Effects of habitual physical activity on the resting metabolic rates and body compositions of women aged 35 to 50 years

Objective To examine the effect habitual physical activity has on resting m etabolic rate (RMR) and body composition (fat-free mass[FFM], fat mass, and percent body fat) in active compared to sedentary adult women. Design RMR was measured (by indirect calorimetry) twice after a 12-hour fas t at the same point of the menstrual cycle and 48 hours after exercise. FFM , fat mass and percent body fat were measured using whole body air displace ment plethysmography. Energy intake and expenditure were determined using 7 -day weighed-food records and activity logs. Subjects healthy, weight-stable premenopausal women aged 35 to 50 years cla ssified as either active (approximately 9 hours per week of physical activi ty for 10 or more years) (n = 18) or sedentary (approximately 1 hour per we ek of physical activity) (n = 14). Statistical analyses Analysis of covariance was used to investigate differe nces in mean RMR (kcal/day) between the groups adjusted for FFM, and indepe ndent t, tests were used to determine differences in demographic, energy ex penditure, and diet variables. Results Percent body fat and fat mass were lower (P < .0005) and RMR (adjus ted for FFM) was significantly higher in the active women (P = .045) compar ed with sedentary controls. In the active and sedentary groups respectively , mean adjusted RMR was 1,510 kcal/day and 1,443 kcal/day, body fat was 18. 9% and 28.8%, and fat mass was 11.1 kg and 18.8 kg. Groups were similar in body mass, FFM,body mass index, and age. Mean energy balance appeared to be more negative in the active group (P = .0059) due to significantly higher mean self-reported energy expenditures (P = .0001) and similar mean self-re ported energy intakes (P = .52) compared with sedentary controls. These dat a indicate that active women who participate in habitual physical activity can maintain lower body fat and a higher RMR than sedentary controls with s imilar body mass, FFM, and body mass index. Applications/Conclusions This research supports and emphasizes the benefits of habitual physical activity in maintaining RMR and lower body fat levels in middle-aged women.