Arm bone loading index predicts DXA musculoskeletal outcomes in two samples of post-menarcheal girls

OBJECTIVE A site-specific bone loading index was developed to predict post-menarcheal arm bone mass, geometry, areal density and non-bone lean mass using organized activity records. METHODS Two cohorts of post-menarcheal girls (A= 55, B= 48) met analysis inclusion criteria: (1) Whole body and non-dominant radius DXA scans +1.0 to +2.6 years post-menarche; (2) detailed, organized activity records available for 36 months prior to the focal DXA scan; (3) accompanying anthropometric data. DXA non-dominant arm and radius regions of interest (1/3, Ultradistal (UD)) were evaluated. An arm bone loading index (arm totBLI) was developed and refined to describe >50 activities. Separate regression analyses for Cohorts A&B tested explanatory value of arm totBLI for DXA outcomes, accounting for gynecological age, height and whole body non-bone lean mass. RESULTS In both cohorts, arm totBLI reflecting 3 years of peri-menarcheal activity exposure exhibited strong explanatory value for post-menarcheal radius and arm outcomes (squared semi-partial r =0.07-0.34, p<0.05), except Arm Area. For both cohorts and most outcomes, arm totBLI explained significant variance, even after adjusting for local muscle mass. CONCLUSIONS In two independent cohorts, arm totBLI may consistently indicate osteogenic and sarcogenic properties of represented activities; additional research is necessary for further refinement and validation.