Patellofemoral pain is also commonly referred to as "runners knee". The condition arises when here is a mismatch between the muscles that control the position of the kneecap during movement. Commonly this occurs when the lateral muscles of the thigh become excessively overactive and the muscles of the inner thigh become underactive. This often results in a lateral shift of the patella during functional tasks such as walking up and down stairs. Normally the patella is held in a groove by optimal muscle activity. In patello femoral pain the aberrant kneecap position creates inflammation and pain.