Leg Power and Velocity Predict the Risk of Major Osteoporotic Fractures (MOF): the Osteoporotic Fractures in Men (MrOS) Study

Lower extremity muscle function has been associated with risk of falls and fractures; however, most studies have examined strength (force), but not power (force*velocity). A jump test on a force plate measures weight-bearing power and allows the dissection of peak power into its components, force and velocity. We investigated the association between jump test power measures and MOF risk in 1841 older men (median age 84 yr). Peak jump power (Watt/kg body weight), force (Newton/kg body weight) at peak power, and velocity (m/s) at peak power were measured by jump tests on a force plate. Fractures were identified by triannual questionnaires, with all self-reported fractures confirmed by medical record. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CIs) by continuous (per one SD increment) and across quartiles of jump test measurements. Participants that were excluded from the jump tests were classified into the "lowest" group (referent; N = 599). A total of 136 incident MOF occurred over 5 yr of follow-up. In the multiply adjusted models, one SD increment of peak power/kg body weight was associated with a lower risk of MOF (HR 0.71, 95% CI 0.54-0.92), with a similar risk reduction observed with velocity at peak power (HR 0.76, 95%CI:0.59-0.98). Further adjustment for femoral neck (FN) bone mineral density (BMD) did not attenuate the association. There was significant trend of decreasing MOF with increasing power and velocity. For force, only the highest quartile was significantly associated with lower risk of MOF, but this was not significant after adjusting for FN BMD. In older men, peak leg power and velocity, but not force, predicted MOF risk independent of FN BMD. Power, which incorporates velocity, may play a more important role than force in reducing the risk of a fracture.