An Increase in School-Based Physical Education Increases Muscle Strength in Children.

INTRODUCTION: Children and adolescents are encouraged to maintain a habitually active lifestyle because of the known health benefits associated with regular physical activity, but there are some reports that a high level of activity may be associated with increased fracture risk. This prospective controlled exercise intervention study in pre-pubertal children evaluated if a school-based exercise intervention could enhance growth related gains in muscle strength and muscular function without affecting fracture risk. METHODS: Fractures were registered in 417 girls and 500 boys aged 7-9 years in the intervention and in 836 age-matched girls and 872 boys. The intervention included 40 minutes/day of school physical education for two years whereas the controls achieved 60 minutes/week. In a subsample consisting of 49 girls and 80 boys in the intervention and 50 girls and 53 boys in the control group, body composition was measured by dual X-ray absorptiometry (DXA), muscle strength by isokinetic Peak Torque (PT) of the knee extensors and flexors at 60 and 180 °/seconds by a computerized dynamometer and neuromuscular performance by Vertical Jump Height (VJH). RESULTS: The rate ratio [RR (95% confidence interval)] for children in the intervention group to sustain a fracture was 1.07 (0.66, 1.68). The annual gain in knee extensor PT at 180°/seconds was significantly higher for both girls (p<0.001) and boys (p<0.01) in the intervention compared to the control group. Boys in the intervention group also had a greater annual gain in knee flexion PT at 180 °/seconds (p<0.001) and girls a greater gain in VJH (p<0.05). CONCLUSIONS: An increase in school-based physical education from 60 to 200 min/week enhanced muscle strength in pre-pubertal children without affecting fracture risk.