It is said that it is impossible for Parkinson's disease to be caused by boxing. I have read about Muhammad Ali and it is believed that his Parkinson's was not caused by boxing. I have seen many boxers step out of the boxing ring without Parkinson's. A lot of them are old and retired, but they do not have Parkinson's. They have taken a lot of punches and blows to the head. You would think that they would have the Parkinson's disease, but they don't.
Speculating about the Disease
I'm wondering if Muhammad Ali has taken shots somewhere down the line in his life. I'm sure he has had at least one shot in his life. It is my belief that shots that we take can cause things later on in life. Just because you took a shot and did not have side affects does not mean that it will not bother you later. Doctors and Scientist are finding out things that could be wrong all of the time. One day you might hear about something that was good for you is suddenly not so good for you. It could be something in certain medicines that we are taking to cause us to have some kind of sickness.
Muhammad Ali was so energetic and healthy. It's funny to me how he suddenly ended up with the Parkinson's disease. If doctors could find out what truly causes the Parkinson's disease, then maybe they could really find a cure.