Moderate Versus High Volume Light-Moderate Intensity Exercise for People With Moderate Parkinson's Disease

Veterans with mid to later stage Parkinson's disease (PD) may not be able to work out as hard as they need to, to prevent brain cell loss. Maybe they could work out longer and more frequently to make up for this during their good times and good weeks and then rest during the bad weeks. The investigators will compare how effective working out a lot one week per month with a break of three weeks is to continuously exercising weekly with no breaks in people with mid stage PD. The investigators will look at how fast participants walk per minute, whether they become more physically active, the biochemicals in their blood, and at how stiff their blood vessels are before and after the exercise.