Well, this is interesting. I have arthritis on both knees and I have an excercise bike at home. I got on it the other day to try to excercise and the pain on my left knee left me without air. I can not understand how with bad knees can anyone do this excercise. The only thing I can do is walk and not too fast because sometimes my knee locks and I lose my balance. Just go to a mall and walk. I am almost 60 and I started at 310 lbs. Beeing stuck at 235 for over 9 months.