There are many reasons for lumbar weakness, including lumbar muscle atrophy, lumbar muscle strain, lumbar spine degenerative lesions and so on. 1. Lumbar muscle atrophy: due to long-term bed-ridden inability to move, resulting in lumbar muscle atrophy, get out of bed activities will feel lumbar weakness, easy to lumbar sprain. 2. Lumbar muscle strain: prolonged sitting or standing, prolonged desk work, bending, etc., resulting in lumbar muscle fatigue, usually manifested as recurrent lumbar pain or swelling, which may radiate to the buttocks, and when the pain is severe, it may limit the muscle strength. 3. Lumbar degenerative disease: It is mainly caused by natural aging, excessive fatigue, muscle weakness, etc., which leads to lumbar disc herniation and lumbar spine instability, and results in symptoms of lumbar weakness when exerting force or exertion. 4. Osteoporosis: The more serious osteoporosis may cause pain around the lumbar vertebrae, which is manifested as lumbar weakness with no obvious cause. If weakness occurs, it is recommended to consult a doctor to clarify the cause of the problem and provide targeted treatment.