A method for continuous monitoring of the ground reaction force during daily activity

Theoretical models and experimental studies of bone remodeling have identified peak cyclic force levels (or cyclic tissue strain energy density), number of daily loading cycles, and load (strain) rate as possible contributors to the bone modeling and remodeling stimulus. To test our theoretical model and further investigate the influence of mechanical forces on bone density, we have focused on the calcaneus as a model site loaded by calcaneal surface tractions which are predominantly determined by the magnitude of the external ground reaction force (GRF). During daily activity the body is subjected to a random external loading history supplied primarily by the GRF consisting of body weight (BW) plus inertial forces (related to intensity of activity) accelerating the body center of mass. We have hypothesized that monitoring the vertical component of the GRF (GRFz) may provide a useful method of quantifying activity level in order to investigate the influence of mechanical forces on muscle and bone. GRF loading histories among individuals are known to vary greatly in peak force levels and daily cycles and we suggest these differences may be reflected in differences in lower limb musculoskeletal properties. We report here development of instrumentation to monitor the vertical component of the ground reaction force during normal daily activity.