Left side low back pain may be caused by lumbar muscle strain, muscle strain, left side organ disease and so on. 1. Lumbar muscle strain: If the patient’s waist is subjected to prolonged high-frequency activities or prolonged sitting and standing for a long time, it may trigger lumbar muscle strain and lead to fasciitis. It will cause obvious pain. 2. Muscle strain: If the patient does not warm up sufficiently before performing high-intensity exercise or performs physical labor for a long time, the muscle contraction pulls excessive spasm, which may lead to lumbar muscle strain. 3. Left-sided organ disease: left-sided low back pain may be the patient’s left-sided organ lesions, mostly caused by kidney disease, such as kidney stones, nephritis, etc., and may be caused by ureteral stones discharged downward. There may also be many other causes of left-sided back pain, patients should go to the hospital in time to find out the cause and then consult a doctor.