Does a novel school-based physical activity model benefit femoral neck bone strength in pre- and early pubertal children?

The effects of physical activity on bone strength acquisition during growth are not well understood. In our cluster randomized trial, we found that participation in a novel school-based physical activity program enhanced bone strength acquisition and bone mass accrual by 2-5% at the femoral neck in girls; however, these benefits depended on teacher compliance with intervention delivery. Our intervention also enhanced bone mass accrual by 2-4% at the lumbar spine and total body in boys. Introduction We investigated the effects of a novel school-based physical activity program on femoral neck (FN) bone strength and mass in children aged 9-11 yrs. Methods We used hip structure analysis to compare 16-month changes in FN bone strength, geometry and bone mineral content (BMC) between 293 children who participated in Action Schools! BC (AS! BC) and 117 controls. We assessed proximal femur (PF), lumbar spine (LS) and total body (TB) BMC using DXA. We compared change in bone outcomes between groups using linear regression accounting for the random school effect and select covariates. Results Change in FN strength (section modulus, Z), cross-sectional area (CSA), subperiosteal width and BMC was similar between control and intervention boys, but intervention boys had greater gains in BMC at the LS (+2.7%, p=0.05) and TB (+1.7%, p=0.03) than controls. For girls, change in FN-Z tended to be greater (+3.5%, p=0.1) for intervention girls than controls. The difference in change increased to 5.4% (p=0.05) in a per-protocol analysis that included girls whose teachers reported 80% compliance. Conclusion AS! BC benefits bone strength and mass in school-aged children; however, our findings highlight the importance of accounting for teacher compliance in classroom-based physical activity interventions.