The pain may be caused by lumbar disc herniation, lumbar muscle strain, lumbar spinal stenosis and other reasons. 1. Lumbar disc herniation: Lumbar disc herniation is mainly due to degenerative changes in the lumbar discs, resulting in structural changes in the nucleus pulposus, annulus fibrosus and cartilage plate, which compresses the spinal nerves or the cauda equina nerve, thus causing lumbar pain and other clinical symptoms, and the pressure on the nerves and other soft tissues is aggravated when bending down, which makes it painful when bending down. 2. Lumbar muscle strain: lumbar muscle strain is a chronic injury to the lumbar muscles and their attachment points of fascia or periosteum of inflammation, resulting in recurrent widespread lumbar pain, and in severe cases, even limited activities, bending and other actions will aggravate lumbar injuries to the point that when you bend over, it hurts. 3. Lumbar spinal stenosis: lumbar spinal stenosis is caused by hypertrophy and hyperplasia of the ligamentum flavum, bulging and protruding intervertebral discs, bony degeneration and other causes of the lumbar spine, central canal, neural root canal, or the lateral fossa of narrowing, so that the cauda equina nerve, the peripheral nerve roots and other compression, a series of symptoms, which is the most common when bending down and pain, but also can be accompanied by urinary and fecal dysfunction and other symptoms. There may be other reasons for the pain when bending over, so it is recommended to consult a doctor in time to avoid aggravating the pain symptoms.