Sudden soreness in the thighs may be related to cold legs, muscle fatigue, hypokalemia and so on. 1. Cold legs: If you have a sudden soreness in your thighs, you should first consider whether your legs are cold. When the legs are cold, it will easily lead to the constriction of blood vessels in the legs, causing ischemia and lack of oxygen in the legs, which will eventually lead to the symptoms of soreness. 2. Muscle fatigue: If prolonged standing or exercise produces too much lactic acid, which cannot be completely metabolized, thus stimulating the muscles and causing localized soreness, it will lead to the phenomenon of sudden soreness in the thighs. 3. Hypocalcemia: Hypocalcemia may cause spasm of gastrocnemius muscle in the thigh area due to the change of calcium ion concentration in the body, which may lead to the symptom of sudden soreness in the thigh. Thigh suddenly very sore, may also be due to other reasons, if through the rest did not get better, need to go to the hospital in time, clear cause and give standardized treatment in a timely manner.