As I [not a neuroscientist but a PWP] read the study, there was not anything shown that would say that the critical factor was the forcing of the pace or the high cadence itself.

As they say in Detroit, your mileage may vary.

I have had Parkinson’s symptoms since 2007 and was diagnosed in 2010 with Parkinson’s disease at stage 2. But in July of 2011 my UPDRS rating was 3 out of 160, an excellent rating. Since diagnosis I have biked daily on a stationary bike for nearly an hour and, except for warm up and cool down (beginning and ending 5 minutes), bike at a cadence of between 90 and 110 RPM (depending on how I feel on the bike). I feel good.

As to cramps, after a frustrating round of unanswered questions about mineral deficiencies with medical doctors, I turned to a dietitian (they are regulated in my state, whereas nutritionists are not). She advised supplements and quantities. In addition to calcium and magnesium supplements I added bananas to my diet to provide potassium. You might also want to read works by Dr. Arnie Baker MD who writes on medical issues pertaining to cyclists.

Using bike shorts I avoid burns from friction.

To avoid boredom I do two things. I read from an android tablet and am enjoying old books. I also listen to jigs, reels, and other fast dance music of my ethnicity--there must be some music that is right for you.
Unexpectedly, I found after doing daily biking for a while that my hands would feel pins and needles. Well, I recalled that carpel tunnel syndrome can be aggravated by vibrating machinery. A stationary bike is a piece of vibrating machinery. A pair of anti-vibration gloves solves the problem!

Overall, after two years since initial diagnosis and taking only selegine and CoQ10 [has all the study data been unlocked?] for PD I am better off than before diagnosis, though still showing symptoms.