Physical activity is associated with bone geometry of premenarcheal girls in a dose-dependent manner

Objective. To determine the relationship between habitual physical activity (PA) level and peripheral qualitative computed tomography-determined quantitative tibia characteristics of premenarcheal girls. Methods. Premenarcheal girls matched for age (10-13 years), bone age and maturity level were assigned into: a) low PA group (LPA, n = 25), b) moderate PA group (MPA, n = 17), and c) high PA group (HPA, n = 18). Participants' daily dietary intake, tibia's geometry and serum levels of calcium and vitamin D were assessed. Results. Premenarcheal girls demonstrating HPA exhibited greater pericortical thickness, cross-sectional area (CSA) and bone mineral content (BMC) (p < .001) in cortical bone, greater BMC, volumetric bone density (vBMD) and polar stress strength index (SSIp) in trabecular bone (p < 0.001-0.05) and greater total BMC (p < .05) and vBMD (p < .01) when compared to their physically inactive or moderately active counterparts. MPA exhibited greater values of cortical BMC (p < .01) and SSIp (p < .05) than LPA. Partial correlation analysis (adjusted for BMI) revealed modest associations between PA score and bone geometry parameters (r = 0.36-0.49, p < .05) at 38% of tibia length. Conclusions. Habitual PA affects geometry of both cortical and trabecular areas of a long bone of premenarcheal girls in a dose-dependent manner. Specifically, PA increases both the density and size of cortical bone but only the density of trabecular bone during preadolescence. Given the importance of peak bone mass for future fracture risk, high levels of PA during childhood could be a major target for public health interventions aimed at optimising bone health in prepubertal children when the greatest bone gains occur. (C) 2013 Elsevier Inc. All rights reserved.