Many bike components can affect your knees, and your seat or saddle is just one of those components. According to the late bike mechanic Sheldon Brown, the correct bicycle seat height can improve your speed and efficiency, while incorrect seat heights cause you to use your strength ineffectively and can lead to knee, leg and back pain.
A high seat position causes you to rock your hips from side to side so you can extend each foot to the bottom of the pedal rotation. A low saddle forces you to keep your knees bent at all times. However, human legs are strongest when nearly straight, not when bent or when the knees are locked straight. Riding in either extreme seat position keeps you from achieving your maximum riding power.
When your saddle is set too low, the forces on your kneecap, or patella, damage its cartilage and cause patellofemoral pain. This pain often feels like it is directly under the kneecap. When your saddle is set too high, you might overextend your knee, irritating the iliotibial band or the front or back of your patella. The iliotibial band, or ITB, runs on the outside of your leg from your ilium, part of the pelvic area, to below your kneecap. With ITB injuries, you feel pain above or below your knee from the ITB rubbing against it. The pain is sharp and intermittent at the beginning, but it can develop into a constant dull ache if not treated.
A custom bike fit at a bike shop or sports medicine clinic can lead to the correct seat height. Working with a friend at home, you also can make adjustments to your seat height. Stand in a doorway with your bike and mount your bike, using the door frame for balance. Put your feet on the pedals, and pedal backward until one foot is at the bottom of the pedal rotation. Have your friend examine your leg angle; the angle of the back of your knee should be 25 to 30 degrees. Dismount the bike and make adjustments as necessary.
Drs. Chad Asplund and Patrick St. Pierre, writing for "The Physician and Sportsmedicine," note that one cause of ITB and posterior knee pain is uneven leg length. Saddle height can be a contributing factor, since the shorter leg must reach farther to the pedal. You can solve this problem by adding height to the pedal or installing a shorter crank on the side of the shorter leg.
According to the Australian Physiotherapy Association, you also can eliminate knee pain or discomfort by changing your crank length, your foot position on the pedals and the front-to-back position of your saddle. However, if the pain persists, consult a physician with expertise in sports medicine.