I was diagnosed with Parkinson's about five years ago.
I asked my doctor what I could do to help myself and questioned whether exercise would be of any benefit (use it or lose it).
He told me "no, just take these (carvadopa/levadopa) pills".
Having a background in engineering and science... I did my *own* research.
I discovered that endorphins promoted the release of dopamine. The slow death of the brain-cells that produce most of your dopamine is the root cause of Parkinson's so I figured that perhaps if I exercised enough to create a release of endorphins, it might help restore some of my dopamine levels.
Tried it... it worked. Now I walk 10-20Km a day (that's 2-4 hours!) and I lift weights (put on an inch and a half of lean-mass around my upper arms).
I also found, during my research, that there are definite links betwee caffeine and dopamine production so I stopped taking the pills and now I use shots of carefully timed espresso during the day to modulate my symptoms to a manageable level.
After five years I'm still (caffeine excepted) drug-free and my symptoms have progress only very slightly. By comparison, I met up with a guy who'd been diagnosed at the same time as me (five years ago) and who'd simply followed his doctor's advice (take these pills). He's now a wobbly mess, suffering from significant levels of diskynesia as a result of the levadopa he's been ingesting during that period.
Subsiquently, in recent years (only *after* I discovered this for myself), the medical community is now strongly recommending exercise as a crucial part of the treatment of Parkinson's. My advice: always do your own research and be prepared to try things for yourself, the medical profession seems to move incredibly slowly when it comes to trying new things.