Body reaction pattern to perturbation during walking.

The aim of this study was to examine the effect of aging on body reactions to perturbation during walking. The subject group comprised 15 young and 15 elderly individuals. Perturbation was produced by abruptly decelerating one side of the walking-belt of a two-belt treadmill for 500 ms during walking. Each subject received 30 perturbations during a 10-minute walking period. Muscle activity in the lower limb muscles and acceleration at the pelvis were recorded using surface electromyographs and accelerometers. Peak values of acceleration following perturbation were significantly greater than in normal walking. Posterior peak values of acceleration appeared prior to anterior peak values of acceleration following perturbation. These outcomes seem to demonstrate that external forces by perturbations act on the center of gravity of the whole body and that external forces work from the rear to the front. In addition, the tibialis anterior muscles demonstrated bilaterally reduced latency of muscle reactions. Latency of the tibialis anterior on the stimulation side was significantly shorter than that on the non-stimulation side. This suggests that perturbation in one leg triggers a righting reaction of that leg within the first 120 ms, facilitating the subsequent stepping reaction of the contralateral leg. Comparisons according to age demonstrated that both the appearance of anterior peak values of acceleration and latency of the tibialis anterior on the non-stimulation side were significantly delayed after perturbation for older subjects. These results suggest that the capacity for postural adjustment during stepping might be deteriorated in elderly individuals.