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Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Chapter 9

Human Energy Expenditure During Rest and Physical Activity


Energy Expenditure at Rest

• Basal metabolic rate (BMR)– Energy to maintain vital functions in awake

state

• Resting metabolic rate (RMR)– Energy to maintain vital functions plus

digestion– Measured 3 – 4 hours following a meal


Metabolism at Rest• Resting energy metabolism varies in

proportion to the body’s surface area

• Allometric scaling is used to – Establish a relationship between body size and

a variable such as• Muscular strength

• Aerobic capacity


Effects of Regular Exercise

• Resistance training increases BMR by increasing FFM.

• Endurance training increases BMR without increasing FFM.

• Exercise can offset the age-related decline in BMR.


“Normalcy” of BMR Values

• Compares a person’s measured BMR with “standard metabolic rates” based on age and gender


Estimating Resting Daily Energy Expenditure

RDEE = BMR × m2

• Contribution of diverse tissues– Muscle is more active than fat mass.– The brain has a high metabolic rate.– During exercise, muscle metabolism may increase

nearly 100 times.


Factors that Affect Energy Expenditure

• Physical activity– Largest variable in daily energy expenditure

• Diet-induced thermogenesis (DIT)– Obligatory thermogenesis– Facultative thermogenesis


Factors that Affect Energy Expenditure

• Climate– Hot or cold environments increase energy

expenditure.

• Pregnancy– Increases BMR due to added weight gained

during pregnancy


Energy Expenditure in Physical Activity

• Classification of physical activities by energy expenditure– Intensity– Duration

• Physical activity ratio (PAR)– Determined by ratio of energy required in relation to

BMR• Light work = 1 – 3 × BMR• Heavy work = 6 – 8 × BMR• Maximal work = > 9 × BMR


The MET

MET = metabolic equivalent

– 1 MET = 3.5 mL × kg−1 × min−1

– Exercise intensity described relative to resting rate

– Used to guide or prescribe exercise intensity


Daily Rates of Average Energy Expenditure

• The average U.S. adult spends 75% of the day in activities requiring light energy expenditure.

• In the United States, 300,000 deaths per year result from physical inactivity and poor eating habits.


Energy Cost of Household, Industrial, and Recreational Activities

• Effect of body mass– Weight-bearing exercise– Weight-supported exercise


Heart Rate to Estimate Energy Expenditure

• Heart rate and oxygen consumption– Linear relationship exists– Linearity is not identical for everyone

• Other factors altering heart rate– Temperature – Humidity– Food intake – Body position– Muscle groups worked – Emotions– Static v. dynamic work

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