Swedish researchers report [1]:

"'Medium' daily exercise tied to lower risk of Parkinson's disease"

The underlying paper is that found at [2]. The authors write:

"... we found that a medium level of daily total physical activity is associated with a lower risk of Parkinson’s disease, especially in males. The inverse association between physical activity and Parkinson’s disease risk was also observed for higher levels of household activity, commuting activity, and exercise. Our meta-analysis supports the inverse association between physical activity and Parkinson’s disease risk. These findings are important for both the general population and the healthcare of patients with Parkinson’s disease."

Reference

[1] MNT, 19 Nov, 2014
http://www.medicalnewstoday.com/articles/285701.php

[2] "Physical activity and risk of Parkinson’s disease in the Swedish National March Cohort"
Fei Yang, Ylva Trolle Lagerros, Rino Bellocco, Hans-Olov Adami, Fang Fang, Nancy L. Pedersen, Karin Wirdefeldt
DOI: http://dx.doi.org/10.1093/brain/awu323 First published online: 19 November 2014
http://brain.oxfordjournals.org/cont...in.awu323.full

John