Calf extension pain refers to the pain when flexing and extending the calf, and the possible causes are over-exercise, trauma, degenerative changes in the knee joint, lumbar disc herniation, and so on. 1. Excessive exercise: after strenuous exercise, long-distance running and other activities, due to the accumulation of lactic acid in the calf muscles, resulting in pain when flexing and extending the calf, which is a normal phenomenon and can be relieved after appropriate rest. 2. Trauma: because of violence caused by calf skin, gastrocnemius muscle, flounder muscle and other soft tissue injuries, calf flexion and extension activities, the injured tissues are pulled, the symptoms of calf pain can occur. 3. Knee degeneration: mostly seen in the elderly, can be caused by old age, obesity, chronic strain and other causes of joint degeneration and cartilage destruction, calf activities, the knee joint lack of articular cartilage cushioning effect and pain. 4. Lumbar intervertebral disc herniation: due to the degeneration of the intervertebral disc, the nucleus pulposus protrudes and oppresses the nerve root at the back, common symptoms include lumbar pain, lower limb pain, numbness, etc. Changes in the position of the calf during the calf activity can induce or aggravate the pain of the calf. Causes of pain when flexing and extending the calf are more reasons, may also be related to gout, goosefoot bursitis, fasciitis, varicose veins of the lower limbs and other diseases, if the symptoms continue to be unrelieved, it is recommended to consult a doctor in time, to clarify the cause of the disease, and targeted treatment.