train low race high

8/11/2019 Train Low Race High

1/11

Review

Fueling strategies to optimize performance: training high ortraining low?

L. M. Burke

Department of Sports Nutrition, Australian Institute of Sport, Belconnen ACT, AustraliaCorresponding author: Louise M Burke, PhD, Department of Sports Nutrition, Australian Institute of Sport, PO Box 176,Belconnen ACT 2616, Australia. Tel: 161 2 6214 1351, Fax: 161 2 6214 1603, E-mail: [email protected]

Accepted for publication 18 June 2010

Availability of carbohydrate as a substrate for the muscleand central nervous system is critical for the performance ofboth intermittent high-intensity work and prolonged aerobicexercise. Therefore, strategies that promote carbohydrateavailability, such as ingesting carbohydrate before, duringand after exercise, are critical for the performance of many

sports and a key component of current sports nutritionguidelines. Guidelines for daily carbohydrate intakes haveevolved from the one size fits all recommendation for ahigh-carbohydrate diets to an individualized approach tofuel needs based on the athletes body size and exerciseprogram. More recently, it has been suggested that athletesshould train with low carbohydrate stores but restore fuel

availability for competition (train low, compete high),based on observations that the intracellular signaling path-ways underpinning adaptations to training are enhancedwhen exercise is undertaken with low glycogen stores. Thepresent literature is limited to studies of twice a daytraining (low glycogen for the second session) or withholding

carbohydrate intake during training sessions. Despite in-creasing the muscle adaptive response and reducing thereliance on carbohydrate utilization during exercise, thereis no clear evidence that these strategies enhance exerciseperformance. Further studies on dietary periodization stra-tegies, especially those mimicking real-life athletic prac-tices, are needed.

The availability of carbohydrate as a substrate formuscle metabolism and central nervous system sup-

port is a critical factor in the performance of pro-longed (490 min) submaximal or intermittent high-intensity exercise, and plays a permissive role in theperformance of brief high-intensity work (Hargreaves,1999). Therefore, a variety of athletes are highlydependent on carbohydrate fuels: these include en-durance atheletes in high-intensity events conductedin the zone between the so-called lactate thresholdand maximal aerobic capacity, and team or racquetsport players who undertake repetitive bursts of high-intensity work. It is interesting to note that even wherethe overall physiological demands of competition varymarkedly between sports and events (e.g. competitionmay range from 1 to 2 min of middle distanceswimming and track events to over 2 h in marathonsand cycling road races), success in such events istypically underpinned by the athletes ability to sus-tain effort in this critical zone. Furthermore, trainingprograms in each of these events share commonelements: longer periods of work at submaximalintensities, sessions focused on sustained higher-in-tensity work and interval sessions involving re-peated high-intensity exercise with variable recoveryperiods. Because of these similarities between appar-

ently diverse events, the focus of this review has far-reaching outcomes across sport.

It is important to note that the total body carbo-hydrate stores are limited, and are often substantiallyless than the fuel requirements of the various trainingand competition sessions undertaken by athletes inthe range of sports noted previously. Therefore,sports nutrition guidelines promote a variety ofoptions for acutely increasing carbohydrate avail-ability for an exercise session, including consumingcarbohydrate before, during and in the recoveryperiod between prolonged exercise bouts (AmericanDietetic Association et al., 2009). When these strate-gies enhance or maintain carbohydrate availability,they delay the onset of fatigue, and enhance ex-ercise capacity or endurance (Wright et al., 1991;Fallowfield & Williams, 1993; Chryssanthopoulos& Williams, 1997). Studies that show benefits ofcarbohydrate support to exercise performance aremore appropriate to sport (Sherman et al., 1991;Below et al., 1995; Tsintzas et al., 1995; Vergauwen etal., 1998), and even include protocols in whichincreased carbohydrate availability has enhancedperformance in field situations or actual sportscompetition (Karlsson & Saltin, 1971; Akermarket al., 1996; Balsom et al., 1999).

Scand J Med Sci Sports 2010: 20 (Suppl. 2): 4858 &2010 John Wiley & Sons A/S

doi: 10.1111/j.1600-0838.2010.01185.x

48
mailto:[email protected]:[email protected]


2/11

The clear benefits of an adequate carbohydratesupply for an acute bout of exercise not only form thebasis of competition nutrition recommendations butalso underpin the guidelines for the athletes every-day nutrition whereby the chronic outcomes oftraining are seen as an accumulation of a series ofindividual exercise bouts. It has been assumed thatrepeated training with optimal fuel support will

lead to better preparation and an enhancementof competition performance (the training betterapproach). This paper will review the evolutionof guidelines for the everyday or training diets ofathletes, summarizing the evolution of guidelines fora carbohydrate-supported training environment andthe criticism that has been leveled at these recom-mendations. It will also examine the emerging inter-est in dietary periodization in which exercising in alow fuel state is suggested to enhance the adaptationsto training and result in superior performance (thetraining smarter approach).

The 1990s the high-carbohydrate approach to

training nutrition

Official guidelines for athletes prepared during the1990s were unanimous in their recommendation ofhigh-carbohydrate intakes in the everyday or train-ing diet, based on the perceived benefit of promot-ing muscle glycogen recovery on a daily basis (Devlin& Williams, 1991; American Dietetic Association,1993; Ekblom & Williams, 1994; Maughan &Horton, 1995). Most guidelines took a one size fits

all approach, or at best a two-tier approach thatdivided athletes into endurance and generalcategories. In addition, the guidelines were com-monly expressed in terms of the percentage of energyintake that should be contributed by carbohydrate inthe training diet. A typical summary of these earlysports nutrition guidelines was that athletes shouldconsume diets providing at least 55% of energy fromcarbohydrate (Maughan & Horton, 1995) or 6065%of energy from carbohydrate (American DieteticAssociation, 1993). In the case of endurance athletes,carbohydrate intake recommendations were setvariously at 460% of dietary energy (Ekblom &Williams, 1994) and 6570% of dietary energy(American Dietetic Association, 1993).

This advice was criticized both outside and withinsport science circles on two accounts. The firstcriticism was the apparent failure of athletes toachieve such carbohydrate-rich diets in training,with the rationale that if it were advantageous totraining adaptations and performance, we wouldexpect athletes to follow the practice (Noakes,1997). Indeed, a review of the dietary surveys ofserious athletes published since the announcement of

the 1991 sports nutrition guidelines found that themean values for the reported daily carbohydrateintakes of endurance athletes were 5055% oftotal energy intake (Burke et al., 2001), comparedwith the 6070% of energy intake suggested byvarious expert groups. Second, it was suggestedthat the available literature failed to provide a clearsupport for the benefits of chronic high-carbohydrate

intakes on training adaptations and performance ofathletes undertaking intensive daily workouts. Theseboth concerns were addressed when dietary guide-lines for athletes were updated in the followingdecade (Burke et al., 2004; American Dietetic Asso-ciation et al., 2009).

The new millennium carbohydrate needs of athletes

re-examined and re-modeled

In the recent decade, updated dietary guidelines haveexamined both the science underpinning the dailycarbohydrate requirements for athletes and theterminology used to define these needs. These ap-proaches have simultaneously addressed the criti-cisms of the previous recommendations for theathletes training diet, as well as produced a morepractical education message.

Support for the chronic benefits of trainingwith high-carbohydrate availability on performanceoutcomes is reliant on a small number of trainingstudies comparing groups or trials with moderate-and high-carbohydrate intakes (see Table 1). It isunfortunate but not surprising that this literature is

so sparse, because such studies require painstakingcontrol over a long duration. Nevertheless, there isclear evidence of superior restoration of muscleglycogen stores when athletes consume a higher-carbohydrate intake. However, the evidence forperformance gains is equivocal: only three studieshave shown enhancement of performance following aperiod of fuel-supported training (Simonsen et al.,1991; Achten et al., 2004; Halson et al., 2004), whileanother shows a potential for better performance viabetter running economy (Kirwan et al., 1988). Animportant finding from two of these investigationswas that a higher daily carbohydrate intake was ableto reduce, but not entirely prevent, the developmentof over-reaching symptoms (fatigue, impaired per-formance, sleep and mood disturbance, altered hor-monal responses to stress, etc.), which can occurwhen a period of intensified training is undertaken(Achten et al., 2004; Halson et al., 2004). The notablecharacteristics of the other study that favored high-carbohydrate availability in training were the useof highly trained athletes, a longer duration ofintervention and the blinding of dietary treatments(Simonsen et al., 1991).

Fueling strategies to optimize performance

49


3/11


4/11

Table1.

(continued)

Study

Athletes

Durationof

study(days)

DailyCHO

intake(g/kg/day)

Effectonmuscle

glycogen

Performa

nceprotocol

Performanc

eadvantagewithHCHO

Simonsenetal.

(1991)

Collegiaterowers

(12M,

10F)

28days

Parallelgroupdesign

10vs5

MCHOallowed

maintenanceofmuscle

glycogenstores,while

HCHOallowedan

increaseinstores

3

2500

m

rowingergometerTTwith

8-minrec

overyintervalundertakenon

days1,3

and5ofeachweek

Trialsundertakenateveningworkout

Yes

Poweroutp

utmaintainedduring

ergometerrowingTToverthecourseof

MCHO,

lead

ingtooverallimprovementof

1.6

%

atendof4weeks.

Improvementin

poweroutp

utinHCHOoversametime

frame5

10.7

%

Shermanetal.

(1993)

Trainedcyclists

(nineM1nineM)

7days

Parallelgroupdesign

10vs5

DeclinedinMCHO

MaintainedinHCHO

2

timetoexhaustiononcycle

ergomete

rat80%

VO2maxwith5-min

recovery

period

Trialsund

ertakenattheendofdayafter

1-htraining

NoNodifferencebetweengroupson

enduranceduringeitherbout.Sum

time5

550

85and613

45sfor

MCHOand

HCHO,respectively,

NS

Vogtetal.(2003)

Welltrained

duathletes

(11M)

35days

Cross-overdesign

6.9vs3.6

Maintainedonbothdiets

VO2max,c

yclingTTundertakenafter

progressivesubmaximalpre-load;

outdoor2

1km

run(allundertakenon

separate

days)

Trialsundertakenpost-meal

(compositionofmealvariedwith

dietarytreatment)

NoNodifferenceinaerobiccapacity,cycling

TTpowero

rhalfmarathonruntime

betweendiets(e.g.

21km

run5

80min

12s

86s

and80min24s

82sfor

HCHOand

MCHO)

Coxetal.(2010)

Welltrained

cyclists/

triathletes

(16M)

28days

Parallelgroupdesign

8vs5.2

(addition

al

CHOconsumed

during/aftertraining

sessions)

Maintainedonbothdiets

100minat70%

VO2max1

25-min

TTTwotrialsundertakenonseparate

days,bot

hafterCHO-richmealwater

onlytrial

CHOintaketrial

NoOverallTTperformanceimprovedby

4%

inbothgroups.

However,only

moderateg

roupimprovedperformance

bothinCHO-fedandwater-fedtrials.

Highgroup

increasedcapacityfor

oxidationofexogenousCHOduring

exercisebu

tonlyimprovedTT

performanc

einCHOfedtrial

M,male;F,

female;NA,notavailable;TT,

timetrial.


51


5/11

It is curious that benefits from high-carbohydrateeating have not been a universal outcome fromtraining studies. However, several methodologicalissues may explain the unclear findings, includingan overlap between what was considered a moderate-and high-carbohydrate diet in various studies.It is possible that the moderate-carbohydrate dietsused in some studies provided sufficient fuel to meet

training requirements, in such a situation, additionalbenefit would not be expected from higher-carbohy-drate intakes. Another consideration is whethersufficient time was allowed for differences in thetraining responses of athletes to lead to significantdifferences in the study performance outcome. Afterall, studies on tapering and reduced training showthat the performance of some types of exercise maybe maintained for up to 3 weeks, despite a reducedtraining stimulus (Mujika & Padilla, 2000a, b). Afurther consideration is how carbohydrate intake isspread over the day in relation to training sessions,and whether simply reporting the total daily intakesof carbohydrate masks how well carbohydrate isconsumed before, during and after exercise to bestpromote fuel availability. Finally, the protocols usedto measure performance in studies should be scruti-nized to see if they are sufficiently reliable to detectsmall but real improvements that would be signifi-cant to a competitive athlete (Hopkins et al., 1999).It is possible that present studies suffer from type IIerrors, in that they fail to recognize potential perfor-mance improvements because of variability of per-formance measures, small sample sizes and thereliance on traditional probability-based statistics

to interpret the results (Hopkins et al., 2009).One possible conclusion from the available studies

of chronic dietary patterns and exercise performanceis that athletes adapt to lower muscle glycogen storesresulting from moderate carbohydrate intake so thatthere is no impairment of training or competitionoutcomes. This shall be discussed further below.However, in setting the most recent dietary guide-lines, it was noted that no study shows that a mode-rate carbohydrate intake promotes superior trainingadaptations and performance compared with higher-carbohydrate diets (Burke et al., 2004). Thus, theguidelines continued to support the concept of train-ing with high-carbohydrate availability.

The apparent mismatch between sports nutritionguidelines and the real-life dietary patterns of athletesis interesting to explore, although of course, it isdifficult to establish cause and effect just from examin-ing the practices of successful athletes. After all, it islikely that talented athletes can excel in spite of theirpractices just as well as because of them. In addition,the literature is largely devoid of studies of truly eliteathletes; in fact, the few studies of the most highlysuccessful athletes such as Kenyan middle-distance

and distance runners (Onywera et al., 2004) reportintakes of carbohydrate that are high when judged perkilogram of body mass (BM) ( 10 g/kg) and as apercentage of dietary energy (470% of energy).Nevertheless, the apparently low carbohydrate intakesreported by most other groups of (typically sub-elite)athletes can be largely explained as a result of confu-sion arising from the terminology used to make sports

nutrition guidelines (Burke et al., 2001).Earlier guidelines for daily carbohydrate intake for

athletes follow the traditional terminology used inpopulation dietary guidelines, where recommenda-tions for the intake of macronutrients are expressedas the proportion of dietary energy that they shouldtypically contribute. However, population guidelinesfor carbohydrate result from taking a group of issuesinto account for a generic group of people (e.g.meeting requirements for protein, achieving benefitsfrom reducing fat intake) rather than trying to meetspecific muscle fuel needs for a specialized sub-group,or more particularly, for an individual. The athletesfuel needs are better estimated from more directinformation, such as the carbohydrate intake re-quired for optimal glycogen recovery, or the carbo-hydrate expenditure of the training program. Suchestimates of carbohydrate needs should be providedrelative to the BM of the athlete to roughly accountfor the size of the muscle mass that must be fueled.General guidelines derived from such informationhave been included in the updated guidelines forathletes (American College of Sports Medicineet al., 2000; Burke et al., 2004; American DieteticAssociation et al., 2009). Even these guidelines (sum-

marized in Table 2) should also be considered asball-park ranges, which can be fine-tuned for theindividual athlete with more specific knowledge oftheir actual training program, past and presentresponse to training and their total energy budget.A re-examination of the dietary surveys of athletespublished between 1990 and 2000 shows mean valuesof reported daily carbohydrate intake (g/kg BM) tobe 7.6 and 5.8 for male endurance and non-endur-ance athletes, and 5.7 and 4.6 for their femalecounterparts (Burke et al., 2001). These values sug-gest that the daily carbohydrate intakes of the typicalmale athlete fell within the suggested ranges for fuelneeds for at least a moderate training load, particu-larly if these athletes have under-reported by 1020%as is common with dietary records (Burke et al.,2001). Of course, these mean estimates do not guar-antee that all athletic groups or specific athletes metthese recommended intakes, or indeed met theiractual fuel requirements; such determinations canonly be made on an individual basis. Female athletesappeared to be at a higher risk of carbohydrateintakes below these ranges, largely as a result oflower energy intakes.

Burke

52


6/11

Newer guidelines for sports nutrition have speci-fically stated the disadvantages of using percentage

of energy terminology to provide advice to athletesabout their carbohydrate needs (Burke et al., 2004;American Dietetic Association et al., 2009), notingthat it is not practical or user-friendly to people witha simple knowledge of nutrition. To convert existinginformation from food labels and food compositioninto a percentage of energy (particularly over a daysintake) requires some expertise and mathematicalskill. Most important, however, the review of dietarysurveys of athletes (Burke et al., 2001) provided clearevidence that the two methods of describing carbo-hydrate intake are not interchangeable and percen-tage of energy intake can be misleading. Amonggroups of male athletes, there was evidence of aloose but positive correlation between reported in-takes of carbohydrate (g/kg) and the energy con-tributed by carbohydrate in the diet. In other words,male athletes who change their eating patterns toincrease the energy contribution of carbohydrate intheir diets are likely to increase their carbohydrateintake per kilogram of BM. Nevertheless, the corre-lation was too low to guarantee that a particulartarget for grams of carbohydrate intake basedon specific fuel needs translates into a certain per-

centage of dietary energy. Furthermore, in the caseof female endurance athletes, the correlation be-

tween the carbohydrateenergy ratio and total car-bohydrate intake (g/kg BM) was minimal. This isbecause of the confounding issue of restricted energyintake in some individuals or groups. These athletesmay consume 7075% of total energy from carbo-hydrate in an energy-restricted diet (i.e. meet oldguidelines) but still only achieve 34 g of carbohy-drate per kilogram of BM (fall below fuel-basedtargets).

In summary, the current sports nutrition guide-lines for the daily training environment encouragestrategies to promote carbohydrate availability forthe majority of training sessions as is practical andwithin the athletes total energy budget (Table 2).These recommendations are based on plentiful evi-dence that strategies enhancing carbohydrate avail-ability also enhance endurance and performanceduring a single session of exercise. They concedethat the literature fails to provide a clear supportthat long-term high-carbohydrate intakes enhancethe training adaptations and performances of endur-ance athletes, but challenges sport scientists to under-take well-controlled studies that will better test thishypothesis.

Table 2. Summary of current guidelines for carbohydrate intake by athletes (adapted from Burke, 2007)

Situation Recommended carbohydrate intake

Acute situationOptimal daily muscle glycogen storage (e.g. for post-exerciserecovery or to fuel up or carbohydrate load before an event)

712 g/kg body mass/day

Rapid post-exercise recovery of muscle glycogen, where recoverybetween sessions is o8 h

11.2 g/kg immediately after exercise; repeated each houruntil meal schedule is resumedThere may be some advantages to consuming carbohydrate

as a series of small snacks every 1560 min in the earlyrecovery phase

Pre-event meal to increase carbohydrate availability before prolongedexercise session

14 g/kg eaten 14 h before exercise

Carbohydrate intake during exerciseSustained high-intensity exercise 1 h when muscle fuel storesare not limiting

Small amounts, including swilling in mouth

Moderate-intensity or intermittent high-intensity exercise of 41 h 0.51.0 g /kg/h (3060 g /h)Prolonged exercise (23h1) 8090 g/h

Chronic or everyday situationDaily recovery or fuel needs for athletes with very light trainingprogram (low-intensity exercise or skill-based exercise). Thesetargets may be particularly suited to athletes with large body mass ora need to reduce energy intake to lose weight

35 g/kg/day*

Daily recovery or fuel needs for athlete with moderate exerciseprogram (i.e. 6090 min)

57 g/kg/day*

Daily recovery or fuel needs for endurance athlete (i.e. 13 h ofmoderate- to high-intensity exercise)

712 g/kg/day*

Daily recovery or fuel needs for athlete undertaking extreme exerciseprogram (i.e.445 h of moderate- to high-intensity exercise such asTour de France)

1012 g/kg/day*

*Note that this carbohydrate intake should be spread over the day to promote fuel availability for key training sessions i.e. consumed before, during or

after these sessions.


53


7/11

Training with low-carbohydrate availability

Discovery of nutrientgene interactions and cellular

signaling pathways has allowed scientists to identify

a range of muscular adaptations to training and form

new hypotheses about the best strategies to promote

these adaptations. Some studies have found that

when exercise is undertaken with low muscle glyco-

gen content, the transcription of a number of genes

involved in training adaptations is enhanced (for

review, see Hawley et al., 2006; Baar & McGee,

2008). It appears that several transcription factorshave glycogen-binding domains, and when muscle

glycogen is low, these factors are released to associate

with different targeting proteins. Indeed, exercising

with low muscle glycogen stores amplifies the activa-

tion of the signaling proteins, AMP-activated protein

kinase and p38 mitogen-activated protein kinase,

which have direct roles in controlling the expression

and activity of several transcription factors involved

in mitochondrial biogenesis and other training adap-

tations (Hawley et al., 2006; Baar & McGee, 2008).

Equally, exercise in a fasted state has been shown topromote different cellular signaling responses toexercise undertaken with carbohydrate intake beforeand during the session (Civitarese et al., 2005). Thisinformation underpins the recently described trainlow, compete high protocol training with lowglycogen/carbohydrate availability to enhance thetraining response, but competing with high-fuelavailability to promote performance. There are anumber of potential ways to reduce carbohydrateavailability for the training environment (see Table3), and it should be pointed out that these do notalways promote a low carbohydrate diet per se norrestrict carbohydrate availability for all trainingsessions.

Great interest in this new hypothesis of train low,compete high was generated by a study by Hansenet al. (2005). In this investigation, seven untrainedmales undertook a 10-week program of leg kneeextensor kicking exercise. In an ingenious experi-mental design, each subjects legs undertook thesame training program (5 h/week) but received a

Table 3. Strategies to reduce carbohydrate availability to alter the molecular responses to endurance-based training sessions

Exercise-diet strategy Main outcomes

Chronically low carbohydrate diet (carbohydrate intake less thanfuel requirements for training)

Chronic reduction in muscle carbohydrate availability (endogenous andpotentially exogenous sources) for all training sessions, depending ondegree of fuel mismatchChronic whole-body effects of low carbohydrate availability includingimpairment of immune system and central nervous system function

Twice a day training (low endogenous carbohydrate availability

for the second session in a day achieved by limiting the durationand carbohydrate intake in recovery period after the firstsession)

Reduction in endogenous and exogenous carbohydrate availability for the

muscle during the second training sessionAcute reduction in carbohydrate availability for immune and central nervoussystems depending on duration of carbohydrate restriction and muscle fuelrequirements of second session

Training after an overnight fast Reduction in exogenous carbohydrate availability for the muscle for thespecific sessionPotential reduction in endogenous carbohydrate availability if there isinadequate glycogen restoration from previous days trainingAcute reduction in carbohydrate availability for immune system and centralnervous system depending on duration of carbohydrate restriction and fuelrequirements of the session

Prolonged training with or without an overnight fast and/orwithholding carbohydrate intake during the session

Reduction in exogenous carbohydrate sources for the muscle for thespecific sessionAcute reduction in carbohydrate availability for immune and central nervous

systems depending on duration of carbohydrate restriction and fuelrequirements of the session

Withholding carbohydrate during the first hours of recovery Could provide adequate fuel availability for the specific session but amplifypost-exercise signaling due to the short but targeted time of lowcarbohydrate availability theoretically achieves both a training harderand training smarter effectCould interfere with re-fuelling for subsequent training sessions if totalcarbohydrate intake is reduced rather than just delayed. Given limits in thetotal rate of glycogen synthesis, delaying the timing of intake may reducethe potential for total glycogen storage between two sessions that areo8 hapart, regardless of total carbohydrate intakeMay reduce immune system function or accentuate the immunesuppression that occurs after exercise

*Note that permutations and combinations of these strategies could alter exogenous and endogenous carbohydrate supplies independently or

interactively.

Burke

54


8/11

different daily schedule: one leg was trained twice-a-day, every second day, whereas the contralateral legwas trained daily. The consumption of a carbohy-drate-rich diet ( 8 g/kg/day) meant that one legexercised with full restoration of glycogen each day,while the twice a day leg undertook the secondsession with depleted muscle glycogen stores. Com-pared with the leg that performed daily training with

normal glycogen reserves, the leg that commencedhalf of training sessions with low muscle glycogenlevels had a more pronounced increase in restingglycogen content (when training and dietary factorswere organized to promote re-fueling) and citratesynthase activity. Although the increase in maximalpower was similar in each leg, there was an almosttwofold greater training-induced increase in one-legged exercise time to fatigue in the train lowleg compared with the leg trained in a glycogen-replete state.

Some caveats were identified in applying the re-sults of this study to real-life athletes. First, the sub-

jects were untrained and the results may not apply tothe training adaptation and performance in alreadywell-trained athletes. Second, the training sessionsundertaken by subjects in that study were clampedat a fixed submaximal intensity for the duration ofthe training program: athletes typically periodizetheir programs to incorporate a hardeasy patternto the overall organization of training, as well asprogressive overload. Third, the mode of training(one-legged knee kicking) and the exercise perfor-mance task (submaximal kicking to exhaustion) bearlittle resemblance to the whole-body training modes

and performance tasks undertaken by the majority ofcompetitive athletes. These issues have been partiallyaddressed by some more recent studies.

Yeo et al. (2008) completed a 3-week trainingstudy using a parallel group design in which endur-ance-trained cyclists consumed diets providing 8 g/kg/day carbohydrate, while completing sixtraining sessions per week ( 8 h/week) divided intothree steady-state cycling sessions (100 min at 70%VO2peak) and three sessions of high-intensity inter-vals (8 5 min at maximal sustained power, with1 min recovery). One group of seven subjects alter-nated between one of these sessions each day (highgroup), while another seven subjects trained everysecond day, with the steady-state session followed anhour later by the interval session (low group). Train-ing intensity was measured as the self-selected poweroutputs achieved in the interval session, while per-formance was measured before and after the trainingblock via a 1-h time trial completed after an hour ofsteady-state cycling. They found that resting muscleglycogen concentrations, rates of whole-body fatoxidation during steady-state cycling and muscleactivities of the mitochondrial enzymes citrate

synthase and b-hydroxyacyl-CoA-dehydrogenase(HAD) were increased only in the group that under-took the interval sessions with low glycogen. How-ever, total work completed in the interval sessionswas less in the low group compared with thehigh training group. Nevertheless, 1-h cycling per-formance improved similarly ( 10% increase inpower) in both groups. Although it is tempting to

suggest that the low group made the same perfor-mance gains with less training stimulus, it must beremembered that both groups trained for the sameduration of time and to their maximum effort. Infact, the low group experienced difficulty in under-taking the interval training.

The findings of this study were confirmed by an-other similarly designed 3-week investigation (Hul-ston et al., 2010) in which participants undertook 90-min aerobic sessions and interval training sessions(8 5 min at self-selected highest sustained intensity)either on alternative days (high group) or in succes-sion on the same day (low group). Mean trainingintensity during the interval training sessions wasagain lower in the low group (297 8 W) comparedwith the high group (323 9 W, Po0.05). In addi-tion, various measurements of metabolic adaptationwere evident only in the low group; there wasincreased mitochondrial content of the enzymeHAD and increased fat oxidation during submax-imal exercise, principally from muscle-derived tria-cylglyceride. Once again, despite these apparentlydifferent training experiences, both groups achievedan equal improvement of performance from the 3-week training block, with 10% reduction in time

to compete a time trial lasting about 60 min.An additional variation to the train low ap-

proach was investigated by Morton et al. (2009).Three groups of recreationally active men undertookfour sessions of fixed-intensity high-intensity runningover a 6-week period with either high-carbohydrateavailability (single day training), train low (twotraining sessions twice a week, such that the secondtraining session was undertaken with low glycogen),or train low1glucose (as for the previous group, butwith glucose intake before and during the secondsession). All groups recorded a similar improvementin VO

2max( 10%) and distance run during a YoYo

intermittent Recovery Test 2 protocol ( 18%),although the group who trained with low availabilityof exogenous and endogenous carbohydrate sourcesshowed greater metabolic advantages such as in-creased activity of the mitochondrial enzyme succi-nate dehydrogenase.

The provision of carbohydrate during workoutsduring 6 weeks of matched training (three sessionsper week for 12 h) in moderately active men hasbeen separately studied by De Bock et al. (2008). Agroup who did the same training in the fasted state


55


9/11

showed increases in proteins involved in fat utiliza-tion and a decrease in muscle glycogen utilizationwhen exercise was undertaken in a fasted state.However, increases in exercise capacity were similarin both groups and fat utilization during exercisewith carbohydrate intake was not different. Addi-tionally, the group who undertook the first trainlow study have completed a further 10-week train-

ing study in previously untrained subjects, with oneleg training in the fasted state, while the contralateralleg undertook training while consuming a carbohy-drate drink (Akerstrom et al., 2009). Both legsresponded equally to the training in terms of in-creases in muscle concentrations of glycogen and theenzymes citrate synthase and HAD, as well asincreases in exercise power and endurance. Finally,another study followed cyclists/triathletes who com-pleted 1520 h/week of training over 4 weeks, withone group consuming a moderate carbohydrate in-take ( 5.3 g/kg/day), while a matched group con-sumed an iso-energetic diet higher in carbohydrate(8 g/kg/day) in which the additional carbohydratewas consumed as glucose during and after trainingsessions. Both groups improved their performanceduring a protocol lasting 2 h equally (Cox et al.2010; see Table 1). Clearly, the current literaturebarely scratches the surface of the work that needs tobe carried out on this topic.

Are there other potential rewards and concerns with

train low concepts?

The hypothesized benefits to train low strategiesinclude enhanced metabolic adaptations to a giventraining stimulus, an increased ability to utilize fat asan exercise fuel and a reduced reliance on carbohy-drate. While there is support for such benefits, thereis currently no clear evidence that this translates intoa performance benefit. In athletic circles, train lowstrategies are purported to enhance loss of body fatand reduce the need for carbohydrate intake duringcompetition (reducing the potential for gastrointest-inal side effects by reducing the amount of food orsports drink an athlete might need to consume).These issues have not been studied, although thestudy from our own group (Cox et al., 2010) foundthat training with carbohydrate intake increasesoxidation rates of exogenous carbohydrate with theadaptation presumably occurring at the level of gutuptake.

It is curious that the muscle and metabolic en-hancements do not translate into performance ben-efits. Reasons for this apparent disconnect includethe brevity of the study period, the possibility thatperformance is not reliant or quantitatively linked tothe markers that have been measured, our failure to

measure other counterproductive outcomes and ourfocus on the muscular contribution to performancewhile ignoring the brain and central nervous system.Most importantly, we may again be simply unable tomeasure performance well enough to detect changesthat would be significant in the world of sport.

Meanwhile, it is important to consider the poten-tial for side effects arising from train low strate-

gies. There is already evidence that training lowreduces the ability to train increasing the percep-tion of effort and reducing power outputs. Mostathletes and coaches fiercely guard the ability togenerate high power outputs and work rates intraining as a preparation for competition. Indeed,in our extensive work on another dietary period-ization strategy for athletes adaptation to high-fatdiets before carbohydrate loading for endurance andultra-endurance events we found evidence that theadaptations that we had considered glycogen spar-ing during exercise were, in fact, glycogen impair-ing (for review, see Burke & Kiens, 2006). These fatadaptation protocols enhanced the pathways for fatutilization, at the expense of the activity of pyruvatedehydrogenase, a rate-limiting enzyme in carbohy-drate utilization (Stellingwerff et al., 2006). Hereagain, we could find no evidence of an expectedimprovement in exercise performance, but instead,a reduction in the ability to perform high-intensityexercise (Havermann et al., 2006). This is an impor-tant consideration because the outcome-defining ac-tivities in most sports are conducted at high intensity.Finally, the effect of repeated training with lowcarbohydrate status on the risk of illness (Gleeson

et al., 2004), injury (Brouns et al., 1986) and over-training (Petibois et al., 2003) need to be considered.

Practical implications

1. Currently, we have insufficient evidence to pro-

vide guidelines to athletes for incorporating train

low strategies into their training programs. While

there may be a sound hypothesis that training in a low

carbohydrate environment can amplify the training

response, there is no clear proof that this leads to

performance enhancements. Indeed, there are poten-

tial disadvantages to the health and performance of

the athlete, including the not insignificant likelihood

that training low may interfere with the volume or

intensity of training.

2. In real life, most elite athletes practice an

intricate periodization of both diet and exercise loads

within their training program, which may change

within a macrocycle or microcycle. Either by intent

or for practicality, some training sessions are under-

taken with low carbohydrate status (overnight fasting,

several sessions in the day, little carbohydrate intake

Burke

56


10/11

during the workout), while others are undertaken

using strategies that promote carbohydrate status

(more recovery time, post-meal, carbohydrate intake

during the session). It makes sense that sessions

undertaken at lower intensity or at the beginning of

a training cycle are most suited, or perhaps, least

disadvantaged by train low strategies. Conversely,

quality sessions done at higher intensities or in the

transition to peaking for competition are likely to thebest undertaken with better fuel support. Athletes

may, by accident or design, develop a mix-and-match

of nutrition strategies that achieves their overall nutri-

tion goals, suits their lifestyle and resources, and

maximizes their training and competition perfor-

mances. Finding this optimal balance is the art of

coaching.

3. This art of coaching may not be fully understood

by sports scientists and the complexity of the ideal

approach to training nutrition may not easily be tested

in conventional scientific studies. Nevertheless, the

real challenge for sports scientists is to design studies

with a multifactorial approach to nutrition support,

combined with clever ways to measure performance

outcomes that will mimic the demands of real-life

sport and detect the small improvements that can

differentiate the podium placed athletes from the

rest of the field.

Key words: dietary periodization, carbohydrate in-

take, sports nutrition guidelines.

Acknowledgement

Conflicts of interest: The author has no potential conflicts ofinterest.

References

Achten J, Halson SH, Moseley L, Rayson

MP, Casey A, Jeukendrup AE. Higher

dietary carbohydrate content during

intensified running training results in

better maintenance of performance and

mood state. J Appl Physiol 2004: 96:

13311340.

Akermark C, Jacobs I, Rasmussen M,

Karlsson J. Diet and muscle glycogen

concentration in relation to physical

performance in Swedish elite ice

hockey players. Int J Sport Nutr 1996:

6: 272284.

Akerstrom TC, Fischer CP, Plomgaard P,

Thomsen C, van Hall G, Pedersen BK.

Glucose ingestion during endurance

training does not alter adaptation.

J Appl Physiol 2009: 106: 17711779.

American College of Sports Medicine,

American Dietetic Association and

Dietitians of Canada. Nutrition and

athletic performance. Med Sci Sports

Exerc 2000: 32: 21302145.

American Dietetic Association. Position

stand of the American Dietetic

Association and the Canadian Dietetic

Association: nutrition for physical

fitness and athletic performance foradults. J Am Diet Assoc 1993: 93:

691696.

American Dietetic Association; Dietitians

of Canada; American College of Sports

Medicine, Rodriguez NR, Di Marco

NM, Langley S. American College of

Sports Medicine position stand.

Nutrition and athletic performance.

Med Sci Sports Exerc 2009: 41:

709731.

Baar K, McGee SL. Optimizing training

adaptations by manipulating glycogen.

Eur J Sport Sci 2008: 8: 97106.

Balsom PD, Wood K, Olsson P, Ekblom

B. Carbohydrate intake and multiple

sprint sports: with special reference to

football (soccer). Int J Sports Med

1999: 20: 4852.

Below PR, Mora-Rodriguez J, Gonzalez-

Alonso J, Coyle EF. Fluid and

carbohydrate ingestion independently

improve performance during 1 h of

intense exercise. Med Sci Sports Exerc

1995: 27: 200210.

Brouns F, Saris WHM, Ten Hoor F.

Nutrition as a factor in the prevention

of injuries in recreational and

competitive downhill skiing. J Sports

Med 1986: 26: 8591.

Burke L. Practical sports nutrition.

Champaign: Human Kinetics, 2007.

Burke LM, Cox GR, Cummings NK,

Desbrow B. Guidelines for daily CHO

intake: do athletes achieve them?

Sports Med 2001: 31: 267299.

Burke LM, Kiens B. Fat adaptation for

athletic performance the nail in the

coffin? J Appl Physiol 2006: 100: 78.

Burke LM, Kiens B, Ivy JL.

Carbohydrates and fat for training and

recovery. J Sports Sci 2004: 22: 1530.Chryssanthopoulos C, Williams C. Pre-

exercise carbohydrate meal and

endurance running capacity when

carbohydrates are ingested during

exercise. Int J Sports Med 1997: 18:

543548.

Civitarese AE, Hesselink MK, Russell

AP, Ravussin E, Schrauwen P. Glucose

ingestion during exercise blunts

exercise-induced gene expression of

skeletal muscle fat oxidative genes. Am

J Physiol Endocrinol Metab 2005: 289:

E1023E1029.

Costill DL, Flynn MG, Kirwan JP,

Houmard JA, Mitchell JB, Thomas

RT, Park SH. Effects of repeated days

of intensified training on muscle

glycogen and swimming performance.

Med Sci Sports Exerc 1988: 20:

249254.

Cox GR, Clark SA, Cox AJ, Halson SL,

Hargreaves M, Hawley JA, Jeacocke

N, Snow RJ, Yeo WK, Burke LM.

Daily training with high carbohydrate

availability increases exogenous

carbohydrate oxidation during

endurance cycling. J Appl Physiol

2010: 109: 126134.

De Bock K, Derave W, Eijnde BO,

Hesselink MK, Koninckx E, Rose AJ,

Schrauwen P, Bonen A, Richter EA,

Hespel P. Effect of training in the

fasted state on metabolic responses

during exercise with carbohydrate

intake. J Appl Physiol 2008: 104:

10451055.

Devlin JT, Williams C. Foods nutrition

and sports performance. Final

consensus statement. J Sports Sci 1991:

9(Suppl.). iii.

Ekblom B, Williams C. Final consensusstatement: foods, nutrition and soccer

performance. J Sports Sci 1994:

12(Suppl.): S3.

Fallowfield JL, Williams C.

Carbohydrate intake and recovery

from prolonged exercise. Int J Sport

Nutr 1993: 3: 150164.

Gleeson M, Nieman DC, Pedersen BK.

Exercise, nutrition and immune

function. J Sports Sci 2004: 22: 115

122.

Halson SH, Lancaster GI, Achten J,

Gleeson M, Jeukendrup AE. Effects of


57


11/11

carbohydrate supplementation on

performance and carbohydrate

oxidation after intensified cycling

training. J Appl Physiol 2004: 97:

12451253.

Hansen AK, Fischer CP, Plomgaard P,

Andersen JL, Saltin B, Pedersen BK.

Skeletal muscle adaptation: training

twice every second day vs. training

once daily. J Appl Physiol 2005: 98:

9399.Hargreaves M. Metabolic responses to

carbohydrate ingestion: effect on

exercise performance. In: Lamb DR,

Murray R, eds. Perspectives in exercise

science and sports medicine. Vol 12.

The metabolic basis of performance in

exercise and sport. Cooper Publishing

Company, Traverse City, MI, 1999:

93124.

Havermann L, West SJ, Goedecke JH,

Macdonald IA, St Clair Gibson A,

Noakes TD, Lambert EV. Fat

adaptation followed by carbohydrate

loading compromises high-intensity

sprint performance. J Appl Physiol2006: 100: 194202.

Hawley JA, Tipton KD, Millard-Stafford

ML. Promoting training adaptations

through nutritional interventions. J

Sports Sci 2006: 24: 709721.

Hopkins WG, Hawley JA, Burke LM.

Design and analysis of research on

sport performance enhancement. Med

Sci Sports Exerc 1999: 31: 472485.

Hopkins WG, Marshall SW, Batterham

AM, Hanin J. Progressive statistics for

studies in sports medicine and exercise

science. Med Sci Sports Exerc 2009: 41:

313.

Hulston CJ, Venables MC, Mann CH,

Martin C, Philp A, Baar K,

Jeukendrup AE. Training with low

muscle glycogen enhances fat

metabolism in well-trained cyclists.

Med Sci Sports Exerc 2010; March 25.

Karlsson J, Saltin B. Diet, muscle

glycogen, and endurance performance.

J Appl Physiol 1971: 31: 203206.

Kirwan JP, Costill DL, Mitchell JB,

Houmard JA, Flynn MG, Fink WJ,

Beltz JD. Carbohydrate balance in

competitive runners during successive

days of intense training. J Appl Physiol

1988: 65: 26012606.

Lamb DR, Rinehardt KF, Bartels RL,

Sherman WM, Snook JT. Dietary

carbohydrate and intensity of interval

swim training. Am J Clin Nutr 1990:

52: 10581063.

Maughan RJ, Horton ES Final consensus

statement: current issues in nutrition inathletics. J Sports Sci 1995: 13(Suppl.):

S1.

Morton JP, Croft L, Bartlett JD,

Maclaren DP, Reilly T, Evans L,

McArdle A, Drust B. Reduced

carbohydrate availability does not

modulate training-induced heat shock

protein adaptations but does

upregulate oxidative enzyme activity in

human skeletal muscle. J Appl Physiol

2009: 106: 15131521.

Mujika I, Padilla S. Detraining: loss of

training-induced physiological and

performance adaptations. Part I: short

term insufficient training stimulus.Sports Med 2000a: 30: 7987.

Mujika I, Padilla S. Detraining: loss of

training-induced physiological and

performance adaptations. Part II:

long term insufficient training

stimulus. Sports Med 2000b: 30:

145154.

Noakes TD. Challenging beliefs: ex

Africa semper aliquid novi. Med Sci

Sports Exerc 1997: 29: 571590.

Onywera VO, Kiplamai FK, Tuitoek PJ,

Boit MK, Pitsiladis YP. Food and

macronutrient intake of elite Kenyan

distance runners. Int J Sport Nutr

Exerc Metab 2004: 14: 709719.

Petibois C, Cazorla G, Poortmans JR,

De le ris G. Biochemical aspects of

overtraining in endurance sports: the

metabolism alteration process

syndrome. Sports Med 2003: 33: 8394.

Sherman WM, Doyle J, Lamb DR,

Strauss RH. Dietary carbohydrate,

muscle glycogen, and exercise

performance during 7 d of training. Am

J Clin Nutr 1993: 57: 2731.

Sherman WM, Peden MC, Wright DA.

Carbohydrate feedings 1 h before

exercise improves cycling per-

formance. Am J Clin Nutr 1991: 54:

866870.

Simonsen JC, Sherman WM, Lamb DR,

Dernbach AR, Doyle JA, Strauss R.

Dietary carbohydrate, muscle

glycogen, and power output during

rowing training. J Appl Physiol 1991:

70: 15001505.Stellingwerff T, Spriet LL, Watt MJ,

Kimber NE, Hargreaves M, Hawley

JA, Burke LM. Decreased PDH

activation and glycogenolysis during

exercise following fat adaptation with

carbohydrate restoration. Am J Physiol

Endocrinol Metab 2006: 290: E380

E388.

Tsintzas OK, Williams C, Singh R,

Wilson W. Influence of carbohydrate-

electrolyte drinks on marathon running

performance. Eur J Appl Physiol 1995:

70: 154160.

Vergauwen L, Brouns F, Hespel P.

Carbohydrate supplementationimproves stroke performance in tennis.

Med Sci Sports Exerc 1998: 30: 1289

1295.

Vogt M, Puntschart A, Howald H,

Mueller B, Mannhart C, Gfeller-

Tuescher L, Mullis P, Hoppeler H.

Effects of dietary fat on muscle

substrates, metabolism, and

performance in athletes. Med Sci

Sports Exerc 2003: 35: 952960.

Wright DA, Sherman WM, Dernbach

AR. Carbohydrate feedings before,

during, or in combination improve

cycling endurance performance. J Appl

Physiol 1991: 71: 10821088.

Yeo WK, Paton CD, Garnham AP,

Burke LM, Carey AL, Hawley JA.

Skeletal muscle adaptation and

performance responses to once a day

versus twice every second day

endurance training regimens. J Appl

Physiol 2008: 105(5): 14621470.

Burke

58

train low race high

Documents