Patellar tendonitis, osteoarthritis, synovitis and meniscus injury are considered as the causes of knee pain when exerting oneself. 1. Patellar tendonitis: mainly caused by strenuous exercise or too much running and jumping, mainly manifested as pain below the knee, not dare to exert oneself, the symptoms can be alleviated through rest. 2. Osteoarthritis: caused by joint degeneration and hyperplasia, mostly occurring in the elderly, the pain is around the joints, serious joint activity is limited, do not dare to squat. 3. Synovitis, usually caused by walking too much or catching a cold, the pain location in the anterior side of the knee joint, exertion on the pain, through rest, external blood circulation and analgesic medication symptoms can be relieved. 4. Meniscus injury: most have a history of knee sprains, flexion and extension of the knee pain, activities have a loud noise or stuck phenomenon. So the knee pain consider the above cases, pay attention to rest, reduce knee flexion activities, if the pain does not get better go to the hospital for examination and active treatment.