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Physical Activity
TAKEAWAY MESSAGES:
Energy Expenditure and Metabolism
1. Total energy expenditure consists of resting metabolic rate (RMR),
PA, and diet thermogenesis.
2. For most individuals, RMR represents ~70% of total daily energy
expenditure.
3. For individuals without excess body fat, skeletal muscle, liver, brain,
heart, and the digestive system each account for ~10–20% of RMR,
totaling about 75% of the total RMR. The kidneys, adipose tissue,
and residual tissue make up the remaining 25%. of total RMR.
4. NEAT varies among individuals and can range between 150–500
kcal/day (often greater than bouts of physical exercise). NEAT
may help account for the perception that some individuals more
easily maintain a healthy body weight despite similar caloric
intake and dedicated physical exercise.
5. Direct calorimetry estimates energy expenditure via measurement
of heat generated by an organism in an enclosed chamber.
6. Indirect calorimetry estimates energy expenditure by measuring
carbon dioxide production and/or oxygen consumption using a
metabolic cart or a portable device.
7. Resting energy expenditure can be estimated by calculations
(Harris-Benedict and Mifflin St Jeor Equations.)
8. Doubly labeled water (used primarily in research settings)
estimates energy expenditure via oral administration of
traceable hydrogen and oxygen isotope, and the estimation of
carbon dioxide production, reflecting energy expenditure due to
tissue respiration.
9. Physical activity expenditure can be estimated by wearable
technologies, such as smart watches, pedometers, and
accelerometers.
10. Alterations in efficiencies and inefficiencies in physiologic and
behavioral process can alter energy expenditure.
