The most common long-term injury when running is the runner’s knee, pain behind the kneecap during running. You probably have a runner’s knee if your kneecap hurts when you walk or run, especially when you go down stairs; and it hurts a lot when you push the kneecap against the bone behind it. It usually doesn’t hurt to pedal a bike.
The back of the kneecap is shaped like a triangle with the tip embedded in a grove on the underside of the bone behind it. During running, the kneecap is supposed to move up and down and not side to side. If you move from side to side, the back of the kneecap will rub against the front lower part of the femur, the long bone of the upper leg, causing pain.
Treatment consists of preventing the patella from touching the bone behind it, which is usually due to the patella being pulled out laterally while the lower leg twists the bone behind it inward medially. When you run, you land on the side sole of your foot and roll inward, causing your lower leg to twist inward. At the same time, three of the four quadruple muscles attached to the patella pull the patella outward and cause the patella to rub against the bone behind it. You can prevent the kneecap from rubbing by using braces, special inserts in your shoes, doing exercises to strengthen the muscle that pulls the kneecap inward. Surgery is rarely necessary.
A study from Long Beach VA Hospital in California shows why runners are much more likely to suffer from knee pain than cyclists. When you run, you land on the outside of the sole of your foot and roll inward toward the big toe, called pronation. This study shows that the amount of internal torsion in the lower leg during running is related to how straight the knee is. Bending the knee reduces internal torsion and the friction of the kneecap against the bone behind it. Therefore, people with a runner’s knee can pedal a bicycle with their seats lower than normal to prevent their knees from straightening, they can use special inserts in their shoes that restrict pronation, and they can do special exercises that strengthen the knee. vastus medialis muscle above the patella. that pulls the kneecap inward when running or pedaling.