Determining the effects of increased demands for voluntary adjustments on the neuromuscular control of walking post-stroke

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Abstract The goal of this proposal is to determine the effects of explicitly driven or implicitly driven walking modifications on muscle activation patterns and co-contraction post-stroke. This work is significant, as studies have shown that muscle activation patterns after neurologic injury cannot generate walking kinematics comparable to those seen in neurotypical individuals; this finding implies that to attain true walking recovery after neurologic injury, interventions should aim to restore the muscle activations underlying walking behaviors. Here, we first explore muscle activations during walking using biofeedback to guide explicit modification of walking patterns, which is a common approach used in clinical and research interventions for walking retraining. We hypothesize that explicit walking modifications might be detrimental at a muscle activation level as they engage cortical pathways for voluntary control that have been interrupted by the stroke lesion, resulting in increased muscle co-contraction. Co-contraction hinders true recovery as it impairs the ability to selectively control different segments during walking, resulting in overreliance on compensatory patterns. We will also explore muscle activation patterns during implicit walking modifications. We will use external modifications in the walking environment, mainly split-belt adaptation followed by tied belt walking, to assess if implicit modifications of walking that rely less on cortical neural control are associated with levels of co-contraction comparable to neurotypical controls—an indication that implicitly-mediated modifications could be a more effective approach to restore muscle activation patterns during walking post-stroke. In this study, we will assess co-contraction during walking in people post-stroke as they reduce asymmetry in step lengths guided by explicit biofeedback (Aim 1) or implicitly following split-belt adaptation and washout (Aim 2). Our central hypothesis is that given differences in the neural control of explicitly- vs. implicitly-mediated walking modifications, we will observe greater levels of co-contraction with interventions that rely on explicit compared to implicit control. Supplementing this central hypothesis, we also predict that co-contraction will be associated with motor impairment, and in more impaired individuals co-contraction will be exacerbated by explicit modifications given the reliance on lesioned cortical pathways. Our results will identify the tasks and conditions that can reduce co- contraction to promote restoration of neuromuscular control post-stroke. This proposal aligns with the NCMRR research priority to develop objective markers of treatment response and functional progress that predict rehabilitation treatment response and enable the tailoring of interventions to the needs, abilities, and resources of the person with disability.