PHYSICAL ACTIVITY BUT NOT ENERGY EXPENDITURE IS REDUCED IN OBESE ADOLESCENTS

Abstract

BACKGROUND: The influence of physical activity (PA) on body weight in children and adolescents is controversial. OBJECTIVE: To test the hypothesis that the intensity and duration of PA differ between obese and normal-weight adolescents without any difference in energy expenditure estimates. METHODS: We compared physical activity in 18 (10 girls) obese (BMI > 30) adolescents (14–19 y) with that in a matched control group (BMI > 27). Total energy expenditure (TEE) was measured by the doubly labeled water (DLW) method and PA was measured simultaneously with by accelerometry. Physical activity level (PAL) was determined as the ratio of TEE to resting metabolic rate (RMR), and activity energy expenditure (AEE) as TEE minus RMR. Accelerometer data included total physical activity (counts/min/d), accumulated and continuous duration of activity, and continuous 10-min periods spent at moderate intensity or higher. RESULTS: There were no differences between groups in adjusted (ANCOVA) TEE, RMR, and AEE. PAL was significantly lower (P > 0.05) in the obese group. No gender by group interaction was observed. Accelerometer data indicated significant differences between groups in total physical activity (P > 0.001), and in accumulated time (P > 0.05), continuous time (P > 0.01) and continuous 10-min periods (P > 0.01) spent at moderate intensity or higher. CONCLUSIONS: Obese adolescents are less physically active than those of normal weight, but nevertheless there is no difference in physical activity related energy expenditure. The data suggest that physical activity is not necessarily equivalent to energy costs of activity.