Knee pain refers to knee joint pain. The possible causes of knee pain after exercise include physiological phenomenon, meniscus injury, ligament injury, knee synovitis, osteosarcoma and so on. 1. Physiological phenomenon: transient synovial edema of the knee joint after strenuous exercise can cause pain, which is a normal phenomenon and can be relieved by proper rest. 2. Meniscus injury: prolonged hiking, climbing stairs, squatting or jumping down from a high place, trauma, resulting in meniscus injury of the knee joint, meniscus injury aggravated by pain after exercise. 3. Ligament injury: If you fall down in sports, car accident trauma, etc., resulting in medial and lateral collateral ligament, anterior and posterior cruciate ligament injuries, pain will also occur after exercise. 4. Knee osteoarthritis: mostly seen in the elderly, due to advanced age, obesity, prolonged weight bearing, etc., resulting in degenerative changes in the knee joints, osteophytes, articular cartilage damage, and knee pain will also occur after exercise. 5. Osteosarcoma: it is a kind of primary malignant bone tumor, mostly seen in adolescents, with high degree of malignancy, the tumor cells erode the surrounding bone, and pain can appear. The causes of double knee pain after exercise are more, may also be related to popliteal cyst, goosefoot bursitis and other diseases, if the symptoms continue to be unrelieved, it is recommended to consult the doctor in time, to clarify the cause of the disease, and to carry out targeted treatment.