I have always been an advocate of exercise. I am 70 and had PD approx 9 yrs. I have been recently deteriorating more quickly. As a consequence my exercise program has consisted only of the treadmill 3 to 4 times a week and very light weight lifting.
This site has been in favor of 1 hour of exercise on a stationary bike 3 to 4 times a week at 80 rpm. I reviewed bike ratings and purchased a highly rated one for $350. It is a great bike but I have very little experience with bikes so can't be relied upon for an opinion.
I didn't believe I could ride a bike for an hour but so far have not had a problem. The bike doesn't have a RPM monitor so I rode it at what I gaged was 80-90 rpm.
I have only done riding 2 times with a day of rest in between.
I know this is to early to offer my opinion but the improvements are so material I thought I should comment.
I had depression in the afternoon every day... that is gone. I was unable to walk in balance, that is much better. A shower before had me concerned about falling now I feel stable. I had back pain that is greatly improved. My attitude is positive.
The reason I write is if you have a bike and haven't used it I would encourage you to use it. I am not suggesting you buy a bike on my 3 day experience.
I will write again in the future when I have more time using the bike.