Patients with muscle pain in the left thigh should consider muscle strain, sciatic nerve pain, and fever, as follows: 1. Muscle strain: it may be muscle strain caused by excessive exercise, such as the usual hiking or excessive running, which can cause lactic acid accumulation in the muscle, resulting in muscle soreness in the leg. 2. Sciatic nerve pain: when there is pear-shaped muscle syndrome, the sciatic nerve is abnormally pear-shaped The pain in the back of the thigh can be caused by the compression of the muscle fibers. In the case of lumbar disc herniation, the nucleus pulposus stimulates or compresses the nerve roots, which can also cause radiating pain in the lower limbs, often radiating from the buttocks to the back of the thighs, all the way to the calves and feet. 3. fever and cold: it may be due to the presence of fever and cold, when the fever is high, the body’s basal metabolic rate increases, glycolysis increases, thus causing lactic acid to accumulate in the muscles and joints of the body, causing muscle pain and joint pain throughout the body. This can cause muscle pain and joint pain throughout the body, including, of course, the pain in the left thigh muscle.