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.