Physical Activity and Body Composition in Adults
Exercise Science and Sport Management
Rates of overweight and obesity have risen significantly since the 1980's, while levels of physical activity have declined. Reductions in physical activity may explain much of the increased body fatness realized over the past several decades, and increases in physical activity may contribute to improved body composition and weight management. PURPOSE: To examine the relationships among markers of energy expenditure and body composition in adults. METHODS: Participants arrived at the laboratory between 6:00 and 9:00 a.m., having fasted for at least 10 hours. Height and body mass (BM) were measured, and 4-compartment body composition (percent body fat [%BF], fat mass [FM] and fat-free mass [FFM]) was determined using data derived from bioelectric impedance analysis and dual energy x-ray absorptiometry. Resting metabolic rate (RMR) was determined via indirect calorimetry. Participants were then provided with accelerometers to allow for measurement of various markers of physical activity (PA), including physical activity energy expenditure (PAEE), sedentary time (SED), time spent in moderate- to vigorous-physical activity (MVPA), and step counts (STEPS). Accelerometers were worn for 21-28 days, and associations between markers of PA and body composition were analyzed. RESULTS: Absolute expressions of PA (e.g., PAEE, STEPS) were not associated with body composition. However, expressions of PA relative to various fractions of BM were significantly correlated with %BF in both men and women. The strongest predictor of %BF was STEPS.kgFM-1.day-1. Power regression analysis yielded the model, 2907.1(STEPS.kgFM-1.day-1)-0.778 in men (R2 = 0.91), and 820.25(STEPS.kgFM-1.day-1)-0.546 in women (R2 = 0.82). CONCLUSIONS: Physical activity expressed per unit of FM strongly predicted %BF. These findings suggest relative expressions of PA (e.g., STEPS.kgBM-1.day-1 or STEPS.kgFM-1.day-1) may be more efficacious than absolute expressions of PA in developing PA prescriptions for weight management.
Medicine & Science in Sports & Exercise
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