There is good evidence from carefully conducted clinical trials that Tai chi can improve balance and reduce falls in patients with mild-to-moderate Parkinson's disease. A large number of studies also indicate that regular physical exercise can improve functional mobility and may help with non-motor symptoms. A range of exercise regimes have been designed for Parkinson's patients with different capabilities http://www.parkinsons.org.uk/content/keeping-moving-exercise-and-parkinsons-booklet-and-dvd and Tai Chi lessons are available on line http://www.relaxharder.com/.
A rarely mentioned advantage of these therapies is that they are empowering - they are an aspect of our symptom management that we as patients can have control over, deciding which options we pursue, and how much, and for how long. A feeling of being back in the driving seat is therapeutic in its self.