A 5-year exercise program in pre- and peripubertal children improves bone mass and bone size without affecting fracture risk.

We studied the effect in children of an exercise intervention program on fracture rates and skeletal traits. Fractures were registered for 5 years in a population-based prospective controlled exercise intervention study that included children aged 6-9 years at study start, 446 boys and 362 girls in the intervention group and 807 boys and 780 girls in the control group. Intervention subjects received 40 min/school day of physical education and controls, 60 min/week. In 73 boys and 48 girls in the intervention group and 52 boys and 48 girls in the control group, bone mineral density (BMD, g/cm(2)) and bone area (mm(2)) were followed annually by dual-energy X-ray absorptiometry, after which annual changes were calculated. At follow-up we also assessed trabecular and cortical volumetric BMD (g/cm(3)) and bone structure by peripheral computed tomography in the tibia and radius. There were 20.0 fractures/1,000 person-years in the intervention group and 18.5 fractures/1,000 person-years in the control group, resulting in a rate ratio of 1.08 (0.79-1.47) (mean and 95 % CI). The gain in spine BMD was higher in both girls (difference 0.01 g/cm(2), 0.005-0.019) and boys (difference 0.01 g/cm(2), 0.001-0.008) in the intervention group. Intervention girls also had higher gain in femoral neck area (difference 0.04 mm(2), 0.005-0.083) and at follow-up larger tibial bone mineral content (difference 0.18 g, 0.015-0.35), larger tibial cortical area (difference 17 mm(2), 2.4-31.3), and larger radial cross-sectional area (difference 11.0 mm(2), 0.63-21.40). As increased exercise improves bone mass and in girls bone size without affecting fracture risk, society ought to encourage exercise during growth.