I tend to challenge the results of the studies on exercise for PD somewhat. I agree that exercise will help keep us fit and somewhat limber. However, when one exercises endorphins are released in the body. Endorphins make you feel good to the point some actually feel high as if they were taking a drug. Seems kind of funny to me that all of a sudden just because someone did a study now the #1 recommendation for PD is to exercise.

From en.wikipedia.org/wiki/Endorphin

Classically, μ opioid receptors are presynaptic, and inhibit neurotransmitter release; through this mechanism, they inhibit the release of the inhibitory neurotransmitter GABA, and disinhibit the dopamine pathways, causing more dopamine to be released. By hijacking this process, exogenous opioids cause inappropriate dopamine release, and lead to aberrant synaptic plasticity, which causes addiction. Opioid receptors have many other and more important roles in the brain and periphery however, modulating pain, cardiac, gastric and vascular function as well as possibly panic and satiation, and receptors are often found at postsynaptic locations as well as presynaptically.

Exercise in itself does nothing to stop or alter PD. It only tricks our bodies into a false sense of well being.
GregD