The tendon pain at the back of the calf may be caused by fasciitis, muscle strain, cold, lactic acid deposition, lumbar disc herniation, pyriformis syndrome and so on. 1. Fasciitis: Calf fasciitis tends to make the fascia edema and bleeding, which will make the localized calf muscle pain, dyskinesia, soreness and other symptoms. 2. Muscle strain: It will cause localized swelling, vague pain, stiffness and difficulty in movement of the calf muscle, and at the same time, it will cause pain and discomfort in the tendon. 3. Cold: Cold will stimulate the calf fascia, which will show localized soreness and recurring pain, accompanied by activity difficulties and discomfort. 4. Lactic acid deposition: Most of the time, lactic acid deposition is caused by overexertion or participation in strenuous sports, which leads to lactic acid deposition in the muscles and causes irritating swelling and pain. 5. Lumbar disc herniation: Herniated discs usually lead to compression of nerves and blood vessels in the lumbar region during the period of illness, resulting in poor blood circulation in the legs, which can easily lead to symptoms of leg pain. 6. Piriformis syndrome: Piriformis syndrome usually occurs when the sciatic nerve is compressed in the buttocks, so that the nerves in the legs are compressed, which may easily lead to pain in the hamstrings behind the legs. There are many reasons for this symptom, you need to go to the hospital in time to do the relevant examination and treatment, which is conducive to controlling the development of the disease, preventing the work and life from being seriously affected, speeding up the recovery of the disease, and avoiding the excessive exertion of the lower limbs and strenuous exercise within a short period of time.