This project aims to determine the effects of the HiBalance program on neuroplastic changes in people with mild to moderate Parkinson´s disease. The main hypothesis is that highly challenging exercise will lead to greater gait and balance ability, increased levels of physical activity and an improved health related quality of life. The investigators further hypothesize that neuroplasticity changes will be seen in corresponding areas of the brain, neuropsychological changes on cognitive test measures, and that exercise will inhibit the degeneration of dopaminergic neurons in the brain through the mediation of neurotrophic factors.