The project aims to evaluate the effects of 24 weeks of treadmill training (TT), with and without a strengthening component, on functional mobility, gait and quality of life in patients with Parkinson's disease (PD). The rationale for a study of this type stems from the hypothesis that treadmill training may act as an external "pacemaker" and enhance some properties of gait. There is a need for larger scale randomized controlled trials comparing the effects of treadmill training to control groups that receive similar amounts of attention. To date, no study has combined TT and muscle strengthening, likely the optimal form of therapy. A kinesiologist supervises the training, 3 times per week, for a total of 72 one-hour exercise sessions. It is hypothesized that at the end of 6 months, treadmill training will considerably improve walking parameters and the well being of people with PD.