Left leg pain can be caused by physiological factors such as catching a cold and heavy exercise, or it can be caused by pathological factors such as pyriformis syndrome and lumbar spine disease. 1. Physiological factors: due to cold legs can lead to aseptic inflammation of the local muscle fascia, which leads to pain symptoms in the left leg, in addition, when a large number of sports after the accumulation of lactic acid in the legs, can also lead to leg muscle pain, these symptoms can be gradually relieved through appropriate rest, without special treatment. 2. Piriformis Syndrome: This disease is caused by the damage and spasm of the piriformis muscle, which compresses the sciatic nerve and leads to sciatica, resulting in pain in the lower back and buttocks, and at the same time, it causes pain and numbness in the back side of the left leg, and the symptoms can be radiated to the calf and foot. 3. Lumbar spine disease: When there is lumbar disc herniation or lumbar spinal stenosis in the lumbar spine, the nerve root is compressed, which can lead to radiating pain or numbness in the leg. Left leg pain may be caused by many other reasons such as lower extremity venous thrombosis, rheumatoid arthritis, etc. It is recommended that the patient consult a doctor in time to find out the cause of the disease and then carry out targeted treatment.