Effects of low- and high-intensity exercise training on body composition and substrate metabolism in obese adolescents

The objective was to investigate the effects of a 3-week weight-management program including moderate energy restriction and exercise training at two intensities (LI:40% and HI:70% V'O2max) on body composition, energy expenditure and fat oxidation rate in severely obese adolescents. Twenty obese adolescents, aged 15-17 years (BMI: 37.5 kg/m2 ; 38.2 % fat mass) participated in this study. Before starting (week 0, W0) and at the end of the weight-management period (week 3, W3), body composition was assessed by a multifrequency tetrapolar impedancemeter (BIA); basal metabolic rate (BMR), energy expenditure and substrate oxidation rate during exercise and post exercise recovery by indirect calorimetry. At W3, body mass and fat mass decreased significantly (p<0.005) in all groups, and the decreases were significantly greater in the LI than in the HI group (-8.1+/-1.6 vs -5.9+/-1.6 kg and -4.2+/-1.9 vs -2.3+/-1.7 kg, p< 0.05, respectively). Predicted V'O2max, expressed in relative values, changed significantly only in the HI group by +0.010+/-0.006 L/(kg FFM x min), (p=0.010). By contrast, no significant changes were observed at W3 in BMR, energy expenditure and substrate oxidation rate during exercise and post-exercise recovery. In conclusion, LI (40% of V'O2max) physical activity favours fat oxidation and it seems advisable to encourage obese adolescents to perform LI physical activity which is more feasible and acceptable than intense exercise.