Standing stability in the frontal plane determined by lateral forces applied to the hip

A method for disturbing standing balance using controlled horizontal forces at the hips is described. Its use is illustrated by two experiments evaluating the effect on hip position of sideways force applied for a fixed period of 5 s. In the first experiment increasing sway in the frontal plane was observed with increasing force (12.5, 25 and 37.5 N). In the second experiment it was observed that sway decreased with stance width. In both experiments there was greater sway at the onset of force than at its termination. The results suggest that the method may offer a simple and reliable method of evaluating the efficacy of neural mechanisms involved in the maintenance of standing balance.