Quantifying force magnitude and loading rate from drop landings that induce osteogenesis

Drop landings increase hip bone mass in children. However, force characteristics from these landings have not been studied. We evaluated ground and hip joint reaction forces, average loading rates, and changes across multiple trials from drop landings associated with osteogenesis in children. Thirteen prepubescent children who had previously participated in a bone loading program volunteered for testing. They performed 100 drop landings onto a force plate. Ground reaction forces (GRF) and two-dimensional kinematic data were recorded. Hip joint reaction forces were calculated using inverse dynamics. Maximum GRF were 8.5 +/- 2.2 body weight (BW). At initial contact, GRF were 5.6 +/- 1.4 BW while hip joint reactions were 4.7 +/- 1.4 BW. Average loading rates for GRF were 472 +/- 168 BW/s. Ground reaction forces did not change significantly across trials for the group. However, 5 individuals showed changes in max GRF across trials. Our data indicate that GRF are attenuated 19% to the hip at the first impact peak and 49% at the second impact peak. Given the skeletal response from the drop landing protocol and our analysis of the associated force magnitudes and average lending rates, we now have a data point on the response surface for future study of various combinations of force, rate, and number of load repetitions for increasing bone in children.