Body Pains Explained - Knee

Knees

Cycling, done properly, is much less stressful to the knees than many other aerobic activities, because there's no impact involved. Nevertheless, knee injuries do occur, again usually as a result of poor technique or position.

Gear Selection
A principal cause of knee problems is over-stress caused by using too high a gear.

Saddle Height
Another common cause of knee problems is incorrect saddle adjustment, particularly if the saddle is too low.

Cleat Adjustment
Some knee problems result from incorrect placement of shoe cleats. Everybody has a natural angle that their feet take when cycling. When you ride with plain pedals, your foot assumes this angle, and everything is fine.

However, if you use cleated shoes and matching pedals, it is important that the cleat is adjusted so as to permit your foot to be at its natural angle. If your cleats are misadjusted, the resulting twist on your lower leg will affect the alignment of the knee joint, and cause problems.

This is less of an issue if you ride pedals with "float" in the cleat attachment. Most newer clipless pedals offer at least some float.

Lateral Movement - Chondromalacia
The knee joint is basically a ball-and-socket joint, with the ball at the bottom of the femur and the socket at the top of the shinbone. A common cycling-related injury is called "chondromalacia", and has to do with irritation of the cartilage pad in the "socket" which provides lubrication for this joint.

Chondromalacia is often blamed on lateral movement of the joint, and a common prescription is to strengthen the quadriceps muscles which run along the front of the thigh and along side the front of the kneecap. It is these muscles which provide lateral positioning for the joint.

Long Cranks
The longer your cranks are, the further your knees will have to flex on each stroke. Different riders will have different amounts of flexibility, but riding with longer cranks than you are used to can definitely cause problems.

Source: cobr