Forced use of the paretic leg induced by repeated exposure to constraint force applied to the non-paretic leg of individuals post-stroke during walking

Abstract

Locomotor training has been used to improve walking function of individuals post-stroke. However, the functional gains are relatively small, which may be due to the compensatory movements of the non-paretic leg during locomotor training. Our previous study indicated that applying a constraint force to the non-paretic leg could increase muscle activations of the paretic leg during treadmill walking. It is still unclear whether muscle responses in the paretic leg are acquired through feedback correction mechanisms or feedforward control mechanisms. The goal of this study was to examine electromyography (EMG) responses in the paretic leg to a repeated constraint force applied to the non-paretic leg during treadmill walking. Fifteen individuals with chronic stroke participated in this study. Subjects walked on a treadmill with no force for 1 minute, i.e., baseline. A controlled resistance force was then applied to the non-paretic leg starting from toe-off to mid-swing through a custom designed cable-driven robotic system for 7 minutes, i.e., adaptation period. The force was released and subjects continued walking on the treadmill for another 1 minute, i.e., post-adaptation period. The magnitude of resistance force was ∼18% of MVC of the hip flexion. EMG from 8 muscles of the paretic leg were recorded using electrodes and ankle movement of both legs were measured using position sensors. Integrated EMGs of ankle plantarflexors and hip extensors during stance phase significantly increased (33–50% increase, P < 0.01) during the early and late adaptation periods, and partially retained (17–22%) during the post-adaptation period. Our results suggest that both feedback correction and feedforward control mechanisms may be involved in response to the constraint force applied to the non-paretic leg. Results from this study may be used to develop a long-term training paradigm to induce a forced use of the paretic leg and improve walking function of individuals post-stroke.