Reactive Response and Adaptive Modifications in Dynamic Stability to Changes in Lower Limb Dynamics in the Elderly while Walking

Abstract

The aim of this study was to examine the reactive responses and adaptive modifications in dynamic stability resulting from a unilateral change in lower limb dynamics in older and younger adults while walking. Eleven older (62- 76yrs) and eleven younger (22-30yrs) subjects walked on a treadmill and performed different gait conditions using an external resistance against lower limb movement. The margin of stability (MoS) at touchdown was calculated as the difference between base of support (BoS) and extrapolated centre of mass. After the resistance was turned on unexpectedly, older adults needed more steps to get back to the MoS baseline level due to a lower increase of the BoS. In the following protocol, a continuous resistance was applied over 11 consecutive steps. Adaptation level in MoS and BoS was lower in the early adaptation phase (trial 1-3) but not in the late adaptation phase (trial 9-11) for the older compared to the younger adults. After removing the resistance, both groups showed similar aftereffects (i.e. increased BoS). Our results indicate that elderly preserve their ability to recalibrate their feedforward motor commands to control dynamic stability during perturbed walking. However, the rate of adaptive improvements and feedback driven postural modifications is diminished in the elderly, increasing the risk of falling.