Physical activity in the post-pubertal period is associated with maintenance of pre-pubertal high bone density-- a 5-year follow-up

OBJECTIVE: To evaluate the association between physical activity (PA) and skeletal growth in girls during adolescence. DESIGN: A 5-year, observational, population-based study (Reykjavik, Iceland). Subjects: Seventy-eight Caucasian girls, mean age 13.4+/-1.0 (mean+/-SD) years at baseline. METHODS: Bone mineral density (BMD, g/cm2) and bone width (cm) were measured in the forearm by single-photon absorptiometry at baseline and with dual-energy X-ray absorptiometry after 3 and 5 years, when lumbar spine, femoral neck (FN) and total body were also evaluated. Half of the physically active girls were compared with the other half of less active girls. RESULTS: BMD in physically active girls was higher in the forearm at both baseline (P=0.001) and after 5 years (P=0.04) in comparison with less active girls. BMD was higher for the total body (P=0.0001), spine L2-L4 (P=0.02) and FN (P=0.002) in the active girls at age 18. The accrual of forearm BMD and bone width from age 13 to 18 was no different when comparing the two groups. CONCLUSIONS: Pre-pubertal PA is associated with high BMD at age 13 and continued PA is associated with maintenance of high BMD until age 18.