This study looks at how exercise affects memory and thinking in people with Parkinson's disease (PD). Parkinson's is a disease that affects the brain and can cause problems with movement and thinking. Participants will be split into two groups for 12 weeks: one doing aerobic exercise (like walking or cycling) and the other doing stretching exercises. They will exercise three times a week. The study will check if aerobic exercise helps improve memory and thinking more than stretching. It will also look at other things like fitness, sleep, and a brain chemical called BDNF, which helps with brain health.

• The study lasts 12 weeks with 3 sessions each week, each session lasting 30 to 55 minutes.
• Participants must have mild to moderate Parkinson's and be able to walk at least 10 meters.
• People who already exercise a lot or have other health issues that could affect the study cannot join.