Hidden pain in the side of the left lower back may be caused by trauma, lumbar muscle strain, lumbar disc herniation and other reasons. 1. Trauma: when the patient’s left lumbar region has blunt force or impact and other traumatic injuries, it may lead to bone and lumbar muscle injuries, resulting in the occurrence of left lumbar side hidden pain. 2. Lumbar muscle strain: if long-term stooping work, long standing, excessive weight bearing, sedentary, etc., may cause the lumbar muscles to be in a state of tension for a long time, resulting in lumbar muscle strain, and the condition of hidden pain in the left side of the waist. 3. Herniated lumbar intervertebral disc: When the herniated intervertebral disc causes compression on the left local nerve, it will easily lead to left lumbar flank pain, accompanied by leg numbness and radiating pain and other manifestations. There are many reasons for the hidden pain in the left side of the waist, you should go to the hospital in time, after clarifying the cause of the disease, under the guidance of the doctor to correct treatment.