The weekly number of hours of vigorous excercise that reasearchers associate with a slower progression of Parkinson's symptoms. 

Young onset PD may progress more slowly, but its symptoms may be felt more intensely, according to the National Parkinson Foundation's Quality Improvement Initiative report.
Habitual excercisers appear less likely to develop Parkinson's, dementia and mild cognitive impairment, according to Mayo Clinic neurologist J. Eric Ahlskog, M.D., Ph.D.

In one study, excercise was found to prevent loss of brain cells, while being sedentary exacerbated cell loss, according to study author Florence Chang, a Mount Sinai movement disorders fellow.