Additional Study Information: Most neurologists and other clinicians treating people with Parkinsons disease (PD) are still unclear about how best to prescribe exercise despite the fact that it is now axiomatic that exercise is therapeutically beneficial for PD. In contrast, drugs for PD are prescribed with care and specificity due to large scientific investigations showing efficacy and side effects. Exercise has great clinical potential given the ease of implementation, safety, and physiological benefits. However, exercise regimens in PD have not undergone the pipeline of testing in Phase II and phase III trials, unlike their pharmacologic counterparts, leaving many unanswered questions about dosing and efficacy. One exercise option that has the potential to slow the rate of the progression of the signs of PD is endurance (aerobic) exercise that increases heart rate and improves overall fitness. Our goal is to establish if high-intensity endurance exercise is efficacious as first-line therapy for recently diagnosed (is less than or equal to 3 years) people with PD. Our hypothesis is that high-intensity endurance exercise attenuates the progression of the signs of PD.