Objective: The doubly labeled water method for the measurement of average daily metabolic rate (ADMR), combined with a measurement of basal metabolic rate (BMR), permits the calculation of energy expenditure for physical activity. Thus, the relation between physical activity and body composition (%body fat) can be determined.
Method: We analyzed existing data sets with observations on ADMR, BMR, and %body fat including 290 healthy subjects, age 18-49 y, 146 females and 144 males, from 22 different studies.
Results: In a regression analysis, age explained 3-7% and 5-20% of the variation in %body fat in females and males, respectively. Adding physical activity to the model raised the explained variation in %body fat in males (partial r = -0.35, P < 0.01). A higher level of physical activity was related to a lower %body fat. In females, there was no relationship between physical activity and body composition (partial r = 0.00, n.s.).
Conclusion: In males, there is a significant inverse cross-sectional relationship between activity energy expenditure and percent body fat, whereas no such relationship was apparent in females.