High Intensity Interval Training in Chronic Stroke

Inclusion Criteria: * 1\) age 35-90 years * 2\) unilateral stroke experienced \>6 months prior to enrollment * 3\) able to walk 10m overground with assistive devices as needed and no physical assistance * 4\) able to walk 3 minutes on the treadmill at \>.13m/s (0.3mph) with no aerobic exercise contraindications * 5\) stable cardiovascular condition (American Heart Association class B, allowing for aerobic capacity \<6 metabolic equivalents) * 6\) discharged from formal rehabilitation Exclusion Criteria: * 1\) significant resting ECG abnormalities * 2\) evidence of significant arrhythmia or myocardial ischemia on treadmill ECG stress test * 3\) hospitalization for cardiac or pulmonary disease within 3 months * 4\) pacemaker or implanted defibrillator * 5\) lower extremity claudication * 6\) unable to communicate with investigators or correctly answer consent comprehension questions * 7\) severe lower extremity spasticity (Ashworth \>2) * 8\) lower extremity weight bearing pain \>4/10 on visual analogue scale For the transcranial magnetic stimulation substudy, additional exclusions will also be applied. These include large cerebral infarcts or other structural defects with the potential to increase seizure risk, uncontrolled seizures, metal implants and previous craniotomy.