Since I started cycling a year ago I have lost 30 lbs and achieved a higher level of fitness. With this new-found fitness level I have begun to try to jog/run. I find that the running is beating myself up. My knees hurt, my back hurts etc... I've got to learn to just stay on the bike! Anyone else ever go through this? I'll be 55 years old this summer, and I am really feeling it.