Subjects with stroke will have behavioral testing and brain imaging before and after a 4-week control period and a 4-week exercise intervention.

Subjects with stroke will have behavioral testing and brain imaging before and after a 4-week control period and a 4-week exercise intervention using high-intensity interval training.

Inclusion Criteria:

• age 30-90 years
• unilateral stroke experienced >6 months prior to enrollment in middle cerebral artery (MCA) territory without complete disruption of the putamen on the lesion side
• 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 physical assistance

Exclusion Criteria:

• MRI incompatibility (e.g. metallic or electronic implants, severe claustrophobia)
• inability to perform mental imagery (time dependent motor imagery screening test [TDMI])
• evidence of significant arrhythmia or myocardial ischemia on treadmill ECG stress test, or significant baseline ECG abnormalities that would make an exercise ECG uninterpretable
• recent (<3 months) cardiopulmonary hospitalization
• unable to communicate with investigators or correctly answer consent comprehension questions
• significant ataxia or neglect (score of 2 on NIH stroke scale item 7 or 11)
• severe lower extremity (LE) spasticity (Ashworth >2)
• recent (<3 months) illicit drug or alcohol abuse or significant mental illness
• major post-stroke depression (PHQ-9 ≥10) in the absence of medical management
• participating in physical therapy or another interventional research study;
• recent (<3 months) paretic LE botulinum toxin injection
• concurrent progressive neurologic disorder or other major medical, orthopedic or peripheral vascular conditions that would limit improvement
• pregnancy

Throughout study participation, which lasted approximately 4 months for each participant. The entire study lasted approximately 17 months.

Each study visit, participant voluntary reporting of adverse events (AEs) was encouraged and AEs of interest were specifically queried, including: falls, orthopedic injuries, faintness, new/increased pain and muscle soreness. During clinical testing and training sessions, participants also had monitoring and post-session questioning to identify any signs or symptoms of cardiorespiratory insufficiency, new/worsening neurological impairments or orthopedic injury.

Outcomes Assessor was blinded to study design, including when participant was in control phase versus intervention phase