Brain Stimulation Enhance Post-stroke Walking Survivors and Healthy Adults

Inclusion Criteria: * Age between 21 and 90 years * Medical history of a unilateral stroke occurring ≥ 6 months prior to enrollment * MRI or CT evidence from the imaging report shown that the stroke involves the corticospinal tract * Hemiparesis involving the lower extremity (Fugl-Meyer Lower Extremity Motor Test) * No passive range of motion limitation in bilateral hips and knees * Limitation of ankle passive range of motion to 10 degrees of dorsiflexion or less * Visual acuity can be corrected by glasses or contact lens to 20/20 * Able to walk independently with/without assistant devices for 10 meters * Able to maintain standing position without any assistance \>= 30 sec (Short Physical Performance Battery) * Evaluation of cognitive status: Mini-mental status examination (MMSE) score ≥ 24 Exclusion Criteria: * Pregnant women * MRI or CT evidence of involvement of the basal ganglia or cerebellum, evidence of multiple lesions, or evidence of any other brain damage or tumors * Have any metal implants, cardiac pacemakers, or history of seizures * Ongoing orthopedic or other neuromuscular disorders that will restrict exercise training * Any vestibular dysfunction or unstable angina * Significant cognitive deficits (inability to follow a 2-step command) or severe receptive or global aphasia