Arm Bone Loading Exercise Is A Weak Predictor Of Shoulder & Elbow Peak Torques

PURPOSE: In 2015, our team created a 3-year arm bone-loading index (BLI3yr) to quantify osteogenic exercise based on magnitude, frequency, and velocity of loading across diverse forms of physical activities. We have shown BLI3yr predicts forearm DXA bone outcomes and muscle mass but have not tested predictive value for Biodex peak torques. We aimed to evaluate BLI3yr prediction of shoulder and elbow peak torques in post-menarcheal females. METHODS: Forty-eight females provided detailed physical activity records for BLI3yr calculation over 3 circum-menarcheal years, leading up to a study visit ~1 to ~2.5 years post-menarche. At the study visit, we measured age relative to menarche date (GYNage, years), body mass (kg), ulna length (cm), non-dominant arm DXA muscle mass (NONarmMM, kg), and upper extremity Biodex peak torques (PkTQs, Nm: Elbow Extension, Elbow Flexion, Shoulder Extension, Shoulder Flexion). Multiple linear regression models were generated to test BLI3yr as a predictor of PkTQs, accounting for GYNage, ulna length, and metrics of body mass or local muscle mass. RESULTS: In regression Model 1, BLI3yr trended towards positive correlations with shoulder PkTQs (see Table 1); BLI3yr was a significant positive predictor of post-menarcheal Shoulder Flexion PkTQ. In Model 2, NONarmMM dominated prediction of all PkTQs. CONCLUSION: With the exception of shoulder flexion PkTQ in Model 1, BLI3yr was a poor predictor of post-menarcheal upper-extremity muscle function. This finding suggests the need for the refinement of a novel muscle-loading index to improve prediction of adolescent motor function development. Combined with BLI3yr, a novel muscle loading index may inform design of exercise interventions to improve adolescent musculoskeletal health.NIH/NIAMS R01 AR54145