Hi,
Am sorry to hear that you're suffering with RA along with Parkinsons.
I'll second what was said. In my case I have sacroilitiis (inflammation of SI joints). I LOVE exercising. I keep asking my dr about it and he keeps saying it'll help, yet everytime I try (stationary bike, brisk walking or eliptical), I am in that much more pain the next day. So just try it in small amounts and see how your body reacts. Unfortunatley for me, not too well, but for others, it really does help.