Exercise-based correlates to calcaneal osteogenesis produced by a chronic training intervention

Thirty workouts on a gravity-independent device (Impulse Training Systems, Newnan GA) evoked significant calcaneal bone mineral content (BMC, +29%) and density (BMD, +33%) gains. High speeds and impact loads were produced per repetition. We examined exercise performance variables from the 30-workout intervention to identify correlates to delta (∆) calcaneal BMC and BMD variance. Workouts included hip extension and seated calf press exercises done with subject's left legs. ∆ values were obtained from the first and 12th workouts for the hip extension movement, and for the first and 24th workouts for the seated calf press exercise. Per exercise the following variables were quantified: peak force (∆PF), peak acceleration (∆PA), impulse (∆I), and dwell times (∆DT). Dwell times are the elapsed time between the end of the eccentric phase, and the start of the next repetition's concentric phase. Pearson Coefficients assessed correlations between performance and criterion variables. With hip extension ∆DT calculated with data from the first and 12th workouts, there were significant correlations with calcaneal ∆BMC (r = -0.64) and ∆BMD (r = -0.63). With seated calf press ∆DT derived as the difference from the first and 24th workouts, there was a significant correlation with calcaneal ∆BMC (r = -0.48), but only a trend (r = -0.45) with ∆BMD as the criterion. No other variables correlated with significant amounts of calcaneal ∆BMC and ∆BMD variance. Negative correlations infer shorter dwell times evoked greater gains. The gravity-independent device warrants continued inquiry to treat and abate calcaneal losses.