This randomized study compares effects of duration vs. velocity-based TM training regimens on fitness and ambulatory function in chronic stroke patients. Phase 1 - patients are screened (Mini Mental Status, CESD for depression, alcohol intake survey) and undergo routine medical and CV evaluations and blood labs in VA RRDC Assessment Clinic to establish medical eligibility. Standard neurological evaluations (NIH Stroke Scale, Modified Asworth Spasticity Scale, range of motion and manual motor testing) and review of imaging records assess neurological eligibility, deficit profiles and stroke subtypes. Physician supervised treadmill tolerance test and peak effort constant velocity exercise stress test with vital signs monitoring determine treadmill safety, functional eligibility to participate (must walk 3 minutes at 0.2 MPH with handrail support), and cardiopulmonary safety in response to strenuous exertion. Eligible candidates undergo baseline testing (phase 2) including measures of fitness (VO2 peak, gait economy), ambulatory function and BOLD fMRI of knee movement. Phase 3 - 6 months TM training with either velocity or duration based progression, followed by Phase 4 -repeat of fitness and ambulatory function tests after 3 months, and Phase 5 - repeat of all baseline tests after 6 months training