Inclusion Criteria:  Berg Balance Scale < 42 Self-selected 10 meter gait speed < 0.8 m/s Diagnosis of unilateral stroke > 2 months < 4 months post-stroke Able to ambulate at least 10 feet with maximum 1 person assist Medically stable  Exclusion Criteria:  Presence of neurological condition other than stroke  Serious cardiac conditions (hospitalization for myocardial infarction or heart surgery within 3 months, history of congestive heart failure, documented serious and unstable cardiac arrhythmias, hypertrophic cardiomyopathy, severe aortic stenosis, angina or dyspnea at rest or during activities of daily living)  Anyone meeting New York Heart Association criteria for Class 3 or Class 4 heart disease will be excluded Severe arthritis or orthopedic problems that limit passive ranges of motion of lower extremity (knee flexion contracture of -10 degrees, knee flexion ROM < 90 degrees, hip flexion contracture > 25 degrees, and ankle plantar flexion contracture > 15 degrees) Severe hypertension with systolic greater than 200 mmHg and diastolic greater than 110 mmHg at rest Pain upon ambulation Receiving physical therapy services for mobility and/or gait Living in a skilled nursing facility Any MRI contraindication, including but not limited to the presence of metal, MR sensitive implanted medical devices, or claustrophobia