been

estimated using predictive equations based on skinfold thickness. Although these

skinfold measurements may provide a more precise assessment of the regional

distribution of gross body fat than BMI or body mass alone, its accuracy depends on the

expertise and consistency of the measurer, the number of sites measured and the specific

equation used (Watts et al., 2006). In addition, skinfold measurements tend to be least

accurate in obese individuals due to limitations in the span width of the calipers (Watts

et al., 2006). Furthermore, this technique cannot reliably measure fat stored internally,

such as visceral fat, which has a more direct link to the detrimental health consequences

associated with obesity (e.g. cardiovascular disease, insulin resistance).

Since obesity is associated with increased body fat, to the extent at which it starts to

negatively impact an individual’s health, ideal classification tools should directly assess

adiposity. In contrast to the two indirect methods mentioned above, bioelectrical

impedance and Dual Energy X-ray Absorptiometry (DEXA) are two methods that

4

provide a more precise measurement of an individuals’ body fat. Bioelectrical

impedance measures the resistance of body fluid and tissues to an electrical current

which is combined with anthropometric data to estimate fat free mass (FFM) and

adiposity. This technique appears to be a valid and reliable means of assessing body

composition in healthy adults (Kyle et al., 2004) and children (Tyrrell et al., 2001) with

stable water and electrolyte balance. However, as the ratio between total body water and

FFM (i.e. the hydration factor) is higher in obese individuals, this method does not

appear to be as accurate for assessing adiposity in obese populations (Deurenberg,

1996). On the other hand, DEXA enables the assessment of body composition by

providing an estimation of total body fat mass and various components of FFM using

low dose x-rays (Lobstein et al., 2004). It is generally acknowledged that DEXA

provides a more reliable and valid method of determining body composition (Ellis et al.,

1994; Jensky-Squires et al., 2008) because it enables individuals with high lean tissue or

muscle mass, as opposed to high fat mass, to be eliminated from the overweight or

obese categories (Crisp et al., 2011). In addition, body fat reference curves have been

developed for children, which enable classification into underfat (< 2nd centile), normal

(2nd-85th centile), overfat (85th-95th centile) and obese (> 95th centile) categories

(McCarthy et al., 2006; Appendix A2).

1.3 THE CAUSES OF OBESITY

The aetiology of the increase and preservation of excess body fat stores in overweight

and obese individuals across all age groups is the result of a complex interaction of a

wide variety of factors. Although genetic susceptibility plays an important role, limited

cases result solely from genetics, medical conditions or psychiatric illness (Yang et al.,

2007). It is well established that the maintenance of body fat stores is achieved when

5

there is an overall balance between energy intake (from food and drink consumption)

and energy expenditure (including resting metabolism and physical activity; Figure 1.1).

Over a prolonged period of time, an excessive energy intake combined with decreased

energy expenditure causes energy storage and increases in adiposity (Klesges et al.,

1992; Maffeis, 2000; Schrauwen & Westerterp, 2000). The balance between food intake

and energy expenditure is also modulated by environmental factors such as

geographical location, culture, diet composition and lifestyle (Cameron et al., 2003;

Klesges et al., 1992; Maffeis, 2000; Schrauwen & Westerterp, 2000). Furthermore,

metabolic factors such as substrate oxidation, resting metabolic rate (RMR) and

thermogenesis also play an important role in fat gain and maintenance in both adults

and children (DeLany et al., 2006; Maffeis, 2000; Schrauwen & Westerterp, 2000;

Zurlo et al., 1990).

Figure 1.1 Body fat maintenance is achieved when energy expenditure is balanced with

energy intake.

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1.3.1 The Role of Genetics

In rare cases, obesity may be monogenic (controlled by a single pair of genes). These

cases often present in childhood and are the result of mutations in genes that encode

proteins with a likely role in appetite regulation (Yang et al., 2007). For example,

mutations in genes coding for leptin, leptin receptor, proopiomelacortin and melacortin-

4 receptor prompt an excessive energy intake relative to energy expenditure which

promotes fat gain (Bell et al., 2005; Yang et al., 2007). To date, mutations in 11

different genes have been identified to contribute to obesity, but only 176 human-cases

of obesity have been reported to occur as a result of these gene mutations (Rankinen et

al., 2006).

Genetics also helps to explain the differences in individuals’ susceptibility to gaining fat

stores, despite similar lifestyles. The results from a number of twin, adoption and family

studies have established that the percentage of obesity that can be attributed to genetics

varies from 6 to 85%, depending on the methodology used to define obesity (i.e. 16-

85% for BMI, 37-81% for waist circumference, 6-30% for waist/hip ratio, 35-63% for

percentage body fat; Yang et al., 2007). An individual’s risk of developing obesity is

significantly increased if they have relatives who are obese. For example, a child under

the age of 10 years is much more likely to become obese in adulthood if they have at

least one parent who is overweight (Whitaker et al., 1997). However, after the child

surpasses 10 years of age, their own weight status is a far stronger determinant of adult

obesity than their parent’s (Whitaker et al., 1997), with the likelihood of obesity

persisting with increasing age. As a result, there should be a strong emphasis placed on

providing support, information and intervention in the early onset of obesity (i.e. before

the individual reaches 10 years of age) to increase the likelihood of promoting healthy

physical activity and dietary habits that can be maintained throughout childhood,

adolescence and adulthood.

7

1.3.2 The Role of Energy Balance (Intake versus Expenditure)

The rate of genetic mutation outlined above only equates to a minute percentage of all

cases of childhood obesity. It is more likely that a child’s risk of developing obesity is

exacerbated by the family environment, irrespective of their genetic predisposition. For

example, physical activity levels, sedentary behaviour, eating habits and television

viewing practices have all been demonstrated to ‘run’ in families (Davison & Birch,

2001; Salmon et al., 2005). Parents tend to mould their children’s lifestyle behaviours

on their own patterns, including the types and quantity of food intake, extracurricular

sporting pursuits and electronic media use (i.e. television, videos and computer games).

For example, children of obese parents have been reported to have a stronger preference

for sedentary activities and fatty foods, a lower liking of vegetables, and an increased

likelihood of overeating than children of lean parents (Wardle et al., 2001).

1.3.2a Energy Intake

Several nutritional factors have been proposed to contribute to the growing prevalence

of childhood obesity including increased overall energy consumption resulting from

larger portion sizes and a change in macronutrient selection to favour food and drinks

that are high in sugar and fat.

It has been reported that the average portion size of meals consumed by both adults and

children, particularly those purchased away from home, are typically much greater than

the recommended guidelines, which promotes increased energy intake (Colapinto, 2007;

Rolls et al., 2002; Steenhuis & Vermeer, 2009). But despite the increased energy intake

associated with large portion sizes, no studies have found a direct link between large

portion sizes and obesity. Some studies have even reported that the average energy

8

intake of children has decreased and that overweight children report lower energy

intake, but similar fat intake, than normal weight children (Patrick et al., 2004). This

finding could be explained by the fact that dietary surveys were used to estimate energy

intake. These surveys tend to underestimate energy intake due to under-reporting, with

greater discrepancies in reported and actual food and drink consumption recorded by

overweight individuals, compared to individuals with a healthy body weight (Hill &

Davies, 2001; Livingstone & Black, 2003; Vance et al., 2008).

In addition to increased portion size, dietary patterns have become more energy-dense,

shifting towards an increased consumption of fat, sugar and refined carbohydrates and a

decreased intake of dietary fibre and wholegrains. For example, a positive association

has been identified between increased soft-drink consumption and obesity development

(Moreno & Rodríguez, 2007). Furthermore, it is not surprising that children with an

excessive intake of fat in their diet carry more body fat than those with more wholesome

diets (Berkey et al., 2000; McGloin et al., 2002) given that, compared with protein and

carbohydrate, dietary fat is more energy-dense and requires significantly less energy to

be converted and stored as body fat. On the other hand, a high intake of dietary fibre

and wholegrains has been reported to positively influence weight status (Murakami et

al., 2007; Howarth et al., 2005). This is likely due to their bulky nature, with increased

demands on chewing, digestion and absorption which increases satiety and delays

gastric emptying (Pereira & Ludwig, 2001).

Increased work stress and time limitations, as well as food advertising and prices, have

had a significant impact on food choices and the adoption of energy-dense dietary

patterns. There is now a greater reliance on the consumption of convenience foods such

as pre-prepared meals and fast foods which generally have a much greater energy

density than foods typically recommended for healthy daily intake (French et al., 2001).

For instance, from 1977 to 1996, the amount of fast food consumed by children

9

increased by 300% (St-Onge et al., 2003). Apart from these ‘fast food’ choices being

higher in total fat, saturated fat, sugar and salt, they are also often deficient in many

important nutrients (e.g. fibre, calcium, vitamins A and C; French et al., 2001). French

et al. (2001) found that individuals who reported eating at fast food restaurants at least

three times a week had energy intakes up to 40% greater than those who reported that

they did not eat at a fast food restaurant. Furthermore, fast food restaurant use was

associated with a lower intake of healthy foods such as fruit, vegetables, grains and milk

(French et al., 2001). Consequently, it is not surprising that fast food consumption is

strongly associated with weight gain and insulin resistance (Pereira et al., 2005).

In summary, increased energy intake through larger portion sizes in combination with

unhealthy food choices rich in fat and sugar is more than likely a strong contributor to

the increased prevalence of childhood obesity. There has however, been considerable

debate as to whether energy intake or the other side of the energy balance equation,

energy expenditure, is more important in the development and maintenance of body fat

stores. However, it is imperative that both aspects be considered as studies show that a

combination of dietary modification to promote decreased energy intake and increased

energy expenditure through exercise provides more favourable fat loss and promotes

long-term success (Boutcher & Dunn, 2009; Stiegler & Cunliffe, 2006).

1.3.2b Energy Expenditure

The two main components that contribute to an individuals’ daily energy expenditure

are RMR and physical activity (McArdle et al., 2001; Molnar & Schutz, 1997). RMR

refers to the rate of energy expenditure that the human body requires to maintain

essential physiological functions such as brain activity, cardiac output, respiration and

body temperature regulation (McArdle et al., 2001). In most healthy individuals, RMR

10

accounts for 60-75% of total daily energy expenditure (Molnar & Schutz, 1997;

Ravussin et al., 1982) and is dependent on genetics, age, gender, hormones, overall

body size and composition, physical fitness and environmental factors such as physical

activity levels, nutritional intake, stress and weather conditions (Johnstone et al., 2005;

McArdle et al., 2001; Molnar & Schutz, 1997; Tounian et al., 2003). Some individuals

may be susceptible to increased body fat stores as a result of having a low RMR, which

is thought to have evolved over times when food supply was sparse and there were large

physical demands for survival. Natural selection resulted in individuals with the ‘thrifty’

genotype (a low RMR characterised by increased fat oxidation and the preservation of

glycogen stores to promote energy sparing) to reproduce and pass on this beneficial

characteristic to their offspring (Yang et al., 2007). These individuals require less

energy intake to maintain normal body functioning and therefore tend to be more prone

to weight gain by overeating in modern society where the food supply is abundant

(Buscemi et al., 2005). Furthermore, a lower RMR in combination with the sedentary

lifestyle of today’s society, characterised by increased motorised transport, the use of

labour saving devices, increased television viewing and computer gaming, and a decline

in leisure pursuits devoted to increasing physical activity (Lobstein et al., 2004;

Schrauwen & Westerterp, 2000; World Health Organisation, 2004), promotes a shift in

the energy balance equation towards decreased energy expenditure.

Physical activity, which is defined as any musculoskeletal activity involving significant

movement of the body or limbs that results in an increase in energy expenditure above

resting levels, is the most easily modified component of energy expenditure (Caspersen

et al., 1985). It is not surprising that a rise in the incidence of childhood obesity in

Australia is associated with a decline in physical activity participation (Boreham &

Riddoch, 2001; Spinks et al., 2007). In fact, children are expending approximately 2500

kJ/day less than their counterparts 50 years ago (Boreham & Riddoch, 2001). Spinks et

11

al. (2007) explored compliance with physical activity guidelines (the participation of at

least 60 min of moderate intensity physical activity every day) amongst children of

varying body composition and reported that non-compliance increased a child’s risk of

being overweight by 28% (Spinks et al., 2007). Irrespective of the impact on weight

status, children and adolescents who participate in lower levels of physical activity are

more likely to display risk factors associated with cardiovascular disease (Boreham &

Riddoch, 2001). One explanation for the decline in physical activity participation in

children is due to their increased reliance on mechanical modes of transportation.

Specifically, it has been reported that only one third of Australian children utilise active

transport (walking and cycling) to and from school (van der Ploeg et al., 2008; Yeung et

al., 2008). In fact, there is evidence that the transportation practices of Australian

children have shifted from active to inactive (motorised transport) which is likely to

contribute to a significant loss of daily energy expenditure and promote an increase in

childhood obesity (van der Ploeg et al., 2008). For example, van der Ploeg et al. (2008)

reported that the average percentage of South Australian children aged 5-14 years that

walked to school halved (from 54 to 27%), and the percentage that were driven to

school by car more than tripled (from 15 to 52%), from 1971 to 1999-2003. This is of

concern because actively commuting to school contributes to an average of 20 min of

physical activity, up to five days a week (van der Ploeg et al., 2008), which is one third

of the minimum amount of physical activity that is recommended for the maintenance

of a healthy lifestyle for children. In addition, it has been suggested that walking to and

from school encourages participation in further physical activities during the day

(Alexander et al., 2005; Cooper et al., 2003).

In combination with a decline in physical activity participation, children devote more of

their leisure time to sedentary activities, especially electronic media use (Berkey et al.,

2000; Hesketh et al., 2007). Hesketh et al. (2007) examined the relationship between

12

electronic media use (including television viewing and electronic game/computer use)

and BMI over three years in Australian children. At baseline, 40% of children met the

recommended guidelines of ≤14 hours of electronic media use each week. Three years

later, this figure had decreased to 18% (Hasketh et al., 2007). Of particular interest was

that children who did not meet the guidelines at baseline were more overweight and

more likely to be overweight or obese after the three year examination period. In fact,

the obese boys spent four times the number of hours using electronic games than the

normal weight boys at the three year follow-up (Hesketh et al., 2007). This outcome is

likely not only due to the sedentary behaviour associated with electronic media use, but

also a decline in physical activity participation (Salmon et al., 2005). The relationship

between electronic media use and obesity is also mediated through energy balance (i.e.

increased energy intake and/or decreased energy expenditure). For example, television

viewing promotes inactivity (Salmon et al., 2005) as well as the consumption of energy

dense food and snacks (Temple et al., 2007), usually ones that are commonly advertised

on television. This detrimental combination promotes increased body fat stores.

1.4 CURRENT APPROACHES FOR MANAGING OBESITY IN CHILDREN

As discussed above, a lifestyle characterised by excessive energy intake coupled with

inadequate energy expenditure results in weight gain (Figure 1.2a). Conversely, weight

loss is achieved when energy expenditure exceeds energy intake in the energy balance

equation (Figure 1.2b). Consequently, strategies aimed at managing obesity may include

decreasing energy intake, increasing energy expenditure through exercise or utilising a

combination of the two methods. Although decreased energy intake alone can be

successful for weight loss, diets that restrict caloric consumption without participation

in regular physical activity often result in weight loss associated with reduced FFM.

13

Figure 1.2 (a) Positive energy balance (i.e. energy intake exceeds energy expenditure)

resulting in fat gain, and (b) Negative energy balance (i.e. energy expenditure exceeds

energy intake) resulting in fat loss.

14

This contributes to decreased RMR (Lennon et al., 1985; Poehlman, 1989) which makes

it more difficult to keep the weight off in the long-term. In addition, dietary restriction

may promote unhealthy eating habits in children and adolescents (Battle & Brownell,

1996; Watts et al., 2005) and cause deficiencies in the essential nutrients required for

healthy growth and development. For these reasons, dietary restriction alone is not the

preferred option for weight management in paediatric populations (Battle & Brownell,

1996; Watts et al., 2005).

On the other hand, physical activity is regarded as a key component for managing

childhood obesity due to its potential for increasing energy expenditure and creating an

energy deficit (Donnelly et al., 2004). The benefit of utilising physical activity for fat

loss, as opposed to caloric restriction alone, is that physical activity prevents weight loss

associated with a reduction in FFM and the subsequent decline in RMR. In fact, RMR

increases over time in physically active individuals due to the associated increases in

FFM (Tremblay et al., 1986). Since RMR is the biggest contributor to total daily energy

expenditure, this increase associated with increases in FFM is important for creating a

negative energy balance and promoting fat loss. In addition, participating in physical

activity promotes many other health benefits independent of fat loss that a dietary

intervention alone cannot provide. These include increased cardiovascular fitness and

muscular strength (Donnelly et al., 2004; Tsiros et al., 2008; Watts et al., 2005), the

promotion of healthy bones and motor skill development (Nowicka & Flodmark, 2007),

and enhanced psychological well-being, including improved self-esteem and self-

confidence, and reduced depression, anxiety and stress (Brooks & Magnusson, 2006;

Calfas & Taylor, 1994; Steptoe & Butler, 1996). Furthermore, the promotion of physical

activity in childhood may result in a behavioural carryover into adulthood, whereby

active children are more likely to become more active and healthy adults (Boreham &

Riddoch, 2001).

15

Childhood is a critical time for developing healthy lifestyle habits (including increased

physical activity practices) which are strongly related to health status in adulthood

(Margarey et al., 2001). In today’s society, it is likely that levels of physical activity

participation are not high enough to counteract the impact of readily available unhealthy

foods and childhood activities that promote sedentary behaviours and encourage

obesity. Therefore, there appears to be a strong need for the development of structured

exercise protocols that maximise energy expenditure, improve fitness and encourage

long-term adherence in children carrying excess body fat.

1.5 OPTIMISING EXERCISE FOR THE OVERWEIGHT OR OBESE CHILD

Despite the well-established benefits of physical activity for fat loss, the optimal type of

exercise for the overweight or obese child is not known. While the main goal is to

maximise energy expenditure, there are also other factors to consider. For instance, high

intensity exercise is associated with increased energy expenditure in the short-term, but

due to the strenuous nature of this type of exercise, feelings of pleasure and levels of

enjoyment may be lower when compared with low to moderate intensity exercise

(Ekkekakis et al., 2011). These lower feelings of pleasure and enjoyment during

exercise may result in decreased long-term adherence and as a result, long-term energy

expenditure may be compromised for high intensity exercise (Ekkekakis et al., 2011).

Post-exercise energy intake should also be considered given that the potential benefits

of increased energy expenditure during exercise may be counteracted by increased

energy intake post-exercise (Hopkins et al., 2010). In addition, it has been suggested

that the amount and type of substrate oxidation during exercise (i.e. fat vs.

carbohydrate) may be important to consider for the management of obesity (Brandou et

al., 2005; Maffeis, 2000; Maffeis et al., 2005; Pérez-Martin et al., 2001). By modifying

16

the intensity, duration or frequency of physical activity, the energy expenditure and rate

of fat oxidation (both during and post-exercise) may be effectively enhanced to promote

increased fat loss.

1.5.1 The Relationship between Exercise Intensity and Fat Oxidation

It is well established that as the exercise intensity increases, so too does the amount of

energy expenditure per unit of time during the exercise bout. The intensity of exercise

also influences the absolute and relative contributions of fat and carbohydrate oxidation

to energy expenditure during exercise (Venables et al., 2005). During low to moderate

intensity exercise, a greater proportion of fat is oxidised by the working muscles

compared to high intensity exercise. However, this proportion shifts towards greater

carbohydrate oxidation at higher exercise intensities because fat cannot be oxidised

rapidly enough to meet the increasing energy requirements of the muscles (Brooks &

Mercier 1994; Venables et al., 2005; Figure 1.3a). In accordance with the crossover

concept (Brooks & Mercier, 1994), absolute carbohydrate oxidation rate increases

exponentially with exercise intensity, while absolute fat oxidation rate increases to a

point above which it starts to decline in favour of carbohydrate oxidation (Figure 1.3b).

This suppression of fat oxidation during higher intensity exercise is due to reduced fatty

acid availability, as a result of decreased muscle pH from accumulating H+ ions (Coyle

et al., 1997) and decreased carnitine availability (Roepstorff et al., 2005; Stephens et al.,

2007). The exercise intensity that maximises fat oxidation has been termed Fatmax

(Achten et al., 2002) and is commonly expressed as a percentage of the peak rate of

oxygen consumption (% O2peak). Paediatric studies report Fatmax to occur at 40-56%

O2peak (Aucouturier et al., 2009; Lazzer et al., 2007; Lazzer et al., 2010; Riddell et al.,

2008; Zakrzewski & Tolfrey, 2011a; Zunquin et al., 2009a; Zunquin et al., 2009b).

17

Figure 1.3 Effect of exercise intensity on the (a) relative contribution of fat ( ) and

carbohydrate ( ) oxidation to energy expenditure, and (b) absolute rate of fat and

carbohydrate oxidation

18

1.5.2 The Benefits of Exercise at Fatmax

Some researchers have suggested that the identification of Fatmax may allow for the

development of more appropriate exercise interventions aimed at reducing fat mass and

other medical consequences associated with obesity (Ben Ounis et al., 2008; Brandou et

al., 2003; Dumortier et al., 2003; Venables & Jeukendrup, 2008; Zakrzewski & Tolfrey,

2011b), particularly for the rapidly growing overweight paediatric population. Studies

have reported improvements in body composition (Brandou et al., 2005), fat oxidation

rate during submaximal exercise, and increased whole-body insulin sensitivity index

(Venables & Jeukendrup, 2008) following exercise training at Fatmax. For example,

Brandou et al. (2005) compared the impact of exercise training at Fatmax (50.8 ± 2.6%

theoretical maximal power; Wmaxth) versus a higher intensity of exercise (60.8 ± 5.3%

Wmaxth) matched for energy expenditure on body composition and substrate oxidation

in fifteen obese boys aged 10-15 years. The exercise training was offered two days a

week for two months and both groups experienced a significant amount of fat loss with

no change in FFM. In the group training at Fatmax, fat and carbohydrate oxidation rates

during a number of different intensities (20, 30, 40, 50 and 60% Wmaxth) of submaximal

exercise were unchanged but in the high intensity exercise group, fat oxidation rate

decreased and carbohydrate oxidation rate increased during exercise at 20 and 30%

Wmaxth (Brandou et al., 2005). The results from this study indicate that exercise training

at Fatmax not only encourages a fat loss similar to that observed during exercise training

at a higher intensity, but also has the potential to maximise fat oxidation rate during

submaximal exercise to a greater extent than higher intensity exercise. In further

support, Venables and Jeukendrup (2008) reported an increase in fat oxidation rate

during steady-state exercise at 50% O2max in adults, as well as improvements in

whole-body insulin sensitivity, following four weeks of continuous exercise training at

Fatmax. However, these improvements occurred despite no change in a range of body

19

composition measures (i.e. body weight, percentage body fat, waist to hip ratio;

Venables & Jeukendrup, 2008), likely as a result of the brief intervention period.

1.5.2a Methodological Issues with the Estimation of Fatmax

Despite the potential benefits of exercise training at Fatmax for managing obesity,

including increased fat oxidation rate and fat loss, there is minimal research examining

the validity and reliability of the techniques used to estimate Fatmax (Achten et al.,

2002), particularly in overweight adults (Bordenave et al., 2007) and paediatric

populations (Aucouturier et al., 2009; Zakrzewski & Tolfrey, 2011a). Fatmax cannot be

defined as a single exercise intensity that suits all individuals (Meyer et al., 2007) and

therefore, individualised testing is important. The optimal procedure for measuring fat

oxidation rate during exercise is to utilise prolonged steady-state exercise bouts to

ensure the valid use of indirect calorimetry (Friedlander et al., 1998; Rowland &

Rimany, 1995), by which the type and rate of substrate oxidation and energy

expenditure are estimated in vivo from gas exchange measurements. This technique can

be used to accurately determine fat and carbohydrate oxidation rate for exercise

intensities up to 80-85% O2max (Romijn et al., 1992). Unfortunately, the utilisation of

prolonged steady-state exercise bouts is time consuming and only allows for the

observation of a small number of exercise intensities, which does not permit a precise

estimation of Fatmax. As a result, the most commonly utilised technique for estimating

Fatmax was developed by Achten et al. (2002) and consists of a single, graded exercise

protocol with 3-min stages. The short stage duration enables fat oxidation rate to be

measured over a wide range of exercise intensities from which a fat oxidation curve is

constructed to determine Fatmax. This protocol was validated in trained men by

comparing the average rate of fat oxidation during 35-80 min of continuous exercise

20

(adjusted to result in similar energy expenditure between intensities) on separate days at

the intensities corresponding to each stage of the single graded exercise test (Achten et

al., 2002). Based on the fact that Fatmax was similar for the two techniques, the authors

concluded that a single graded exercise test on a cycle ergometer, starting at 95 W and

with 35 W increments every 3 min, can be used for the estimation of Fatmax and the

maximal rate of fat oxidation in trained adult males.

The simplicity of the protocol developed by Achten et al. (2002) has prompted its

adaptation to further studies in adults (Achten et al., 2003; Riddell et al., 2008;

Venables et al., 2005) and children (Riddell et al., 2008; Zakrzewski & Tolfrey, 2011a).

However, despite its convenience, there are potential limitations to the single graded

exercise protocol with 3-min stages that may affect the validity of Fatmax estimates.

Firstly, the rate of fat oxidation has been observed to increase as the duration of exercise

progresses in both adults (Chenevière et al., 2009; Meyer et al., 2007; Pillard et al.,

2007) and children (Delamarche et al., 1992) suggesting that Fatmax also has the

potential to change over time. In the study by Achten et al. (2002), the rate of fat

oxidation that was used for comparison between the different protocols was averaged

across the duration of each steady-state exercise bout (i.e. fat oxidation rate across time

was not reported), thus not excluding the possibility that fat oxidation rate, and therefore

Fatmax, may have changed as the exercise progressed. Furthermore, ‘carry-over effects’

may occur between consecutive stages of the graded exercise protocol and the increased

cumulative duration of exercise as the test progresses might affect fat oxidation rate,

particularly during the latter stages of the protocol. All of the above mentioned factors

may ultimately affect the estimation of Fatmax.

Given the potential for exercise training at Fatmax to assist with weight management

(Brandou et al., 2003; Dumortier et al., 2003; Venables & Jeukendrup, 2008), it would

also be beneficial to accurately determine Fatmax in overweight or obese populations.

21

Since sedentary individuals take longer than trained individuals to reach a steady-state

in respiratory gas exchange, the 3-min stage duration of the protocol developed and

validated by Achten et al. (2002) in trained men may be too short for an accurate

determination of Fatmax in sedentary and/or overweight individuals (Bordenave et al.,

2007). This concern was explored by Bordenave et al. (2007), who measured substrate

oxidation during the third minute, compared to the sixth minute, of a graded exercise

protocol with four 6-min submaximal stages (20, 30, 40 and 50% Wmax) in 17 sedentary

adults. Although Bordenave et al. (2007) observed that fat oxidation rate and Fatmax

were well correlated at the group level between the third and sixth minutes, individual

analysis revealed an average overestimation of 16.2 mg/min (and a maximum difference

of 114 mg/min) for fat oxidation rate and an underestimation of 1.88 W (and a

maximum difference of 8 W) for Fatmax at the third minute. Based on these results, the

authors concluded that the preferred stage duration for graded exercise protocols that are

used for the determination of Fatmax in sedentary individuals is 6 min, as 3-min stages

do not allow for accurate measures of indirect calorimetry. The few studies that have

estimated Fatmax in overweight adults have utilised protocols with longer stage durations

ranging from six (Dériaz et al., 2001; Pérez-Martin et al., 2001) to 20 min (Bircher et

al., 2005; Bircher & Knechtle, 2004). Unfortunately, in the study by Bordenave et al.

(2007), fat oxidation rates for the four examined exercise intensities were not presented.

Since it has been observed that fat oxidation rate remains high over a wide range of

exercise intensities (Achten et al., 2002; Zakrzewski & Tolfrey, 2011a), it would be

interesting to know whether the maximum difference in Fatmax estimation of 8 W in the

study by Bordenave et al. (2007) had a significant impact on fat oxidation rate, given

that Meyer et al. (2009) considered an increment of 26 W to be minimal when

estimating Fatmax.

22

1.5.2b Estimating Fatmax in Paediatric Populations

It is important to determine whether the protocols used to estimate Fatmax in adults are

also suitable for children, because differences in oxygen uptake and substrate oxidation

have been found between these two populations (Fawkner et al., 2002; Riddell et al.,

2008). Moreover, although the majority of studies have estimated Fatmax to occur at a

moderate intensity of about 40-56% O2peak in paediatric populations (Table 1.1), the

influence of body composition (Maffeis et al., 2005; Zunquin et al., 2009a), pubertal

status (Brandou et al., 2006; Riddell et al., 2008; Stephens et al., 2006; Zunquin et al.,

2009b), gender (Lazzer et al., 2007), aerobic fitness levels and training (Brandou et al.,

2003) results in large individual variability within studies and supports the need for an

individualised determination of Fatmax. A number of protocols have been utilised to

estimate Fatmax in paediatric populations, the majority of which have used incremental

exercise tests with stage durations varying between 3-10 min (Table 1.1). The shorter

the stage duration, the greater the number of stages participants are able to complete,

which allows for a more precise estimation of Fatmax. On the other hand, longer exercise

stages increase the likelihood that participants reach a physiological steady state which

encourages a valid use of indirect calorimetry (Frayn, 1983). Of particular interest is the

finding that children reach a physiological steady state faster than adults (Fawkner et al.,

2002) which may support the use of shorter stages for protocols to estimate Fatmax in

children.

Given the potential for shorter exercise stages to increase the number of examinable

intensities and allow for a more precise estimate of Fatmax, and the fact that children

appear to reach a physiological steady state faster than adults (Fawkner et al., 2002), it

is surprising that only one study has attempted to validate the use of a single graded

exercise test with 3-min stages to determine Fatmax in children (Zakrzewski & Tolfrey,

23

2011a). In this study, Zakrzewski and Tolfrey (2011a) estimated Fatmax in 26 healthy,

pre-pubertal children aged 8-10 years from an incremental protocol with 3-min stages

compared to that estimated from six 10-min constant load bouts at intensities

corresponding to those in the incremental protocol. For each individual, the results from

the two techniques were used to construct second order polynomial curves of fat

oxidation rate against exercise intensity from which Fatmax was determined (Figure

1.4a). In addition, the technique utilised by Achten et al. (2002) was examined, whereby

Fatmax is taken as the single measured exercise intensity at which fat oxidation is

maximal (Figure 1.4b). Comparable results were obtained between the two protocols

using the two techniques (i.e. both at the group and individual level) and for this reason,

the authors recommended that a 3-min incremental protocol could be used to provide an

accurate estimation of Fatmax in healthy, pre-pubertal children (Zakrzewski & Tolfrey,

2011a). However, it is important to note that one limitation with the study by

Zakrzewski and Tolfrey (2011a) was that the exercise duration of 10 min utilised in the

constant load bouts may not have been long enough to observe any potential increase in

fat oxidation rate over time (Chenevière et al. 2009; Meyer et al. 2007; Pillard et al.

2007). Furthermore, although the constant load exercise bouts were performed in a

counterbalanced order and were separated by 15-min rest periods, they were not all

completed on separate days which cannot completely rule out carryover effects. In

addition, there is still a need to examine the use of a 3-min graded exercise protocol for

the estimation of Fatmax in children carrying excess body fat. The identification of Fatmax

in this population is of particular interest given that an early intervention may enable

more effective management of obesity (i.e. to promote increased fat loss and long term

weight maintenance).

i

Table 1.1 Studies that have estimated Fatmax in paediatric populations (adapted from Zakrzewski & Tolfrey, 2011b) Protocol Constituents

Author n Weight Status Pubertal Status

Mean Age (yrs) Gender Mode of

Exercise Incremental/

Isolated Stage Duration

(min) Number of Intensities Fatmax

Aucouturier et al. (2009) 20 Ob Not Stated 13.0 M + F CE INC 4 5 53% O2peak Brandou et al. (2003) 7 Ob Mixed 13.7 M + F CE INC 6 5 32% Wmaxth

(pre-training) 45% Wmaxth

(post-training) Brandou et al. (2005) 7 Ob Mixed 11.8 M CE INC 6 5 51% Wmaxth Brandou et al. (2006) 7

8 Ob Pre-pubertal

Post-pubertal 10.6 13.5

M M

CE INC 6 5 ~50% Wmaxth ~47% Wmaxth

Lazzer et al. (2007) 15 15 15 15

Ob Ob N N

Pubertal and Post-pubertal

15.9 15.6 15.0 15.0

M F M F

CE INC 5 4 40% O2peak 38% O2peak 45% O2peak 42% O2peak

Lazzer et al. (2008) 19 Ob Mixed 8-12 M + F CE INC 4 Not Stated 48% O2peak Lazzer et al. (2010) 20 Ob Pubertal and

Post-pubertal 14-16 M T INC 4 Not Stated 42% O2peak

Maffeis et al. (2005) 24 Ob Pre-pubertal 10.0 M T ISOL 8-10 3 ~50% O2peak Riddell et al. (2008) 5

5 5 9

N N N N

Pre-pubertal, Pubertal and Post-pubertal

12.0 13.2 14.7 23.8

M M M M

CE INC 3 Not Stated 56% O2peak 55% O2peak 45% O2peak 31% O2peak

Stephens et al. (2006) 9 12 11

N N N

Pubertal 10.3 12.3 15.0

M M M

CE ISOL 5-6 5 40% O2peak 40% O2peak 30% O2peak

Zakrzewski & Tolfrey (2011a) 26 N Pre-pubertal 9.5 M + F CE INC + ISOL 3-10 6 55% O2peak Zunquin et al. (2009a) 17

13 Ob N

Pubertal 12.1 12.0

M M

CE INC 3.5 Not Stated 47% O2peak 55% O2peak

Zunquin et al. (2009b) 16 16 14

Ob Ob Ob

Pre-pubertal Pubertal

Post-pubertal

9.7 11.9 14.6

M M M

CE INC 3.5 Not Stated 49% O2peak 47% O2peak 45% O2peak

Abbreviations: Ob = Obese, N = Non-obese, CE = Cycle Ergometry, T = Treadmill, INC = Incremental, ISOL = Isolated, O2peak = Peak Oxygen Uptake, Wmaxth = Theoretical Maximal Power

24

25

Figure 1.4 Fat oxidation rate relative to exercise intensity and Fatmax estimation using

the technique developed by (a) Zakrzewski and Tolfrey (2011a) and (b) Achten et al.

(2002)

26

1.5.3 The Benefits of High Intensity Exercise

As outlined previously, it is not uncommon for researchers and fitness practitioners to

recommend continuous low to moderate intensity exercise, particularly at Fatmax, for fat

loss because the proportion of fat oxidised during this type of exercise is greater than

during high intensity exercise (Melanson et al., 2002) and it may be easier to adhere to

(Kilpatrick et al., 2007; Lind et al., 2008; Perri et al., 2002). However, this mode of

exercise is more time consuming, given the longer duration of exercise required to

achieve the same total energy expenditure as that attained with higher intensity exercise.

This is of particular importance given that the primary excuse for not complying with an

exercise program is lack of time (Dishman et al., 1985). Furthermore, although exercise

at Fatmax may maximise the rate of fat oxidation during exercise, higher intensity

exercise has been associated with increased fat oxidation rate post-exercise (Yoshioka et

al., 2001). In addition, the increased energy expenditure that results from high intensity

exercise per unit of time, both during and post-exercise, may be more effective in

inducing a negative energy balance required for fat loss (Hunter et al., 1998). In fact, it

has been reported that individuals engaging in regular vigorous exercise have less

subcutaneous fat than those participating in less intense exercise (Dionne et al., 2000;

Tremblay et al., 1990).

The post-exercise period is often overlooked in studies exploring the impact of exercise

intensity on energy expenditure and fat oxidation. Following an acute bout of exercise,

oxygen consumption, and therefore metabolism, remains elevated (LaForgia et al.,

2006; Speakman & Selman, 2003) and this is referred to as the excess post-exercise

oxygen consumption (EPOC; Figure 1.5). The magnitude of EPOC is exponentially

related to the exercise intensity, regardless of energy expenditure during exercise, with

substrate oxidation during this time typically characterised by the preferential oxidation

of fat to spare further depletion of glycogen stores (Jamurtas et al., 2004, Kuo et al.,

27

2005). Dawson et al. (1996) compared the magnitude and duration of EPOC following

submaximal cycling at lower (~45% O2max), moderate (~55% O2max) and higher

(~65% O2max) intensity exercise of matched energy cost. Although the duration of

EPOC was similar between the three protocols, post-exercise energy expenditure and

oxygen consumption was significantly greater for the higher intensity protocol than both

the low and moderate intensity protocols. Other studies have noted this increased

magnitude of EPOC associated with high intensity exercise (Phelain et al., 1997). In

addition to increased EPOC, Phelain et al. (1997) observed that overall fat oxidation

rate (including a 3-hr post-exercise period) was similar for moderate (50% O2max) and

high (75% O2max) intensity exercise of matched energy cost in active young women.

Fat oxidation rate was in fact higher at the end of the 3-hr post-exercise period for the

high intensity protocol compared to the moderate intensity protocol, demonstrating the

impact of high intensity exercise to deplete muscle glycogen stores during the exercise

bout, which results in a higher rate of fat oxidation during a prolonged period of EPOC.

Figure 1.5 Excess post-exercise oxygen consumption (EPOC) following submaximal

exercise (adapted from LaForgia et al., 1997)

28

As well as the potential of high intensity exercise to maximise EPOC and post-exercise

fat oxidation, studies consistently demonstrate that exercise training at a higher intensity

is more effective in increasing cardiorespiratory fitness than moderate intensity exercise

training of the same energy cost (Duncan et al., 2005; Gutin et al., 2002; O’Donovan et

al., 2005). For example, Gutin et al. (2002) demonstrated that 8 months of bi-weekly

lifestyle education combined with high intensity exercise training (29 min at 75-80%

O2max, 5 days/wk), but not equicaloric moderate intensity exercise training (43 min at

55-60% O2max, 5 days/wk), resulted in increases in cardiorespiratory fitness compared

to the same lifestyle education program without exercise training in obese adolescents.

This is particularly noteworthy given that increases in cardiorespiratory fitness,

regardless of body composition, have been shown to reduce the risk of mortality in men

(Lee et al., 1999). Despite the above mentioned benefits of high intensity exercise, there

is still considerable debate as to the optimal exercise intensity required for fat

management in both adults and children.

1.5.4 Interval Exercise as an Alternative to Continuous High Intensity Exercise

The increased energy expenditure associated with high intensity exercise (during and

post-exercise) coupled with the increased rate of fat oxidation post-exercise may have a

significant impact on long-term fuel storage and fat loss. Furthermore, the increased

cardiovascular fitness associated with high-intensity exercise is beneficial for reducing

the detrimental health consequences associated with obesity. However, one major

concern with prescribing continuous high intensity exercise to individuals carrying

excess body fat is that they may find the strenuous training load unpleasant (Kilpatrick

et al., 2007; Lind et al., 2008) and therefore, are not likely to adhere to a program of this

nature in the long-term (Perri et al., 2002). This could be particularly true for

29

overweight children who may lack the motivation to participate in, or be less likely to

withstand the discomfort associated with, sustained high intensity exercise.

An alternative to continuous high intensity exercise is high intensity intermittent

exercise (HIIE) which involves short repeated bouts of high intensity exercise

interspersed with longer periods of recovery (i.e. lower intensity exercise or rest). One

of the first studies to compare continuous versus intermittent exercise established that

intermittent exercise produces higher heart rates, ventilation, oxygen utilisation and

lactate production than continuous exercise matched for average power output (Edwards

et al., 1973). This demonstrates the effectiveness of intermittent exercise to maximise

the physiological response to exercise, which is important for improving health and

fitness, and potentially for maximising fat loss. In support of this, Jakicic et al. (1995)

demonstrated that a 20-wk home-based exercise intervention conducted in intervals

(progressive 20-40 min of exercise prescribed in several 10-min bouts, 5 times/wk)

produced similar increases in cardiorespiratory fitness, but also encouraged increased

adherence and tended towards greater weight loss than the same duration of exercise

prescribed in one continuous bout (progressive 20-40 min, 5 times/wk) in obese,

sedentary females.

There is compelling evidence that HIIE is more time-efficient than other modes of

exercise for reducing fat mass in overweight individuals (Boutcher, 2011; Trapp et al.,

2007; Tremblay et al., 1994). For example, Tremblay et al. (1994) compared the impact

of 20 weeks of moderate intensity endurance training (cycling 4-5 times/wk for 30-45

min at 60-85% of the maximal heart rate reserve; HRres) to 15 weeks of HIIE training (a

combination of short-interval sessions [10-15 bouts of 15-30 sec at 60% of the maximal

work output in 10 sec], long-interval sessions [4-5 bouts of 60-90 sec at 70% maximal

work output in 90 sec] and continuous sessions [30 minutes cycling at 70% HRres]) on

adiposity in healthy, non-obese adults. Despite the fact that the mean estimated energy

30

expenditure of the HIIE training was less than half of that elicited by the endurance

training, and required a much lower investment of time, the HIIE training resulted in a

greater loss of subcutaneous fat and improvement in skinfold measurements (Tremblay

et al., 1994). In fact, it appears as though whenever researchers compare low to

moderate intensity continuous exercise training to HIIE training, the health benefits are

more favourable for HIIE despite a much lower investment of time (Trapp et al., 2008;

Tremblay et al., 1994).

No studies have examined the impact of continuous exercise training compared with

HIIE training on fat mass in overweight children. However, a recent study by Tjønna et

al. (2009) explored the potential impact that interval training might have on lifestyle

changes, fat loss and aerobic fitness in overweight children by comparing a 12 month

multidisciplinary approach (exercise, diet and psychological advice, 2 times/month) to 3

months of aerobic interval training (4 x 4-min intervals at 90% HRmax separated by 3

min at 70% HRmax, 2 times/wk). It was found that the aerobic interval training initiated

a greater decline in BMI and body fat, had a better impact on diet, and elicited greater

improvements in aerobic fitness and other cardiovascular risk factors than the

multidisciplinary approach (Tjønna et al., 2009). While the study by Tjønna et al.

(2009) has provided valuable evidence that interval training may be an effective

modality of training for paediatric populations carrying excess body fat, there is a need

for further research to explore the impact of HIIE training compared with continuous

exercise training on cardiovascular fitness and fat loss in this population.

1.5.4a Sprint Interval Exercise

A specific type of HIIE is sprint interval exercise which involves low to moderate

intensity exercise or rest interspersed with short supramaximal (> 100% O2max) sprint

31

efforts that last 1 min or less (Smith, 2008). Studies have found that the metabolic

adaptations associated with sprint interval exercise usually occur very quickly after a

relatively small volume of training (Burgomaster et al., 2005; Gibala et al., 2006;

Tabata et al., 1996). For example, Tabata et al. (1996) found that although six weeks of

moderate intensity continuous exercise training (60 min of continuous cycling at 70%

O2max performed 5 times/wk) resulted in a comparable increase in aerobic capacity as

six weeks of sprint interval exercise training (7-8 sets of 20-sec bouts at 170% O2max

with 10 sec recovery periods performed 5 times/wk), only the sprint interval exercise

resulted in increased anaerobic capacity in physically active males. It should also be

noted that these improvements occurred for the sprint interval exercise despite only

exercising one fifteenth of the duration of time required for the continuous exercise.

Furthermore, Gibala et al. (2006) observed muscle adaptations (e.g. muscle oxidative

capacity, buffering capacity, glycogen content) and exercise performance improvements

in active men following sprint interval exercise (4-6 sets of 30-sec maximal sprint

efforts [~250% O2max] with a 4-min recovery between bouts performed 3 times/wk) to

a similar extent as those observed following moderate intensity continuous exercise (90-

120 min at 65% O2max performed 3 times/wk), despite the fact that the training volume

was 90% less for the sprint interval exercise. These studies demonstrate the potential for

sprint interval exercise to improve both aerobic and anaerobic measures of fitness in a

time effective manner which is particularly beneficial for individuals who lack the time

or desire for lengthy workouts.

Supramaximal exercise also appears to have a greater effect on the duration and

magnitude of EPOC than submaximal exercise (LaForgia et al., 1997). To demonstrate

this point, LaForgia et al. (1997) compared the impact of continuous treadmill running

(30 min at 70% O2max) with a supramaximal interval protocol of a matched energy

cost (20 1-min intervals at 105% O2max interspersed with 2-min rest periods) on EPOC

32

in male athletes. It was observed that the supramaximal exercise resulted in greater than

double the EPOC of the equicaloric submaximal exercise. Furthermore, the respiratory

exchange ratio was significantly lower for the first four hours post-exercise following

the supramaximal exercise bout, indicating a more pronounced shift towards fat

oxidation after the cessation of exercise. The study by LaForgia et al. (1997)

demonstrates the potential for supramaximal sprint interval exercise to induce a higher

overall energy expenditure with enhanced fat oxidation rates post-exercise compared

with moderate intensity continuous exercise. This is the only study that has examined

the impact of supramaximal exercise compared with submaximal exercise on EPOC and

indicators of substrate oxidation.

Despite the noticeable superiority of sprint interval exercise in healthy adults, and its

potential to manage body fat stores, the intense nature of the protocols used in the two

previously mentioned studies by Gibala et al. (2006; 4-6 sets of 30-sec maximal sprint

efforts [~250% O2max] with 4 min recovery between bouts) and Tabata et al. (1996; 7-

8 sets of 20-sec bouts at 170% O2max with 10 sec recovery periods) raises the issue of

whether this type of exercise is manageable for sedentary and/or overweight individuals.

However, Harmer et al. (2008) utilised a similar protocol (4-10 sets of 30-sec maximal

sprint efforts with 3-4 min recovery) in sedentary and recreationally active type 1

diabetic patients. The authors made particular note that the high intensity sprint interval

exercise bouts were well tolerated and did not have any adverse effects on their

participants. In another study, Whyte et al. (2010) observed that two weeks of sprint

interval training (4-6 sets of 30-sec maximal sprint efforts with 4.5 min recovery

between each repetition performed 3 times/wk) resulted in significant increases in

aerobic fitness and improvements in the waist circumference of overweight/obese

sedentary men. The nature of sprint interval exercise to increase the intensity of exercise

without making the exercise unsustainable for overweight or unfit individuals may be

33

beneficial for fat control. To date, no studies have examined the acute effects of sprint

interval exercise on energy expenditure and substrate oxidation, particularly post-

exercise in an overweight paediatric population. Given the benefits of continuous

exercise at Fatmax for increasing fat oxidation, it may be particularly beneficial to

examine the impact of adding short maximal sprint efforts to continuous exercise at

Fatmax on energy expenditure and fat oxidation.

1.6 OTHER CONSIDERATIONS WHEN PRESCRIBING EXERCISE FOR OVERWEIGHT

CHILDREN

Although maximising the amount of energy that is expended during exercise is likely

important for fat loss, there are other factors that need to be considered. For example,

there is little point in prescribing exercise that maximises energy expenditure if the extra

energy that is expended is counteracted by increased post-exercise energy intake.

Furthermore, the more successful exercise training programs specific for fat loss are

undoubtedly those that individuals are able to adhere to in the long term. For this

reason, enjoyment during exercise should also be considered, particularly for children.

1.6.1 Appetite and Post-exercise Energy Intake

To fully understand the influence of an acute bout of exercise on energy balance, it is

also important to consider post-exercise energy consumption from food and drinks. As

previously mentioned, the additional energy expenditure that is associated with high

intensity exercise may be of little additional benefit if there is a greater compensation of

energy intake post-exercise. There is evidence that high intensity exercise may acutely

suppress appetite to a greater extent than low or moderate intensity exercise (King et al.,

34

1994; Thompson et al., 1988), but whether this suppression of appetite leads to

decreased energy intake is unclear. Thompson et al. (1988) compared the effect of

equicaloric low (35% O2max) and higher (68% O2max) intensity exercise on appetite

ratings in young men and found that feelings of hunger were briefly suppressed

following the higher intensity protocol, but not the low intensity protocol. Likewise,

King et al. (1994) observed that feelings of hunger were significantly suppressed during

and following a bout of high intensity exercise (75% O2max), but not low intensity

exercise (30% O2max) matched for energy expenditure, in healthy lean men. It has

been proposed that this suppression of hunger in response to higher intensity exercise is

influenced by ghrelin, a hormone that stimulates hunger (Erdmann et al., 2007). In

support of this notion, Erdmann et al. (2007) reported that 30 min of cycling at a low

exercise intensity (50 W) resulted in a significant increase in ghrelin, while the same

duration of exercise at a higher exercise intensity (100 W) did not. It is particularly

noteworthy from the three previously mentioned studies in adults (Erdmann et al., 2007;

King et al., 1994; Thompson et al., 1988), that despite the participants reporting

differences in feelings of hunger, absolute post-exercise energy consumption was

similar between the protocols of differing intensities. Nonetheless, these results suggest

that high intensity exercise may initially suppress appetite, when compared with lower

intensity exercise, without prompting an increase in post-exercise energy intake to

replace the extra energy that is expended during the exercise bout. As a result, studies

that have reported energy intake relative to the amount of energy expended during the

exercise bout have noted a short-term negative energy balance following high, but not

low intensity exercise (Imbeault et al., 1997; King et al., 1994) which may be of

particular benefit for fat management.

The effect of exercise intensity on energy intake may be modulated by body

composition. For example, a significantly lower post-exercise energy intake following

35

strenuous exercise (40 min at 90 W), but not moderate intensity exercise (40 min at 30

W), has been observed in non-obese women, but not in obese women in whom post-

exercise energy intake was similar following these two protocols (Kissileff et al., 1990).

This outcome is surprising given that hunger scores for the obese women alone were

significantly greater following the moderate intensity exercise compared to the

strenuous exercise. The authors suggested that obese individuals may be less responsive

to this physiological challenge to energy balance regulation compared with non-obese

individuals, and may feel the need to reward themselves after a strenuous workout

(Kissileff et al., 1990). In addition to body fatness, differences in gender and eating

behaviours may influence the results of studies that explore the influence of exercise

intensity on appetite and energy intake (Bilski et al., 2009). However, there is still a

need to examine the impact of HIIE on appetite and energy intake, an issue which to the

best of my knowledge, remains to be investigated.

Only two studies have examined the impact of exercise intensity on appetite and energy

intake in children (Moore et al., 2004; Thivel et al., 2012). In the study by Moore et al.

(2004), appetite ratings and energy intake were compared between two days during

which 9-10 year old girls of varying body compositions were exposed to two sessions of

either lower (50% O2peak) or high (75% O2peak) intensity equicaloric exercise (at

1030 and 1430 h). Feelings of appetite were assessed prior to and following the exercise

sessions and daily food intake (a selection of foods provided at lunch and in the evening

which were weighed before and after participants were instructed to eat ad libitum) was

recorded. Participants reported that they felt they “could eat less right now” prior to the

second high intensity exercise session at 1430 h compared to the same time of day for

the lower intensity sessions, but there was no significant difference between the two

intensities for all remaining appetite measures. Likewise, total energy intake (both daily

and for the separate meals) was not significantly different between the lower and high

36

intensity exercise days and, as the amount of energy that was expended during the

exercise bouts was similar, there was no significant difference in daily energy balance

(Moore et al., 2004). Thivel et al. (2012) compared appetite ratings, energy intake and

energy balance over 24 hours when a single bout of exercise was prescribed at 1100 h at

either a low (59 min at 40% O2peak) or high (30 min at 75% O2peak) intensity of

matched energy cost in obese adolescent boys. These authors observed that 24-hr

energy intake was significantly lower in the high intensity exercise condition compared

with the low intensity condition, which resulted in a significantly lower 24-hr energy

balance. This outcome occurred despite no significant difference in ratings of subjective

hunger, fullness or prospective food consumption between the two conditions (Thivel et

al., 2012). The difference between these two studies may be explained by the different

sample populations studied or the fact that energy expenditure was precisely measured

using a calorimetric chamber only in the study of Thivel et al. (2012). Nonetheless, as

the results from previously mentioned studies suggest a greater suppression of appetite

(Erdmann et al., 2007; King et al., 1994; Moore et al., 2004; Thompson et al., 1988),

and attenuated 24-hr energy intake and energy balance in obese adolescents (Thivel et

al., 2012) for higher intensity exercise compared with lower intensity exercise, it is

possible that supramaximal exercise may lead to an even greater suppression of appetite

and reduced post-exercise energy intake. To date, the effect of sprint interval exercise

on appetite and energy intake has not been examined in either normal weight or

overweight adults or children.

1.6.2 Enjoyment and Adherence

Irrespective of the type of exercise that provides better outcomes in relation to energy

balance (i.e. increased energy expenditure and decreased energy intake), there is little

37

point prescribing exercise for weight management if the individual is unlikely to adhere

to it in the long-term. Evidence suggests that the most influential factors to increase an

individual’s motivation to start exercising and to promote long-term adherence to an

exercise program are feelings of enjoyment and pleasure (Dishman et al., 1985). Given

that an estimated 45% of individuals who initiate exercise programs drop out (Marcus et

al., 2006), it seems vital to ensure that these aspects are examined closely for programs

aimed at long-term weight management.

Feelings of enjoyment during exercise and the resulting adherence levels are dependent

on prescription of the appropriate volume, intensity and duration of exercise to work

within the individuals’ capabilities. Perri et al. (2002) examined the adherence of

sedentary individuals to exercise prescribed at either a moderate (45-55% HRres) or high

(65-75% HRres) exercise intensity, with either a moderate (3-4 times/wk) or high (5-7

times/wk) frequency, while controlling for the mode (walking) and duration of exercise

(30 min). It was observed that participants in the higher intensity conditions completed

significantly less cumulative exercise than the participants in the moderate intensity

conditions, but a greater amount of exercise was completed in the high frequency

conditions compared to the moderate frequency conditions. These results suggest that

higher frequency, moderate intensity exercise may be preferable for exercise

prescription in sedentary populations. However, one limitation with the study by Perri et

al. (2002) relates to the fact that the participants’ ratings of pleasure and perceived

exertion towards the exercise bouts were not recorded, which could have explained why

62% of the participants completed only the minimum amount of exercise that they were

prescribed (Perri et al., 2002). In order to address this limitation, more recent studies

have been conducted to assess feelings of pleasure and perceived exertion (Kilpatrick et

al., 2007; Lind et al., 2008). Lind et al. (2008) observed that sedentary adults’ ratings of

pleasure during 20 min of exercise at a self-selected intensity remained stable, but when

38

the exercise was performed at an imposed intensity that slightly exceeded their preferred

level, ratings of pleasure declined. The authors concluded that declined ratings of

pleasure associated with higher intensity exercise, particularly at intensities above an

individual’s ventilatory threshold (Kilpatrick et al., 2007; Lind et al., 2008), could lower

their levels of adherence, although this was not specifically measured. To date, no

studies have directly examined whether the decrease in ratings of pleasure during higher

intensity exercise results in declines in long-term exercise adherence.

It is noteworthy to highlight that the above mentioned studies (Kilpatrick et al., 2007;

Lind et al., 2008; Perri et al., 2002) only examined the impact of exercise intensity on

measures of enjoyment and adherence for continuous exercise bouts. Rating of

perceived exertion (RPE) is another important factor that should be considered. Coquart

et al. (2008) observed that RPE during 32 min of intermittent exercise (alternating 80%

and 120% of the power output at ventilatory threshold every 2 min) were significantly

lower than those observed during continuous exercise (100% of the power output at

ventilatory threshold) of the same duration (and intensity) in type 2 diabetic and non-

diabetic obese women. These results indicate that intermittent exercise may be

perceptually easier than continuous exercise (Coquart et al., 2008; Jakicic et al., 1995)

which may be advantageous given that individuals tend to prefer participating in

exercise conditions that are associated with lower RPE (Robertson & Noble, 1997).

Furthermore, Bartlett et al. (2011) recently measured the perceived enjoyment of high-

intensity interval running (6 3-min bouts at 90% O2max interspersed with 3-min active

recovery at 50% O2max) compared with equicaloric continuous running (70% O2max)

in recreationally active men. This study found that ratings of enjoyment were higher for

the high-intensity interval running compared with the continuous exercise bout, despite

the fact that RPE was higher for the high intensity interval running. There is still a need

39

for studies to examine the relationship between perceived exertion and enjoyment

during interval exercise, particularly sprint interval exercise, in children.

Feelings of pleasure and enjoyment during exercise are also important to increase

motivation and adherence to exercise protocols suitable for weight loss in paediatric

populations. Despite this, studies examining the enjoyment of acute bouts of exercise in

children are limited (Sheppard & Parfitt, 2008). Sheppard and Parfitt (2008) examined

affective responses during 15 min of a self-selected exercise intensity and two

prescribed exercise bouts of low (80% of the ventilatory threshold) and high (130% of

the ventilatory threshold) intensity in fit adolescents. It was observed that the

participants’ feelings remained positive and fairly stable during the self-selected and

low intensity exercise bouts, but declined during the high intensity exercise bout.

Although it is possible that different responses may be observed in sedentary children,

this outcome supports the use of low-moderate intensity exercise in paediatric

populations and suggests that continuous high intensity exercise should be avoided

because it is associated with more negative feelings during exercise (Sheppard & Parfitt,

2008), which may result in decreased enjoyment and adherence. However, it is

important to note that once again, this study was only concerned with continuous

exercise protocols and it is possible that the results may be different for interval

exercise. In fact, when children are observed during spontaneous physical activity or

free-play, they most commonly engage in high intensity (Hoos et al., 2004) unstructured

games or sports that require multiple short sprint efforts of approximately 3-4 sec,

interspersed with longer duration low and moderate intensity exercise (Bailey et al.,

1995), rather than continuous exercise of a long duration. Therefore, it may be more

appropriate to increase the intensity of exercise for children by utilising sprint interval

exercise that reflects these spontaneous free-play patterns, to promote enjoyment during

exercise, which may enhance long-term adherence.

40

1.7 SUMMARY

1.7.1 Statement of the Problem

Exercise is important in the management of childhood obesity. However, the optimal

type of exercise for the overweight or obese child is not known. Studies have suggested

that exercise training at Fatmax is superior to other modalities of exercise because at this

intensity, fat oxidation rates are enhanced which may promote fat loss in the long term.

However, limited research has been conducted on the utilisation of exercise at Fatmax in

children. There is also a need for the development of a protocol that enables an accurate

estimation of Fatmax in overweight children.

Another type of exercise regime that might be beneficial for fat loss is sprint interval

exercise, since it results in increased energy expenditure per unit of time and increased

fat oxidation rates post-exercise. However, irrespective of the exercise modality that is

adopted for body fat management, it is important to stress that in order to determine the

optimal type of exercise for the overweight or obese child, one should also consider

post-exercise energy intake and enjoyment. For example, there is little point in

prescribing exercise that maximises energy expenditure if the individual compensates

for the extra energy expended by increasing post-exercise energy intake. Furthermore,

exercise that is difficult or boring, or simply not enjoyable for the individual decreases

the likelihood of long-term adherence which is essential for ongoing successful weight

management. The effect of sprint interval exercise on these parameters is not known.

Therefore, studies are required to provide new insight into the utilisation of sprint

interval exercise for increasing the enjoyment and energy expenditure of exercise for

children to assist in combating childhood obesity.

41

1.7.2 Aims

A preliminary aim of this thesis was to determine whether there is potential for a single

graded exercise protocol with 3-min stages to be utilised for the accurate estimation of

Fatmax in boys carrying excess body fat (overfat). Following this, the primary aim was to

explore the influence of moderate intensity continuous exercise at Fatmax compared with

sprint interval exercise reflecting the activity patterns of children’s spontaneous play

(i.e. continuous exercise at Fatmax interspersed with a 4-sec maximal sprint effort every

2 min) on energy expenditure, fat oxidation (both during and post-exercise), post-

exercise energy intake and enjoyment in overfat boys.

Specifically, the aims of this thesis were to investigate;

Whether Fatmax remains stable across 30-min constant load exercise bouts (i.e.

whether the duration of exercise affects fat oxidation rates and ultimately, the

Fatmax

Whether the cumulative duration of a graded exercise test affects Fat

estimate) in overfat boys.

max (i.e. by

comparing Fatmax

The influence of adding 4-sec sprint efforts every 2 min to continuous exercise at

Fatmax, compared with continuous exercise at Fatmax alone, on energy expenditure

and substrate oxidation (inclusive of the acute post-exercise recovery period),

enjoyment and acute post-exercise energy intake in overfat and control (carrying

normal levels of body fat) boys.

estimated from a single graded exercise test with 3-min stages

against 30-min bouts of prolonged steady-state exercise) in overfat boys.

The extent to which the frequency of 4-sec sprints can be increased (i.e. every 2

min, 1 min or 30 sec) in order to maximise the amount of energy expended during

exercise, before enjoyment of the exercise bout starts to decline.

42

1.7.3 Research Hypotheses

The hypotheses relating to these aims are that;

Fatmax will remain stable across 30 min of constant load exercise in overfat boys.

The cumulative duration of a graded exercise test will not affect the estimation of

Fatmax in overfat boys.

The addition of 4-sec maximal sprint efforts every 2 min to continuous exercise at

Fatmax will increase energy expenditure (both during and post-exercise), as a result

of increased carbohydrate oxidation rates, without compromising the rate of fat

oxidation compared with continuous exercise at Fatmax alone.

The addition of 4-sec sprint efforts every 2 min to continuous exercise at Fatmax will

suppress appetite and result in decreased acute post-exercise energy intake, as well

as make the exercise more enjoyable for both overfat and control boys.

Energy expenditure will increase with increasing sprint frequency as a result of

increased carbohydrate oxidation rates. However, fat oxidation rates may be

compromised when sprints are introduced every 1 min and every 30 sec.

Increasing sprint frequency will result in a greater suppression of appetite and post-

exercise energy intake compared with continuous exercise at Fatmax.

Enjoyment of exercise will be compromised when the sprint frequency is increased

to every 1 min and every 30 sec, compared with every 2 min and no sprints (i.e.

continuous exercise at Fatmax).

43

1.7.4 Organisation and Structure of this Thesis

Following this Literature Review is a series of three chapters that address particular

aspects relating to the utilisation of Fatmax and sprint interval exercise for overfat

children. In particular, these chapters relate to the accurate determination of Fatmax in

overfat children (Chapter 2), the influence of continuous exercise at Fatmax compared

with sprint interval exercise (selected to reflect the spontaneous physical activity

preferences of children) on energy expenditure, fat oxidation, acute post-exercise energy

intake and enjoyment (Chapter 3), and the extent to which the frequency of sprints can

be increased to maximise energy expenditure before levels of enjoyment start to decline

(Chapter 4). Finally, the last chapter aims to integrate the overall findings of the thesis

by providing a General Discussion (Chapter 5) including the conclusions, implications,

limitations and directions for future research.

44

2 STUDY 1

DOES EXERCISE DURATION AFFECT FATMAX

IN OVERFAT BOYS?

Based on a manuscript published in the European Journal of Applied Physiology:

Crisp NA, Guelfi KJ, Licari MK, Braham R, Fournier PA (2012) Does exercise duration

affect Fatmax

in overweight boys? European Journal of Applied Physiology 112(7):

2557-2564

45

2.1 ABSTRACT

The purpose of this study was to compare the assessment of Fatmax using a single

graded exercise test with 3-min stages against 30-min bouts of prolonged exercise in ten

boys aged 8-12 years carrying excess body fat (overfat). Participants attended the

laboratory on seven separate occasions. On the first visit, body composition and

anthropometry and peak aerobic capacity ( O2peak) were assessed. Following this, each

participant attended the laboratory after an overnight fast for six morning cycling

sessions. During the first session, participants completed a continuous, submaximal

graded exercise protocol (GRAD) with seven 3-min stages at 35, 40, 45, 50, 55, 60 and

65% O2peak. The final five visits each consisted of a 30-min bout of prolonged

exercise (PROL) performed in a counterbalanced order at 40, 45, 50, 55 and 60%

O2peak. There was no effect of exercise duration on Fatmax or the absolute rate of fat

oxidation during PROL (p > 0.05). At the group level, GRAD and PROL provided

similar estimates of Fatmax (GRAD: 53 ± 10% O2peak; PROL: 53 ± 10% O2peak; p =

0.995); however, individual variation between the two protocols is shown by a

systematic bias and residual error of 0 ± 11% O2peak. Fat oxidation rates were stable

across 30 min of steady-state exercise in overfat boys. Furthermore, Fatmax was similar

at 3, 10, 20 and 30 min of exercise, suggesting that for exercise lasting 30 min or less,

exercise duration does not affect Fatmax. However, Fatmax

determined with GRAD may

need to be interpreted with caution at the individual level, given the variation between

protocols.

2.2 INTRODUCTION

The absolute and relative contributions of fat and carbohydrate oxidation to support

energy demands during exercise are influenced by the exercise intensity. During low to

46

moderate intensity exercise, a greater proportion of fat is oxidised by the working

muscles compared to high intensity exercise. However, this proportion shifts towards

greater carbohydrate oxidation at higher exercise intensities because fat cannot be

oxidised rapidly enough to meet the increasing energy requirements of the working

muscles (Brooks & Mercier, 1994; Venables et al., 2005). Moreover, absolute fat

oxidation rate increases with exercise intensity to a point above which it starts to

decline. The intensity at which fat oxidation is the greatest has been termed Fatmax

(Achten et al., 2002) and is commonly expressed as a percentage of maximal or peak

oxygen uptake (% O2max/peak). Some researchers suggest that the identification of

Fatmax may allow for the development of more appropriate exercise interventions aimed

at reducing fat mass and other medical consequences associated with obesity (Ben

Ounis et al., 2008; Brandou et al., 2003; Dumortier et al., 2003; Venables & Jeukendrup,

2008; Zakrzewski & Tolfrey, 2011b). As it is important to intervene in the early onset of

obesity, before any long-term consequences have a chance to develop (e.g. diabetes,

musculoskeletal abnormalities, poor self-esteem), it may be particularly beneficial to be

able to determine Fatmax

Many studies have implemented a single graded exercise test with 3-min stages to

identify Fat

in a paediatric population.

max in adults (Achten et al., 2002; Achten et al., 2003; Riddell et al., 2008;

Venables et al., 2005). Using this protocol, the rate of fat oxidation at each stage of the

test is measured and plotted against its respective exercise intensity to construct a curve

of fat oxidation rate from which Fatmax is determined. This method has been validated in

trained men by comparing the average rate of fat oxidation during 35-80 minutes of

continuous exercise (adjusted to result in similar energy expenditure between

intensities) on separate days at intensities corresponding to the stages of the graded

exercise test (Achten et al., 2002). However, this validation study did not examine

whether the rate of fat oxidation changed over time during each continuous exercise

47

bout. This could be important given that fat oxidation rates have been observed to

increase as the duration of exercise progresses (Chenevière et al., 2009; Meyer et al.,

2007; Pillard et al., 2007), suggesting that Fatmax might also change over time.

Furthermore, in the context of graded exercise protocols using consecutive stages to

determine Fatmax, the increase in the cumulative duration of exercise as the test

progresses might affect fat oxidation rates, particularly during the latter stages of the

protocol, which may ultimately affect the estimation of Fatmax. Finally, although Achten

et al. (2002) provided valuable information regarding the use of a single graded exercise

protocol in trained individuals, there has been limited research validating its use in

sedentary (Bordenave et al., 2007) and/or overweight individuals. This is important

given the potential for exercise training at Fatmax

The few studies that have determined Fat

to assist with weight management

(Brandou et al., 2003; Dumortier et al., 2003) and to reduce the risk of other medical

consequences associated with obesity (i.e. insulin sensitivity; Venables & Jeukendrup,

2008), particularly for the rapidly growing overweight paediatric population.

max in children and adolescents have also

utilised incremental protocols with 3-6 min stages, adapted from Achten et al. (2002),

and report Fatmax to occur between 40-56% O2peak (Aucouturier et al., 2009; Lazzer et

al., 2007; Lazzer et al., 2010; Riddell et al., 2008; Zakrzewski & Tolfrey, 2011a;

Zunquin et al., 2009a; Zunquin et al., 2009b). However, only one study has attempted to

validate the use of a single, incremental protocol to determine Fatmax in children.

Zakrzewski and Tolfrey (2011a) compared Fatmax estimated from 3-min incremental

stages to that estimated from six 10-min constant load bouts and found comparable

results between the two protocols in healthy prepubertal children. Based on these

results, the authors recommended that a 3-min incremental protocol could be used to

provide an estimation of Fatmax in this population, but acknowledged that it might not

be appropriate for obese children (Zakrzewski & Tolfrey, 2011a). Furthermore, the

48

exercise duration of 10 min utilised in the constant load bouts may not have been long

enough to observe any potential increase in fat oxidation rate over time (Chenevière et

al., 2009; Meyer et al., 2007; Pillard et al., 2007). For these reasons, the primary

purpose of the present study was to determine whether Fatmax remains stable across 30

min of constant load exercise (i.e. whether the duration of exercise affects fat oxidation

rates and ultimately, the Fatmax estimate) in overfat boys. A secondary aim was to

compare the Fatmax estimated from a single graded exercise test with 3-min stages

(GRAD) against 30-min bouts of prolonged exercise (PROL) to determine whether the

cumulative duration of a graded exercise test affects Fatmax

.

2.3 METHODS

2.3.1 Participants

Eleven participants were initially recruited from the local community via advertisements

presented in school newsletters, public flyers and paediatric wellness centres to

participate in this study. A screening process ensured all participants were (a) free of

risk factors associated with cardiovascular, pulmonary or metabolic disease; (b) not

diabetic or hypertensive; (c) deemed safe to perform maximal exercise. Of these 11

participants, one elected not to complete the study due to personal reasons. As a result,

10 overfat boys (10.3 ± 1.9 years) completed all experimental procedures and were

included in the final analysis. Their general characteristics are presented in Table 2.1.

Prior to recruitment, human ethics approval was sought from the Human Research

Ethics Committee at The University of Western Australia (UWA; Appendix B). Before

involvement in the study, written consent was obtained from each participant and their

parent/guardian (Appendix C).

49

Table 2.1 Participant Characteristics

Mean ± SD Range

Height (cm) 149.8 ± 8.4 137.6 - 164.8

Body mass (kg) 56.4 ± 13.2 45.6 - 89.8

BMI (kg/m2 25.0 ± 4.0 ) 20.6 - 33.1

Waist circumference (cm) 83.9 ± 11.5 70.5 - 108.0

Fat mass (kg) 22.5 ± 8.1 15.4 - 41.5

Body fat (%) 39.1 ± 5.5 30.2 - 47.0

Fat free mass (kg) 34.0 ± 5.9 29.3 - 48.3

O2peak 1.87 ± 0.35 (L/min) 1.23 - 2.39

O2peak 34.0 ± 7.2 (mL/kg/min) 25.1 - 45.0

O2peak, rate of peak oxygen uptake

2.3.2 Research Design

Each participant was asked to attend the Exercise Physiology Laboratory at UWA on

seven separate occasions. On the first visit, body composition and anthropometry and

O2peak were assessed. Following this, each participant attended the laboratory after an

overnight fast for six morning cycling sessions (each separated by one week) completed

on a stationary front access cycle ergometer (Repco Cycle Company, Exertech EX-10,

Huntingdale, Victoria) which was interfaced with a customised software program

50

(Cyclemax, School of Sport Science, Exercise and Health, The University of Western

Australia) to provide a visual display of each participant’s cycling power output.

During the first morning session, participants completed a submaximal graded exercise

protocol (GRAD) with seven 3-min stages at 35, 40, 45, 50, 55, 60 and 65% O2peak.

The final five visits each consisted of a prolonged 30-min steady-state exercise bout at

40, 45, 50, 55 and 60% O2peak (PROL), administered in a counterbalanced order.

These intensities were based on the results from previous studies in overweight children

and adolescents suggesting that Fatmax occurs at 40-56% O2peak

(Aucouturier et al.,

2009; Lazzer et al., 2007; Lazzer et al., 2010; Riddell et al., 2008; Zakrzewski &

Tolfrey, 2011a; Zunquin et al., 2009a; Zunquin et al., 2009b). Participants were

instructed to maintain their normal dietary and physical activity practices between

testing sessions. They were also asked to complete a food record (Appendix F) for 24

hours prior to the first session and to replicate their food intake as closely as possible on

the day before each subsequent session. In addition, participants were asked to refrain

from strenuous physical activity for at least 24 hours before all testing sessions.

2.3.3 Anthropometry and Body Composition

Height was measured to the nearest 0.1 cm on a standardised, wall-mounted stadiometer

with participants standing in bare feet and their head in the Frankfort plane. Body mass

was determined to the nearest 0.01 kg using electronic scales (August Sauter GmbH D -

7470 Albstadt 1 Ebingen, West Germany) with participants dressed in light clothing and

without shoes. Body mass index (BMI) was calculated as body mass (kg) divided by

height (m) squared (Cole et al., 2000; Appendix A). Waist circumference (cm) was

taken at the minimum circumference between the top of the iliac crest and the distal end

of the rib cage along the midaxillary line with participants standing in an upright

51

position and their feet together. Body composition was assessed using Dual Energy X-

Ray Absorptiometry (DEXA; Lunar Prodigy, encore 2004, GE Medical Systems,

Madison, Wis., USA) with participants scanned in light clothing. The DEXA results for

total percentage of body fat mass (% FM) provided confirmation that the participants

were overfat (i.e. carrying excess body fat rather than increased lean muscle mass)

based on the classification index of McCarthy et al. (2006; Appendix A2).

2.3.4 Determination of Peak Aerobic Capacity

Following the determination of anthropometry and body composition, all participants

completed a graded exercise test to determine O2peak. Participants started cycling with

a power output of 20 watts (W) and every three minutes, they were instructed to

increase their power output by 20 W. Each participant exercised continuously until their

individual end point of fatigue, or other limiting signs or symptoms (e.g. dizziness)

were recognised. As the participants approached volitional exhaustion, strong verbal

encouragement was provided while they performed a maximal sprint effort to ensure a

true O2peak

Throughout the duration of the graded exercise test, participants breathed through a

mouthpiece attached to a two-way Hans-Rudolph valve which was connected to a

computerised gas analysis system. Ventilation was recorded using a turbine ventilometer

(Morgan, 225A, Kent, England) which was calibrated before the test using a one litre

syringe. Oxygen (O

was attained (Barker et al., 2011). Heart rate was measured continuously

and recorded at the end of each stage.

2) and carbon dioxide (CO2) concentration in the expired air was

continuously analysed using Ametek gas analysers (Applied Electrochemistry, SOV S-

3A11 and COV CD-3A, Pittsburgh, PA, USA) which were also calibrated immediately

before and verified after each test using a certified beta-grade gravimetric gas mixture

52

of known physiological concentration (~16% O2 & ~4% CO2; BOC Gases, Chatswood,

Australia). Both the ventilometer and gas analysers were connected to a PC which

measured and displayed variables every 15 sec. The sum of the four highest 15-sec

consecutive volumes of O2 consumption was recorded as the participants O2peak.

Furthermore, a graph of the cycling power output (W) versus exercise intensity

(% O2peak

) was constructed to determine the stages used for GRAD at the next session.

2.3.5 Fatmax

One week after

Determination Using a 3-min Graded Exercise Test

O2peak determination, participants arrived at the laboratory in the

morning after an overnight fast to complete GRAD. Participants started cycling at a

power output equivalent to 35% O2peak and every three minutes, the power output was

increased until seven stages corresponding to 35, 40, 45, 50, 55, 60 and 65% O2peak

For the duration of GRAD, participants breathed through a mouthpiece connected to a

two-way Hans-Rudolf valve enabling the collection of expired air into a 120 litre Tissot

gasometer tank (Collins Inc, Braintree, Massachusetts). The tank was flushed twice with

the participants own air prior to collecting expired air samples over the last min of each

stage of the graded exercise test. From these samples of expired air, the concentration of

O

were completed. Heart rate was recorded at the end of each stage. In addition, capillary

blood samples (5 µL) were collected from the fingertip and analysed for lactate

concentration using a Lactate Pro (Arkray, LT-1710, Kyoto, Japan) within the final 30

sec of the last stage to ensure that the incremental cycling protocol did not result in a

marked lactate increase.

2 and CO2 were determined using the previously described Ametek gas analysers.

Each participant’s fat and carbohydrate oxidation rate (g/min) was calculated using

equations from Frayn (1983). It was assumed that protein oxidation contributed to

53

approximately 12% of energy expenditure based on previous studies in children (Lazzer

et al., 2007; Lazzer et al., 2010; Maffeis et al., 2005). A scatterplot of fat oxidation rate

versus exercise intensity, fitted with a second order polynomial curve, was constructed

for each participant (Figure 2.1). The individual exercise intensity (i.e. 35, 40, 45, 50,

55, 60 or 65% O2peak) at which Fatmax occurred and the corresponding maximal rate of

fat oxidation (MFO) was visually identified (Riddell et al., 2008; Zakrzewski & Tolfrey,

2011a), along with the 10% Fatmax

zone (range of exercise intensities whereby fat

oxidation rates are within 10% of MFO; Achten et al., 2002).

Figure 2.1 Example scatterplot of fat oxidation rate ( ) vs. exercise intensity during a

submaximal graded exercise test with 3-min stages (GRAD) used to identify Fatmax

( )

2.3.6 Fatmax

Over the five subsequent sessions, participants completed 30 min of steady-state cycling

sessions (PROL) at workloads corresponding to 40, 45, 50, 55 and 60%

Determination Using 30-min Constant Load Protocols

O2peak

54

administered in a counterbalanced order and each separated by one week. Throughout

the 30-min exercise sessions, participants breathed through a mouthpiece continuously

but expired air was only collected in the Tissot gasometer tank across min 2-3, 9-10, 19-

20 and 29-30 to determine the rate of fat and carbohydrate oxidation using the methods

previously described. Scatterplots representing the rate of fat oxidation versus exercise

intensity were constructed for each participant at the four measured time-points

separately. These graphs allowed for the identification of Fatmax, MFO and the 10%

Fatmax zone at 3, 10, 20 and 30 min of exercise to assess the effect of exercise duration

on Fatmax

. Capillary blood samples (5 µL) were collected from each participant’s

fingertip immediately after completion of each 30-min protocol.

2.3.7 Statistical Analysis

Repeated measures ANOVA was utilised to examine the effect of PROL exercise

duration and intensity on Fatmax, the rate of fat and carbohydrate oxidation and energy

expenditure. At the group level, the difference in Fatmax and MFO estimated from

GRAD and PROL was also compared using repeated measures ANOVA. Limits of

agreement (LoA) were used to compare individual differences between GRAD and

PROL (Bland & Altman, 1986). Systematic bias (SB) was determined by calculating the

mean difference between the two protocols and the residual error (RE) was the SD of

the paired differences (Bland & Altman 1986). The LoA were then calculated by

determining a 95% limit above and below the SB (i.e. SB ± [1.96 × RE]). The 10%

Fatmax

zone for GRAD was adopted as the a priori critical value against which to define

the agreement between PROL and GRAD (Achten et al., 2002).

55

2.4 RESULTS

2.4.1 Effect of Exercise Duration and Intensity on Fat and Carbohydrate Oxidation

As shown in Figure 2.2, energy expenditure and the absolute rate of fat and

carbohydrate oxidation were stable across all 30-min PROL exercise bouts (i.e. there

was no effect of exercise duration; p > 0.05). However, the absolute amounts of energy

expenditure and fat and carbohydrate oxidation during the 30-min exercise bouts were

significantly influenced by the exercise intensity (p < 0.05; Table 2.2). Specifically, the

amount of energy expended and carbohydrate oxidised at 60% O2peak was

significantly greater than all other exercise intensities (p < 0.05; Table 2.2). In addition,

the amount of energy expended at 55% O2peak was significantly greater than at 40% (p

= 0.042) and 45% (p = 0.036) O2peak (Table 2.2). There was also a tendency for the

amount of energy expended at 50% O2peak to be greater than at 40% (p = 0.057) and

45% O2peak (p = 0.080; Table 2.2). Finally, the absolute amount of fat oxidised during

30 min of exercise at 40% O2peak was significantly lower than all other exercise

intensities (p < 0.05; Table 2.2). There was also a tendency for the amount of fat

oxidised at 45% O2peak to be less than at 55% O2peak

(p = 0.056; Table 2.2).

2.4.2 Effect of Exercise Duration on Fat

The exercise intensity that resulted in Fat

max

max was similar at 3, 10, 20 and 30 min of

PROL (i.e. there was no effect of exercise duration on Fatmax; p = 0.190; Figure 2.3).

For this reason, only the Fatmax identified at the 30-min time-point of PROL was used

for statistical comparison to the Fatmax identified by GRAD.

54

Figure 2.2 Mean (± SE) energy expenditure and contributions of fat and carbohydrate oxidation at 10, 20 and 30 min of the 30-min steady-state

exercise sessions at 40, 45, 50, 55 and 60% O2peak (PROL)

56

55

Table 2.2 Absolute amount of energy expenditure, and fat and carbohydrate oxidation (mean ± SD) during the 30-min steady-state exercise bouts at 40,

45, 50, 55 and 60% O2peak

(PROL)

Exercise Intensity (% O2peak

)

40% 45% 50% 55% 60%

Energy Expenditure (kJ) 512 ± 111 538 ± 80 580 ± 103 621 ± 82 680 ± 73†

Fat Oxidation (kJ)

#

251 ± 34* 299 ± 62 309 ± 66 337 ± 69 321 ± 61

Carbohydrate Oxidation (kJ) 149 ± 69 146 ± 78 161 ± 75 180 ± 79 249 ± 73

* Significantly lower than all other intensities (p < 0.05)

#

#

† Significantly greater than 40% and 45%

Significantly greater than all other exercise intensities (p < 0.05)

O2peak (p < 0.05)

57

58

Figure 2.3 Mean (± SE) exercise intensity that maximises fat oxidation (Fatmax) at 3,

10, 20 and 30 min of the 30-min steady state exercise bouts at 40, 45, 50, 55 and 60%

O2peak

(PROL)

2.4.3 Fatmax

At the group level, there was no significant difference in Fat

Estimated from a Single Graded Exercise Test

max (GRAD: 53 ± 10%

O2peak; PROL: 53 ± 10% O2peak; p = 0.995) or MFO (GRAD: 0.303 ± 0.08 g/min;

PROL: 0.328 ± 0.06 g/min; p = 0.363) estimated from the two protocols. The 10%

Fatmax zone ranged from 50 ± 2% to 66 ± 2% O2peak for GRAD and 46 ± 3% to 65 ±

7% O2peak for PROL. Polynomial R2 values indicated a moderate to high goodness of

fit for GRAD (R2 = 0.80 ± 0.18) and PROL (R2 = 0.86 ± 0.26). However, noticeable

individual variability between the two protocols prompted further investigation using

Bland-Altman analysis (Figure 2.4) which provided a SB ± RE of 0 ± 11% O2peak and

resulted in 95% LoA of ± 21% O2peak. Five participants had Fatmax estimates from

GRAD and PROL that were within 6% O2peak of each other but the remaining five

participants had residuals of 11-16% O2peak (Figure 2.4).

59

Figure 2.4 (a) Individual variability, and (b) Bland-Altman plot for average difference

in the exercise intensity that maximises fat oxidation (Fatmax), determined using a single

graded exercise protocol with 3-min stages (GRAD) compared with 30-min steady-state

exercise sessions at 40, 45, 50, 55 and 60% O2peak (PROL)

60

2.4.4 Heart Rate and Lactate Measurements

For GRAD, the maximum heart rate and lactate level attained while cycling at 60%

O2peak was 145 ± 10 bpm and 1.8 ± 0.6 mmol/L, respectively. The difference in power

output between each stage of GRAD (i.e. 5% O2peak) ranged from 5-10 W (7.2 ± 1.4

W). For PROL, the maximum heart rate and lactate level attained while cycling at 60%

O2peak

was 147 ± 8 bpm and 1.7 ± 0.3 mmol/L, respectively.

2.5 DISCUSSION

It has been suggested that identification of Fatmax may allow for the development of

exercise interventions that are more successful at reducing body fat mass in the long

term (Brandou et al., 2003; Dumortier et al., 2003). As it is important to intervene in the

early onset of obesity to ensure that healthy habits are carried on into adulthood, it

appears particularly beneficial to be able to determine Fatmax in a paediatric population.

A single graded exercise protocol with 3-min stages is the most commonly utilised

protocol for determining Fatmax in adults (Achten et al., 2003; Venables et al., 2005);

however, only one study has attempted to validate its use in children (Zakrzewski &

Tolfrey, 2011a) and no studies have investigated the overfat paediatric population. This

is important given that differences in oxygen uptake kinetics and substrate oxidation

have been found between adults and children (Fawkner et al., 2002; Riddell et al., 2008)

and also normal weight and overweight individuals (Cooper et al., 1990). Furthermore,

despite its convenience, there are potential limitations to the single graded exercise

protocol that may affect the validity of Fatmax estimates. Firstly, the rate of fat oxidation

has been observed to increase as the duration of exercise progresses (Chenevière et al.,

2009; Meyer et al., 2007; Pillard et al., 2007) suggesting that Fatmax also has the

potential to change across time. Further, the carry-over effects between consecutive

61

stages of graded exercise tests may influence substrate oxidation, particularly during the

latter stages of the protocol. Here we show however, that Fatmax

In many respects, the findings of previous studies attempting to validate methods of

determining Fat

remains stable with

exercise lasting 30 min or less in overfat boys and there was no evidence of a carry-over

effect of substrate oxidation between consecutive stages of a graded exercise test.

max should be interpreted with caution. Achten et al. (2002) utilised a

single graded exercise test with 3-min stages to determine O2max and Fatmax and

validated the protocol against 35-80 min of steady-state exercise protocols at intensities

corresponding to each stage of the graded exercise test. Zakrzewski and Tolfrey (2011a)

validated their 3-min protocol against 10-min constant load tests. Using these

approaches, the authors’ concluded that their 3-min graded exercise protocols provided

a valid estimate of Fatmax in the observed populations. However, one potential limitation

that these two studies share is that the rate of fat oxidation used for comparison between

the protocols was averaged across the duration of each steady-state exercise bout (i.e.

fat oxidation rate across time was not reported), thus not excluding the possibility that

fat oxidation rate, and therefore Fatmax, may change as the duration of exercise

increases. It has been observed that longer exercise durations may promote enhanced fat

oxidation (Chenevière et al., 2009; Meyer et al., 2007; Pillard et al., 2007). Furthermore,

in Zakrzewski and Tolfrey (2011a), the 10-min constant load bouts were not completed

on separate days which cannot completely rule out carryover effects. The

aforementioned limitations are not shared by the current study as the rate of fat

oxidation was recorded at four different time-points across the steady-state exercise

bouts, which were completed on separate mornings. In this study, substrate oxidation

measured across 30 min of continuous cycling at 40, 45, 50, 55 and 60% O2peak

revealed no significant differences in fat and carbohydrate oxidation rate or energy

expenditure across time, as well as no change in Fatmax. It is important to note however,

62

that our results do not exclude the possibility that changes in fat oxidation rate and

Fatmax may develop in children with exercise durations longer than 30 min (Chenevière

et al., 2009; Meyer et al., 2007). In any case, a likely explanation for the fact that we

observed no change in fat oxidation rate across 30 min of exercise, while other studies

in adults have observed increased rates of fat oxidation across time (Chenevière et al.,

2009; Meyer et al., 2007; Pillard et al., 2007), is that there are differences in substrate

oxidation between adults and children (Riddell et al., 2008). As this is the first study to

explore whether Fatmax

An interesting finding of the current study is that for the simultaneous determination of

changes across time as the duration of exercise progresses,

rather than examining the influence of exercise duration on the rate of fat oxidation

alone, similar validation studies need to be completed in adults.

O2peak and Fatmax with a single graded exercise test, it is important to ensure that the

difference in exercise intensity between stages is not too large as the results from PROL

demonstrate that differences as small as 5% O2peak may significantly affect the overall

rate of fat oxidation. For example, fat oxidation rates were significantly lower at 40%

O2peak than 45% O2peak. This is particularly noteworthy given that the majority of

previous studies conducted in overweight children utilise incremental protocols with

increases of 10% O2peak between stages. On the other hand, the practical disadvantage

of adopting a protocol with several, small increments in exercise intensity is that the

length of testing could be substantially increased, particularly if used as part of a single,

maximal exercise test for the determination of O2peak. For example, the differences in

exercise intensity between the stages of our GRAD protocol (i.e. 5% O2peak equated to

approximately 7 W on the cycle ergometer) are such that participants would be required

to complete over 15 stages on average to measure both Fatmax and O2peak within the

one test, which would equate to a test duration of greater than 45 min. Based on our

experience, most children find it difficult to motivate themselves to exercise on a

63

stationary bike for longer than 30 min which suggests that 10 stages is the maximum

amount that would be tolerated by this population. In regards to the stage duration for

determining Fatmax using a single incremental protocol, it has been suggested that four

min may be preferable for obese children (Zakrzewski & Tolfrey, 2011a), but here we

have shown that 3-min stages appears sufficient. Future research is required to develop

a protocol that successfully locates both Fatmax and O2peak

It is important to note that although there was no significant difference in the group

average estimations for Fat

in overweight children,

while minimising the number of stages and hence, the duration of testing.

max based on the GRAD and PROL protocols, analysis of the

individual variation revealed the 95% LoA were ± 21% O2peak. For GRAD, the 10%

Fatmax zone ranged from 50 ± 2% to 66 ± 2% O2peak, corresponding to an a priori

limit of around 8% O2peak for Fatmax. Although five participants had Fatmax estimates

between the two protocols that differed by less than 6% O2peak, which is below this

limit, the remaining five participants had residuals of ± 11-16% O2peak. The variation

observed in these participants is likely to be explained by the fact that it was necessary

for GRAD and the five sessions that made up PROL to be completed on separate days

to minimise the effect of prior exercise on substrate oxidation. Day-to-day fluctuations

in substrate oxidation have been observed as a result of differences in climatic

influences, nutrition and the time of day (Bagger et al., 2003). Although the influence of

these factors were controlled as much as possible in the current study by having the

participants fast overnight before coming into the laboratory at the same time each

morning, it is possible that these measures were not stringent enough to control for the

aforementioned fluctuations. This outcome highlights another practical advantage of

utilising a single graded exercise protocol to determine Fatmax, rather than protocols that

require multiple visits to the laboratory which may require precise replication of food

intake and energy expenditure on the days preceding each experimental session.

64

However, future studies should seek to refine GRAD to improve Fatmax

In conclusion, the present study explored whether a single incremental cycling protocol

with 3-min stages could be used to estimate Fat

estimation at the

level of the individual. It should also be noted that although the five sessions that made

up PROL were conducted in a counterbalanced order, GRAD was completed prior to

PROL for all participants; therefore, we cannot exclude a possible order effect.

max for exercise lasting up to 30 min in

duration in overfat boys. We have shown that the rate of fat oxidation remains stable

across 30 min of cycling at intensities between 40-60% O2peak and that the Fatmax

estimate was similar at 3, 10, 20 and 30 min of exercise. However, although the Fatmax

estimate from GRAD and PROL was similar at the group level, suggesting that the

cumulative duration of a graded exercise test does not affect Fatmax, there was some

marked variation in these estimates of Fatmax at the individual level. Nonetheless,

determining Fatmax from the multiple visits required for PROL is not feasible in most

clinical settings, therefore future studies are required to refine GRAD to successfully

locate Fatmax and O2peak at the individual level in overweight children. Furthermore,

whether exercise training at the Fatmax

equates to significantly greater fat loss in the

long term, as a result of the increased fat oxidation, is yet to be established in both

overfat adults and children. Finally, from a health perspective, it should be determined

whether it is more beneficial to focus on maximising physical activity participation and

energy expenditure, rather than defining such specific exercise intensity guidelines.

65

3 STUDY 2

ADDING SPRINTS TO EXERCISE AT FATMAX: IMPLICATIONS FOR

ACUTE ENERGY BALANCE AND ENJOYMENT IN BOYS

Based on a manuscript accepted for publication in Metabolism:

Crisp NA, Guelfi KJ, Licari M, Braham R, Fournier P (2012) Adding sprints to

continuous exercise at the intensity that maximises fat oxidation: Implications for acute

energy balance and enjoyment. Metabolism DOI: 10.1016/j.metabol.2012.02.009

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3.1 ABSTRACT

The aim of this study was to examine the impact of the addition of short maximal sprint

efforts to continuous exercise at the intensity that maximises fat oxidation (Fatmax) on

energy expenditure, substrate oxidation, enjoyment and acute post-exercise energy

intake in boys. Nine overfat (carrying excess levels of body fat) and nine control

(carrying normal levels of body fat) boys aged 8-12 years attended the laboratory on

three separate mornings. At the first session, body composition was measured and

participants completed a graded exercise test to determine peak aerobic capacity and

Fatmax. On the remaining two sessions, resting metabolic rate was determined before the

participants completed 30-min of either continuous cycling at Fatmax (MOD) or sprint

interval exercise consisting of continuous cycling at Fatmax interspersed with 4-sec

maximal sprint efforts every 2-min (SI). Energy expenditure and substrate oxidation

was measured during exercise and for 30 minutes post-exercise, while participants

completed a modified Physical Activity Enjoyment Scale (PACES). Following this,

participants were provided with a buffet-type breakfast from which they could consume

ad libitum to measure post-exercise energy intake. Fat oxidation rate was similar

between the overfat and normal weight groups and between the two exercise protocols

(p > 0.05). Both groups expended more energy with SI compared to MOD, resulting

from increased carbohydrate oxidation (p < 0.05), which was not compensated by

increased acute post-exercise energy intake. Participants indicated that they preferred SI

more than MOD, although there was no significant difference in PACES score between

the protocols (p > 0.05). These results suggest that the addition of short sprint efforts to

continuous exercise at Fatmax increases energy expenditure without compromising fat

oxidation or stimulating increased post-exercise energy intake. Boys prefer participating

in SI and do not perceive it to be any harder than MOD, indicating that sprint interval

exercise should be considered in exercise prescription for this population.

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3.2 INTRODUCTION

Childhood obesity rates are continually on the rise (Booth et al., 2003) and as a result,

exercise for weight control is becoming increasingly important for children. It has

recently been proposed that exercise training aimed at Fatmax (40-55% O2peak;

Aucouturier et al., 2009; Lazzer et al., 2007; Lazzer et al., 2010; Maffeis et al., 2005;

Zakrzewski and Tolfrey, 2011a; Zunquin et al., 2009a; Zunquin et al., 2009b) should be

encouraged for weight management (Brandou et al., 2003; Dumortier et al., 2003) and

may be more effective than other exercise intensities in reducing the risk of medical

consequences associated with obesity such as insulin resistance (Venables and

Jeukendrup, 2008). However, although exercise at this moderate intensity may

maximise fat oxidation rates during the exercise bout, higher intensity exercise has been

associated with increased fat oxidation rates post-exercise (Yoshioka et al., 2001).

Furthermore, the increased energy expenditure resulting from high intensity exercise

may be more effective in inducing a negative energy balance required for weight loss

(Hunter et al., 1998). Based on this, there is considerable debate as to the optimal

exercise intensity required for weight management in both adults and children.

The major concern with prescribing continuous high intensity exercise to overweight

and obese individuals is that they may find the strenuous training load unpleasant

(Kilpatrick et al., 2007; Lind et al., 2008) and therefore, are not likely to adhere to a

program of this nature in the long-term (Perri et al., 2002). This could be particularly

true for overweight children who may lack the motivation to participate in, or be less

likely to withstand the discomfort associated with, sustained high intensity exercise. A

promising alternative is sprint interval exercise which involves low to moderate

intensity exercise or rest, interspersed with short (≤ 1 min) supramaximal (> 100%

O2max) sprints. This type of exercise has a pronounced effect on energy expenditure

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both during the exercise bout and post-exercise (Burns et al., 2012; LaForgia et al.,

1997), and has been shown to promote greater fat loss (Boutcher, 2011; Trapp et al.,

2008; Whyte et al., 2010), than traditional endurance training. Furthermore, due to the

fact that children often engage in spontaneous physical activity, characterised by

unstructured games or sports that require multiple short sprint efforts interspersed with

longer duration low and moderate intensity exercise (Bailey et al., 1995), it may be

more appealing for overweight children to participate in sprint interval exercise than

continuous exercise to promote better long term adherence and fat loss. Studies

examining the enjoyment of acute bouts of exercise (i.e. specific intensities and

protocols) appear to be limited to adult cohorts (Kilpatrick et al., 2007; Lind et al.,

2008; Perri et al., 2002). Given that enjoyment could be one of the most influential

factors to increase a child’s adherence to an exercise program (Mulvihill et al., 2000),

there is a specific need to examine this in children.

Another important consideration in exercise prescription for weight management is the

effect of exercise intensity on post-exercise energy intake. It is possible that any

additional energy expenditure resulting from sprint interval exercise may be of no

benefit if there is greater compensation in energy intake from the post-exercise meal.

Therefore it is important to consider both the energy expended during exercise and the

energy consumed after exercise to fully understand the potential influence of different

types of exercise on weight management. An acute suppression of appetite after high,

but not low intensity exercise has been noted in adults (Imbeault et al., 1997; King et

al., 1994; Thompson et al., 1988). To our knowledge, no studies have examined the

effect of sprint interval exercise on appetite and post-exercise energy intake in adults or

children. It is important to examine individuals with varying body composition given

that differences in post-exercise energy intake have been observed between normal

weight and overweight children (Nemet et al., 2010).

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Given the potential for exercise at Fatmax to increase fat oxidation during exercise, and

that of sprint interval exercise to enhance enjoyment and energy expenditure, without

stimulating increased energy intake, the purpose of this study was to examine the

addition of short sprint efforts to continuous exercise at Fatmax on energy expenditure

and substrate oxidation (inclusive of the acute post-exercise recovery period),

enjoyment and post-exercise energy intake in boys carrying either excess (overfat) or

normal (control) levels of body fat. It was hypothesised that the sprint interval exercise

would increase energy expenditure, suppress appetite and be more enjoyable for the

boys to participate in than the continuous exercise at Fatmax. However, the addition of

sprints to continuous exercise at Fatmax may compromise fat oxidation rates.

3.3 METHODS

3.3.1 Participants

Twenty four participants were initially recruited from the local community via

advertisements presented in school newsletters, public flyers and paediatric wellness

centres to participate in this study. A screening process ensured all participants were (a)

free of risk factors associated with cardiovascular, pulmonary or metabolic disease; (b)

not diabetic or hypertensive; (c) deemed safe to perform maximal exercise. Of the 24

participants, six completed the first session but were unable to continue as a result of

their inability to maintain a constant cycling cadence which was essential for the

experimental trials. As a result, nine overfat (10.7 ± 2.4 years) and nine control (10.1 ±

1.8 years) boys completed all experimental procedures and were included in the final

analysis. Although pubertal status was not directly assessed, the age range was selected

to focus on pre-pubertal boys only. This status was supported by parental confirmation.

Human ethics approval was granted by the Human Research Ethics Committee at UWA

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prior to recruitment (Appendix B) and before involvement in the study, Child Assent

was obtained (Appendix D).


All participants attended the Laboratory on three mornings each separated by at least

five days. All sessions were completed at the same time of morning within participants

to control for diurnal variation, after at least a 10-hr overnight fast. On the first session,

anthropometry and body composition were assessed and participants completed a

graded exercise test to determine O2peak and Fatmax. For the two subsequent visits,

energy expenditure and substrate oxidation were determined before, during and after 30

min of continuous moderate intensity cycling at Fatmax (MOD) or continuous cycling at

Fatmax interspersed with a 4-sec maximal sprint effort every 2 min (selected to reflect

the spontaneous physical activity patterns of children [Bailey et al., 1995]; i.e. 29-min

of MOD and 1 min of maximal sprint efforts; SI), administered in a randomised

counterbalanced order. In addition, enjoyment and post-exercise energy intake were

assessed for each protocol. All participants were instructed to maintain their normal diet

between testing sessions. However, they were asked to complete records of all food and

drink consumption in the 24 hours prior to each visit and to replicate their energy intake

as closely as possible on the days before subsequent sessions (Jeacocke & Burke, 2010).

Compliance was confirmed upon arrival to the laboratory for the second experimental

trial after inspection of all food records by the investigator. In addition, participants

were asked to maintain their normal physical activity practices but to refrain from

strenuous physical activity for at least 24 hours prior to all experimental sessions.

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3.3.3 Baseline Measures

3.3.3a Anthropometry and Body Composition

Height was measured to the nearest 0.1 cm using a standardised, wall-mounted

stadiometer with participants standing in bare feet and their head in the Frankfort plane.

Body mass was determined to the nearest 0.01 kg using electronic scales (August Sauter

GmbH D -7470 Albstadt 1 Ebingen, West Germany) with participants dressed in light

clothing and without shoes. Waist circumference was measured at the minimum

circumference between the top of the iliac crest and the distal end of the rib cage with

participants standing in an upright position and their feet together. Body composition

was assessed using DEXA (Lunar Prodigy, encore 2004, GE Medical Systems,

Madison, Wis., USA). The DEXA results for total percentage of body fat mass allowed

for classification into the overfat and control groups based on the classification index of

McCarthy et al. (2006; Appendix A2).

3.3.3b Determination of Peak Aerobic Capacity & Fatmax

Participants completed a graded exercise test on a stationary front access cycle

ergometer (Repco Cycle Company, Exertech EX-10, Huntingdale, Victoria) to

determine O2peak and Fatmax. The ergometer was interfaced with a customised software

program (Cyclemax, School of Sport Science, Exercise and Health, The University of

Western Australia) which provided a visual display of each participant’s cycling power

output. Each participant was familiarised with the 10-point Pictorial Children’s Effort

Rating Table (PCERT; Marinov et al., 2007; Roemmich et al., 2006; Appendix G)

before cycling with a power output of 10 W. Every three min, the power output

increased by 15 W and each participant exercised continuously until their individual end

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point of fatigue, or other limiting signs or symptoms (i.e. dizziness) were recognised. As

the participants approached volitional exhaustion, strong verbal encouragement was

provided while they performed a maximal sprint effort to ensure a true O2peak was

attained (Barker et al., 2011; Crisp et al., 2012a: Chapter 2). Heart rate was measured

continuously (Polar Electro, F4, Kempele, Finland) and recorded at the end of each

stage along with PCERT. In addition, capillary blood samples (5 µL) were collected

from the fingertip and analysed for lactate concentration using a Lactate Pro (Arkray,

LT-1710, Kyoto, Japan) within the final 30 sec of each stage.



computerised gas analysis system. Ventilation was recorded using a turbine

ventilometer (Morgan, 225A, Kent, England) which was calibrated before the test using

a 1 litre syringe. The oxygen (O2) and carbon dioxide (CO2) concentration in the

expired air was continuously analysed using Ametek gas analysers (Applied

Electrochemistry, SOV S-3A11 and COV CD-3A, Pittsburgh, PA, USA) which were

also calibrated immediately before and verified after each test using a certified beta-

grade gravimetric gas mixture of known concentration (~16% O2 & ~4% CO2; BOC

Gases, Chatswood, Australia). Both the ventilometer and gas analysers were connected

to a PC which measured and displayed variables every 15 seconds. The sum of the four

highest consecutive volumes of O2 consumption was recorded as the participants

O2peak. In addition, a scatterplot of fat oxidation rate versus exercise intensity

expressed as a percentage of O2 was constructed for each participant to determine

their individual Fatmax (Achten et al., 2002; Crisp et al., 2012a: Chapter 2; Zakrzewski

and Tolfrey, 2011a; Figure 3.1). A graph of the cycling power output versus exercise

intensity expressed as a percentage of O2 enabled determination of the W to be used

for subsequent sessions (i.e. power output at Fatmax).

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Figure 3.1 Example scatterplot of fat oxidation rate ( ) and lactate concentration ( )

vs. exercise intensity during a graded exercise test with 3-min stages used for the visual

determination of Fatmax

( ) for one participant

3.3.4 Experimental Sessions

3.3.4a Resting Metabolic Rate and Substrate Oxidation

Upon arrival to the laboratory in the morning, participants were encouraged to sit

quietly while watching a documentary film for 30 min while maintaining normal

breathing patterns. Throughout this time, participants breathed through a mouthpiece

into a 120 litre Tissot gasometer tank (Collins Inc, Braintree, Massachusetts). The

Tissot gasometer tank was flushed twice with the participants own air in the initial 25

min of rest prior to collecting a sample over the final five min. From this sample of

expired air, the concentrations of O2 and CO2 were determined for the calculation of

resting substrate oxidation and resting metabolic rate. The oxidation rates of fat and

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carbohydrate (g/min) were calculated using equations from Frayn (1983). It was

assumed that protein oxidation contributed to approximately 12% of energy expenditure

based on similar studies in children (Lazzer et al., 2007; Maffeis et al., 2005).

3.3.4b Exercise Protocols

Next, each participant performed 30 min of either MOD or SI on the cycle ergometer

previously described. The wind-braked nature of the cycle ergometer allowed for the

cycling power output to be controlled by the work rate of the participant, thereby

allowing for the performance of maximal sprint efforts. This specific type of ergometer

has been used extensively in the literature in studies employing exercise protocols that

require alternation between more moderate intensities of exercise and short maximal

sprint efforts (Bishop & Maxwell, 2009; Guelfi et al., 2005; Yaicharoen et al., 2012).

The cycle ergometer was connected to the same Cyclemax program outlined previously

which provided a continuous visual display of power output.

Throughout exercise, participants breathed into a mouthpiece connected to the same

computerised gas analysis system used for the determination of O2peak and Fatmax. The

volume and concentrations of O2 and CO2 in the expired air were analysed continuously

as previously described, with the readings across minutes 9-10, 19-20 and 29-30 used

for the calculation of energy expenditure as well as fat and carbohydrate oxidation rates

using the kilojoule equivalent of the corresponding respiratory exchange ratio (Fox et

al., 1988). This technique was employed to minimise respiratory gas exchange

instability, given that the generation of H+ may result in an overestimation of metabolic

CO2 production. The validity of such a use of indirect calorimetry for the determination

of substrate oxidation during sustained intermittent exercise has been demonstrated

previously (Christmass et al., 1999). Heart rate and PCERT were recorded at 10, 20 and

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30 min into the exercise bout. In addition, capillary blood samples (5 µL) were collected

within the final two min of each protocol to ensure that blood lactate did not markedly

increase.

3.3.4c Post-exercise Recovery

Immediately after the cessation of exercise, measurements of post-exercise oxygen

consumption and substrate oxidation were made for 30 min while the participants sat

quietly watching a documentary film. Expired air samples were collected in the Tissot

gasometer tank previously described at 5, 10, 15, 20, 25 and 30 min post-exercise.

3.3.4d Enjoyment

Within the first two min of the post-exercise recovery period, participants were asked to

indicate how enjoyable they found the exercise bout by completing the modified

Physical Activity Enjoyment Scale (PACES; Motl et al., 2001; Appendix H).

Furthermore, after the completion of the two exercise sessions, they were asked to

indicate which exercise session they preferred to participate in (MOD or SI).

3.3.4e Post-exercise Energy Intake and Perceived Hunger and Satiety

After the post-exercise recovery period, participants were provided with a buffet-type

array of breakfast foods (Appendix J) to replicate free-living conditions and were

instructed to eat ad libitum until satisfaction. This procedure has been shown to be

reproducible in the measurement of energy intake (Arvaniti et al., 2000) and is

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considered the method of choice for quantifying the effect of an intervention on food

intake (Stubbs et al., 1998). The foods were selected to reflect typical breakfast choices

of the boys and were of varied macronutrient composition (i.e. cereal, milk, bread,

condiments, fruit, juice and baked beans [Halse et al., 2011; Shorten et al., 2009]). The

breakfast items were weighed before the participants arrived at the lab and after they

had left to determine net energy intake and macronutrient composition. In addition,

energy balance was calculated by subtracting the energy cost of the exercise bout above

resting energy expenditure from post-exercise energy intake (Imbeault et al., 1997; King

et al., 1994; Shorten et al., 2009).

After exercise and prior to the breakfast meal, participants were asked to rate their

perceptions of hunger and satiety using a 10 cm horizontal visual analogue scale (VAS;

Appendix H). The response to the question “how hungry do you feel?” was rated on the

left as “not hungry at all” and on the right as “as hungry as I have ever felt”. “How full

do you feel?” was rated as “not full at all” and “as full as I have ever felt” (Imbeault et

al., 1997; Moore et al., 2004).


One-way between-groups ANOVA were used to compare participant characteristics

between the overfat and control groups. Two-way repeated measures ANOVA were

used to determine whether there were any differences between the two groups in energy

expenditure, fat and carbohydrate oxidation rates, energy intake, enjoyment and PCERT

between MOD and SI. When a significant effect was noted, independent samples t-tests

were utilised to determine where differences lay. In addition, effect sizes were

calculated for relationships approaching significance. All proportions were compared

using Chi-squared analysis.

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3.4 RESULTS

3.4.1 Participant Characteristics

Characteristics of the two groups are presented in Table 3.1. Age, height and fat free

mass were similar between the two groups (p > 0.05). As expected, the overfat group

had a significantly higher body mass (p = 0.004), BMI (p = 0.001), waist girth (p =

0.001), fat mass (p = 0.001) and total percentage of body fat (p < 0.001) than the control

group. Absolute O2peak (L/min) was similar for the two groups (p = 0.799), but the

overfat group had significantly lower mass specific O2peak (mL/kg/min) than the

control group (p = 0.002).

Table 3.1 Participant Characteristics (mean ± SD)

Overfat (n = 9) Control (n = 9)

Age (years) 10.7 ± 2.4 10.1 ± 1.8

Height (cm) 147.6 ± 9.1 142.1 ± 8.3

Body Mass (kg) 47.9 ± 13.8 31.6 ± 5.41

Body Mass Index (kg/m2) 21.7 ± 4.7 15.5 ± 0.91

Waist Circumference (cm) 76.1 ± 13.2 57.3 ± 3.11

Fat Mass (kg) 16.4 ± 8.4 4.4 ± 1.21

Body Fat (%) 32.4 ± 8.2 13.9 ± 3.42

Fat Free Mass (kg) 29.7 ± 5.4 25.9 ± 4.6

O2peak (L/min) 1.7 ± 0.5 1.7 ± 0.5

O2peak (mL/kg/min) 36.4 ± 6.2 52.4 ± 11.41

O2peak, rate of peak oxygen uptake

Significantly different from overfat, 1 p < 0.05; 2 p < 0.001

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3.4.2 Protocol Characteristics

The characteristics of each exercise protocol for the overfat and control groups are

presented in Table 3.2. The mean exercise intensity and cycling power output were

similar within protocols between the two groups (p > 0.05), but increased from MOD to

SI for both the overfat and control groups (p < 0.05; Table 3.2). Likewise, lactate levels

were similar within protocols between groups (p > 0.05) but increased from MOD to SI

for both the overfat (p = 0.019) and control (p = 0.006) groups (Table 3.2). Mean heart

rate increased from MOD to SI for both the overfat (p = 0.001) and control (p = 0.004)

groups, while mean heart rate for MOD was significantly greater for the control group

compared with the overfat group (p = 0.028) but similar between groups for SI (p =

0.303; Table 3.2).

Table 3.2 Protocol characteristics (mean ± SD) for the overfat and control groups for 30

min of moderate intensity continuous exercise at Fatmax (MOD) and sprint interval

exercise consisting of continuous exercise at Fatmax interspersed with a 4-sec maximal

sprint every 2 min (SI)

Overfat Control

MOD SI MOD SI

Mean Intensity (% O2peak) 50 ± 8 58 ± 6* 52 ± 7 60 ± 13*

Exercise Lactate (mmol/L) 1.4 ± 0.4 2.1 ± 0.7* 1.5 ± 0.9 3.2 ± 2.0*

Mean Heart Rate (bpm) 129 ± 9 148 ± 10* 144 ± 121 157 ± 16*

Mean Power Output (W) 52 ± 13 62 ± 14* 66 ± 17 75 ± 19*

1 Indicates significantly different from overfat (within protocol; p < 0.05)

* Indicates a significant difference between MOD and SI (within group; p < 0.05)

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3.4.3 Energy Expenditure

Total energy expenditure for SI was significantly greater than MOD for both the overfat

(SI: 558 ± 169 kJ; MOD: 450 ± 117 kJ; p = 0.006) and control (SI: 548 ± 184 kJ; MOD:

476 ± 150 kJ; p = 0.019) groups. As illustrated in Figure 3.2, energy expenditure for SI

was significantly higher than MOD throughout the exercise bout and for 10 min post-

exercise in the overfat group (p < 0.05). In the control group, energy expenditure was

significantly higher for SI than MOD at 10 min (p = 0.029) and 30 min (p = 0.013) of

the exercise bout, and the difference approached significance at 20 min (p = 0.076; ES =

0.35) of the exercise bout and at five min post-exercise (p = 0.062; ES = 0.78). There

was no significant difference in the amount of energy expended between the overfat and

control groups for SI (p = 0.902) or MOD (p = 0.690).

3.4.4 Fat and Carbohydrate Oxidation

Total fat oxidation was not significantly different between the two protocols and

between the overfat and control groups (p > 0.05; Figure 3.3). However, total

carbohydrate oxidation for SI was significantly greater than MOD in the overfat group

(SI: 239 ± 147 kJ; MOD: 112 ± 66 kJ; p = 0.012) and this relationship approached

significance in the control group (SI: 306 ± 222 kJ; MOD: 214 ± 172 kJ; p = 0.058; ES

= 0.44). A comparison of each measured time-point revealed that carbohydrate

oxidation rates for SI were significantly greater than MOD throughout the exercise bout

(i.e. at 10, 20 and 30 min) and for 10 min post-exercise in the overfat group (p < 0.05;

Figure 3.4). While in the control group, carbohydrate oxidation rates were not

statistically different between the protocols at any measured time-point (p > 0.05;

Figure 3.4). Despite this, there was no difference in the total amount of carbohydrate

oxidised between the two groups for SI (p = 0.460) or MOD (p = 0.116).

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Figure 3.2 Energy expenditure (mean ± SE) before, during and after 30 min of

moderate intensity continuous exercise at Fatmax (MOD; ) and sprint interval exercise

consisting of continuous exercise at Fatmax interspersed with 4-sec maximal sprint

efforts every 2 min (SI; ) in the (a) overfat and (b) control groups.

* Indicates a significant difference between MOD and SI (p < 0.05)

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Figure 3.3 Rate of fat oxidation (mean ± SE) before, during and after 30 min of

moderate intensity continuous exercise at Fatmax ( ) and sprint interval exercise

consisting of continuous exercise at Fatmax interspersed with 4-sec maximal sprint

efforts every 2 min ( ) in the (a) overfat and (b) control groups

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Figure 3.4 Rate of carbohydrate oxidation (mean ± SE) before, during and after 30 min

of moderate intensity continuous exercise at Fatmax (MOD; ) and sprint interval

exercise consisting of continuous exercise at Fatmax interspersed with 4-sec maximal

sprint efforts every 2 min (SI; ) in the (a) overfat and (b) control groups.

* Indicates a significant difference between MOD and SI (p < 0.05)

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3.4.5 Enjoyment

All controls reported that they liked SI more than MOD (χ2 [1, N = 9] = 9, p = 0.003)

but the difference in response to the PACES between the two protocols did not reach

significance (p = 0.174; Figure 3.5). For the overfat boys, all except two stated that they

enjoyed SI more than MOD (χ2 [1, N = 9] = 2.778, p = 0.096) but again, this was not

reflected in their response on the PACES (p = 0.964; Figure 3.5).

Figure 3.5 Ratings of enjoyment using the Physical Activity Enjoyment Scale (PACES;

mean ± SE) in the overweight and control groups for 30 min of moderate intensity

continuous exercise at Fatmax (MOD) and sprint interval exercise consisting of

continuous exercise at Fatmax interspersed with 4-sec maximal sprint efforts every 2 min

(SI).

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3.4.6 Perceived Exertion

RPE increased significantly from min 10 to 20 (p < 0.001) and from min 20 to 30 (p <

0.001) but was similar between protocols and groups at each measured time point (p >

0.05; Figure 3.6).

Figure 3.6 Ratings of perceived exertion (RPE; mean ± SE) at 10, 20 and 30 min of

moderate intensity continuous exercise at Fatmax (MOD: overfat ; control ) and

sprint interval exercise consisting of continuous exercise at Fatmax interspersed with 4-

sec maximal sprints every 2 min (SI: overfat ; control ).

a Indicates significantly greater than min 10 (p < 0.05)

b Indicates significantly greater than min 20 (p < 0.05)

85

3.4.7 Perceived Hunger, Satiety and Post-exercise Energy Intake

All post-exercise VAS scores for hunger and satiety were similar for MOD and SI, and

for the overfat and control groups (p > 0.05; Table 3.3).

Table 3.3 Post-exercise VAS scores (cm) for hunger and satiety (mean ± SD)

following moderate intensity continuous exercise at Fatmax (MOD) and sprint interval

exercise consisting of continuous exercise at Fatmax interspersed with 4-sec sprints

every 2 min (SI)

Hunger Satiety

Overfat MOD 6.9 ± 3.0 1.9 ± 2.4

SI 7.9 ± 3.2 2.0 ± 3.5

Control MOD 7.0 ± 3.2 2.0 ± 2.8

SI 7.5 ± 2.2 2.2 ± 2.4

Post-exercise energy intake was similar between protocols for both the overfat (MOD,

2090 ± 362 kJ; SI, 1902 ± 262 kJ; p = 0.542) and control (MOD, 2258 ± 188 kJ; SI,

2119 ± 283 kJ; p = 0.574) groups (Figure 3.7). There was also no significant difference

between the two groups for MOD (p = 0.686) and SI (p = 0.581; Figure 3.7). Likewise,

post-exercise fat and carbohydrate intake was similar between protocols for both the

overfat (fat: p = 0.517; carbohydrate: p = 0.581) and control (fat: p = 0.515;

carbohydrate: p = 0.442) groups and there was no significant difference between the

two groups for MOD (fat: p = 0.250; carbohydrate: p = 0.136) and SI (fat: p = 0.218;

carbohydrate: p = 0.254; Figure 3.7).

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Figure 3.7 Post-exercise energy intake (mean ± SE) for the overfat and control groups following moderate intensity continuous exercise at Fatmax

(MOD) and sprint interval exercise consisting of continuous exercise at Fatmax interspersed with 4-sec maximal sprints every 2 min (SI). 86

87

3.4.8 Energy Balance

When the energy cost of exercise was subtracted from energy intake at the post-exercise

meal, the resulting acute energy balance was similar between the two protocols (p =

0.186) for both the overfat group (p = 0.350) and the control group (p = 0.391; Figure

3.8). There was also no significant difference in acute energy balance between the

overweight and control groups for MOD (p = 0.736) and SI (p = 0.536; Figure 3.8).

Figure 3.8 Energy balance (intake - expenditure; mean ± SE) in the overfat and control

groups for moderate intensity continuous exercise at Fatmax (MOD) and sprint interval

exercise consisting of continuous exercise at Fatmax interspersed with 4-sec maximal

sprints every 2 min (SI).

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3.5 DISCUSSION

Exercise training programs for children carrying excess body fat need to maximise the

acute physiological effects of exercise, while enhancing enjoyment in order to achieve

optimal adherence in the long-term. Recent research on the acute responses to exercise

suggests that training at Fatmax may be advantageous for overweight individuals because

it could enhance fat loss in the long-term (Achten et al., 2002; Dumortier et al., 2003;

Venables and Jeukendrup, 2008) and its moderate intensity is easy to adhere to

(Kilpatrick et al., 2007; Lind et al., 2008; Perri et al., 2002). However, given the

evidence that children participate in intermittent forms of exercise more often than

continuous exercise (Bailey et al., 1995), and that sprint interval exercise has been

reported to produce greater declines in total body fat mass than moderate intensity

continuous exercise (Boutcher, 2011; Trapp et al., 2008), the addition of short sprint

efforts to continuous exercise at Fatmax may offer more promising outcomes by

promoting a greater short-term energy balance and enjoyment in overweight boys than

continuous exercise at Fatmax alone. In support of this, our results show that SI resulted

in increased energy expenditure, ascribable to higher carbohydrate oxidation rates,

without compromising fat oxidation rates. Furthermore, despite the increased energy

expenditure for SI, acute post-exercise energy intake was similar between the two

protocols. In addition, participants did not feel like they were exercising harder during

SI, compared with MOD, based on PCERT. Finally, all of the control boys and 7/9 of

the overfat boys reported that they preferred to participate in SI over MOD.

The increased energy expenditure associated with SI, compared to MOD, indicates that

this type of exercise may be more beneficial for both normal weight and overweight

boys to assist with long-term fat management. As the SI and MOD protocols were not

matched for work output, it is not surprising that the addition of 4-sec maximal sprint

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efforts every two min to 30 min of continuous exercise at Fatmax resulted in greater

overall energy expenditure than 30 minutes of continuous exercise at Fatmax alone. This

increase in energy expenditure appears to be the result of increased carbohydrate

oxidation which was significantly greater for SI than MOD in the overfat boys, and

approached significance in the controls. Of interest was that SI also had a more

pronounced effect on post-exercise energy expenditure than MOD, particularly in the

overfat boys, which was attributable to increased post-exercise carbohydrate oxidation

rates. The reason for this apparent difference is unclear however, is consistent with our

previous research showing increased reliance on carbohydrate oxidation during early

recovery in overweight compared to normal weight boys (Crisp et al., 2011). It is

important to note that only the acute post-exercise period was examined in the current

study. Due to the paucity of research examining the influence of high intensity interval

exercise on the post-exercise response, it is unknown whether SI will result in greater

daily energy expenditure than other exercise intensities. However, Treuth et al. (1996)

found that 24 hour energy expenditure after a high intensity interval session (2 min

exercise/recovery at 100% O2max) was significantly greater than energy expenditure

following a continuous low intensity session (50% O2max) matched for work output in

women. Therefore, it is possible that sprint interval exercise may significantly increase

daily energy expenditure, contributing to the required negative energy balance for fat

loss more effectively than continuous moderate intensity exercise in overfat children.

As well as energy expenditure, another important consideration in exercise prescription

for weight management is the rate of fat oxidation. Typically, low to moderate intensity

exercise, particularly at Fatmax, is prescribed because the proportion of fat oxidised is

greater than high intensity exercise (Lazzer et al., 2010; Melanson et al., 2002) which

could promote fat loss in the long term (Brandou et al., 2003; Dumortier et al., 2003;

Achten et al., 2002). In support of this, Dumortier et al. (2003) noted significant

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increases in fat oxidation rate during exercise at Fatmax, as well as reductions in body

weight, in 28 obese individuals following eight weeks of exercise training at Fatmax (40

min, 3 days/week). However, it is important to note that despite the proportion of fat

oxidation being greater during continuous exercise at Fatmax than other exercise

intensities, this does not necessarily mean that the absolute amount of fat oxidation is

greater (Melanson et al., 2002). Furthermore, similar beneficial outcomes have been

noted after high intensity/sprint interval training in adults (e.g. fat loss [Tremblay et al.,

1994] and increased fat oxidation [Burgomaster et al., 2008; Talanian et al., 2007;

Tremblay et al., 1994]). Therefore, it is yet to be established whether exercise training

at Fatmax is truly superior to sprint interval training protocols for increased fat oxidation

and ultimately fat loss in overweight adults and children. Of particular interest in the

current study was that the addition of short, maximal sprint efforts to a continuous bout

of exercise at Fatmax did not compromise the rate of fat oxidation, with a similar rate

observed between SI and MOD. These results suggest that there is potential for sprint

interval exercise, in combination with continuous exercise at Fatmax, to increase energy

expenditure without compromising fat oxidation rates to the same extent as continuous

high intensity exercise. It would also be interesting for future research to explore this

outcome using other modalities of exercise given that higher fat oxidation rates have

been noted during treadmill exercise in comparison to cycling for children aged 8-11

years (Zakrzewski & Tolfrey, 2012). Despite previous validation of the use of indirect

calorimetry for the determination of substrate oxidation during sustained SI (Christmass

et al., 1999), it is possible that the non-steady-state nature of SI may have influenced the

estimations of fat oxidation. However, this is unlikely in the present study given the low

level of lactate observed (2.6 mmol/L for SI vs. 1.4 mmol/L for MOD). Future research

will be required to compare the long-term benefits (e.g. increased fat oxidation and fat

loss) of these two forms of exercise.

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To fully understand the influence of sprint interval exercise on short-term energy

balance, it is also important to consider post-exercise energy consumption from food

and drinks. To date, the effect of sprint interval exercise on appetite and energy intake

has not been examined in either adults or children. In the current study, we found no

significant difference in post-exercise hunger and satiety or acute post-exercise energy

intake between SI and MOD. These observations suggest that continuous exercise

Fatmax in combination with maximal sprint efforts does not prompt an immediate

increase in appetite or acute compensatory increase in energy intake to replace the extra

energy expended during exercise in boys. Furthermore, SI favours an acute negative

energy balance to a greater extent than MOD, as a result of the higher energy cost of the

exercise bout. Only two other studies have examined the effect of exercise intensity on

subsequent energy intake in children (Moore et al., 2004). Moore et al. (2004) observed

no significant difference in energy intake (including lunch and the evening meal) in 9-

10 year old girls on two separate days when either lower (50% HRmax) or high (75%

HRmax) intensity equicaloric exercise was prescribed at two time-points (10:30 and

14:30) following a standardised breakfast meal. Taken together, these results suggest

that children do not compensate for increased energy expenditure by increasing energy

intake, at least in the short-term. However, it is important to acknowledge that we only

examined the acute post-exercise breakfast meal and it is possible that differences in

energy intake may emerge across the duration of the day. Although, Thivel et al. (2012)

noted that 24-hr energy intake was significantly lower when a single bout of exercise

was prescribed at 1100 h at a high (30-min at 75% O2peak) intensity, compared with an

equicaloric low (59-min at 40% O2peak) intensity, despite no significant difference in

ratings of subjective hunger, fullness or prospective food consumption between the two

conditions, in obese adolescent boys.

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Irrespective of whether SI provides better outcomes related to energy balance than

MOD, there is little point prescribing this type of exercise for weight loss if the

individual is unlikely to adhere to the program in the long-term. There is evidence that

enjoyment is one of the most influential factors to increase an individuals’ adherence to

a program, particularly for children (Mulvihill et al., 2000), and it is often dependent on

prescribing the appropriate volume, intensity and duration of exercise to work within

the individuals’ capabilities. For instance, Perri et al. (2002) found that prescribing

continuous high intensity exercise to sedentary adults decreased their adherence and

resulted in the completion of less total exercise than moderate intensity exercise

performed over a six month period. Although the influence of exercise intensity on the

enjoyment of a single bout of exercise has not been examined in children, we have

demonstrated that both the overfat and control boys preferred SI more than MOD

because “it was more fun”, “it felt shorter”, “it was more interesting going at different

speeds” and “it can make my legs stronger and make me more fit”. Furthermore, despite

working harder and expending on average almost 20% more energy during SI than

MOD, RPE was similar for both protocols indicating that the participants did not

perceive SI to be harder. These enjoyment and exertion ratings are not particularly

surprising based on the fact that SI was made to reflect the spontaneous nature of

children’s physical activity patterns during free-play (Bailey et al., 1995). However, it is

important to acknowledge that despite their preference for SI over MOD, the

participants’ scores from the PACES did not reflect this outcome. This is likely

explained by the fact that the PACES may not be sensitive enough to pick up the

preference for SI over MOD, with only two out of five numbers on the scale indicating

a positive response.

In summary, SI resulted in greater energy expenditure compared with MOD, without

compromising the rate of fat oxidation, and did not prompt increased post-exercise

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energy intake in both overfat and control boys. Furthermore, the boys did not perceive

SI to be harder than MOD, with the majority indicating that they preferred participating

in SI. Given the health benefits of an active lifestyle, these results suggest that it may be

more beneficial to prescribe sprint interval exercise in combination with continuous

exercise at Fatmax, rather than continuous exercise at Fatmax alone, for both normal

weight and overweight children. This form of exercise has the potential to increase

energy expenditure and moderate energy intake, but also to increase aerobic fitness and

promote exercise adherence which may result in more effective long-term weight

management. While the findings of this study have revealed the benefits of SI both

during the exercise bout and immediately post-exercise, further research is needed to

explore the long-term implications.

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4 STUDY 3

OPTIMISING SPRINT INTERVAL EXERCISE TO MAXIMISE ENERGY

EXPENDITURE AND ENJOYMENT IN OVERFAT BOYS

Based on a manuscript accepted for publication in Applied Physiology, Nutrition and

Metabolism:

Crisp NA, Guelfi KJ, Licari M, Braham R, Fournier P (in press) Optimising sprint

interval exercise to maximise energy expenditure and enjoyment in overweight boys.

Applied Physiology, Nutrition and Metabolism

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4.1 ABSTRACT

The aim of this study was to identify the sprint frequency that, when supplemented to

continuous exercise at the intensity that maximises fat oxidation (Fatmax), optimises

energy expenditure, acute post-exercise energy intake and enjoyment in boys carrying

excess body fat. Eleven overfat boys aged 8-12 years attended the laboratory after an

overnight fast on five mornings. First, body composition and anthropometry were

assessed and participants completed a graded exercise test to determine peak aerobic

capacity and Fatmax. On the remaining four sessions, participants completed 30 min of

either continuous cycling at Fatmax (MOD), or sprint interval exercise consisting of

continuous cycling at Fatmax interspersed with 4-sec maximal sprints performed either

every 2 min (SI120), every 1 min (SI60), or every 30 sec (SI30). Energy expenditure and

substrate oxidation was assessed during exercise, after which participants completed a

modified Physical Activity Enjoyment Scale (PACES) followed by a buffet-type

breakfast to measure acute post-exercise energy intake. Energy expenditure increased

with increased sprint frequency (p < 0.001), but the difference between SI60 and SI30 did

not reach significance (p = 0.076), likely as a result of decreased sprint quality as

indicated by a significant decline in peak power output from SI60 to SI30 (p = 0.034).

Post-exercise energy intake was similar for MOD, SI120 and SI30 (p > 0.05), but was

significantly less for SI60 compared to MOD (p = 0.025). PACES was similar for MOD,

SI120 and SI60 (p > 0.05), but was less for SI30 compared with MOD (p = 0.038), SI120 (p

= 0.009) and SI60 (p = 0.052). In conclusion, SI60 appears optimal for overweight boys

given that it maximises energy expenditure (i.e. there was no additional increase in

expenditure with a further increase in sprint frequency), without prompting increased

energy intake. In fact, energy intake at the acute post-exercise meal was the lowest for

this protocol. This, coupled with the fact that enjoyment was not compromised, may

have important implications for increased adherence and long-term energy balance.

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4.2 INTRODUCTION

Exercise training programs for the overweight or obese child need to maximise the

acute physiological effects of exercise, at the same time as enhancing enjoyment to

favour optimal adherence in the long-term (Dishman et al., 2005; Hagberg et al., 2009).

Currently, the ideal type of exercise that may result in these outcomes remains to be

identified. Some studies promote exercise training at the intensity that maximises the

acute rate of fat oxidation (Fatmax; 40-56% O2peak; Aucouturier et al., 2009; Lazzer et

al., 2007; Lazzer et al., 2010; Maffeis et al., 2005; Zakrzewski & Tolfrey, 2011a;

Zunquin et al., 2009a; Zunquin et al., 2009b), because increased fat oxidation during

exercise may assist with weight management in the long term (Ben Ounis et al., 2009;

Brandou et al., 2003; Dumortier et al., 2003). However, this form of continuous

exercise is often considered “boring” (Tjønna et al., 2008; Wisløff et al., 2007),

particularly for children (Crisp et al., 2012b: Chapter 3), and may therefore result in

poor long-term adherence. On the other hand, the variable nature of sprint interval

exercise may be preferable for children because it reflects their spontaneous physical

activity patterns, which have been reported to consist of repeated short bursts of high

intensity exercise interspersed with prolonged periods of low-moderate intensity

exercise (Bailey et al., 1995). Sprint interval exercise training has also been reported to

have a significantly greater impact on total body and fat mass than traditional endurance

training matched for energy expenditure, despite a much lower investment of time for

sprint interval exercise (Trapp et al., 2008). This is likely due to the potential for sprint

interval exercise to increase energy expenditure both during and post-exercise, without

prompting an acute compensatory increase in energy intake in the post-exercise meal

(Crisp et al., 2012b: Chapter 3).

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In support of the indirect evidence that sprint interval exercise might be the exercise

regime of choice to optimise energy expenditure and long-term adherence in children, it

has recently been shown that both overfat (carrying excess body fat) and control

(carrying normal levels of body fat) boys prefer participating in a sprint interval

exercise session consisting of continuous exercise at Fatmax interspersed with a 4-sec

maximal sprint effort every 2 min, compared to continuous exercise at Fatmax alone,

despite the former involving a greater amount of total work (Crisp et al., 2012b:

Chapter 3). In addition, introducing the short sprint efforts to continuous exercise at

Fatmax did not compromise enjoyment or cause an increase in ratings of perceived

exertion (RPE) when compared to continuous exercise at Fatmax alone (Crisp et al.,

2012b: Chapter 3). Finally, despite the higher energy expenditure associated with the

sprint interval exercise compared with the continuous exercise at Fatmax, acute energy

intake in the post-exercise meal did not differ between the two exercise protocols (Crisp

et al., 2012b: Chapter 3). This lack of compensatory increase in acute energy intake to

replace the extra energy expended during sprint interval exercise is of particular

interest, given that it may result in a more significant long-term negative energy balance

compared to continuous exercise, provided that a compensatory increase in energy

intake does not occur over the remainder of the day (Thivel et al., 2012).

Given the findings that the addition of 4-sec maximal sprint efforts repeated every 2

min to continuous exercise at Fatmax increases energy expenditure without stimulating

increased acute post-exercise energy intake or compromising enjoyment of the exercise

bout (Crisp et al., 2012b; Chapter 3), this raises the question as to whether increasing

the frequency of sprints will lead to further benefits in relation to energy expenditure

and enjoyment, or whether these factors start to be compromised. Furthermore, it is not

known whether increasing the sprint frequency will cause an increase in acute post-

exercise appetite and energy intake as a means to compensate for any extra energy

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expenditure during exercise. For these reasons, the purpose of the present study was to

compare energy expenditure, acute post-exercise energy intake and enjoyment between

continuous moderate intensity cycling at Fatmax (MOD) and three sprint interval

protocols consisting of continuous cycling at Fatmax interspersed with 4-sec maximal

sprint efforts performed either every 2 min (SI120), every 1 min (SI60) or every 30 sec

(SI30) in overfat boys.

4.3 METHODS

4.3.1 Participants

Eleven overfat boys aged 8-12 years were recruited from the local community via

advertisements presented in school newsletters, public flyers and paediatric wellness

centres to participate in this study. Their general characteristics are presented in Table

4.1. A screening process ensured all participants were (a) free of risk factors associated

with cardiovascular, pulmonary or metabolic disease; (b) not diabetic or hypertensive;

(c) deemed safe to perform maximal exercise. The specific age range was selected to

focus on pre-pubertal boys only and this status was supported by parental confirmation

based on the absence of pubic hair. Human ethics approval was sought from the Human

Research Ethics Committee at The University of Western Australia (UWA) prior to

recruitment (Appendix B) and before involvement in the study, Child Assent was

obtained (Appendix E).

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Table 4.1 Participant Characteristics

Mean ± SD Range

Age (years) 11.1 ± 1.3 8.6 - 12.6

Height (cm) 153.2 ± 7.8 142.0 - 166.8

Body Mass (kg) 50.2 ± 8.6 35.6 - 61.5

BMI (kg/m2 21.3 ± 3.0 ) 17.7 - 28.9

BMI Percentiles 85 ± 8 75 - 98

Waist Circumference (cm) 72.7 ± 8.3 64.0 - 95.0

Fat Mass (kg) 15.6 ± 5.8 8.9 - 26.7

Body Fat (%) 30.4 ± 7.3 21.6 - 43.4

Body Fat Percentiles 93 ± 9 85 - 98

Fat Free Mass (kg) 32.9 ± 5.1 25.5 - 43.7

O2peak 1.81 ± 0.37 (L/min) 1.29 - 2.60

O2peak 36.4 ± 7.3 (mL/kg/min) 26.1 - 44.8

Fatmax (% O2peak 52 ± 7 ) 40 - 61

BMI, body mass index; O2peak, peak oxygen uptake; Fatmax

, exercise

intensity that maximises fat oxidation


Each participant was asked to attend the Exercise Physiology Laboratory at UWA on

five separate mornings. All sessions were completed at the same time of morning within

participants to control for potential diurnal variation, after at least a 10-hr overnight

fast. During the first session, body composition and anthropometry were assessed and

participants completed a graded exercise test to determine their peak aerobic capacity

( O2peak) and Fatmax. Across the four subsequent visits which were each separated by at

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least five days, the energy expenditure, substrate oxidation, enjoyment and perceived

exertion were assessed in response to 30 min of continuous moderate intensity exercise

at Fatmax and three different sprint interval protocols of varying sprint frequency.

Participants were instructed to maintain their normal dietary and physical activity

practices between testing sessions, but were asked to refrain from strenuous physical

activity for at least 24 hours before all testing sessions. In addition, they were asked to

complete a record of all food and drink consumption in the 24 hours prior to each visit

and to replicate their energy intake as closely as possible on the days before subsequent

sessions (Jeacocke & Burke, 2010). Compliance was confirmed upon arrival to the

laboratory for each experimental trial after inspection of the food records by the chief

investigator, and total energy and macronutrient consumption was analysed using a

commercially available software program (Foodworks, Xyris Software, Queensland,

Australia).

4.3.3 Baseline Measures

4.3.3a Anthropometry and Body Composition

Height was measured to the nearest 0.1 cm using a standardised, wall-mounted

stadiometer with participants standing in bare feet and their head in the Frankfort plane.

Body mass was determined to the nearest 0.01 kg using electronic scales (August Sauter

GmbH D -7470 Albstadt 1 Ebingen, West Germany) with participants dressed in light

clothing and without shoes. Body mass index (BMI) was calculated as body mass (kg)

divided by height (m) squared (Cole et al., 2000). Waist circumference was measured at

the minimum circumference between the top of the iliac crest and the distal end of the

rib cage with participants standing in an upright position and their feet together. Body

composition was assessed using Dual Energy X-Ray Absorptiometry (DEXA; Lunar

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Prodigy, encore 2004, GE Medical Systems, Madison, Wis., USA) with participants

scanned in light clothing. The DEXA results for total percentage of body fat mass (%

FM) allowed for confirmation of an overfat status based on the classification index of

McCarthy et al. (2006; Appendix A2).

4.3.3b Determination of Peak Aerobic Capacity and Fatmax

Following the measurement of body composition and anthropometry, all participants

completed a graded exercise test. Before beginning the exercise test, all participants

were shown and given a verbal description of the pictorial version of the 10-point

Children’s Effort Rating Table (PCERT; Marinov et al., 2007; Roemmich et al., 2006;

Yelling et al., 2002; Appendix G). Participants were then fitted with a heart rate

monitor (Polar Electro, F4, Kempele, Finland) before they commenced cycling on a

stationary wind-braked front access cycle ergometer (Repco, Melbourne, Australia) that

was interfaced with a customised software program (Cyclemax, School of Sport

Science, Exercise and Health, The University of Western Australia) which provided a

continuous record and visual display of each participant’s cycling power output. The

test commenced with an initial resistance of 10 W. Every three min, the resistance

increased by 15 W and each participant exercised continuously until their individual

end point of fatigue or other limiting signs or symptoms (e.g. dizziness) were

recognised. As the participants approached volitional exhaustion, strong verbal

encouragement was provided while they performed a final maximal sprint effort to

ensure a true O2peak was attained (Barker et al., 2011; Crisp et al., 2012a: Chapter 2).

Heart rate was measured continuously and recorded at the end of each stage along with

the participants’ perceived exertion. In addition, capillary blood samples (5 µL) were

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collected from the fingertip within the final 30 sec of each stage for the determination

of lactate concentration using a Lactate-Pro (Arkray, LT-1710, Kyoto, Japan).



computerised gas analysis system. Ventilation was recorded using a turbine

ventilometer (Morgan, 225A, Kent, England) which was calibrated before the test using

a one litre syringe. Oxygen (O2) and carbon dioxide (CO2) concentrations in the expired

air were continuously analysed using Ametek gas analysers (Applied Electrochemistry,

SOV S-3A11 and COV CD-3A, Pittsburgh, PA, USA), calibrated immediately before

and verified after each test using a certified beta-grade gravimetric gas mixture of

known concentration (BOC Gases, Chatswood, Australia). Both the ventilometer and

gas analysers were connected to a PC which measured and displayed variables every 15

sec. The sum of the four highest consecutive volumes of O2 consumption ( O2

mL/kg/min) was recorded as the participants’ O2peak. In addition, a graph of fat

oxidation rate versus exercise intensity expressed as a percentage of O2peak was

constructed for each participant to determine their individual Fatmax (Achten et al.,

2002; Crisp et al., 2012a: Chapter 2). A graph of the resistance (W) versus exercise

intensity expressed as a percentage of O2peak enabled determination of the W to be

used for subsequent sessions (i.e. the resistance at which Fatmax occurred).

4.3.4 Experimental Sessions

4.3.4a Exercise Protocols

The exercise sessions consisted of continuous moderate intensity exercise at the

participants’ individually predetermined Fatmax (MOD) and three sprint interval

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protocols consisting of continuous exercise at the workload equivalent to Fatmax

interspersed with 4-sec maximal sprint efforts repeated either every 2 min (SI120), every

1 min (SI60), or every 30 sec (SI30), with all treatments administered in a randomised

counterbalanced order. The wind-braked nature of the cycle ergometer allowed for the

cycling power output to be controlled by the work rate of the participant, thereby

allowing for the performance of maximal sprint efforts. This specific type of ergometer

has been used extensively in the literature in studies employing exercise protocols that

require alternation between more moderate intensities of exercise and short maximal

sprint efforts (Bishop & Maxwell, 2009; Guelfi et al., 2005; Yaicharoen et al., 2012).

The cycle ergometer was connected to the same Cyclemax program outlined previously

which provided a continuous visual display of power output and was programmed to

report both mean and peak power output every 2 min. Although a different number of

sprints were performed during each protocol, peak power output was taken as the single

highest power output recorded during each 2-min period.

Throughout exercise, participants breathed into a mouthpiece connected to the same

computerised gas analysis system used for the determination of O2peak and Fatmax. The

volume and concentrations of O2 and CO2 in the expired air were analysed continuously

as previously described, with the readings across minutes 9-10, 19-20 and 29-30 used

for the calculation of energy expenditure as well as fat and carbohydrate oxidation rates

using the kilojoule equivalent of the corresponding respiratory exchange ratio (Fox et

al., 1988). This technique was employed to minimise respiratory gas exchange

instability, given that the generation of H+ may result in an overestimation of metabolic

CO2 production. The validity of such a use of indirect calorimetry for the determination

of substrate oxidation during sustained intermittent exercise has been demonstrated

previously (Christmass et al., 1999). At 10, 20 and 30 min of exercise, heart rate and

lactate were recorded and participants indicated their RPE using the PCERT scale.

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4.3.4b Perceived Hunger and Satiety, Enjoyment and Post-exercise Energy Intake

Immediately after exercise, participants were asked to rate their perceptions of hunger

and satiety using a 10 cm horizontal visual analogue scale (VAS). The response to the

question “how hungry do you feel?” was rated on the left as “not hungry at all” and on

the right as “as hungry as I have ever felt”. “How full do you feel?” was rated as “not

full at all” and “as full as I have ever felt” (Imbeault et al., 1997; Moore et al., 2004;

Appendix G). At this time, participants also indicated how enjoyable they found the

exercise bout by completing the modified Physical Activity Enjoyment Scale (PACES;

Motl et al., 2001; Appendix G). Upon completion of the four exercise sessions,

participants were asked to indicate which exercise protocol they liked best and which

one they thought was the worst and why.

Energy intake at the post-exercise meal was initiated within 5-10 minutes after the

cessation of exercise for all participants, following the measurements of hunger, satiety

and enjoyment. Participants were provided with a buffet-type array of breakfast foods

(Appendix J) to replicate free-living conditions and were instructed to eat ad libitum

until satisfaction. This procedure has been shown to be reproducible in the

measurement of energy intake (Arvaniti et al., 2000) and is considered the method of

choice for quantifying the effect of an intervention on food intake (Stubbs et al., 1998).

The foods were selected to reflect typical breakfast choices and were of varied

macronutrient composition (i.e. cereal, milk, bread, condiments, fruit, juice and baked

beans; Crisp et al., 2012b: Chapter 3; Halse et al., 2011; Shorten et al., 2009). No time

limit was imposed on the duration of the meal. The breakfast items were weighed

before the participants arrived at the lab and after they had left to determine net energy

intake and macronutrient composition.

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Two-way repeated measures ANOVA with LSD post-hoc analyses were used to

examine the effect of protocol and time on energy expenditure, fat and carbohydrate

oxidation and RPE. One-way repeated measures ANOVA with LSD post-hoc analyses

were used to examine any differences between protocols in total energy and

macronutrient consumption in the 24 hours prior to the experimental sessions, total

energy expenditure, fat and carbohydrate oxidation, post-exercise energy intake, energy

balance, enjoyment and cycling power output measures. All proportions were compared

using Chi-squared analyses.

4.4 RESULTS

4.4.1 Dietary Standardisation Prior to the Experimental Sessions

Total energy consumption and carbohydrate, fat and protein intake (kJ) were well

matched in the 24 hours prior to each experimental session, with no significant

difference between protocols (energy intake: p = 0.832; carbohydrate intake: p = 0.754;

fat intake: p = 0.900; protein intake: p = 0.712; Figure 4.1).

4.4.2 Protocol Characteristics

The characteristics of each exercise protocol are presented in Table 4.2. The intensity of

the exercise bout, as well as corresponding heart rates, increased significantly across the

four protocols (i.e. MOD < SI120 < SI60 < SI30; p < 0.001; Table 4.2). In general, lactate

levels in response to exercise also increased across the protocols (MOD < SI120, p <

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0.001; SI60 < SI30, p = 0.007), but there was no significant difference between SI120 and

SI60 (p = 0.713; Table 4.2).

Mean power output increased significantly across the four protocols (i.e. MOD < SI120

< SI60 < SI30; p < 0.05), while average peak power output was similar for SI120 and SI60

(p = 0.950) but was significantly less for SI30 compared with SI60 (p = 0.034; Table

4.2). When mean and peak power output were plotted over time, it was evident that

mean power output declined during the second half of SI30 (Figure 4.2a) and the sprint

quality was compromised for this protocol, with significantly lower peak power output

observed at various time-points when compared with SI120 and SI60 (Figure 4.2b).

Figure 4.1 Contributions of carbohydrate, fat and protein to total energy intake (kJ) in

the 24 hours prior to 30 min of moderate intensity continuous exercise at Fatmax (MOD)

and sprint interval exercise consisting of continuous exercise at Fatmax interspersed with

4-sec maximal sprints every 2 min (SI120), every 1 min (SI60) and every 30 sec (SI30).

101

Table 4.2 Protocol characteristics (mean ± SD) for 30 min of moderate intensity continuous exercise at Fatmax (MOD) and sprint interval

exercise consisting of continuous exercise at Fatmax interspersed with 4-sec maximal sprints every 2 min (SI120), every 1 min (SI60), or every

30 sec (SI30)

MOD SI120 SI60 SI30

Mean Intensity (% O2peak) 50 ± 6 61 ± 5a 72 ± 4a,b 81 ± 6a,b,c

Exercise Lactate (mmol/L) 1.2 ± 0.2 2.8 ± 0.9a 2.9 ± 1.1a 3.7 ± 1.4a,b,c

Mean Heart Rate (bpm) 133 ± 11 149 ± 11a 163 ± 10a,b 173 ± 11a,b,c

Mean Power Output (W) 62 ± 14 77 ± 18a 89 ± 18a,b 98 ± 23a,b,c

Mean Peak Power (W) - 570 ± 55 571 ± 49d 516 ± 39

a Indicates significantly greater than MOD (p < 0.05)

b Indicates significantly greater than SI120 (p < 0.05)

c Indicates significantly greater than SI60 (p < 0.05)

d Indicates significantly greater than SI30 (p < 0.05) 107

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Figure 4.2 Cyclemax data for (a) mean power output and (b) peak power output across

30 min of moderate intensity continuous exercise at Fatmax (MOD; ) and sprint

interval exercise consisting of continuous exercise at Fatmax interspersed with a 4-sec

maximal sprint every 2 min (SI120; ), 1 min (SI60; ) and every 30 sec (SI30; ).

a Indicates significantly greater than MOD (p < 0.05).

b Indicates significantly greater than SI120 (p < 0.05).

c Indicates significantly greater than SI60 (p < 0.05).

d Indicates significantly greater than SI30 (p < 0.05).

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4.4.3 Energy Expenditure, and Fat and Carbohydrate Oxidation

There was a significant main effect of protocol on the rate of energy expenditure during

exercise (p < 0.001). Energy expenditure progressively increased from MOD to SI120 (p

< 0.001) and SI120 to SI60 (p < 0.001), but the difference between SI60 and SI30 was not

significant (p = 0.076; Figure 4.3).

There was a progressive increase in the overall rate of carbohydrate oxidation with

increasing sprint frequency (p < 0.001), such that MOD < SI120 (p < 0.001), SI120 < SI60

(p = 0.012) and SI60 < SI30 (p = 0.014; Figure 4.3). The overall rate of fat oxidation was

significantly greater for MOD compared to SI120 (p = 0.023) and SI30 (p = 0.049), but

was similar for MOD and SI60 (p = 0.127) and between the three sprint interval

protocols (p > 0.05; Figure 4.3). When each of the time-points (i.e. min 10, 20 and 30)

were examined separately, the rate of fat oxidation was stable throughout MOD (p =

0.139), but increased across time for SI120 (p = 0.008), SI60 (p = 0.056) and SI30 (p =

0.001; Figure 4.4).

4.4.4 Hunger, Satiety and Post-Exercise Energy Intake

There was no significant difference in post-exercise VAS scores for hunger and satiety

between the four exercise protocols (p > 0.05). Likewise, ad libitum post-exercise

energy intake was similar for MOD, SI120 and SI30 (p > 0.05), but was significantly less

for SI60 compared to MOD (p = 0.025; Figure 4.5). With respect to specific

macronutrient intake at the acute post-exercise meal, the amount of carbohydrate

ingested post-exercise was similar for the four protocols (p > 0.05; Figure 4.5), but the

amount of fat ingested was significantly less for SI60 compared with both MOD (p =

0.005) and SI120 (p = 0.046), and also tended to be less than SI30 (p = 0.089; ES = 0.39;

Figure 4.5).

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Figure 4.3 Contributions of fat and carbohydrate oxidation to total energy expenditure

(mean ± SE) for 30 min of moderate intensity continuous exercise at Fatmax (MOD) and


sec maximal sprints every 2 min (SI120), every 1 min (SI60), or every 30 sec (SI30).





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Figure 4.4 Fat oxidation rate (kJ/min) at 10, 20 and 30 min of moderate intensity

continuous exercise at Fatmax (MOD; ) and sprint interval exercise consisting of

continuous exercise at Fatmax interspersed with 4-sec maximal sprints every 2 min

(SI120; ), every 1 min (SI60; ) and every 30 sec (SI30; ).



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Figure 4.5 Post-exercise energy intake (mean ± SE) for 30 min of moderate intensity

continuous exercise at Fatmax (MOD) and sprint interval exercise consisting of

continuous exercise at Fatmax interspersed with 4-sec maximal sprints every 2 min

(SI120), every 1 min (SI60), or every 30 sec (SI30).


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4.4.5 Enjoyment

Enjoyment of the exercise bouts, assessed by PACES, was similar for MOD, SI120 and

SI60 (p > 0.05), but was significantly less for SI30 compared with MOD (p = 0.038) and

SI120 (p = 0.009), and tended to be less than SI60 (p = 0.052; Figure 4.6). When

participants were asked to indicate which protocol was the best and worst, 9/11

participants (χ2 [1, N = 11] = 4.455, p = 0.035) rated SI60 (7/11) and SI120 (2/11)

altogether as the best, and the remaining participants rated MOD (1/11) or SI30 (1/11) as

the best. SI30 was rated the worst exercise protocol by 9/11 participants (χ2 [1, N = 11] =

4.455, p = 0.035), with the remaining participants rating MOD as the worst.

Figure 4.6 Ratings of enjoyment using the Physical Activity Enjoyment Scale (PACES;

mean ± SE) for 30 min of moderate intensity continuous exercise at Fatmax (MOD) and


sec maximal sprints every 2 min (SI120), every 1 min (SI60), or every 30 sec (SI30).


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4.4.6 Perceived Exertion

There was a significant main effect of both time and protocol on RPE during exercise (p

< 0.001; Figure 4.7). Average RPE increased as the frequency of sprints increased, such

that MOD < SI120 (p = 0.05), SI120 < SI60 (p = 0.038) and SI60 < SI30 (p = 0.003; Figure

4.7).

Figure 4.7 Rates of Perceived Exertion (RPE; mean ± SE) at 10, 20 and 30 min of

moderate intensity continuous exercise at Fatmax (MOD; ) and sprint interval exercise

consisting of continuous exercise at Fatmax interspersed with 4-sec maximal sprints

every 2 min (SI120; ), every 1 min (SI60; ) and every 30 sec (SI30; ).




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4.5 DISCUSSION

When exercise is prescribed for fat loss or energy balance, the focus should be on

increasing energy expenditure by maximising the acute physiological effect of exercise,

and enhancing enjoyment in order to achieve optimal long-term adherence (Dishman et

al., 2005; Mulvihill et al., 2000). We have recently reported that children prefer

participating in sprint interval exercise (consisting of moderate intensity continuous

exercise at Fatmax interspersed with a 4-sec maximal sprint every 2 min) compared with

moderate intensity continuous exercise at Fatmax alone, despite the fact that the sprint

interval exercise was of a higher intensity and involved a greater total amount of work

(Crisp et al., 2012b: Chapter 3). Furthermore, the increased energy expenditure

associated with the sprint interval exercise was not compensated for by an acute

increase in energy intake at the post-exercise meal, which may have an important

implication for overall energy balance. The current study explored the extent to which

the frequency of sprints could be increased, to further maximise energy expenditure

during exercise, before the enjoyment and preference for sprint interval exercise started

to decline in overfat boys.

Based on the finding that energy expenditure increases by introducing as little as a 4-sec

maximal sprint every 2 min to continuous exercise at Fatmax (Crisp et al., 2012b:

Chapter 3), it was expected that, as the sprint frequency increased, so too would the

amount of energy expended over a given time period. In support of this view, energy

expenditure was significantly greater for SI60 compared with SI120, but interestingly,

SI30 resulted in a similar energy expenditure compared to SI60. These latter results are

likely a reflection of the decline in the quality of sprints (i.e. power output) when

performed every 30 sec, as a result of an insufficient recovery between sprint efforts, as

well as the participants’ inability to maintain the required intensity between sprints due

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to leg fatigue. This interpretation is supported by the lower mean and peak power

output throughout the last half of SI30 when compared to the other protocols, suggesting

that energy expenditure during exercise is not optimised by completing the maximal

number of sprints that can be tolerated by an individual if the sprint quality is

compromised. Rather, there needs to be a balance between the number of sprints that

can be performed whilst maintaining the quality of sprints and recovery intensity. The

present results suggest that SI60 may be optimal for boys carrying excess body fat for

exercise lasting 30-min, given that this protocol enables the maintenance of sprint

quality and power output throughout the duration of exercise.

As well as energy expenditure, it has been suggested that the rate of fat oxidation during

exercise should be taken into consideration when prescribing exercise for weight

management, given that enhanced fat oxidation during exercise (particularly for

exercise at Fatmax) could promote increased fat loss in the long term (Achten et al.,

2002; Brandou et al., 2003; Dumortier et al., 2003). Despite this suggestion, it is yet to

be established whether exercise training at Fatmax is superior to sprint interval training

protocols for increased fat oxidation and ultimately weight loss in either overweight

adults or children. Furthermore, we have recently reported that the addition of 4-sec

maximal sprint efforts every 2 min to a continuous bout of exercise at Fatmax did not

compromise the rate of fat oxidation during exercise (Crisp et al., 2012b: Chapter 3). In

the current study however, fat oxidation rates were lower during SI120 compared to

MOD. The difference between these two studies could be explained by the higher

number of participants in the current study which allowed for the detection of a

significant difference in fat oxidation rates between MOD and SI120, a difference which

did not reach significance in our previous study. What is interesting to note is that for

all three sprint interval protocols, but not MOD, fat oxidation rate increased over time

which supports the use of longer exercise durations for maximising fat oxidation during

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sprint interval exercise. Clearly, more research is required to better understand the

factors that control fat oxidation rates during sprint interval exercise.

To fully understand the influence of specific bouts of exercise on overall energy

balance, it is also important to consider post-exercise energy consumption. An acute

suppression of appetite has been noted after higher compared with lower intensity

exercise in adults (Imbeault et al., 1997; King et al., 1994; Thompson et al., 1988) and

children (Moore et al., 2004; Thivel et al., 2012). However, the effect of sprint interval

exercise on appetite and post-exercise energy intake has only been examined in one

recent study in children (Crisp et al., 2012b: Chapter 3). In this study, Crisp et al.

(2012b: Chapter 3) observed no significant difference in post-exercise feelings of

hunger and satiety, or acute energy intake in the subsequent meal following moderate

intensity continuous exercise at Fatmax compared with a similar bout of exercise

interspersed with 4-sec maximal sprint efforts every 2 min in overfat boys. Likewise,

there was no significant difference in post-exercise hunger and satiety across the four

protocols examined in the current study. Post-exercise energy intake was also similar

for MOD, SI120 and SI30, but was significantly less for SI60 compared with MOD. The

mechanism for the decreased energy intake following SI60 is not known but may be

related to alterations in appetite-related hormones (Erdmann et al. 2007; Martins et al.

2008; Ueda et al. 2009), decreased plasma leptin (van Aggel-Leijssen et al. 1999), or

the inverse relationship between splanchnic blood flow (Rowell et al. 1964) in relation

to the volume and quality of the maximal sprint efforts. As can be seen from our results,

the quality of sprints (based on peak power output) was compromised in SI30, compared

with SI120 and SI60, but the number of high intensity efforts was twice as high in SI60

compared with SI120. It is possible that the combination of the high volume and quality

of sprints in SI60 influenced the factors outlined above. No previous studies have

examined the effect of sprint interval exercise on these parameters in children and

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future research should be directed here. Regardless, our results further support the

notion that high intensity sprint interval exercise does not prompt an immediate increase

in appetite or acute compensatory increase in energy intake to replace the extra energy

expended during exercise in overfat children, at least in the short term. In particular, the

finding of decreased acute energy intake for SI60 compared with MOD may have

important implications for weight management because this sprint interval protocol is

more likely to promote a negative energy balance. It is important to acknowledge that

only energy intake from the acute post-exercise breakfast meal was examined in the

present study. This meal was presented 5-10 min after the completion of exercise and it

is possible that different results may be obtained if post-exercise energy intake is

delayed for a longer time period following exercise. Furthermore, it is also possible that

differences in energy intake may emerge later during the day. However, there is

evidence to suggest that this trend is maintained, with no compensation in energy intake

following higher intensity exercise over 24 hours (Thivel et al., 2012). In fact, Thivel et

al. (2012) noted that 24-hr energy intake was significantly lower when a single bout of

exercise was prescribed at 1100h at a high intensity (75% O2peak), compared with an

equicaloric bout of low intensity exercise (40% O2peak), despite no significant

difference in ratings of subjective hunger, fullness or prospective food consumption

between the two conditions in obese adolescent boys.

Another important issue to consider when prescribing exercise for fat management, is

that of long-term adherence. There is evidence to suggest that adults prefer exercise

conditions that are associated with a lower RPE (Coquart et al., 2008; Robertson &

Noble, 1997). Furthermore, Coquart et al. (2008) reported that intermittent exercise is

preferable for sedentary adults, rather than continuous exercise of the same intensity

and duration, because it is perceived to be easier as indicated by lower RPE. Of interest,

the majority of boys in the current study indicated that they preferred participating in

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SI60 despite reporting higher RPE for this protocol compared with MOD. Participants

indicated that they preferred SI60 because it was “a challenge”, “more interesting” and

“there was a perfect amount of rest time in between the sprints to get [my] energy back

without getting too bored in between”. In contrast, SI30 was the least preferred exercise

protocol by the majority of participants because it was simply “too hard” and “too

tiring” because “[my] legs didn’t have time to recover in between the sprints”. Another

possible explanation for the participants’ preference for SI60, followed by SI120, is that

these two protocols more closely reflect the spontaneous nature of children’s physical

activity patterns during free-play, characterised by short bursts of intense activity (3-4

sec in duration) interspersed with low-moderate intensity exercise or rest (Bailey et al.,

1995). On the other hand, despite MOD being easier for the participants, as indicated by

lower RPE, it was also reported to be more “boring” and therefore, not preferable.

Other studies in adults and children have also reported continuous exercise as being

boring (Crisp et al., 2012b: Chapter 3; Tjønna et al., 2008; Wisløff et al., 2007) and this

may decrease adherence to long-term exercise training programs.

In summary, SI120 and SI60 resulted in greater energy expenditure compared with MOD,

without compromising enjoyment of the exercise bout, and did not prompt increased

post-exercise energy intake in overfat boys. In fact, despite energy expenditure being

higher for SI60, energy intake was significantly lower compared to MOD, a finding

which is likely to have important implications for overall energy balance. On the other

hand, a further increase in sprint frequency (i.e. SI30) caused levels of enjoyment to

decline, without any extra benefits in relation to energy expenditure or post-exercise

energy intake. Given the health benefits of an active lifestyle, these results suggest that

it may be more beneficial to prescribe sprint interval exercise (consisting of 4-sec

sprints every minute) in combination with continuous exercise at Fatmax, rather than

continuous exercise at Fatmax alone, for boys carrying excess body fat. This nature of

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exercise (particularly SI60 and SI120) appears to be superior to continuous exercise at

Fatmax because it increases energy expenditure without prompting a compensatory

increase in acute post-exercise energy intake or compromising enjoyment, provided the

sprint frequency is not too high (i.e. SI30). While the findings of this study reveal the

short-term benefits of various sprint interval exercise protocols, further research is

required to explore the long-term implications of sprint interval exercise training on

energy balance, exercise adherence and fat loss.

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5 GENERAL DISCUSSION

5.1 SUMMARY

It is well established that fat loss occurs when energy expenditure exceeds energy

intake over a prolonged period of time. As dietary restriction should not be promoted as

the primary means of fat loss for children (Battle & Brownell, 1996; Watts et al., 2005),

an important focus should be on increasing long-term energy expenditure through

increased adherence to physical activity and exercise. However to date, the optimal type

of exercise for fat management in children is not known.

It has been suggested that training at the exercise intensity that maximises fat oxidation

(Fatmax) may be favourable for fat loss (Brandou et al., 2005) not only because of the

increased rate of fat oxidation at this intensity (Melanson et al., 2002; Venables &

Jeukendrup, 2008), but also because low-moderate intensity exercise below anaerobic

threshold is more easily adhered to than higher intensities of exercise (Kilpatrick et al.,

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2007; Lind et al., 2008; Perri et al., 2002). However, higher intensity exercise results in

increased energy expenditure per unit of time, which is more likely to invoke a greater

negative energy balance (Hunter et al., 1998) with a much lower investment of time

(Boutcher, 2011; Tremblay et al., 1994). One of the major concerns with prescribing

continuous high intensity exercise to overweight individuals is that they may not adhere

to a long-term training program (Perri et al., 2002), due to feelings of discomfort and

displeasure (Kilpatrick et al., 2007; Lind et al., 2008). But interestingly, when children

are observed during spontaneous physical activity or free-play, they most commonly

engage in unstructured games or sports that require multiple short sprint efforts of

approximately 3-4 sec in duration, interspersed with longer duration low-moderate

intensity exercise (Bailey et al., 1995). This suggests that higher intensity sprint interval

exercise may be preferable as a means to increase the energy expenditure and maximise

the enjoyment of paediatric-specific exercise training protocols. Since this prediction

has never been tested before, the primary purpose of this thesis was to explore the acute

influence of continuous exercise at Fatmax with or without the addition of repeated 4-sec

maximal sprint efforts on energy expenditure, fat oxidation rate, acute post-exercise

energy intake and enjoyment in boys carrying excess body fat (overfat). As a

preliminary aim, we sought to investigate the use of a single graded exercise protocol

with 3-min stages for estimating Fatmax in this population.

The first study of this thesis (Chapter 2) explored whether fat oxidation rate and Fatmax

remained stable across 30 min of constant load exercise (i.e. whether the duration of

exercise affects fat oxidation rates and ultimately, the Fatmax estimate) in overfat boys.

The Fatmax estimated from a single graded exercise test with 3-min stages (GRAD) was

also compared against 30-min bouts of prolonged, steady-state exercise at five different

intensities (PROL) to determine whether the cumulative duration of a graded exercise

test affects Fatmax. It was observed that the rate of fat oxidation remained stable during

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30 min of steady-state exercise. Fatmax was similar at 3, 10, 20 and 30 min of PROL,

suggesting that for exercise lasting 30 min or less, exercise duration does not affect

Fatmax. In addition, although GRAD and PROL provided a similar estimate of Fatmax at

the group level, the Fatmax identified using GRAD may need to be interpreted with

caution as there was considerable variation in Fatmax estimated between the two

protocols at the individual level. Nonetheless, determining Fatmax from the multiple

visits required for PROL is not feasible in most clinical settings, indicating that GRAD

is preferable to PROL. These results add to the current body of knowledge, since no

studies have determined whether Fatmax is stable over time during exercise, or explored

the use of a single graded exercise test with 3-min stages for estimating Fatmax

Given the recommendation that exercising at Fatmax may be beneficial for managing

body fat stores and the observation that children spontaneously engage in intermittent

high intensity exercise, the second study of this thesis (Chapter 3) examined energy

expenditure and fat oxidation rate (both during and post-exercise), acute post-exercise

energy intake, and enjoyment associated with 30 min of continuous exercise at Fatmax

(MOD) compared with 30 min of sprint interval exercise (consisting of continuous

exercise at Fatmax interspersed with 4-sec maximal sprint efforts every 2 min; SI) in

both overfat boys and control boys with a healthy body composition. It was found that

the addition of multiple short sprint efforts to continuous exercise at Fatmax increased

energy expenditure, without compromising fat oxidation rates, or stimulating increased

acute post-exercise energy intake. In addition, although there was no significant

difference in enjoyment between the two protocols, as reflected by results from the

PACES, the boys indicated that they preferred SI and did not perceive it to be any

harder than MOD. This is the first study to uncover the acute benefits of sprint interval

in

overfat children. In fact, only one other study has explored its use in a healthy

paediatric population (Zakrzewski & Tolfrey, 2011a).

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exercise for increasing both the energy expenditure and enjoyment associated with

exercise in overfat boys, which may have important implications for the prescription of

exercise for fat management in children.

Once it was established that overfat boys preferred participating in SI over MOD, the

final study of this thesis (Chapter 4) explored the extent to which the frequency of

sprints could be increased (i.e. every 2 min [SI120], 1 min [SI60] or every 30 sec [SI30])

to maximise the amount of energy expended during the exercise bout, before their

enjoyment and preference for sprint interval exercise over continuous exercise at Fatmax

was compromised. The results from this study not only corroborate those from the

second study of this thesis, but also show that energy expenditure increases as the sprint

frequency increases, but a plateau is reached at SI60 (i.e. there was no additional

increase in energy expenditure for SI30). This is likely the result of a decline in the

quality of sprints and the participants’ inability to maintain the required intensity

between sprints when the sprints were performed every 30 sec. In addition, the

increased energy expenditure resulting from the addition of short sprint efforts to

continuous exercise at Fatmax did not prompt a compensatory increase in acute post-

exercise energy intake. In fact, energy intake at the acute post-exercise breakfast meal

was significantly less for SI60 compared with MOD. The boys also preferred

participating in SI60 and SI120 over MOD, despite perceiving the exercise to be harder.

However, their enjoyment declined when the sprints were performed every 30 sec (i.e.

for SI30).

Overall, the findings from this series of research papers suggest that the acute benefits

of exercise may be optimised by encouraging overfat boys to participate in sprint

interval exercise consisting of no more than 4-sec sprints performed every min, rather

than continuous exercise at Fatmax. The benefits of adding short sprint efforts to

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continuous exercise at Fatmax include increased energy expenditure, without a

compensatory increase in acute energy intake at the post-exercise meal, and increased

enjoyment. These outcomes may have important implications for long-term exercise

adherence and weight management.

5.2 CONCLUSIONS

In conclusion, these three studies show that;

Fat oxidation rate is stable across 30 min of cycling at intensities between 40-60%

O2peak in overfat boys, and the Fatmax estimate is similar at 3, 10, 20 and 30 min of

exercise. There is no evidence of a carry-over effect of substrate oxidation between

consecutive stages of a graded exercise test with 3-min increments in overfat boys,

thus indicating that this testing protocol provides and adequate estimate of Fatmax.

Continuous exercise at Fatmax interspersed with a 4-sec maximal sprint effort every

2 min results in greater energy expenditure compared with continuous exercise at

Fatmax alone, without prompting an increase in energy intake at the acute post-

exercise breakfast meal in boys with varying body compositions. Despite this

increase in energy expenditure, these boys do not perceive SI to be harder than

MOD, with the majority indicating that they prefer participating in SI.

Although overall fat oxidation rates may be compromised with high-quality sprint

interval exercise, fat oxidation rate per unit of time increases as the duration of

exercise progresses for SI120, SI60, and SI30, but remains stable during MOD.

Overall energy expenditure increases with an increase in sprint frequency, but there

is no additional gain when the sprints are performed every 30 sec compared with

every 1 min. The increased energy expenditure associated with increased sprint

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frequency does not prompt an increase in energy intake at the acute post-exercise

meal. In fact, acute post-exercise energy intake is significantly lower following SI60

compared to MOD. Finally, in addition to these benefits of SI for energy balance,

overfat boys prefer participating in the sprint interval protocols compared to MOD,

except when the sprints are performed every 30 sec.

5.3 IMPLICATIONS

Although studies in adults suggest that Fatmax may be accurately determined using a

single graded exercise test with 3-min stages (Achten et al., 2002), only one study has

explored the validity of such a protocol in children (Zakrzewski & Tolfrey, 2011a).

This study suggests that a 3-min incremental protocol provides an estimate of Fatmax in

healthy children, but acknowledges that it may not be appropriate for obese children

(Zakrzewski & Tolfrey, 2011a). The results from Study 1 of this thesis indicate that a

single graded exercise protocol with 3-min stages is sufficient for the estimation of

Fatmax in overweight children. This protocol allows for the examination of fat oxidation

rates over a wide range of exercise intensities, and provides a more precise estimation

of Fatmax than protocols that examine fewer intensities over a prolonged duration of

exercise.

Since fat loss occurs when energy expenditure consistently exceeds energy intake over

a prolonged period of time, the main focus of exercise training programs for fat loss

should be to increase energy expenditure with each exercise bout to promote a negative

energy balance. However, successful weight management occurs when adherence to

regular exercise is achieved which results when enjoyment is optimised, particularly for

children. The results from Studies 2 and 3 of this thesis suggest that it may be more

beneficial to prescribe sprint interval exercise (consisting of 4-sec sprints every min or

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every 2 min) in combination with continuous exercise at Fatmax, rather than continuous

exercise at Fatmax alone, for boys with varying body compositions. This form of

exercise has the potential to increase energy expenditure without prompting increased

acute post-exercise energy intake which may be more effective in contributing to the

negative energy balance required for weight loss in the long term. Furthermore, given

that fat oxidation rates increase as the duration of exercise progresses for each of the

sprint interval exercise protocols tested in the current studies, but not for MOD, there is

a greater potential for fat oxidation rates to be enhanced with durations of sprint interval

exercise lasting longer than 30 min. Finally, the increased preference for sprint interval

exercise, particularly SI60 and SI120, may help to promote greater adherence to regular

exercise in the long-term. It is important to note however, that there needs to be a

balance between the number of sprints (i.e. to increase energy expenditure) and

enjoyment of the exercise bout given that the current results suggest that introducing

too many sprints (i.e. SI30) decreases levels of enjoyment which may negatively

influence long-term adherence.

5.4 LIMITATIONS

Although the results of this thesis have important practical implications, the following

limitations do apply:

The outcomes of this research cannot be applied to other modalities of exercise,

only cycling.

Post-exercise energy expenditure and fat and carbohydrate oxidation rates were

only measured for 30 min post-exercise in Study 2. In addition, there were no post-

exercise measurements collected following the exercise protocols in Study 3.

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For both Studies 2 and 3, energy intake was only examined at the acute post-

exercise breakfast meal and it is possible that differences in energy intake may

emerge later during the day.

The findings of all of these studies were obtained in boys and may not be shared by

girls due to physiological and psychological differences between genders,

particularly in relation to exercise.

The novelty of attending the laboratory to be involved in these studies may have

influenced the boys’ self-reported measures of enjoyment.

In fact, the majority of the measures obtained in this thesis (i.e. Fatmax, energy

expenditure, substrate oxidation, acute energy intake) required a laboratory-based

assessment. Therefore, the results may not reflect free-living conditions.

5.5 DIRECTIONS FOR FUTURE RESEARCH

Although the Fatmax estimated from a single graded exercise test with 3-min stages

was not different from that obtained from multiple 30-min bouts of prolonged

steady-state exercise at the group level (Study 1), there was some marked variation

in these estimates of Fatmax at the individual level. As this is the first study to

examine the potential of a single graded exercise protocol to estimate Fatmax in

overweight children, further research is required to explore this shortcoming.

Furthermore, Study 1 provided a strong basis for further exploration of a single

graded exercise protocol used for the determination of both Fatmax and O2peak in

overweight children.

Studies 2 and 3 revealed that by increasing the intensity of exercise through sprint

interval exercise, energy expenditure is enhanced without prompting an acute

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increase in post-exercise energy intake. However, in order to fully understand the

impact of these two variables on weight management, future research is required to

examine the influence of sprint interval exercise on energy intake and expenditure

across the duration of the day (i.e. across 24 hours).

The results from Studies 2 and 3 suggest that it may be more appealing for boys to

participate in sprint interval exercise, rather than continuous exercise of a moderate

intensity. However, whether this preference for sprint interval exercise continues

over a longer period of exercise training is yet to be determined. Specifically, it

needs to be determined whether the increased preference for sprint interval exercise

equates to long-term adherence.

In Study 3, it was suggested that fat oxidation rates may be compromised with

sprint interval exercise. However, it was interesting to observe a significant

increase in fat oxidation rates over the duration of the 30-min exercise bout for

SI120, SI60 and SI30, but not for MOD. Therefore, future research should investigate

whether longer durations of sprint interval exercise results in increased fat

oxidation.

Although Study 3 revealed that SI30 results in declined enjoyment with no extra

benefit in relation to energy expenditure and acute energy intake in the post-

exercise meal, there is potential for these outcomes to change as cardiovascular and

musculoskeletal adaptations occur in response to exercise training. For example, it

is possible that as cardiovascular fitness and leg strength increases, boys may be

able to withstand a greater frequency of sprints (i.e. SI30) and energy expenditure

may be further enhanced with this protocol. Therefore, future research could also

examine the change over time in relation to these variables.

130

The sample population of the research presented in this thesis consisted of boys

aged 8-12 years only (overfat and/or control). It is unknown whether the results

from this research are applicable to girls, adolescents or adults and further research

is required to determine this.

Future research could examine energy intake and the enjoyment associated with

these sprint interval protocols under free-living conditions. In particular, this would

help to eliminate the limitation of the novelty associated with attending the

laboratory on measures of enjoyment.

Finally, given our interpretation that SI120, SI60, and perhaps SI30 with training,

might be more beneficial for fat loss than MOD, this prediction should be tested by

comparing the long term efficacy of these regimes on adherence and body fat loss.

131

REFERENCES

Access Economics (2008) The Cost of Obesity, Access Economics, Canberra

Achten J, Gleeson M & Jeukendrup AE (2002) Determination of the exercise intensity

that elicits maximal fat oxidation. Medicine and Science in Sports and Exercise 34

Achten J, Venables MC & Jeukendrup AE (2003) Fat oxidation rates are higher during

running compared with cycling over a wide range of intensities. Metabolism 52(6): 747-

752

: 92-

97

Alexander LM, Inchley J, Todd J, Currie D, Cooper AR & Currie C (2005) The broader

impact of walking to school among adolescents: Seven day accelerometry based study.

British Medical Journal 331: 1061-1062

Arvaniti K, Richard D & Tremblay A (2000) Reproducibility of energy and

macronutrient intake and related substrate oxidation rates in a buffet-type meal. British

Journal of Nutrition 83: 489-495

Aucouturier J, Rance M, Meyer M, Isacco L, Thivel D, Fellmann N, Duclos M &

Duché P (2009) Determination of the maximal fat oxidation point in obese children and

adolescents: Validity of methods to assess maximal aerobic power. European Journal

of Applied Physiology 105: 325-331

Australian Bureau of Statistics (2009) Australian Social Trends 2009, Cat 4102.0

Bailey RC, Olson J, Pepper SL, Porszasz J, Barstow TJ & Cooper DM (1995) The level

and tempo of children’s physical activity: An observational study. Medicine and

Science in Sports and Exercise 27(7): 1033-1041

Barker AR, Williams CA, Jones AM & Armstrong N (2011) Establishing maximal

oxygen uptake in young people during a ramp cycle test to exhaustion. British Journal

of Sports Medicine 45: 498-503

Battle EK & Brownell KD (1996) Confronting a rising tide of eating disorders and

obesity: Treatment vs. prevention and policy. Addictive Behaviours 21(6): 755-765

132

Beaver WL & Wasserman K (1991) Muscle RQ and lactate accumulation from analysis

of the VCo2-Vo2 relationship during exercise. Clinical Journal of Sport Medicine 1(1):

27-34

Bell CG, Walley AJ & Froguel P (2005) The genetics of human obesity. Nature

Reviews Genetics 6(3): 221-234

Ben Ounis O, Elloumi M, Amri M, Trabelsi Y, Lac G & Tabka Z (2009) Impact of

training and hypocaloric diet on fat oxidation and body composition in obese

adolescents. Science and Sport 24: 178-185

Ben Ounis O, Elloumi M, Amri M, Zbidi A, Tabka Z & Lac G (2008) Impact of diet,

exercise and diet combined with exercise programs on plasma lipoprotein and

adiponectin levels in obese girls. Journal of Sports Science and Medicine 7: 437-445

Bartlett JD, Close GL, MacLaren DPM, Gregson W, Drust B & Morton JP (2011)

High-intensity interval running is perceived to be more enjoyable than moderate-

intensity continuous exercise: Implications for exercise adherence. Journal of Sports

Sciences 29(6): 547-553

Berkey CS, Rockett HRH, Field AE, Gillman MW, Frazier AL, Camargo CA & Colditz

GA (2000) Activity, dietary intake, and weight changes in a longitudinal study of

preadolescent and adolescent boys and girls. Pediatrics 105(4): e56

Bilski J, Teległów A, Zahradnik-Bilska J, Dembiński A, Warzecha Z (2009) Effects of

exercise on appetite and food intake regulation. Medicina Sportiva 13(2): 82-94

Bircher S, Knechtle B, Müller G & Knecht H (2005) Is the highest fat oxidation rate

coincident with the anaerobic threshold in obese women and men? European Journal of

Sport Science 5(2): 79-87

Bircher S & Knechtle B (2004) Relationship between fat oxidation and lactate threshold

in athletes and obese women and men. Journal of Sports Science and Medicine 3: 174-

181

Bishop D, Maxwell NS (2009) Effects of active warm up on thermoregulation and

intermittent-sprint performance in hot conditions. Journal of Science and Medicine in

Sport 12: 196-204

133

Boreham C & Riddoch C (2001) The physical activity, fitness and health of children.

Journal of Sports Sciences 19: 915-929

Booth ML, Chey T, Wake M, Norton K, Hesketh K, Dollman J & Robertson I (2003)

Change in the prevalence of overweight and obesity among Australians, 1969-1997.

American Journal of Clinical Nutrition 77(1): 29-36

Bordenave S, Flavier S, Fédou C, Brun JF & Mercier J (2007) Exercise calorimetry in

sedentary patients: procedures based on short 3 min steps underestimate carbohydrate

oxidation and overestimate lipid oxidation. Diabetes Metabolism 33: 379-384

Boutcher SH (2011) High-intensity intermittent exercise and fat loss. Journal of

Obesity doi:10.1155/2011/868305

Boutcher SH & Dunn SL (2009) Factors that may impede the weight loss response to

exercise-based interventions. Obesity Reviews 10(6): 671-680

Brandou F, Dumortier M, Garandeau P, Mercier J & Brun JF (2003) Effects of a two-

month rehabilitation program on substrate utilization during exercise in obese

adolescents. Diabetes Metabolism 29: 20-27

Brandou F, Savy-Pacaux AM, Marie J, Brun JF & Mercier J (2006) Comparison of the

type of substrate oxidation during exercise between pre and post pubertal markedly

obese boys. International Journal of Sports Medicine 27: 407-414

Brandou F, Savy-Pacaux AM, Marie J, Bauloz M, Maret-Fleuret I, Borrocoso S,

Mercier J & Brun JF (2005) Impact of high- and low-intensity targeted exercise training

on the type of substrate utilization in obese boys submitted to a hypocaloric diet.

Diabetes and Metabolism 31: 327-335

Brooks F & Magnusson J (2006) Taking part counts: Adolescents’ experiences of the

transition from inactivity to active participation in school-based physical education.

Health Education Research 21(6): 872-883

Brooks GA & Mercier J (1994) Balance of carbohydrate and lipid utilization during

exercise: The “crossover” concept. Journal of Applied Physiology 76(6): 2253-2261

Burgomaster KA, Howarth KR, Phillips SM, Rakobowchuk M, MacDonald MJ,

McGee SL & Gibala MJ (2008) Similar metabolic adaptations during exercise after low

https://webmail.staff.uwa.edu.au/owa/redir.aspx?C=3aab31321d9e4ff19f245b66535b4d71&URL=http%3a%2f%2fwww.ncbi.nlm.nih.gov%2fpubmed%2f19538438�

https://webmail.staff.uwa.edu.au/owa/redir.aspx?C=3aab31321d9e4ff19f245b66535b4d71&URL=http%3a%2f%2fwww.ncbi.nlm.nih.gov%2fpubmed%2f19538438�

134

volume sprint interval and traditional endurance training in humans. Journal of

Physiology 586: 151-160

Burgomaster KA, Hughes SC, Heigenhauser JF, Bradwell SN & Gibala MJ (2005) Six

session of sprint interval training increases muscle oxidative potential and cycle

endurance capacity in humans. Journal of Applied Physiology 98: 1985-1990

Buscemi S, Verga S, Caimi G & Cersola G (2005) Low relative resting metabolic rate

and body weight gain in adult Caucasian Italians. International Journal of Obesity 29:

287-291

Calfas KJ & Taylor WC (1994) Effects of physical activity on psychological variables

on adolescents. Pediatric Exercise Science 6(4): 406-423

Cameron AJ, Welborn TA, Zimmet PZ, Dunstan DW, Owen N, Salmon J, Dalton M,

Jolley D & Shaw JE (2003) Overweight and obesity in Australia: The 1999-2000

Australian diabetes, obesity and lifestyle study (AusDiab). Medical Journal of Australia

178: 427-432

Caspersen C, Powell K & Christenson G (1985) Physical activity, exercise and physical

fitness: Definitions and distinctions for health-related research. Public Health Reports

100(2): 126-131

Chenevière X, Borrani F, Ebenegger V, Gojanovic B & Malatesta D (2009) Effect of 1-

hour single bout of moderate-intensity exercise on fat oxidation kinetics. Metabolism

58: 1778-1786

Christmass MA, Dawson B, Passeretto P & Arthur PG (1999) A comparison of skeletal

muscle oxygenation and fuel use in sustained continuous and intermittent exercise.

European Journal of Applied Physiology 80: 423-435

Colapinto CK, Fitzgerald A, Taper J & Veugelers PJ (2007) Children’s preference for

large portions: Prevalence, determinants, and consequences. Journal of the American

Dietetic Association 107: 1183-1190

Cole TJ, Bellizzi MC, Flegal KM & Dietz WH (2000) Establishing a standard

definition for child overweight and obesity worldwide: International survey. British

Medical Journal 320: 1240-1245

135

Coquart JBJ, Lemaire C, Dubart A-E, Luttembacher D-P, Douillard C & Garcin M

(2008) Intermittent versus continuous exercise: Effects of perceptually lower exercise in

obese women. Medicine and Science in Sports and Exercise 40(8): 1546-1553

Cooper AR, Page AS, Foster LJ & Qahwaji D (2003) Commuting to school: Are

children who walk more physically active? American Journal of Preventative Medicine

25(4): 273-276

Cooper DM, Poage J, Barstow TJ & Springer C (1990) Are obese children truly unfit?

Minimising the confounding effect of body size on the exercise response. The Journal

of Pediatrics 116(2): 223-230

Coyle EF, Jeukendrup AE, Wagenmakers AJ & Saris WH (1997) Fatty acid oxidation

is directly regulated by carbohydrate metabolism during exercise. American Journal of

Physiology, Endocrinology and Metabolism 273(2): E268-E275

Crisp NA, Guelfi KJ, Braham R & Licari M (2011) Substrate oxidation in overweight

boys at rest, during exercise and acute post-exercise recovery. International Journal of

Pediatric Obesity 6(2-2): e615-e621

Crisp NA, Guelfi KJ, Licari MK, Braham R & Fournier PA (2012a) Does exercise

duration affect Fatmax in children? European Journal of Applied Physiology 112(7):

2557-2564

Crisp NA, Fournier PA, Licari MK, Braham R & Guelfi KJ (2012b) Adding sprints to

exercise at Fatmax: Implications for acute energy balance and enjoyment in boys.

Metabolism doi: 10.1016/j.metabol.2012.02.009

Daniels SR (2006) The consequences of childhood overweight and obesity. The Future

of Children 16(1): 47-67

Davison KK & Birch LL (2001) Childhood overweight: A contextual model and

recommendations for future research. Obesity Reviews 2(3): 159-171

Dawson B, Straton S & Randall N (1996) Oxygen consumption during recovery from

prolonged submaximal cycling below the anaerobic threshold. Journal of Sports

Medicine and Physical Fitness 36(2): 77-84

http://www.ajpm-online.net/article/S0749-3797(03)00205-8/abstract�

http://www.ajpm-online.net/article/S0749-3797(03)00205-8/abstract�

136

DeLany JP, Bray GA, Harsha DW & Volaufova J (2006) Energy expenditure and

substrate oxidation predict changes in body fat in children. The American Journal of

Clinical Nutrition 84: 862-870

Delamarche P, Monnier M, Gratasdelamarche A, Koubi HE, Mayet MH & Favier R

(1992) Glucose and free fatty acid utilization during prolonged exercise in prepubertal

boys in relation to catecholamine responses. European Journal of Applied Physiology

and Occupational Physiology 65: 66-72

Dencker M, Thorsson O, Linden C, Wollmer P, Andersen LB & Karlsson K (2007)

BMI and objectively measured body fat and body fat distribution in prepubertal

children. Clinical Physiology and Functional Imaging 27: 12-16

Dériaz O, Dumont M, Bergeron N, Després J-P, Brochu M & Prud’homme D (2001)

Skeletal muscle low attenuation area and maximal fat oxidation rate during submaximal

exercise in male obese individuals. International Journal of Obesity 25: 1579-1584

Deurenberg P (1996) Limitations of the bioelectrical impedance method for the

assessment of body fat in severe obesity. American Journal of Clinical Nutrition 64:

449S-452S

Dishman RK, Motl RW, Saunders R, Felton G, Ward D, Dowda M & Pate R (2005)

Enjoyment mediates effects of a school-based physical activity intervention. Medicine

and Science in Sports and Exercise 37: 478-487

Dishman RK, Sallis JF & Orenstein DR (1985) The determinants of physical activity

and exercise. Public Health Reports 100: 158-171

Dionne I, Alméras N, Bouchard C & Tremblay A (2000) The association between

vigorous physical activities and fat deposition in male adolescents. Medicine and


Donnelly JE, Smith B, Jacobsen DJ, Kirk E, DuBose K, Hyder M, Bailey B &

Washburn R (2004) The role of exercise for weight loss and maintenance. Best Practice

and Research Clinical Gastroenterology 18(6): 1009-1029

Dumortier M, Brandou F, Pérez-Martin A, Fedou C, Mercier J & Brun JF (2003) Low

intensity endurance exercise targeted for lipid oxidation improves body composition

137

and insulin sensitivity in patients with the metabolic syndrome. Diabetes Metabolism

29: 509-518

Duncan GE, Anton SD, Sydeman SJ, Newton Jr RL, Corsica JA, Durning PE, Ketterson

TU, Martin AD, Limacher MC & Perri MG (2005) Prescribing exercise at varied levels

of intensity and frequency: A randomized trial. Archives of Internal Medicine 165(20):

2362-2369

Edwards RHT, Ekelund LG, Harris RC, Hesser CM, Hultman E, Melcher A & Wigertz

O (1973) Cardiorespiratory and metabolic costs of continuous and intermittent exercise

in man. Journal of Physiology 234(2): 481-497

Ekkekakis P, Parfitt G & Petruzzello SJ (2011) The pleasure and displeasure people feel

when they exercise at different intensities. Sports Medicine 41(8): 641-671

Ellis KJ, Shypailo RJ, Pratt JA & Pond WG (1994) Accuracy of Dual-energy X-ray

Absorptiometry for body-composition measurement in children. American Journal of

Clinical Nutrition 60(5): 660-665

Erdmann J, Tahbaz R, Lippl F, Wagenpfeil S & Schusdziarra V (2007) Plasma ghrelin

levels during exercise - Effects of intensity and duration. Regulatory Peptides 143(1-3):

127-135

Fawkner SG, Armstrong N, Potter C & Welsman JR (2002) Oxygen uptake kinetics in

children and adults after the onset of moderate-intensity exercise. Journal of Sports

Science 20: 319-329

Frayn KN (1983) Calculation of substrate oxidation rates in vivo from gaseous

exchange. Journal of Applied Physiology 55: 628-634

Friedlander AL, Casazza GA, Homing MA, Buddinger TF & Brooks GA (1998) Effects

of exercise intensity and training on lipid metabolism in young women. American

Journal of Physiology, Endocrinology and Metabolism 276: E853-E863

French SA, Story M, Neumark-Sztainer D, Fulkerson JA & Hannan P (2001) Fast food

restaurant use among adolescents: Associations with nutrient intake, food choices and

behavioural and psychosocial variables. International Journal of Obesity 25: 1823-

1833.

138

Fox EL, Bowers RW & Foss ML (1988) The physiological basis of physical education

and athletics. Dubuque, Iowa, pp 68

Gibala MJ, Little JP, van Essen M, Wilkin GP, Burgomaster KA, Safdar A, Raha S &

Tarnopolsky MA (2006) Short-term sprint interval versus traditional endurance

training: Similar initial adaptations in human skeletal muscle and exercise performance.

Journal of Physiology 575(3): 901-911

Guelfi KJ, Jones TW, Fournier PA (2005) The decline in blood glucose levels is less

with intermittent high-intensity compared with moderate exercise in individuals with

type 1 diabetes. Diabetes Care 28: 1289-1294

Gutin B, Barbeau P, Owens S, Lemmon CR, Bauman M, Allison J, Kang H-S &

Litaker MS (2002) Effects of exercise intensity on cardiovascular fitness, total body

composition, and visceral adiposity of obese adolescents. American Journal of Clinical

Nutrition 75: 818-826

Hagberg LA, Lindahl B, Nyberg L, Hellénius M-L (2009) Importance of enjoyment

when promoting physical exercise. Scandinavian Journal of Medicine and Science in

Sports 19(5): 740-747

Halse RE, Wallman KE & Guelfi KJ (2011) Postexercise water immersion increases

short-term food intake in trained men. Medicine and Science in Sports and Exercise

43(4): 632-638

Harmer AR, Chisholm DJ, McKenna MJ, Hunter SK, Ruell PA, Naylor JM, Maxwell

LJ & Flack JR (2008) Sprint training increases muscle oxidative metabolism during

high-intensity exercise in patients with type 1 diabetes. Diabetes Care 31(11): 2097-

2102

Hesketh K, Wake M, Graham M & Waters E (2007) Stability of television viewing and

electronic game/computer use in a prospective cohort study of Australian children:

Relationship with body mass index. International Journal of Behavioural Nutrition and

Physical Activity 4: 60

Hill RJ & Davies PSW (2001) The validity of self-reported energy intake as determined

using the doubly labelled water technique. British Journal of Nutrition 85: 415-430

139

Hoos MB, Kuipers H, Gerver W-JM & Westerterp KR (2004) Physical activity pattern

of children assessed by triaxial accelerometry. European Journal of Clinical Nutition

58: 1425-1428

Hopkins M, King NA & Blundell JE (2010) Acute and long-term effects of exercise on

appetite control: Is there any benefit for weight control? Current Opinion in Clinical

Nutrition and Metabolic Care 13: 635-640

Howarth NC, Huang TT-K, Roberts SB & McCrory MA (2005) Dietary fiber and fat

are associated with excess weight in young and middle-aged US adults. Journal of the

American Dietetic Association 105(9): 1365-1372

Hunter GR, Weinsier RL, Bamman MM & Larson DE (1998) A role for high intensity

exercise on energy balance and weight control. International Journal of Obesity 22:

489-493

Imbeault P, Saint-Pierre S, Alméras N & Tremblay A (1997) Acute effects of exercise

on energy intake and feeding behaviour. British Journal of Nutrition 77: 511-521

Jakicic JM, Wing RR, Butler BA & Robertson RJ (1995) Prescribing exercise in

multiple short bouts versus one continuous bout: Effects on adherence,

cardiorespiratory fitness, and weight loss in overweight women. International Journal

of Obesity Related Metabolic Disorders 19(12): 893-901

Jamurtas AZ, Koutedakis Y, Paschalis V, Tofas T, Yfanti C, Tsiokanos A, Koukoulis

G, Kouretas D & Loupos D (2004) The effects of a single bout of exercise on resting

energy expenditure and respiratory exchange ratio. European Journal of Applied

Physiology 92: 393-398

Jeacocke NA & Burke LM (2010) Methods to standardize dietary intake before

performance testing. International Journal of Sport, Nutrition, Exercise and

Metabolism 20: 87-103

Jensky-Squires NE, Diele-Conwright CM, Rossuello A, Erceg DN, McCauley S &

Schroeder T (2008) Validity and reliability of body composition analysers in children

and adults. British Journal of Nutrition 100: 859-865

Johnstone AM, Murison SD, Duncan JS, Rance KS & Speakman JR (2005) Factors

influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B758G-4GYY39P-8&_user=10&_coverDate=09%2F30%2F2005&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1262688541&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=1b687902c25bf1d26a1818ff15fb4af2#vt1�




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140

circulating thyroxine but not sex, circulating leptin, or triiodothyronine. The American

Journal of Clinical Nutrition 82(5): 941-948

Kilpatrick M, Kraemer R, Bartholomew J, Acevedo E & Jarreau D (2007) Affective

responses to exercise are dependent on intensity rather than total work. Medicine and


King NA, Burley VJ & Blundell JE (1994) Exercise-induced suppression of appetite:

Effects on food intake and implications for energy balance. European Journal of

Clinical Nutrition 48(10): 715-724

Klesges RC, Klesges LM, Haddock CK & Eck LH (1992) A longitudinal analysis of

the impact of dietary intake and physical activity on weight change in adults. American

Journal of Clinical Nutrition 55: 818-822

Kuo CC, Fattor JA, Henderson GC & Brooks GA (2005) Lipid oxidation in fit young

adults during postexercise recovery. Journal of Applied Physiology 99: 349-356

Kyle UG, Bosaeus I, De Lorenzo AD, Deurenberg P, Elia M, Gómez JM, Heitmann

BL, Kent-Smith L, Melchior J-C, Pirlich M, Scharfetter H, Schols AMWJ & Pichard C

(2004) Bioelectrical impedance analysis: Part 1 - Review of principles and methods.

Clinical Nutrition 23: 1226-1243

LaForgia J, Withers RT & Gore CJ (1997) Comparison of energy expenditure

elevations after submaximal and supramaximal running. Journal of Applied Physiology

82(2): 661-666

LaForgia J, Withers RT & Gore CJ (2006) Effects of exercise intensity and duration on

the excess post-exercise oxygen consumption. Journal of Sports Sciences 24(12): 1247-

1264

Lazzer S, Busti C, Agosti F, De Col A, Pozzo R & Sartorio A (2007) Optimizing fat

oxidation through exercise in severely obese Caucasian adolescents. Clinical

Endocrinology 67: 582-588

Lazzer S, Lafortuna C, Busti C, Galli R, Tinozzi T, Agosti F & Sartorio A (2010) Fat

oxidation rate during and after a low- or high- intensity exercise in severely obese

Caucasian adolescents. European Journal of Applied Physiology 108(2): 383-391

141

Lazzer S, Molin M, Stramare D, Facchini S & Francescato (2008) Effects of an eight-

month weight-control program on body composition and lipid oxidation rate during

exercise in obese children. Journal of Endocrinological Investigation 31: 509-514

Lee CD, Blair SN & Jackson AS (1999) Cardiorespiratory fitness, body composition,

and all-cause and cardiovascular disease mortality in men. American Journal of Clinical

Nutrition 69(3): 373-380

Lee JM, Pilli S, Gebremariam A, Keirns CC, Davis MM, Vijan S, Freed GL, Herman

WH & Gurney JG (2010) Getting heavier, younger: Trajectories of obesity over the life

course. International Journal of Obesity 34: 614-623

Lemieux S, Prud’homme D, Bouchard C, Tremblay A, Després J-P (1996) A single

threshold value of waist girth identifies normal-weight and overweight subjects with

excess visceral adipose tissue. American Journal of Clinical Nutrition 64: 685-693

Lennon D, Nagle F, Stratman F, Shrago E & Dennis S (1985) Diet and exercise training

effects on resting metabolic rate. International Journal of Obesity 9(1): 39-47

Lind E, Ekkekakis P & Vazou S (2008) The affective impact of exercise intensity that

slightly exceeds the preferred level: ‘Pain’ for no additional ‘gain’. Journal of Health

Psychology 13(4): 464-468

Livingstone MBE & Black AE (2003) Markers of the validity of reported energy intake.

The Journal of Nutrition 133: 895S-920S

Lobstein T, Baur L & Uauy R (2004) Obesity in children and young people: A crisis in

public health. Obesity Reviews 5(1): 4-85

Maffeis C (2000) Aetiology of overweight and obesity in children and adolescents. The

European Journal of Pediatrics 159: S35-S44

Maffeis C, Zaffanello M, Pellegrino M, Banzato C, Bogoni G, Viviani E, Ferrari M &

Tatò L (2005) Nutrient Oxidation during Moderately Intense Exercise in Obese

Prepubertal Boys. The Journal of Clinical Endocrinology & Metabolism 90(1): 231-236

Marcus BH, Williams DM, Dubbert PM, Sallis JF, King AC, Yancey AK, Franklin BA,

Buchner D, Daniels SR & Claytor RP (2006) Physical activity intervention studies.

Circulation 114: 2739-2752

142

Margarey AM, Daniels LA & Boulton JC (2001) Prevalence of overweight and obesity

in Australian children and adolescents: Reassessment of 1985 and 1995 data against

new standard international definitions. The Medical Journal of Australia 174: 561-564

Marinov B, Mandadjieva S & Kostianev S (2007) Pictorial and verbal category-ratio

scales for effort estimation in children. Child Care, Health and Development 34(1): 35-

43

Martins C, Morgan L, Truby H (2008) A review of the effects of exercise on appetite

regulation: An obesity perspective. International Journal of Obesity 32: 1337-1347

McArdle WD, Katch FI & Katch VL (2001) Exercise Physiology: Energy, nutrition and

human performance (5th Ed.). USA: Lippincott Williams & Wilkins.

McCarthy HD, Cole TJ, Fry T, Jebb SA & Prentice AM (2006) Body fat reference

curves for children. International Journal of Obesity 30: 598-602

McGloin AF, Livingstone MBE, Greene LC, Webb SE, Gibson JM, Cole TJ, Coward

TJ, Wright A & Prentice AM (2002) Energy and fat intake in obese and lean children at

varying risk of obesity. International Journal of Obesity and Related Metabolic

Disorders 26(2): 200-207

Melanson EL, Sharp TA, Seagle HM, Horton TJ, Donahoo WT, Grunwald GK,

Hamilton JT & Hill JO (2002) Effect of exercise intensity on 24-h energy expenditure

and nutrient oxidation. Journal of Applied Physiology 92: 1045-1052

Meyer T, Folz C, Roseberger F & Kindermann W (2009) The reliability of Fatmax

Meyer T, Gäβler N & Kindermann W (2007) Determination of “Fatmax” with 1 h

cycling protocols of constant load. Applied Physiology, Nutrition and Metabolism 32:

249-256

.

Scandinavian Journal of Medicine and Science in Sports 19: 213-221

Molnar D & Schutz Y (1997) The effect of obesity, age, puberty and gender on

metabolic rate in children and adolescents. European Journal of Pediatrics 156: 376-

381

143

Moore MS, Dodd CJ, Welsman JR & Armstrong N (2004) Short-term appetite and

energy intake following imposed exercise in 9- to 10-year-old girls. Appetite 43(2):

127-134

Moreno LA & Rodríguez G (2007) Dietary risk factors for development of childhood

obesity. Current Opinion in Clinical Nutrition and Metabolic Care 10(3): 336-341

Motl RW, Dishman RK, Saunders R, Dowda M, Felton G & Pate RR (2001) Measuring

enjoyment of physical activity in adolescent girls. American Journal of Preventative

Medicine 21(2): 110-117

Mulvihill C, Rivers K & Aggleton P (2000) Views of young people towards physical

activity: Determinants and barriers to involvement. Health Education 100(5): 190-199

Murakami K, Sasaki S, Okubo H, Takahashi Y, Hosoi Y & Itabashi M (2007) Dietary

fiber intake, dietary glycemic index and load, and body mass index: A cross-sectional

study of 3931 Japanese women aged 18–20 years. European Journal of Clinical


Must A, Spadano J, Coakley EH, Field AE, Colditz G & Dietz WH (1999) The disease

burden associated with overweight and obesity. The Journal of the American Medical

Association 282: 1523-1529

Nowicka P & Flodmark CE (2007) Physical activity - Key issues in treatment of

childhood obesity. Acta Paediatrica 96: 39-45

O’Donovan G, Owen A, Bird SR, Kearney EM, Nevill AM, Jones DW & Woolf-May

K (2005) Changes in cardiorespiratory fitness and coronary heart disease risk factors

following 24 weeks of moderate- or high-intensity exercise of equal energy cost.

Journal of Applied Physiology 98(5): 1619-1625

Olds T, Tomkinson G, Maher C & Ferrer K (2010) Trends in the prevalence of

childhood overweight and obesity in Australia between 1985 and 2008. International

Journal of Obesity 34(1): 57-66

Patrick K, Norman GJ, Calfas KJ, Sallis JF, Zabinski MF, Rupp J & Cella J (2004)

Diet, physical activity, and sedentary behaviours as risk factors for overweight in

adolescence. Archives of Pediatrics and Adolescent Medicine 158: 385-390

144

Pereira MA, Kartashov AI, Ebbeling CB, Van Horn L, Slattery ML, Jacobs DR &

Ludwig DS (2005) Fast-food habits, weight gain, and insulin resistance (the CARDIA

study): 15-year prospective analysis. The Lancet 365(9453): 36-42

Pereira MA & Ludwig DS (2001) Dietary fibre and body-weight regulation:

Observations and mechanisms. Pediatric Clinics of North America 48: 969-980

Pérez-Martin A, Dumortier M, Raynaud E, Brun JF, Fédou C, Bringer J & Mercier J

(2001) Balance of substrate oxidation during submaximal exercise in lean and obese

people. Diabetes and Metabolism 27: 466-474

Perri MG, Anton SD, Durning PE, Ketterson TU, Sydeman SJ, Berlant NE, Kanasky

WF, Newton Jr RL, Limacher MC & Martin AD (2002) Adherence to exercise

prescriptions: Effects of prescribing moderate versus higher levels of intensity and

frequency. Journal of Health Psychology 21(5): 452-458

Phelain JF, Reinke E, Harris MA & Melby CL (1997) Postexercise energy expenditure

and substrate oxidation in young women resulting from exercise bouts of different

intensity. Journal of the American College of Nutrition 16: 140-146

Pillard F, Moro C, Harant I, Garrigue E, Lafontan M, Berlan M, Crampes F, de

Glisezinski I & Rivière D (2007) Lipid oxidation according to intensity and exercise

duration in overweight men and women. Obesity 15: 2256-2262

Poehlman ET (1989) A review: Exercise and its influence on resting energy metabolism

in man. Medicine and Science in Sports and Exercise 21(5): 515-525

Rankinen T, Zuberi A, Chagnon YC, Weisnagel SJ, Argyropoulos G, Walts B, Pérusse

L & Bouchard C (2006) The human obesity gene map: The 2005 update. Obesity 14:

529-544

Ravussin E, Burnand B, Schutz Y & Jequier E (1982) Twenty-four hour energy

expenditure and resting metabolic rate in obese, moderately obese and control subjects.

American Journal of Clinical Nutrition 35: 566-573

Reilly JJ (2005) Descriptive epidemiology and health consequences of childhood

obesity. Best Practice and Research Clinical Endocrinology and Metabolism 19(3):

327-341

145

Reilly JJ & Kelly J (2011) Long-term impact of overweight and obesity in childhood

and adolescence on morbidity and premature mortality in adulthood: Systematic

Review. International Journal of Obesity 35: 891-898

Riddell

Robertson RJ & Noble BJ (1997) Perception of physical exertion: Methods, mediators

and applications. Exercise and Sports Science Review 25: 407-452

MC, Jamnik VK, Iscoe KE, Timmons BW & Gledhill N (2008) Fat oxidation

rate and the exercise intensity that elicits maximal fat oxidation decreases with pubertal

status in young male subjects. Journal of Applied Physiology 105: 742-748

Roemmich JN, Barkley JE, Epstein LH, Lobarinas CL, White TM & Foster JH (2006)

Validity of PCERT and OMNI walk/run ratings of perceived exertion. Medicine and


Roepstorff C, Halberg N, Hillig T, Saha AK, Ruderman NB, Wojtaszewski JFP,

Richter EA & Kiens B (2005) Malonyl-CoA and carnitine in regulation of fat oxidation

in human skeletal muscle during exercise. American Journal of Physiology,

Endocrinology and Metabolism 288(1): E133-E142

Rolls BJ, Morris EL & Roe LS (2002) Portion size of food affects energy intake in

normal-weight and overweight men and women. American Journal of Clinical

Nutrition 76: 1207-1213

Romijn JA, Coyle EF, Hibbert J, Wolfe RR (1992) Comparison of indirect calorimetry

and a new breath 13C/12C ratio method during strenuous exercise. Endocrinology and

Metabolism 263(1): E64-E71

Rowell LB, Blackmon JR, Bruce RA (1964) Indocyanine green clearance and estimated

hepatic blood flow during mild to maximal exercise in upright man. Journal of Clinical

Investigations 43: 1677-1690

Rowland TW & Rimany TA (1995) Physiological responses to prolonged exercise in

premenarcheal and adult females. Pediatric Exercise Science 7: 183-191

Salmon J, Timperio A, Telford A, Carver A & Crawford D (2005) Association of

family environment with children’s television viewing and with low level of physical

activity. Obesity Research 13(11): 1939-1951

146

Schrauwen P & Westerterp KR (2000) The role of high fat diets and physical activity in

the regulation of body weight. British Journal of Nutrition 84: 417-427

Schwimmer JB, Burwinkle TM & Varni JW (2003) Health related quality of life of

severely obese children and adolescents. The Journal of the American Medical

Association 289(14): 1813-1819

Sheppard KE & Parfitt G (2008) Acute affective responses to prescribed and self-

selected exercise intensities in young adolescent boys and girls. Pediatric Exercise

Science 20: 129-141

Shorten AL, Wallman KE & Guelfi KG (2009) Acute effect of environmental

temperature during exercise on subsequent energy intake in active men. American

Journal of Clinical Nutrition 90: 1215-1221

Smith MJ (2008) Sprint Interval Training – “It’s a HIIT!” Available online: http://assets.usoc.org/assets/documents/attached_file/filename/15738/Sprint_Interval_Training.

pdf

Speakman JR & Selman C (2003) Physical activity and resting metabolic rate.

Proceedings of the Nutrition Society 62: 621-634

Spinks AB, Macpherson AK, Bain C & McClure RJ (2007) Compliance with the

Australian national physical activity guidelines for children: Relationship to overweight

status. Journal of Science and Medicine in Sport 10(3): 156-163

St-Onge M-P, Keller KL & Heymsfield SB (2003) Changes in childhood food

consumption patterns: A cause for concern in light of increasing body weights.


Steenhuis IHM & Vermeer WM (2009) Portion size: Review and framework for

interventions. International journal of Behavioural Nutrition and Physical Activity 6:

58

Stephens BR, Cole AS & Mahon AD (2006) The influence of biological maturation on

fat and carbohydrate metabolism during exercise in males. International Journal of

Sport Nutrition and Exercise Metabolism 16(2): 166-179

147

Stephens FB, Constantin-Teodosiu D & Greenhaff PL (2007) New insights concerning

the role of carnitine in the regulation of fuel metabolism in skeletal muscle. Journal of

Physiology 581(2): 431-444

Steptoe AS & Butler N (1996) Sports participation and emotional wellbeing in

adolescents. The Lancet 347(9018): 1789-1792

Stiegler P & Cunliffe A (2006) The role of diet and exercise for the maintenance of fat-

free mass and resting metabolic rate during weight loss. Sports Medicine 36: 239–262

Stubbs RJ, Johnstone AM, O'Reilly LM & Poppitt SD (1998) Methodological issues

relating to the measurement of food, energy and nutrient intake in human laboratory-

based studies. Proceedings of the Nutrition Society 57(3): 357-372

Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M & Yamamoto K

(1996) Effects of moderate intensity endurance and high-intensity intermittent training

on anaerobic capacity and O2max. Medicine and Science in Sports and Exercise

28(10): 1327-1330

Talanian JL, Galloway SDR, Heigenhauser GJF, Bonen A & Spriet LL (2007) Two

weeks of high-intensity aerobic interval training increases the capacity for fat oxidation

during exercise in women. Journal of Applied Physiology 102: 1439-1447

Temple JL, Giacomelli AM, Kent KM, Roemmich JN & Epstein LH (2007) Television

watching increases motivated responding for food and energy intake in children.


Thivel D, Isacco L, Montaurier C, Boirie Y, Duche P & Morio B (2012) The 24-h

energy intake of obese adolescents is spontaneously reduced after intensive exercise: A

randomized controlled trial in calorimetric chambers. PLoS ONE 7(1): e29840 doi:

10.1371/journal.pone.0029840

Thompson DA, Wolfe LA & Eikelboom R (1988) Acute effects of exercise intensity on

appetite in young men. Medicine and Science in Sports and Exercise 20(3): 222-227

Tjønna AE, Stølen TO, Bye A, Volden M, Slørdahl SA, Ødegárd R, Skogvoll E &

Wisløff U (2009) Aerobic interval training reduced cardiovascular risk factors more

than a multitreatment approach in overweight adolescents. Clinical Science 116: 317-

326

148

Tjønna AE, Lee SJ, Rognmo Ø, Stølen TO, Bye A, Haram PM, Loennechen JP, Al-

Share QY, Skogvoll E, Slørdahl SA, Kemi OJ, Najjar SM & Wisløff U (2008) Aerobic

interval training versus continuous moderate exercise as treatment for the metabolic

syndrome: A pilot study. Circulation 118: 346-354

Tounian P, Dumas C, Veinberg F & Girardet JP (2003) Resting energy expenditure and

substrate utilisation rate in children with constitutional leanness or obesity. Clinical


Trapp EG, Chisholm DJ & Boutcher SH (2007) Metabolic response of trained and

untrained women during high-intensity intermittent cycle exercise. American Journal of

Physiology Regulation and Integral Compliance Physiology 293: R2370-R2375

Trapp EG, Chisholm DJ, Freund J & Boutcher SH (2008) The effects of high-intensity

intermittent exercise training on fat loss and fasting insulin levels of young women.

International Journal of Obesity 32: 684-691

Tremblay A, Després J-P, Leblanc C, Craig CL, Ferris B, Stephens T & Bouchard C

(1990) Effect of intensity of physical activity on body fatness and fat distribution.


Tremblay A, Fontaine E, Poehlman ET, Mitchell D, Perron L & Bouchard C (1986)

The effect of exercise-training on resting metabolic rate in lean and moderately obese

individuals. International Journal of Obesity 10(6): 511-517

Tremblay A, Simoneau J-A & Bouchard C (1994) Impact of exercise intensity on body

fatness and skeletal muscle metabolism. Metabolism 43(7): 814-818

Treuth MS, Hunter GR & Williams M (1996) Effects of exercise intensity on 24-h

energy expenditure and substrate oxidation. Medicine and Science in Sports and

Exercise 28(9): 1138-1143

Tsiros MD, Sinn N, Coates AM, Howe PRC & Buckley JD (2008) Treatment of

adolescent overweight and obesity. European Journal of Pediatrics 167(1): 9-16

Tyrrell VJ, Richards G, Hofman P, Gillies GF, Robinson E & Cutfield WS (2001)

Foot-to-foot bioelectrical impedance analysis: A valuable tool for the measurement of

body composition in children. International Journal of Obesity 25(2): 273-278

149

Ueda S, Yoshikawa T, Katsura Y, Usui T, Nakao H, Fujimoto S (2009) Changes in gut

hormone levels and negative energy balance during aerobic exercise in obese young

males. Journal of Endocrinology 201: 151-159

van Aggel-Leijssen DPC, van Baak MA, Tenenbaum R, Campfield LA, Saris WHM

(1999) Regulation of average 24 h human plasma leptin level; the influence of exercise

and physiological changes in energy balance. International Journal of Obesity 23: 151-

158

van der Ploeg HP, Merom D, Corpuz G & Bauman AE (2008) Trends in Australian

children travelling to school 1971–2003: Burning petrol or carbohydrates? Preventative

Medicine 46(1): 60-62

Vance VA, Woodruff SJ, McCargar LJ, Husted J & Hanning RM (2008). Self-reported

dietary energy intake of normal weight, overweight and obese adolescents. Public

Health Nutrition 12(2): 222-227

Venables MC, Achten J & Jeukendrup AE (2005) Determinants of fat oxidation during

exercise in healthy men and women: A cross-sectional study. Journal of Applied

Physiology 98(1): 160-167

Venables MC & Jeukendrup AE (2008) Endurance training and obesity: Effect on

substrate metabolism and insulin sensitivity. Medicine and Science in Sports and

Exercise 40(3): 495-502

Wardle J, Guthrie C, Sanderson S, Birch L & Plomin R (2001) Food and activity

preferences in children of lean and obese parents. International Journal of Obesity

25(7): 971-977

Watts K, Jones TW, Davis EA & Green D (2005) Exercise training in obese children

and adolescents: Current concepts. Sports Medicine 35(5): 375-392

Watts K, Naylor LH, Davis EA, Jones TW, Beeson B, Bettenay F, Siafarikas A, Bell L,

Ackland T & Green D (2006) Do skinfolds accurately assess changes in body fat in

obese children and adolescents? Medicine and Science in Sports and Exercise 38(3):

439-444

150

Whitaker RC, Wright JA, Pepe MS, Seidel KD & Dietz WH (1997) Predicting obesity

in young adulthood from childhood and parental obesity. The New England Journal of

Medicine 337(13): 869-873

Whyte LJ, Gill JMR & Cathcart AJ (2010) Effect of 2 weeks of sprint interval training

on health-related outcomes in sedentary overweight/obese men. Metabolism 59(10):

1421-1428

Wisløff U, Støylen A, Loennechen JP, Bruvold M, Rognmo Ø, Haram PM, Tjønna AE,

Helgerud J, Slørdahl SA, Lee SJ, Videm V, Bye A, Smith GL, Najjar SM, Ellingsen Ø

& Skjaerpe T (2007) Superior cardiovascular effect of aerobic interval training versus

moderate continuous training in heart failure patients: A randomized study. Circulation

115: 3086-3094

World Health Organisation (2004) Obesity: Preventing and managing the global

epidemic. WHO Technical Report Series no. 894. WHO: Geneva

Yaicharoen P, Wallman K, Bishop D, Morton A (2012) The effect of warm up on single

and intermittent-sprint performance. Journal of Sports Science 30: 833-840

Yang W, Kelly T & He J (2007) Genetic epidemiology of obesity. Epidemiologic

Reviews 29: 49-61

Yelling M, Lamb KL & Swaine AL (2002) Validity of a pictorial perceived exertion

scale for effort estimation and effort production during stepping exercise in adolescent

children. European Physical Education Review 8(2): 157-175

Yeung J, Wearing S & Hills AP (2008) Child transport practices and perceived barriers

in active commuting to school. Transport Research Part A: Policy and Practice 42(6):

895-900

Yoshioka M, Doucet E, St-Pierre S, Alméras N, Richard D, Labrie A, Després JP,

Bouchard C & Tremblay A (2001) Impact of high-intensity exercise on energy

expenditure, lipid oxidation and body fatness. International Journal of Pediatric

Obesity 25: 332-339

Zakrzewski J & Tolfrey K (2011a) Exercise protocols to estimate Fatmax and maximal

fat oxidation in children. Pediatric Exercise Science 23: 122-135

151

Zakrzewski J & Tolfrey K (2011b) Fatmax in children and adolescents: A review.

European Journal of Sports Science 11(1): 1-18

Zakrzewski JK & Tolfrey K (2012) Comparison of fat oxidation over a range of

intensities during treadmill and cycling exercise in children. European Journal of

Applied Physiology 112(1): 163-71

Zunquin G, Theunynck D, Sesboűé B, Arhan P & Bouglé D (2009a) Comparison of fat

oxidation during exercise in lean and obese pubertal boys: Clinical implications. British

Journal of Sports Medicine 43: 869-870

Zunquin G, Theunynck D, Sesboűé B, Arhan P & Bouglé D (2009b) Evolution of fat

oxidation during exercise in obese pubertal boys: Clinical implications. Journal of

Sports Sciences 27: 315-318

Zurlo F, Lillioja S, Esposito-Del Puente A, Nyomba BL, Raz I, Saad MF, Swinburn

BA, Knowler WC, Bogardus C & Ravussin E (1990) Low ratio of fat to carbohydrate

oxidation as predictor of weight gain: Study of 24-h RQ. American Journal of

Physiology, Endocrinology and Metabolism 259: E650-E657

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6 APPENDICES

APPENDIX A: Definitions of Obesity for 8-12 Year Old Boys (Re: Chapter 1) 153

APPENDIX B: Human Ethics and DEXA Approval Forms 155

APPENDIX C: Information Sheets and Consent Forms (Re: Chapter 2 - Study 1) 162

APPENDIX D: Information Sheets and Consent Forms (Re: Chapter 3 - Study 2) 168

APPENDIX E: Information Sheets and Consent Forms (Re: Chapter 4 - Study 3) 172

APPENDIX F: Food Records (Re: Chapters 2,3 & 4 - Studies 1, 2 & 3) 176

APPENDIX G: PCERT (Re: Chapters 3 & 4 - Studies 2 & 3) 188

APPENDIX H: VAS and PACES (Re: Chapter 3 - Study 2) 190

APPENDIX I: VAS and PACES (Re: Chapter 4 - Study 3) 194

APPENDIX J: Data Collection Sheets 197

APPENDIX K: Publications Arising from this Thesis 204

153

APPENDIX A

Definitions of Obesity for 8-12 Year Old Boys

(Re: Chapter 1)

154

Appendix A1: Body Mass Index (BMI) cut off values by age (Cole et al., 2000)

BMI Classification (kg/m2)

Age (years) Normal Overweight Obese

8.0 < 18.4 18.4 - 21.6 > 21.6

8.5 < 18.8 18.8 - 22.2 > 22.2

9.0 < 19.1 19.1 - 22.8 > 22.8

9.5 < 19.5 19.5 - 23.4 > 23.4

10.0 < 19.8 19.8 - 24.0 > 24.0

10.5 < 20.2 20.2 - 24.6 > 24.6

11.0 < 20.5 20.5 - 25.1 > 25.1

11.5 < 20.9 20.9 - 25.6 > 25.6

12.0 < 21.2 21.2 - 26.0 > 26.0

Appendix A2: Percentage Fat Mass (%FM) cut off values by age (McCarthy et al., 2006)

Body Composition Classification (%FM)

Age (years) Normal Overfat Obese

8.0 < 21.3 21.3 - 25.5 > 25.5

9.0 < 22.2 22.2 - 26.8 > 26.8

10.0 < 22.8 22.8 - 27.9 > 27.9

11.0 < 23.0 23.0 - 28.3 > 28.3

12.0 < 22.7 22.7 - 27.9 > 27.9

155

APPENDIX B

Human Ethics Approval Form

DEXA Approval Form

156

Our Ref. RA/4/1/2197 28 November 2008 Dr K Guelfi Sport Science, Exercise & Health - M408 UWA HUMAN RESEARCH ETHICS COMMITTEE Project: Impact of moderate intensity continuous exercise compared with

sprint interval exercise on energy expenditure, enjoyment, substrate oxidation and body composition in overweight boys

Student: Nicole Crisp - PhD - 10418305 Please be advised that ethical approval of the above project has been granted by the Human Research Ethics Committee. The Committee is bound by NHMRC Guidelines to monitor the progress of all approved projects until completion to ensure that they continue to conform to approved ethical standards. The committee requires that all Chief Investigators report immediately anything that might affect or impact upon ethical approval of the project, including adverse events affecting subjects. Approval should be sought in writing in advance for any amendments to the original application. You are also required as a condition of this approval to inform the Committee if for any reason the research project is discontinued before the expected date of completion. A report form for completion will be sent to you twelve months from this date or one month after your indicated completion date. Please note that approval has been granted for a period of four years. Initial approval is for a period of one year, and, thereafter for future periods of one year at a time subject to the receipt of satisfactory annual reports. At the end of the four-year period you will be required to complete a new "Application to Undertake Research Involving Human Subjects" should you wish to continue with your research.

Research Ethics Research Services M459 35 Stirling Highway, Crawley, WA 6009 Telephone: (08) 6488 3703 Facsimile: (08) 6488 8775 Email: [email protected] http://www.research.uwa.edu.au/human_ethics

mailto:[email protected]�

http://www.research.uwa.edu.au/human_ethics�

157

However, in special circumstances, the Chair has the authority to extend the approval period in order to complete a project. Failure to submit a final report may result in delays for future applications. Please quote Project No RA/4/1/2197 all correspondence associated with this study. Yours sincerely

KATE KIRK Executive Officer (Human Research Ethics Committee) cc: Dr Sato Juniper

158

Dr Kym Guelfi School of Sport Science, Exercise and Health The University of Western Australia 35 Stirling Highway, Crawly WA, 6009 Phone: +61 8 6488 2602

11th September 2008

Estimated Effective Doses for Radiographic Procedures School: Sport Science, Exercise and Health Project Title: Determining the Exercise Intensity that Maximises Fat Oxidation in

Overweight Adults and Children Chief Investigators: Dr Kym Guelfi and Miss Nicole Crisp X-ray procedures: Total body scan (thick) – 1 per subject

15 overweight adults (aged 18-30 years) 15 overweight or obese boys (aged 7-12 years)

Subjects will all be volunteers Start date: Once ethics has been approved until September 2009 Written consent will be obtained from all participants prior to scanning Radiation License details: Licensee Name: Prof Tim Ackland License No. LX337/2004 14265 School of Sport Science, Exercise and Health

The University of Western Australia Only trained operators will have permission to use the x-ray machine. A software password system is available on the machine to prevent unauthorized use. The training course is a half-day regulator approved course and trained operators have received certification for operation of the machine. Machine data from manufacturer’s literature From: Operator’s Guide X-ray machine: Lunar prodigy X-ray beam: 76kV, 2.9mmAl at 70kVp, focal spot 0.5 mm. Max 76 kV, 3 mA

Focal spot to image receptor distance 67 cm Table attenuation 0.7 mm Al

Summary: A total body (thick) scan has a calculated effective dose of 0.8 µSv.

Safety and Health Office The University of Western Australia 35 Stirling Highway Crawley WA 6009 Phone +61 8 9380 7932 Fax +61 8 9380 1179 Email [email protected] Web http://www.safety.uwa.edu.au

159

The patient consent form will state the estimated effective dose and place the radiation dose into a context understandable by all parties. The effective dose may be compared to that which is received from natural background sources eg. “The tests involve the use of a low dose x-rays about equal to one thousandth of the background radiation you would receive in one year living in Perth. The total background radiation in Western Australia is about 2mSv per year. The radiation dose from cosmic rays from flying in a jet from Perth to London is approximately 0.1 mSv." The hypothetical risk of developing cancer from the radiation exposure may be calculated using the ICRP 103 risk factor of 5%/Sv (Table 1, p.53). For participation in the complete procedure the fatal cancer risk is (0.8 x 10-6) x (5 x 10-2) = 0.4 x 10-6 = 0.4 in ten million. Since the estimated effective dose to patients will be much less than 5 mSv in a year, a submission to the West Australian Radiological Council for approval is not required. Yours faithfully

Jonathon Thwaites Radiation and Safety Officer Cc: Dr Kym Guelfi

Prof Tim Ackland References: ICRP 60. 1991. Recommendations of the international commission on radiological protection. 21 (1-3) Shleien, B (ed). 1992. The health physics and radiological health handbook, Revised Edition. Scinta, Inc.

160

Dr Kym Guelfi School of Sport Science, Exercise and Health The University of Western Australia 35 Stirling Highway, Crawly WA, 6009 Phone: +61 8 6488 2602

11th September 2008

Estimated Effective Doses for Radiographic Procedures School: Sport Science, Exercise and Health Project Title: Impact of Moderate Intensity Continuous Exercise compared with

Sprint Interval Exercise on Energy Expenditure, Enjoyment and Perceived Exertion in Boys.

Chief Investigators: Dr Kym Guelfi and Miss Nicole Crisp X-ray procedures: Total body scan (thick) – 1 per subject 15 overweight or obese boys (aged 7-12 years) Subjects will all be volunteers Start date: Once ethics has been approved until September 2010 Written consent will be obtained from all participants prior to scanning Radiation License details: Licensee Name: Prof Tim Ackland License No. LX337/2004 14265 School of Sport Science, Exercise and Health

The University of Western Australia Only trained operators will have permission to use the x-ray machine. A software password system is available on the machine to prevent unauthorized use. The training course is a half-day regulator approved course and trained operators have received certification for operation of the machine. Machine data from manufacturer’s literature From: Operator’s Guide X-ray machine: Lunar prodigy X-ray beam: 76kV, 2.9mmAl at 70kVp, focal spot 0.5 mm. Max 76 kV, 3 mA

Focal spot to image receptor distance 67 cm Table attenuation 0.7 mm Al

Summary: A total body (thick) scan has a calculated effective dose of 0.8 µSv.

Safety and Health Office The University of Western Australia 35 Stirling Highway Crawley WA 6009 Phone +61 8 9380 7932 Fax +61 8 9380 1179 Email [email protected] Web http://www.safety.uwa.edu.au

161

The patient consent form will state the estimated effective dose and place the radiation dose into a context understandable by all parties. The effective dose may be compared to that which is received from natural background sources eg. “The tests involve the use of a low dose x-rays about equal to one thousandth of the background radiation you would receive in one year living in Perth. The total background radiation in Western Australia is about 2mSv per year. The radiation dose from cosmic rays from flying in a jet from Perth to London is approximately 0.1 mSv." The hypothetical risk of developing cancer from the radiation exposure may be calculated using the ICRP 103 risk factor of 5%/Sv (Table 1, p.53). For participation in the complete procedure the fatal cancer risk is (0.8 x 10-6) x (5 x 10-2) = 0.4 x 10-6 = 0.4 in ten million. Since the estimated effective dose to patients will be much less than 5 mSv in a year, a submission to the West Australian Radiological Council for approval is not required. Yours faithfully

Jonathon Thwaites Radiation and Safety Officer Cc: Dr Kym Guelfi

Prof Tim Ackland References: ICRP 60. 1991. Recommendations of the international commission on radiological protection. 21 (1-3) Shleien, B (ed). 1992. The health physics and radiological health handbook, Revised Edition. Scinta, Inc.

162

APPENDIX C

Information Sheet

Consent Form

(Re: Chapter 2 - Study 1)

163

Nicole Crisp BSc (Hons) School of Sport Science, Exercise and Health

Determining the Exercise Intensity that Maximises Fat Oxidation in Children

~ Parent Information Sheet ~

Nicole Crisp is a PhD student from The School of Sports Science, Exercise and Health at UWA. The aim of her PhD research is to identify the type of exercise that is both enjoyable and effective for weight loss in children. Purpose The amount of fat that is burnt during exercise is influenced by the exercise intensity (how hard the exercise is). The intensity which burns the most fat has been termed the Fatmax. Some researchers have suggested that identification of Fatmax may allow for the development of more appropriate for exercise interventions aimed at reducing fat mass. However, there appears to be a lack of consensus as to the most appropriate method to accurately determine Fatmax, especially in overweight individuals. The purpose of this study is to determine whether a graded exercise test with 3-min stages can accurately determine Fatmax in overweight individuals. If it is found to be accurate, this protocol may be used for the development of exercise interventions that result in more effective weight loss and long-term weight maintenance.

Procedures

Participants will be asked to attend the Exercise Physiology Laboratory at UWA on eight separate occasions. On the first visit, height, weight and waist/hip ratio will be recorded. Body composition (the amount of fat and muscle in your body) will be assessed using Dual Energy X-ray Absorptiometry (DEXA) which requires participants to lie for approximately 5 minutes while a low dose X-ray scans the body. Also on this visit, participants will be familiarised with the 3-min graded exercise test protocol detailed below. This session should not take longer than 40 minutes. Following this, participants will be required to attend the lab at 7:00am after an overnight fast on seven separate occasions. During the first morning session, the proper 3-min graded exercise test to determine your fitness level will be completed. For this, participants will be required to cycle continuously on a stationary bike which will increase in resistance every three minutes until they can’t go any further (to

Study 1

164

exhaustion). Expired air will be collected by breathing into a mouthpiece which enables us to work out aerobic fitness and Fatmax. At the end of each 3-min stage of the exercise test, one drop of blood will be collected from the fingertip using a sterile lancet device so that we can measure blood lactate. The following six visits will be conducted over six weeks (one morning session each week). At the first morning session, participants will complete an easy incremental exercise test to accurately pinpoint the Fatmax. The following five sessions will consist of 30 minutes of continuous exercise (cycling) at five different moderate (not very difficult) intensities. Participants will be asked to complete a food record for 24 hours prior to the first morning session and to replicate what they eat as closely as possible on the day before each subsequent morning session.

Risks

The DEXA machine that measures the amount of muscle and fat in the body uses a small but safe amount of radiation so participants won’t be at any risk. The fitness test on the bike is exhausting and uncomfortable but participants can stop the test at any time. A slight pin prick and minimal redness will be experienced with the blood sampling, but this should subside in less than a day.

Benefits

Participants will be provided with a report of their body composition (how much muscle and fat your body is made up of) and bone mineral density. Participants will also find out their fitness level and the exercise intensity that is best to work at to increase fitness, to maximise weight loss and maintain a healthy body weight. The results from this study will help us to develop exercise interventions that may result in more effective weight loss and long-term weight maintenance.

Your Rights

Participation in this research is voluntary and you can stop being involved at any time

without giving a reason. If you have any questions, queries or would just like further

information about this research, please feel free to contact Nicole Crisp

([email protected] or 0438 944 464) at any time.

The Human Research Ethics Committee at The University of Western Australia requires that all participants are informed that, if

they have any complaints regarding the manner in which a research project is conducted, it may be given to the researcher or,

alternatively to The Secretary, Human Research Ethics Committee, Registrar’s Office, The University of Western Australia, 35

Stirling Highway, Crawley, WA 6009 (phone number 6488 3703). All participants will be supplied with a copy of the Information

Sheet and Consent Form for their personal records.

165



~ Participant Information Sheet ~

Purpose The amount of fat that is burnt during exercise depends on how hard the exercise is (its intensity). The exercise intensity that burns the most fat is called the Fatmax. The purpose of this study is to determine what the Fatmax is for children.

What will I have to do?

You and your parent/guardian will need to come into The University of Western Australia for eight cycling sessions on separate occasions. On the first visit, we will measure the amount of muscle and fat in your body and find out how strong your bones are. To do this, you will need to lie down for five minutes while a low-dose X-ray scans your body. We will also get you to practice the exercise test that you will be doing on the next visit to measure how fit you are. You will not be able to eat breakfast before the exercise test which will be done on a separate morning. For this test, you will cycle on a bike for 10-20 minutes while breathing into a mouthpiece to collect the air you breathe out. You will need to pedal harder every three minutes until you cannot go any further. We will also collect a small amount of blood every three minutes to measure lactate (how hard your muscles are working). To do this, there will be a small prick on the fingertip and collection of just one drop of blood. At the next morning session, you will complete an easy incremental exercise test to accurately pinpoint the Fatmax. After these three sessions, you will need to come back for five more morning sessions. These sessions will be separated by about one week and will consist of 30 minutes of continuous exercise at five different moderate levels (not very hard). During the exercise, you will need to breathe through a facemask to collect the air that you breathe out. You (with the help of your parent/guardian) will need to write down all of the food that you eat on the day before the forth morning session and try and eat the same things before all remaining morning sessions.

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Risks

The X-ray machine that measures the amount of muscle and fat in your body and measures your bone density uses a small but safe amount of radiation so you won’t be at any risk. Also, you may find the fitness test on the bike hard but you can stop the test at any time. You just have to do your best! During blood sampling, you may feel a slight pin prick and your finger might go a bit red, but this should go away in less than a day. Benefits

If you participate in this study, you will be provided with a report of how much muscle and fat is in your body and learn how strong your bones are. You will also find out how fit you are and how much exercise you need to do to keep your body healthy. Your results will also help us to make better exercise programs for other children that may make it easier for them to keep their bodies healthy.

Your Rights




([email protected] or 0438 944 464) at any time.






167



~ Consent Form ~

I have read the information provided and any questions I have asked have been

answered to my satisfaction. I agree to participate in this activity, which will involve a

DEXA body scan exposing me to about one thousandth of the background radiation I

would receive in one year living in Perth, realising that I may withdraw at any time

without reason and without prejudice. I understand that if I withdraw from the study,

the data that has been recorded may be retained but only if I agree to it.

I understand that all information provided is treated as strictly confidential and will not

be released by the investigator unless required to by law. I have been advised as to

what data is being collected, what the purpose is, and what will be done with the data

upon completion of the research. I agree that research data gathered for the study may

be published provided my name or other identifying information is not used.

______________________ ________________________

Child’s Name Child’s Signature

______________________ ________________________ ___________

Parent/Guardian’s Name Parent/Guardian’s Signature Date






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APPENDIX D

Information Sheet

Consent Form


169


Impact of Moderate Intensity Continuous Exercise compared with Sprint Interval Exercise on Energy Expenditure, Enjoyment and Perceived Exertion in Boys


Purpose

The amount of energy that the body burns during exercise is different depending on the type of exercise you do. The purpose of this study is to look at the amount of energy that your body uses during two different types of exercise - continuous and sprint interval exercise. We will also be finding out how hard you think the exercise was and how much you enjoyed it.


You and your parent/guardian will come into The University of Western Australia on three separate occasions. All visits will need to be in the morning and you will not be able to have breakfast (which will be provided) until after the testing is finished. On the first morning, we will measure the amount of muscle and fat you have in your body, find out how strong your bones are and see how fit you are. To measure the amount of muscle and fat in your body and how strong your bones are, you will need to lie down for about five minutes while an X-ray scans your body. We will then test how fit you are by having you cycle on a bike for about 30 minutes while you breathe into a mouthpiece to collect the air you breathe out. We will ask you to pedal harder every three minutes until you cannot go any further. This visit shouldn’t take any longer than one hour. On the second and third mornings, you will start off by sitting quietly and watching a movie for 30 minutes while you breathe through a mouthpiece to collect the air you breathe out. After this, you will cycle on a bike for 30 minutes while still breathing through a mouthpiece. You will be doing two different types of exercise each morning; (1) pedalling at the same moderate level (not very hard) the whole time and (2) pedalling at the same moderate level as the first exercise but with four second sprints (pedalling as fast as you can for four seconds) every minute. We will also collect one drop of blood from your fingertip at 0, 15 and 30 minutes of each exercise bout to measure blood lactate (how hard your muscles are working). After the exercise is finished, you will sit quietly watching the movie again for 30 minutes while breathing

Study 2

170

through the facemask. We can work out how much energy you are burning using the air we collect. A blood sample will also be collected 5 minutes after exercise. Breakfast will be provided for 30 minutes after all three visits and you can eat as much as you need to. You (with the help of your parent/guardian) will need to write down all of the food that you eat on the day before the first session and the days before and after the last two sessions. You will also be asked to eat the same dinner meal before the last two sessions. Risks

The X-ray machine that measures the amount of muscle and fat in your body uses a small but safe amount of radiation so you won’t be at any risk. Also, you may find the fitness test on the bike hard but you can stop the test at any time. You just have to do your best! During the blood sampling, you may feel a slight pin prick and your finger might go a bit red, but this should go away in less than a day. Benefits

If you participate in this study, you will be provided with a report of how much muscle and fat is in your body and learn how strong your bones are. You will also find out how fit you are and how much energy your body burns during two different types of exercise. Your results will also help improve our understanding of how different types of exercise can change how much energy the body burns and how hard or pleasant the exercise is so that we can help make exercise more enjoyable for children in the future.

Your Rights




([email protected] or 0438 944 464) or Dr Kym Guelfi

([email protected] or 6488 2602) at any time.






171


Impact of Moderate Intensity Continuous Exercise compared with Sprint Interval Exercise on Energy Expenditure, Enjoyment and Perceived Exertion in Boys

~ Consent Form ~












______________________ ________________________


______________________ ________________________ ____________



they have any complaints regarding the manner in which a research project is conducted, it may be given to the researcher or

alternatively, to The Secretary, Human Research Ethics Committee, Registrar’s Office, The University of Western Australia, 35



Study 2

172

APPENDIX E

Information Sheet

Consent Form


173


Maximising the Energy Expenditure and Enjoyment of Exercise in Boys


Purpose

The amount of energy that the body burns during exercise is different depending on the type of exercise you do. The purpose of this study is to look at the amount of energy that your body uses during four different exercise sessions. We will also be finding out how hard you think the exercise was and how much you enjoyed it.


You and your parent/guardian will come into The University of Western Australia on five separate occasions. All visits will need to be in the morning and you will not be able to have breakfast (which will be provided) until after the testing is finished. On the first morning, we will measure the amount of muscle and fat you have in your body, find out how strong your bones are and see how fit you are. To measure the amount of muscle and fat in your body and how strong your bones are, you will need to lie down for about five minutes while an X-ray scans your body. We will then test how fit you are by having you cycle on a bike for about 30 minutes while you breathe into a mouthpiece to collect the air you breathe out and work out how much energy you are burning. You will be asked you to pedal harder every three minutes until you cannot go any further. One drop of blood will be collected from your fingertip at the end of each stage to measure blood lactate (how hard your muscles are working).This visit shouldn’t take any longer than one hour. On the four remaining sessions, you will be asked to cycle on a bike for 30 minutes while breathing into the mouthpiece. You will be doing four different exercise sessions each morning; (1) pedalling at the same moderate level (not very hard) the whole time, (2) pedalling at the same moderate level as the first exercise but with four second sprints (pedalling as fast as you can for four seconds) every two minutes, (3) pedalling at the same level as the first exercise but with four second sprints every minute and (4) pedalling at the same level as the first exercise but with four second sprints every 30 seconds. For these sessions, we will only collect one drop of blood from your fingertip before the exercise bout, one drop at 10 and 20 minutes into the exercise bout and one

Study 3

174

drop after the exercise bout. Breakfast will be provided after all five visits and you can eat as much as you need to. You (with the help of your parent/guardian) will need to write down all of the food that you eat on the day before final four sessions. You will also be asked to eat a similar dinner meal before these sessions. Risks

The X-ray machine that measures the amount of muscle and fat in your body uses a small but safe amount of radiation so you won’t be at any risk. Also, you may find the fitness test on the bike hard but you can stop the test at any time. You just have to do your best! During the blood sampling, you may feel a slight pin prick and your finger might go a bit red, but this should go away in less than a day. Benefits

If you participate in this study, you will be provided with a report of how much muscle and fat is in your body and learn how strong your bones are. You will find out how fit you are and how much energy your body burns during four different types of exercise. It is also likely that your legs will get more powerful from the sprint exercises. Your results will also help improve our understanding of how different types of exercise can change how much energy the body burns and how hard or pleasant the exercise is so that we can help make exercise more enjoyable for children in the future.

Your Rights




([email protected] or 0438 944 464) or Dr Kym Guelfi

([email protected] or 6488 2602) at any time.






175


Maximising the Energy Expenditure and Enjoyment of Exercise in Boys

~ Consent Form ~












______________________ ________________________


______________________ ________________________ ____________



they have any complaints regarding the manner in which a research project is conducted, it may be given to the researcher or

alternatively, to The Secretary, Human Research Ethics Committee, Registrar’s Office, The University of Western Australia, 35



Study 3

176

APPENDIX F

Food Records

(Re: Chapters 2,3 & 4 - Studies 1,2 & 3)

177

FFoooodd RReeccoorrdd -- SSttuuddyy 11

Record all of the food and drink that you consume on the day prior to your next

testing session - remember no hard exercise on this day too. Information about how

the food is cooked (i.e. grilled, baked, fried, steamed, etc.), the amounts eaten (i.e.

millilitres of fluid, grams of solid food) and whether regular, low fat or low kJ foods are

consumed (i.e. HILO milk vs. regular) must be recorded.

For example:

DDeessccrriippttiioonn AAmmoouunntt BBrreeaakkffaasstt Toasted Muesli 75g Raw Banana 1 medium HILO milk 100mL SSnnaacckk Raw Almonds 25g Raw Apple 1 small LLuunncchh Mixed Grain Bread Roll 1 large Chicken Breast - without skin, baked/roasted 150g Regular Mayonnaise 10g Raw Lettuce ½ cup shredded Raw Tomato 3 thin slices SSnnaacckk Starburst Jelly Beans 20 pieces DDiinnnneerr Salt Reduced Baked Beans - canned 420g Light Rye Bread 1 thick slice DDeesssseerrtt Connoisseur - Rich Chocolate Ice Cream 150mL DDrriinnkkss Water - Bottled 1.5L If you are unsure of the information you need to record, feel free to give me a call -

Nicole; 0438 944 464. Otherwise, simply record everything you can about the food and

drinks consumed on the day. Remember, try and break down all the meals. For

example, Dinner = Stew (but what did the stew consist of?) - i.e. carrot, celery, 4 bean

mix, corn, cubed lean rump steak (and roughly how much of each?) - i.e. ½ cup.

178

DDaattee::

DDeessccrriippttiioonn AAmmoouunntt BBrreeaakkffaasstt LLuunncchh DDiinnnneerr DDeesssseerrtt SSnnaacckkss DDrriinnkkss

179

DDaattee::

DDeessccrriippttiioonn AAmmoouunntt BBrreeaakkffaasstt LLuunncchh DDiinnnneerr DDeesssseerrtt SSnnaacckkss DDrriinnkkss

Etc.

180



testing session (at the time it was eaten) - remember no hard exercise on this day too.

Provide as much information as possible including the name, brand (i.e. Uncle Tobys,

Tip Top), how the food is cooked (i.e. grilled, baked, fried, steamed, etc.), the amount

eaten (i.e. millilitres of fluid, grams of solid food) and whether regular, low fat or low

kJ foods are consumed (i.e. HILO milk vs. regular). Water doesn’t need to be broken

down, give an overall measure at the end of the day.

For example:

DDeessccrriippttiioonn AAmmoouunntt 77::0000aamm Toasted Muesli 75g Raw Banana 1 medium HILO milk 100mL 1100::0000aamm Raw Almonds 25g Raw Apple 1 small 1122::3300ppmm Mixed Grain Bread Roll 1 large Chicken Breast - without skin, baked/roasted 150g Regular Mayonnaise 10g Raw Lettuce ½ cup shredded Raw Tomato 3 thin slices 33::0000ppmm Starburst Jelly Beans 20 pieces 66::0000ppmm Salt Reduced Baked Beans - canned 420g Light Rye Bread 1 thick slice 77::3300ppmm Connoisseur - Rich Chocolate Ice Cream 150mL WWaatteerr:: 1.5L

If you are unsure of the information you need to record, feel free to give me a call -





181

2244hhrrss pprriioorr ttoo CCoonnttiinnuuoouuss SSeessssiioonn DDaattee::

DDeessccrriippttiioonn AAmmoouunntt 55::0000aamm 66::0000aamm 77::0000aamm 88::0000aamm 99::0000aamm 1100::0000aamm 1111::0000aamm 1122::0000ppmm 11::0000ppmm 22::0000ppmm 33::0000ppmm 44::0000ppmm 55::0000ppmm 66::0000ppmm 77::0000ppmm 88::0000ppmm 99::0000ppmm 1100::0000ppmm WWaatteerr::

182

2244hhrrss pprriioorr ttoo SSpprriinntt IInntteerrvvaall SSeessssiioonn DDaattee::


183



testing session (at the time it was eaten) - remember no hard exercise on this day too.

Provide as much information as possible including the name, brand (i.e. Uncle Tobys,

Tip Top), how the food is cooked (i.e. grilled, baked, fried, steamed, etc.), the amount

eaten (i.e. millilitres of fluid, grams of solid food) and whether regular, low fat or low

kJ foods are consumed (i.e. HILO milk vs. regular). Water doesn’t need to be broken

down, give an overall measure at the end of the day.

For example:

DDeessccrriippttiioonn AAmmoouunntt 77::0000aamm Toasted Muesli 75g Raw Banana 1 medium HILO milk 100mL 1100::0000aamm Raw Almonds 25g Raw Apple 1 small 1122::3300ppmm Mixed Grain Bread Roll 1 large Chicken Breast - without skin, baked/roasted 150g Regular Mayonnaise 10g Raw Lettuce ½ cup shredded Raw Tomato 3 thin slices 33::0000ppmm Starburst Jelly Beans 20 pieces 66::0000ppmm Salt Reduced Baked Beans - canned 420g Light Rye Bread 1 thick slice 77::3300ppmm Connoisseur - Rich Chocolate Ice Cream 150mL WWaatteerr:: 1.5L If you are unsure of the information you need to record, feel free to give me a call -





184

2244hhrrss pprriioorr ttoo SSeessssiioonn 11 DDaattee::


185



186



187



188

APPENDIX G

Pictorial Children’s Effort Rating Table (PCERT)

(Re: Chapters 3 & 4 - Studies 2 & 3)

177

189

190

APPENDIX H

Visual Analogue Scale (VAS)

Physical Activity Enjoyment Scale (PACES)


191

HHooww eenneerrggeettiicc ddoo yyoouu ffeeeell??

Not energetic at all energetic as I have ever felt

HHooww hhuunnggrryy ddoo yyoouu ffeeeell??

Not hungry at all As hungry as I have ever felt

HHooww ffuullll ddoo yyoouu ffeeeell??

Not full at all As full as I have ever felt

HHooww ssoorree ddoo yyoouurr mmuusscclleess ffeeeell??

Not sore at all As sore as they have ever felt

192

MMooddeerraattee IInntteennssiittyy CCoonnttiinnuuoouuss

WWhheenn II wwaass eexxeerrcciissiinngg......

Disagree a lot

Agree a lot

I enjoyed it 1 2 3 4 5

I felt bored 1 2 3 4 5

I disliked it 1 2 3 4 5

I found it pleasurable 1 2 3 4 5

It was no fun at all 1 2 3 4 5

It gave me energy 1 2 3 4 5

It made me depressed 1 2 3 4 5

It was very unpleasant 1 2 3 4 5

My body felt good 1 2 3 4 5

I got something out of it 1 2 3 4 5

It was very exciting 1 2 3 4 5

It frustrated me 1 2 3 4 5

It was not at all interesting 1 2 3 4 5

It gave me strong feelings of success

1 2 3 4 5

It felt good 1 2 3 4 5

It felt as though I would rather be doing something else

1

2

3

4

5

WWhhiicchh eexxeerrcciissee wwaass tthhee mmoosstt eennjjooyyaabbllee?? WWhhyy??

TThhaannkk YYoouu!!

193

SSpprriinntt IInntteerrvvaall EExxeerrcciissee

WWhheenn II wwaass eexxeerrcciissiinngg......

Disagree a lot

Agree a lot

I enjoyed it 1 2 3 4 5

I felt bored 1 2 3 4 5

I disliked it 1 2 3 4 5

I found it pleasurable 1 2 3 4 5

It was no fun at all 1 2 3 4 5

It gave me energy 1 2 3 4 5

It made me depressed 1 2 3 4 5

It was very unpleasant 1 2 3 4 5

My body felt good 1 2 3 4 5

I got something out of it 1 2 3 4 5

It was very exciting 1 2 3 4 5

It frustrated me 1 2 3 4 5

It was not at all interesting 1 2 3 4 5

It gave me strong feelings of success 1 2 3 4 5

It felt good 1 2 3 4 5

It felt as though I would rather be doing something else

1

2

3

4

5

WWhhiicchh eexxeerrcciissee wwaass tthhee mmoosstt eennjjooyyaabbllee?? WWhhyy??

TThhaannkk YYoouu!!

194

APPENDIX I

Visual Analogue Scale (VAS)

Physical Activity Enjoyment Scale (PACES)


195

HHooww eenneerrggeettiicc ddoo yyoouu ffeeeell??

Not energetic at all As energetic as I have ever felt

HHooww hhuunnggrryy ddoo yyoouu ffeeeell??

Not hungry at all As hungry as I have ever felt

HHooww ffuullll ddoo yyoouu ffeeeell??

Not full at all As full as I have ever felt

HHooww ssoorree ddoo yyoouurr mmuusscclleess ffeeeell??

Not sore at all As sore as they have ever felt

HHooww mmuucchh ddiidd yyoouu eennjjooyy tthhee eexxeerrcciissee??

It was not enjoyable at all It was the most enjoyable exercise ever

184

PPlleeaassee rraattee hhooww yyoouu ffeeeell aatt tthhee mmoommeenntt aabboouutt tthhee eexxeerrcciissee yyoouu jjuusstt ddiidd..

I enjoyed it 1 2 3 4 5 6 7 I hated it

I felt bored 1 2 3 4 5 6 7 I felt interested

I disliked it 1 2 3 4 5 6 7 I liked it

It was pleasurable 1 2 3 4 5 6 7 It was not pleasurable

It was no fun at all 1 2 3 4 5 6 7 It was lots of fun

It gave me energy 1 2 3 4 5 6 7 It was tiring

It made me depressed 1 2 3 4 5 6 7 It made me happy

It was very unpleasant 1 2 3 4 5 6 7 It was very pleasant

My body felt good 1 2 3 4 5 6 7 My body felt bad

I got something out of it 1 2 3 4 5 6 7 I got nothing out of it

It was very exciting 1 2 3 4 5 6 7 It was not at all exciting

It frustrated me 1 2 3 4 5 6 7 It didn’t frustrate me

It was not at all interesting 1 2 3 4 5 6 7 It was very interesting

It gave me strong feelings of success 1 2 3 4 5 6 7 It didn’t give me feelings of success

It felt good 1 2 3 4 5 6 7 It felt bad

I would rather be doing something else 1 2 3 4 5 6 7 There is nothing else I would rather be doing

196

197

APPENDIX J

Data Collection Sheets

198

Data Sheet - Study 1

Anthropometry

Height: Waist: % FM:

Weight: Hip: VO2peak:

Familiarisation Max Test

W 20 40 60 80 100 120 140

Actual (W)

HR

Maximal Exercise Test Barometric Pressure:

Incremental Exercise Test Barometric Pressure:

% VO2peak 35 40 45 50 55 60 65

Watts

Actual W Initial Final Gas Temp. FEO2 FECO2 HR La+

Actual W Initial Final Gas Temp. FEO2 FECO2 HR La+

20

40

60

80

100

120

140

ID # Bike:

199

Constant Load Protocols

Session 1 2 3 4 5

Watts

Min W Initial Final Gas

Temp. FEO2 FECO2 HR La+

1 BP

2-3 -

9-10 -

14-15 - - - - - -

19-20 -

29-30

2 BP

2-3 -

9-10 -

14-15 - - - - - -

19-20 -

29-30

3 BP

2-3 -

9-10 -

14-15 - - - - - -

19-20 -

29-30

4 BP

2-3 -

9-10 -

14-15 - - - - - -

19-20 -

29-30

5 BP

2-3 -

9-10 -

14-15 - - - - - -

19-20 -

29-30

Comments:

200


Height: Waist:


Maximal Exercise Test Fatmax:

___ Moderate Intensity Continuous Barometric Pressure:

Time

Gas Temp.

Initial

Final

FEO2

FECO2

RMR

PE (3-5)

PE (8-10)

PE (13-15)

PE (18-20)

PE (23-25)

PE (28-30)

Exercise Protocols Fatmax = w

Continuous

Sprint Interval

Min

HR

RPE

La+

Min

HR

RPE

La+

9 - 10

9 - 10

19 - 20

19 - 20

29 - 30

29 - 30

Waverage: Waverage:

Power Output: Power Output:

WAIM

W

HR

RPE

La+

ID # Bike:

201

___ Sprint Interval Exercise Barometric Pressure:

Time

Gas Temp.

Initial

Final

FEO2

FECO2

RMR

PE (3-5)

PE (8-10)

PE (13-15)

PE (18-20)

PE (23-25)

PE (28-30)

Energy Intake Measurements

Continuous Sprint Interval

Pre- Post- Diff. EI Pre- Post- Diff. EI

Bread:

Butter

Peanut Butter

Honey

Jam

Vegemite

Weet-bix

Coco Pops

CrunchyNut Cornflakes

Milk (Full Cream)

Milk (Skim)

Baked Beans

Banana

Apple

Orange Juice

Sugar

Water

Total Energy Intake CHO: % Fat: % CHO: % Fat: %

202


Height: Waist:


Maximal Exercise Test

Exercise Protocols Fatmax = w

CON

HR

RPE

Feeling

SI1

HR

RPE

Feeling

9 - 10

9 - 10

19 - 20

19 - 20

29 - 30

29 - 30

Waverage: La+: Waverage: La+:


SI2

HR

RPE

Feeling

SI3

HR

RPE

Feeling

9 - 10

9 - 10

19 - 20

19 - 20

29 - 30

29 - 30

Waverage: La+: Waverage: La+:


WAIM 10 25 40 55 70 85 100 115 130

W

HR

RPE

Feeling

La+

ID # Bike:

203

Energy Intake Measurements

CON SI1 SI2 SI3

Pre- Post- Pre- Post- Pre- Post- Pre- Post-

Bread:

Butter

Peanut Butter

Honey

Jam

Vegemite

Weet-bix

Muesli

Cornflakes

Milk (Full Cream)

Milk (Skim)

Yoghurt

Baked Beans

Banana

Apple

Orange Juice

Apple Juice

Sugar

Water

Which session was the best? Why?

204

APPENDIX K

Publications Arising from this Thesis

nicole annette crisp - research-repository.uwa.edu.au · single graded exercise test with 3-min...

Documents