Moderate to vigorous physical activity and impact loading independently predict variance in bone strength at the tibia but not at the radius in children.

The objectives of this study were (i) to assess whether daily minutes of moderate to vigorous physical activity (MVPA) or vigorous physical activity (VPA) and impact counts (acceleration peaks ≥3.9g) independently predict variance in bone strength in children and youth and (ii) to estimate bone strength gain associated with increases in daily MVPA, VPA, or impact counts. We recorded 7-day activity of 49 participants (mean age 11.0 years, SD 1.7) using accelerometers and estimated radius and tibia bone strength using peripheral quantitative computed tomography. We used linear regression models adjusted for sex, body mass, and muscle area to address our objectives. Daily MVPA (mean 50 min, SD 23) and VPA (mean 17 min, SD 11) or impacts (mean 71 counts, SD 59) did not predict variance in radius strength. Daily VPA (β = 0.24) predicted variance in tibia strength at the distal and shaft sites, and shaft strength was also predicted by MVPA (β = 0.20) and impact counts (β = 0.21). Our models estimated a 3%-6%, 4%, or 4%-11% gain in tibia strength after increasing daily MVPA by 10-20 min, VPA by 5 min, or impacts by 30-100 counts, respectively. In conclusion, daily minutes of MVPA or VPA and impact counts are independent predictors of tibia but not radius strength. Objective recording of activities associated with forearm bone strength and trials testing the efficacy of increasing daily MVPA, VPA, and related impacts on bone strength development in children and youth are warranted.