Asymmetries of Ground Reaction Forces among Dancers and Non-Dancers

The purpose of this study was to determine if there were asymmetries in ground reaction forces (GRF) between dancers and non-dancers, and to see the effect of GRF on external (ER) and internal rotator (IR) strength. Subjects performed double- and single-legged jumps on a force plate with a motion capture marker system attached at anatomical landmarks, and then had strength and range of motion (ROM) of their internal and external rotators tested along at degrees of hip flexion. There were no significant differences in GRF between legs for all subjects involved. However, stronger hip ER was negatively correlated with vertical GRF (z-axis), positively correlated with anteroposterior (y-axis) GRF, and higher mediolateral (x-axis) GRF from double-leg trials was positively correlated with knee abduction. Thus, future studies should further investigate GRF broken into axial components as well as the time to peak GRF to determine any relation of these factors to knee valgus and ACL injury risk.