Aim 3: Determine the impact of 12 weeks of locomotor training on in-vivo muscle metabolic properties, the metabolic cost of walking as well as MMEE in persons with chronic post-stroke hemiparesis. There is emerging evidence that chronic neurologic deficits due to stroke can be improved through intensive, repetitive task-oriented motor training (e.g. locomotor training). The basis for locomotor training (LT) improvements is thought to involve mechanisms of central neuroplasticity that are responsive to fundamental principles of motor learning 37,38,39. In addition, our pilot data demonstrate that LT may also result in peripheral adaptations in the plantar flexor muscles. Thus, the potential seemingly exists to induce both central and peripheral adaptations with this intervention strategy. We expect that LT will attenuate existing deficits, resulting in an increased oxidative capacity and a decreased resting phosphorylation potential in ankle plantar flexor muscles. In addition, LT will result in a reduced MMEE and a reduced metabolic cost of walking, reflective of improved mechanical and metabolic efficiency. We believe it will prove important to describe adaptations in walking mechanics as well as within peripheral muscle that occur following LT and relate them to the metabolic cost of walking. In addition, continued deficits will reflect a need for additional or adjunctive intervention strategies, thus providing information on how to modify or augment future rehabilitation interventions in order to improve individual outcomes.