The phenomenon of collapse behind the waist, that is, the concave line of the waist is very obvious, which may be caused by the state of the pelvis leaning forward.

The sacrum and coccyx are the posterior lateral walls of the pelvis. When the overall horizontal position of the pelvis is tilted forward, the sacrum and coccyx will also tilt forward, so that the lower half of the lumbar spine will also tilt forward gradually, which will cause the entire lumbar spine to collapse.

Because of the symptoms of lumbar collapse caused by pelvic anteversion, people generally can't rest in supine position for a long time. Once they lie on their backs for a long time, their waist will feel sore.

There are also some people who exercise regularly, especially those who exercise the back muscles and hip muscles, which often make the back muscles and hip muscles in a state of tension, and also pull the entire lumbar spine to collapse.