This study is about helping people who have had a stroke and have trouble walking. They will join a special exercise program called High Intensity Interval Training (HIIT) to see if it helps them improve. HIIT involves cycling exercises at Emory University, three times a week for 12 weeks, with each session lasting 25-60 minutes. During some sessions, a small blood test will be done to check how hard their body is working. Participants will also have brain scans with an MRI, which is a special machine that takes pictures of the brain, and motor function tests to check their walking and movement before and after the exercise program.

• Participation is for 14-16 weeks, with up to 42 visits.
• Blood samples will be collected during some exercise sessions.
• Participants must be able to do a stress test or have a doctor's approval to join.

This study aims to find out if exercise can help improve walking speed and how the brain changes in response to it. It's important for people who have had a subcortical stroke and want to try improving their walking abilities.