Effects of strength training on body composition and bone mineral content in children who are obese

The purpose of this study was to test the hypothesis that strength training benefits diet-controlled obese children with respect to lean mass and bone mineral acquisition. Eighty-two Hong Kong school children (aged 10.4 +/- 1.0 years, 70 in Tanner stage 1, 12 in stage 2) who were obese/overweight were randomly assigned to receive either a balanced low-energy (900-1200 cal) diet plus strength training (n = 41) (training group) or the diet alone (n = 41) (control group). The training group attended a 75-minute strength exercise program 3 times/week for 6 weeks (phase 1), after which they were offered and 22 children opted to continue a once-weekly program for a further 28 weeks (phase 2). All children were evaluated at baseline, after 6 weeks, and at the end of the 36-week study (including an intervening 2-week introduction to phase 2). Body composition and bone mineral content were measured by dual-energy X-ray absorptiometry, and diet was assessed by food-frequency questionnaire. The results showed that the exercise programs were well accepted, with good attendance at the exercise classes. After 6 weeks, the children in the training group showed significantly larger increases in lean body mass (+ 0.8 kg [2.4%] vs. +0.3 kg [1.0%], p < 0.05) and total bone mineral content (+46.9 g [3.9%] vs. +33.6 g [2.9%], p < 0.05) than those in the control group. At the end of the study, these trends were maintained in the continued-training subgroup, though no longer reaching statistical significance. We conclude that in diet-controlled prepubertal obese/overweight children, participation in an exercise program with emphasis on strength training resulted in improved lean mass and bone mineral accrual.