I had been having trouble with my knees and occasionally with my right hip for the last two years. It had gotten to the point that I was avoiding riding. After reading a post in the forums (recumbent I think) about using shorter cranks and spinning more I decided to give it a try. I went from 170mm to 140mm because that is what I had. No more knee or hip pain. Not even so much as uncomfortable. I'm never going back. I may not be fast but at least I can hang in there.