Knee pain is the most common symptom of injury in runners. The most common cause of knee pain in runners is patellofemoral pain syndrome. The hallmark of this syndrome is the gradual onset of pain in the front of the knee, near the kneecap. The pain is worse after sitting for a long time or when going up and down stairs or hills. Another cause of knee pain is iliotibial band syndrome, which affects the outside of the knee and can travel up the outer side of the thigh to the hip.