HIT-Stroke Trial 2

Inclusion Criteria: * Age 30-85 years at time of consenting * Hemiparesis from ischemic and/or hemorrhagic strokes * Most recent stroke for which participant sought treatment, at least 6 months prior to study consent * Walking speed \<1.0 m/s on the 10-meter walk test * Able to walk 10m over ground with assistive devices as needed and no continuous physical assistance from another person (guarding and intermittent assistance for loss of balance allowed) * Able to walk at least 3 minutes on the treadmill at ≥0.13m/s (0.3 mph) * Stable cardiovascular condition (AHA class B, allowing for aerobic capacity \<6 metabolic equivalents) * Able to communicate with investigators, follow a 2-step command and correctly answer consent comprehension questions Exclusion Criteria: * Exercise testing uninterpretable for ischemia or arrhythmia (e.g. resting ECG abnormality that makes exercise ECG uninterpretable for ischemia and no other clinical testing from the past year available to rule out these conditions) * Evidence of significant arrhythmia or myocardial ischemia on treadmill ECG graded exercise test in the absence of recent (past year) more definitive clinical testing (e.g. stress nuclear imaging) with negative result * Hospitalization for cardiac or pulmonary disease within past 3 months * Implanted pacemaker or defibrillator with an upper heart rate limit that would interfere with exercise testing or prescription, or with unknown limit * Significant ataxia or neglect (score of 2 on NIH stroke scale item 7 or 11) * Severe lower limb spasticity (Ashworth \>2) * Known recent history (\<3 months) of unstable substance abuse or unstable mental illness * Major post-stroke depression (Patient Health Questionnaire \[PHQ-9\] ≥ 10) in the absence of depression management by a health care provider * Currently participating in physical therapy or another interventional study targeting walking function * Recent (\<2 weeks) or planned changes in lower limb orthotic or spasticity management * Foot drop or lower limb joint instability without adequate stabilizing device, as assessed by a physical therapist * Clinically significant neurologic disorder other than stroke or unable to walk outside the home prior to stroke * Unable to walk outside the home prior to stroke * Other significant medical condition likely to limit improvement or jeopardize safety as assessed by a physical therapist (e.g. joint contracture, gait limited by pain) * Pregnancy * Previous exposure to fast treadmill walking (\>3 cumulative hours) in the past year