A seven-year physical activity intervention for children increased gains in bone mass and muscle strength

Aim: This study evaluated the musculoskeletal effects of increased physical activity on children, starting at six to nine years of age. Methods: In one school we increased the physical education of 72 girls and 100 boys to 200 minutes per week over seven years. In three other schools, 45 girls and 47 boys continued to receive 60 minutes per week. We measured areal bone mineral density (aBMD) with dual energy X-ray absorptiometry and muscle strength with computerised dynamometer at baseline and after seven years and tibial cortical thickness with peripheral quantitative computed tomography after seven years. Results: Girls in the intervention group gained 0.04 g/cm² (0.01-0.08) more total spine aBMD (p <0.05) and 6.2Nm (1.6, 10.7) more knee flexion strength (p <0.01) than control group girls and had a 0.1 mm (0.0, 0.3) higher tibial cortical thickness at follow-up (p <0.05). Boys in the intervention group gained 7.3Nm (0.4, 14.2) more knee extension strength (p <0.05) and 7.4Nm (2.3, 12.4) more knee flexion strength (p <0.01) than the control group boys, but their aBMD was no higher than the control group. Conclusion: A seven-year, population-based moderately intense exercise intervention enhanced gains in spine bone mass in girls and knee muscle strength in both genders.