Neuroprotective therapy (i.e. therapy that slows the disease process) is an unmet medical need in Parkinson's disease (PD). Animal studies have shown that 'intensive' exercise improves motor function and may have neuroprotective properties. The promising animal results have not been translated to patients with PD so far. This is a two-cluster randomised control trial in which twenty patients (10 at each site) will undergo a 6-month exercise intervention on a stationary virtual reality bike and twenty patients (10 at each site)will serve as controls.