Is the bone response to physical activity related to skeletal maturity? A cross-sectional pQCT examination of children and young adults aged 5-29 Years

Growth is the opportune time to modify bone accrual. The relative responsiveness of the skeleton to loading according to timing in relation to puberty is unclear. The differences in strain that are experienced around the cross-section of a long bone under load are reflected in location-specific adaptative responses. We therefore speculated that examining differences in bone strength parameters at different locations around tibial cross sections between individuals who vary in terms of physical activity exposure and pubertal status may enlighten the question of optimal timing of loading during growth. Data from 304 individuals aged 5-29 years (172 male, 132 female) were examined. Peripheral quantitative computed tomography (pQCT) was applied at 4%, 14%, 38%, and 66% of tibial length. Maturity was established by estimating age at peak height velocity (APHV). Loading history was quantified with the bone-specific physical activity questionnaire (BPAQ). Comparisons, adjusted for height, weight and age were made between sex, maturity, and BPAQ tertile groups. Few to no differences were observed between sexes or BPAQ tertiles prior to APHV, whereas marked sexual dimorphism and differences between BPAQ tertiles were observed after APHV. Cross-sectional location-specific differences between BPAQ tertiles were not evident prior to APHV, whereas clear location-specificity was observed after APHV. In conclusion, the skeletal benefits of physical activity are location-specific in the tibia. The present results indicate that the peri- or post-pubertal period is likely a more favourable window of
opportunity for enhancing cross-sectional bone geometry than pre puberty. Further, increased loading during the peripubertal period may be expected to effectively enhance the bone of both sexes.