Change in Physical Activity Intensity Predicts Change in Percent Body Fat

Abstract The purpose of this study was to determine the extent to which objectively measured physical activity (PA) and intensity of physical activity (INT) predict changes in percent body fat (BF%) over 20 months in middle-aged women. All subjects were age 35-45 at baseline (mean=40.0 yrs), pre-menopausal, non-smokers, and had BMI’s of <30. There were two assessments, one at baseline and another approximately 20 months later. Each assessment consisted of 7 consecutive days of monitoring. Computer Science and Applications (CSA) accelerometers were worn to provide an objective measure of PA and INT BF% was assessed using the Bod Pod. To examine the association between PA and changes in body fat, subjects were divided into three groups based on changes in body fat (increased, maintained, and decreased), then differences in CSA activity counts were compared across groups. To examine INT, subjects were divided into intensity categories in which they accumulated at least seven 10-minute epochs during the test week (70+ minutes duration) at a given intensity range. Change was calculated by subtracting follow-up values from baseline values. Over the 20-month period, mean PA decreased 5.2 %, BF% increased 1.1 percentage points, weight increased 0.78 kg, and energy intake decreased 94.5 kcal/day. Those who increased their PA over the 20 months tended to decrease in BF% (F=5.20, P=0.01). Those who increased INT (F=4.48, P=0.02) or maintained INT (F=2.68, P=0.05) experienced attenuated increases in BF% compared to those who decreased INT. Clearly, physical activity and intensity of physical activity play major roles in the management of body fat in middleaged women.