The effect of high-intensity progressive resistance training on adiposity in children: a randomized controlled trial.

Background: High-intensity progressive resistance training (PRT) improves adiposity and metabolic risk in adults, but has not been investigated in children within a randomized controlled trial (RCT). Objective: We hypothesized that high-intensity PRT (8 weeks, twice a week) would decrease central adiposity in children, as assessed via waist circumference. Methods Design/Setting/Participants: Concealed randomization stratified by age and gender was used to allocate rural New Zealand school students to the wait-list control or PRT group. Intervention: Participants were prescribed two sets (eight repetitions per set) of 11 exercises targeting all the major muscle groups at high intensity. Primary Outcome: Waist circumference; secondary outcomes included whole body fat, muscular fitness (one repetition maximum), cardiorespiratory fitness (peak oxygen consumption during a treadmill test), lipids, insulin sensitivity and fasting glucose. Results: Of the 78 children (32 girls and 46 boys; mean age 12.2(1.3) years), 51% were either overweight (33%) or obese (18%). High-intensity PRT significantly improved waist circumference (mean change PRT '0.8 (2.2)'cm vs +0.5 (1.7)'cm control; F=7.59, P=0.008), fat mass (mean change PRT +0.2 (1.4)'kg vs +1.0 (1.2)'kg control; F=6.00, P=0.017), percent body fat (mean change PRT '0.3 (1.8)% vs +1.2 (2.1)% control; F=9.04, P=0.004), body mass index (mean change PRT '0.01 (0.8)'kg'm'2 vs +0.4 (0.7)'kg'm'2 control; F=6.02, P=0.017), upper body strength (mean change PRT+11.6(6.1)'kg vs +2.9(3.7)'kg control; F=48.6, P<0.001) and lower body strength (mean change PRT +42.9(26.6)'kg vs +28.5(26.6)'kg control; F=4.72, P=0.034) compared to the control group. Waist circumference decreased the most in those with the greatest baseline relative strength (r='0.257, P=0.036), and greatest relative (r='0.400, P=0.001) and absolute (r=0.340, P=0.006) strength gains during the intervention.Conclusion: Isolated high-intensity PRT significantly improves central and whole body adiposity in association with muscle strength in normal-weight and overweight children. The clinical relevance and sustainability of these changes in adiposity should be addressed in future long-term studies.