Purpose: The purpose of this study was to examine the extent to which changes in nonexercise physical activity contribute to individual differences in body fat loss induced by exercise programs.
Methods: Thirty-four overweight or obese sedentary women (age (mean ± SD) = 31.7 ± 8.1 yr, BMI = 29.3 ± 4.3 kg·m−2) exercised for 8 wk. Body composition, total energy expenditure, exercise energy expenditure (ExEE), activity energy expenditure calculated as energy expenditure of all active activities minus ExEE, sedentary energy expenditure, sleeping energy expenditure, and energy intake were determined before and during the last week of the exercise intervention.
Results: Over the 8-wk exercise program, net ExEE was 30.2 ± 12.6 MJ, and on the basis of this, body fat loss was predicted to be 0.8 ± 0.2 kg. For the group as a whole, change in body fat (−0.0 ± 0.2 kg) was not significant, but individual body fat changes ranged from −3.2 to +2.6 kg. Eleven participants achieved equal or more than the predicted body fat loss and were classified as "responders," and 23 subjects achieved less than the predicted fat loss and were classified as "nonresponders." In the group as a whole, daily total energy expenditure was increased by 0.62 ± 0.30 MJ (P < 0.05), and the change tended to be different between groups (responders = +1.44 ± 0.49 MJ, nonresponders = +0.29 ± 0.36 MJ, P = 0.08). Changes in daily activity energy expenditure of responders and nonresponders differed significantly between groups (responders = +0.79 ± 0.50 MJ, nonresponders = −0.62 ± 0.39 MJ, P < 0.05). There were no differences between responders and nonresponders for changes in sedentary energy expenditure and sleeping energy expenditure or energy intake.
Conclusion: Overweight and obese women who achieved lower than predicted fat loss during an exercise intervention were compensating by being less active outside exercise sessions.