Dr, Lieberman's theoretical basis, at:

http://www.parkinsonresearchfoundati...349&Itemid=104

http://www.parkinsonresearchfoundati...d=79&Itemid=95

http://www.parkinsonresearchfoundati...=219&Itemid=83

examples of active exercise:

Cycling: Inevergiveup.org, tandem bycicling, static byke.

Examples of passive exercise:
As mentioned by Dr. Lieberman: acceleration therapeutics, EECP,and found elsewhere, blood modulation therapy.