If you can’t straighten your waist, it hurts when you straighten it. Consider acute lumbar sprain, lumbar muscle strain, lumbar intervertebral disc herniation and other causes. 1. Acute lumbar sprain: if the lumbar region is suddenly pulled by external forces, it is easy to be damaged, resulting in localized muscle bleeding, hematoma, often manifested as lumbar pain, limited activities. 2. Lumbar muscle strain: chronic aseptic inflammation caused by long-term cumulative injury to the lumbar muscles, often manifested as recurrent lumbar pain, pain aggravated by standing straight or body twisting. 3. Lumbar disc herniation: the essence is that the lumbar disc degenerates, the annulus fibrosus ruptures, and the nucleus pulposus protrudes. In the early stage, the main manifestation is the symptom of lumbar pain when standing or walking in an upright position. There may be other causes of lumbar pain, such as small joint disorders of the lumbar spine and compulsory spondylitis. If the symptoms persist, it is advisable to seek medical attention to identify the cause.