There are many reasons for calf swelling and pain, such as lactic acid accumulation, deep vein thrombosis, traumatic factors and so on. 1. Lactic acid accumulation: excessive calf activity can cause local lactic acid accumulation, such as climbing stairs, climbing mountains, running, long-distance walking, etc. Due to excessive exercise, a large amount of lactic acid is produced, which accumulates locally in the calf and causes calf swelling and pain. 2. Deep vein thrombosis: It occurs in people who have been lying in bed for a long time, after trauma, and the elderly, etc. Deep vein thrombosis is caused by factors such as stagnant blood flow, damage to vein wall, and high coagulation state of blood, which leads to distension and pain in the calf. 3. Traumatic factors: soft tissue injury of the calf due to blows, car accidents and other factors, pain and swelling of the calf, accompanied by obvious local bruising, and in severe cases, there may even be a fracture. The causes of calf pain and swelling are very many, in addition to the above factors, lumbar spinal canal disease, varicose veins of the lower extremities, myofasciitis and other diseases, may also cause calf pain and swelling. It is recommended that patients with calf pain should go to the hospital as soon as possible, and take standardized treatment according to the doctor’s instructions, so as not to delay the condition.