Soreness and numbness of the left leg may be caused by lumbar disc herniation, sciatica, etc. The right leg is fine. 1. Herniated lumbar intervertebral disc: when the lumbar intervertebral disc is subjected to different degrees of degenerative changes, the fibrous ring of the intervertebral disc ruptures under the action of external factors, resulting in stimulation or compression of the spinal nerve root, which leads to the left leg soreness and numbness. 2. Sciatica: due to the nerve root compression caused along the sciatic nerve pathway, from the lumbosacral region through the thighs, has reached the foot, so that the patient appeared in the left leg soreness and numbness phenomenon. If the symptoms are more serious, it is recommended that patients go to the hospital in a timely manner, under the guidance of the doctor, according to the patient’s specific condition, targeted treatment.