Here is my situation. I played a lot of volleyball in my younger days(before kids). Now that the kids are getting older and more self sufficient I took up playing volleyball again. It is competitive volleyball not just a back yard get together thing. I pride myself on my jumping abilities. Yes, I am a clyde, 235lbs 6'2". For some reason I have a talent to jump high. I can still touch a basketball rim. However, after playing for a year or 2 , 2 to 3 times a week my knees said "We had enough fat boy" and started to cause pain, severe at times. It was diagnosed as patellar tendonitis which takes a very long time to go away. I cut my playing time down to maybe 1 month if at all. I have been relegated to a sub, which is OK with me, as long as I get to play sometimes. When I started having all the knee pain, I started riding bike more. This past year I have ridden more then I ever have and my knees feel great. I have been road and MTB riding. I hadn't played Volleyball since last spring and have been playing every other week. My knees felt great. Two Sundays ago, I went for an MTB epic ride of about 15 miles and there was a lot of hill climbing. I had an hour rest between the ride and playing volleyball that night. My knees were pain free while playing and the next 2 weeks after. I rode that following Wednesday and they were still pain free. That was the last time I rode. Then this past Sunday I played volleyball again(1.5 weeks without riding). My knees started to get sore in the 3rd game. Then on Monday through today they hurt like a ......, they hurt alot. I am making a direct correlation between consistently riding my bike and my knees being pain free. When I ride I usually include some decent hill climbing which does not hurt my knees. Can there be degradation in the muscles around the knees when I don't ride? Does the constant motion of riding increase the blood flow around the knee joint to keep things strong in there? I am guessing here but was wondering if any one had any input. I enjoy playing volleyball and riding but the weather has hit the crapper here in Central Pennsylvania and with the day light decreasing, and hunting season in full swing I am finding difficulty fitting in riding time to keep my knees strong. I am cringing going to the gym and ride a stationary(I do have a trainer but I want to be on the road or trails) it's just not the same workout.