This is an interesting video from a couple years ago of a 58-year old man who has Parksinson’s disease. As you can see, walking is very difficult for him. What was truly remarkable was that despite his advanced PD, he is able to ride a bike. It was astonishing, since despite being unable to walk, he is able to ride a bike almost completely normally. He does need to be helped onto the bike and given a little push to start, but while he is riding, he is capable of doing it on his own. After this discovery, they found that other severe PD patients were also able to ride bikes. They are not sure exactly why they are able to ride bikes, but it must be accomplished through a different mechanism in the brain than walking. Also, since exercise has been shown to slow the progress of PD in animal models, it might be that it would do the same in humans, so those with severe PD might be able to find ways to exercise (like riding a bike) when they cannot do others.
[Video Source-Dr Bloem’s paper in the New England Journal of Medicine]