I have the same issue, but I did this pre PD. I have read that exercise creates a positive feedback loop in our dopa mediated reward center in the brain. Essentially it gets slightly "addicted" to exercise, so you want to keep doing it because it released feel good hormones. It is just enough to keep you exercising but not enough to prevent another part of the brain from slacking.

I think for me a lot of it is that I am both skeptical and too hopeful at the same time. I see Nan's results for example and have too high expectations in it truly being disease altering. I am skeptical that is because there is no scientific means for comparison purposes and from what I have read symptoms return if you stop exercising. I think it is definitely good for us and cannot hurt.

BTW, with all respect to our pedaling Parkies, dopamine agonists will just as easily have one of us obsessively exercising. I see it in the YO groups on Facebook. Some are so focused on running that they would only post on it and quickly formed their own groups. Not all judging but we cannot separate how the meds may affect results of exercise for each of us. Further, we could just be tapping back into a compensatory mechanism or finding a new one.

I would like to think that it slows progression, but why do professional athletes or dancers, people with their bodies in peak form, still come down with PD in the first place? I think there is a lot scientists might uncover if they studied this at a deeper level, but I think meds are a confounding factor in all of our research.

On a practical note the easiest way to form a new good habit is to schedule it and reward your self for sticking with it. It helps if you have an exercise partner too.