This study is looking at how exercise affects people with early-stage Parkinson's disease, a condition that affects movement. The study will have 370 participants aged 40-80 who have not started medication for Parkinson's disease. Participants will be divided into two groups, exercising on a treadmill four times a week. One group will aim for a heart rate of 60-65% of their maximum (HRmax), while the other will aim for 80-85% HRmax. The main goal is to see if exercise can slow down the progression of Parkinson's symptoms after 12 months. **Key Points:** - The study lasts for 12 months, with exercise 4 times a week. - Participants should not have started Parkinson's medication. - Participants must be able to perform the exercise and meet health criteria. Eligibility includes being diagnosed with Parkinson's disease for less than 3 years and being aged 40-80. Participants should not have serious health issues or be on certain medications. This study may help find new ways to manage Parkinson's disease symptoms.