Lateral calf swelling and pain may be caused by physiological factors such as overexertion and prolonged standing, as well as pathological factors such as myofasciitis, varicose veins of the lower limbs or trauma. 1. Physiological factors: if overwork, long-term standing, strenuous exercise, may lead to excessive accumulation of local lactic acid, resulting in muscle soreness, pain, manifested as lateral calf swelling and pain. This kind of situation is a normal phenomenon, no need to worry too much, generally can be relieved after rest. 2. Myofasciitis: the cause of myofasciitis is not yet clear, may be due to cold, fatigue, trauma, improper posture and other factors. The main symptoms of myofasciitis are local muscle pain, muscle tension, limited activities, especially in the morning or cold, the symptoms are aggravated, may appear on the outside of the calf swelling and pain. 3. Varicose veins of the lower limbs: Varicose veins of the lower limbs are mainly caused by structural abnormalities of the vein walls and venous hypertension. The symptoms of varicose veins in lower limbs are mainly due to the abnormal structure of vein wall and venous hypertension, which can be manifested as soreness, mild edema, muscle spasm, etc., and pain in the outer side of calves. 4. Trauma: Painful lateral calf swelling is also considered to be caused by trauma, which is accompanied by localized swelling and activity limitation and other symptoms. There are many other causes of lateral calf pain, such as lumbar disc herniation, etc. If rest does not relieve, it is recommended to go to the hospital in a timely manner to improve the relevant examination, so as to clarify the cause of the disease, and comply with the doctor’s instructions for targeted treatment, so as to avoid delays in the condition.