Inclusion Criteria:  the diagnosis of first time unilateral stroke more than 6 months before the ability to walk for at least 15 m without person assistance apparent gait deficits upon visual inspection by a trained physical therapist or inability in community ambulation, i.e. walking speed < 0.8 m/s resting blood pressure lower than 150/90 mmHg.  Exclusion Criteria:  older than 75 years inability to follow the experimental instructions or procedures any pain, inflammation, or other conditions that could affect walking medically unstable.