Inclusion Criteria1. Age 21-85
2. Chronic stroke (>6 months post stroke)
3. Able to walk at self-selected speed without assistance from another person (assistive devices are allowed)
4. Self-selected walking speed >0.3 m/s and <1.0 m/s
5. Average steps/day <8,000
6. Resting heart rate between 40-100 beats per minute
7. Resting blood pressure between 90/60 to 170/90.
Exclusion Criteria1. Evidence of cerebellar stroke
2. Other potentially disabling neurologic conditions in addition to stroke
3. Lower limb Botulinum toxin injection <4 months earlier
4. Current participation in physical therapy
5. Inability to walk outside the home prior to the stroke
6. Coronary artery bypass graft, stent placement or myocardial infarction within past 3 months
7. Musculoskeletal pain that limits activity
8. Inability to communicate with investigators
9. score >1 on question 1b and >0 on question 1c on the NIH Stroke Scale.