I partially tore my ACl and MCL riding BMX and instead of being out of commision for 5-8 months, I went to rehab, during the session the guy told me that riding a bike with clipless pedals would build up the muscles around my knee. So I bought a fixie like 3 years ago and all my knee pains went away. I ride a 48x18 and work as a cook standing up for sometimes 12 hours a day and my knee has been fine. But my bike got jacked about a month ago so I haven't been riding...the knee pain is slowly creeping back....