Bilateral adaptation during locomotion following a unilaterally applied resistance to swing in nondisabled adults.

Human walking must be flexible enough to accommodate many contexts and goals. One form of this flexibility is locomotor adaptation: a practice-dependent alteration to walking occurring in response to some novel perturbing stimulus. Although studies have examined locomotor adaptation and its storage by the CNS in humans, it remains unclear whether altered movements occurring in the leg contralateral to a perturbation are caused by true practice-dependent adaptation or whether they are generated via feedback corrective mechanisms. To test this, we recorded leg kinematics and electromyography (EMG) from nondisabled adults as they walked on a treadmill before, during, and after a novel force was applied to one leg, which resisted its forward movement during swing phase. The perturbation produced kinematic changes to numerous walking parameters, including swing phase durations, step lengths, and hip angular excursions. Nearly all occurred bilaterally. Importantly, kinematic changes were gradually adjusted over a period of exposure to the perturbation and were associated with negative aftereffects on its removal, suggesting they were adjusted through a true motor adaptation process. In addition, increases in the EMG of both legs persisted even after the perturbation was removed, providing further evidence that the CNS made and stored changes to feedforward motor commands controlling each leg. Our results show evidence for a feedforward adaptation of walking involving the leg opposite a perturbation. This result may help support the application of locomotor adaptation paradigms in clinical rehabilitation interventions targeting recovery of symmetric walking patterns in a variety of patient populations.