RecruitingClinical trialVirtual Cycling Environments for Persons With Parkinson DiseaseThis study asks three questions about Persons with Parkinson Disease that use a bicycle for exercise. 1. Does the use of virtual reality increase the intensity and and enjoyment of the experience compared to bicycling without virtual reality? 2. Does the way in which the bicycling (interval compared to continous) is performed affect the experience? 3. How does the way the virtual reality is delivered (with goggles or projected on a screen) affect the experience?