Flexion is the anatomical name for forward bending. When treating back pain, many spine specialists encourage exercises to strengthen the muscles that act to bring the spine into flexion.
In the lower back, approximately 50% of flexion occurs at the hips, and 50% occurs at the lower spine. Motion is divided between the five motion segments in the lower back, although a disproportionate amount of the motion is at L4-L5 (lumbar segment 4 and 5) and L3-L4 (lumbar segment 3 and 4). Consequently, these two segments of the lower back are the most likely to break down and become unstable from osteoarthritis (degenerative spondylolisthesis), with an excess of motion creating low back pain.