Current approaches for rehabilitation of walking following stroke do not sufficiently restore mobility function. For instance, fewer than 50% of individuals with stroke-induced walking dysfunction recover the ability to walk independently in the community. New breakthroughs in rehabilitation are needed that will target the motor impairments responsible for poor walking function in individuals post-stroke. Functional recovery can occur in response to task-specific neuroplasticity of damaged brain circuitry. The corticospinal tract is an important target for neuroplasticity because it plays an important role for control of walking in humans. Research has shown that, compared to steady state walking, accurate gait modification (ACC) tasks are a potent behavioral stimulus for activating the corticospinal tract. Therefore, the investigators propose that training with ACC tasks (e.g., obstacle crossing/avoidance, accurate foot placement, etc.) may be superior to training with steady state walking (SS) for eliciting corticospinal neuroplasticity and recovery of walking function. Most rehabilitation paradigms have previously focused on SS training. This is largely because therapists consider it premature to progress to ACC tasks when persistent deficits of steady state walking still remain. However, this reasoning might be counter-productive, because training only steady state walking may not sufficiently stimulate neuro-plasticity of the damaged corticospinal pathway. In contrast, ACC training is specifically designed to stimulate corticospinal neuroplasticity. Importantly, since ACC training targets a central mechanism, its benefits are expected to generalize across walking conditions. Furthermore, it is expected to benefit most stroke survivors who possess at least a minimal residual capability to activate the corticospinal tract. ACC training also provides an opportunity to practice tasks that are analogous to challenges encountered in the home and community environments. Accordingly, there is strong mechanistic and practical rationale for ACC training.

A number of earlier studies have cumulatively established exciting preliminary evidence showing that walking function is enhanced by training with ACC tasks. However, no prior study has been specifically designed and sufficiently powered to determine the extent to which the "accurate gait modification" ingredient is crucial for recovery of walking function. Also not known is the extent to which ACC training reduces the neural impairments underlying poor walking function. The central hypothesis of this study is that ACC training will be superior to SS training for increasing walking function and for reducing underlying neural control of the paretic leg in adults with post-stroke hemiparesis. Each intervention will involve twelve weeks of training, 3 days per week (36 sessions total), and will emphasize the motor learning principles of high intensity, repetition and task-specificity. Assessments will be conducted immediately pre-intervention, immediately post-intervention and at a follow-up session 3 months later. Walking function will be measured in the lab and in the "real world". Neural impairment measures will include electromyography-based measures of inter-muscular coordination and corticospinal drive.

The investigators expect that the benefits of ACC training will justify larger randomized controlled trials to optimize the use of ACC training, including timing relative to stroke, combination with other therapeutic approaches, and identifying individuals who are most likely to benefit from this approach. This research is expected to enhance walking function in stroke survivors, including for the 15,000 Veterans who suffer a stroke each year.