This study is researching how exercise can help people with early-stage Parkinson's disease, a brain disorder that affects movement. Participants will be split into two groups, each doing treadmill exercises four times a week, either at a moderate (60-65% of their maximum heart rate) or high intensity (80-85%). The goal is to see if high-intensity exercise can slow the worsening of Parkinson's symptoms over 12 months. The study will involve 370 people aged 40-80 who haven't started Parkinson's medication yet. They will be monitored for changes in symptoms, walking ability, and overall health. The study will take place across 29 locations in the USA and Canada. Participants must have been diagnosed with Parkinson's disease for less than three years and not be on Parkinson's medications. This study lasts for 12 months, with additional check-ins at 18 and 24 months.

• Study Length: 12 months with follow-ups at 18 and 24 months
• Visits: Regular treadmill exercise (4 times a week)
• Eligibility: Ages 40-80, early-stage Parkinson's, no Parkinson's medication