Low Back Overextension

by Mark Rippetoe | May 14, 2019

It's not usually a problem for people of normal bodyweight, but lumbar overextension – excessive arch in the lower back – is actually a bigger problem than lumbar flexion because of its injury potential. To see the problem, you'll have to look carefully at the vertebral anatomy of the lumbar area.

The vertebral bodies are the fat parts of the bones in front which are separated by the intervertebral discs, fibrocartilaginous “wedges” that cushion the load-bearing components of the spinal column. But the back side of the vertebrae is composed of the parts of the bones to which attach the muscles that support and control the position of the spine. Bilaterally symmetrical, this structure consists of the pedicles, the transverse processes, the superior and inferior articular processes, and the mammilary processes, the laminae, and the single spinous process located directly posterior.

The lumbar muscles attach to these processes and control the spinal position from the posterior, while the abdominal musculature provides pressure and support from the anterior by contracting between the ribs and the pelvis against the minimally compressible gut contents. The combined action of the back and abdominal muscles support the spine as it transmits the force generated by knee and hip extension to the external resistance being acted against.

The posterior vertebral architecture overlaps itself and is separated by the facet joints formed by the articular processes. The facet joints are synovial joints, with a capsular ligament, articular cartilages, and synovial fluid, similar to the more familiar (and much larger and more robust) knee and hip joints. Their function is to limit motion between the vertebral segments and thereby protect spinal integrity. When the spine is in normal anatomical position (extension) the facet joints are in a neutral position, under tension when the spine is in flexion, and in compression when in overextension.

The spine tolerates flexion pretty well, since the discs are somewhat compressible in all directions, and since the facets are merely being stretched. But overextension (the position of extension beyond normal anatomical extension) impinges the facet joints – it brings them together in the synovial capsule as the spinal curvature increases past the point of normal synovial separation. If it's severe enough, the cartilaginous articular surfaces in the facet joint can grind together. If the overextension results in an injury, it is referred to as a hyperextension, as it would be with any joint.

And if it's loaded with enough weight, or if there is a dynamic component to the loading, the processes and the associated structures can actually fracture. This can be a severe injury. Fortunately, most people are not able to overextend to this extent. It primarily occurs in hyper-flexible underweight women, and men at a light bodyweight who stretch a lot, since a lot of muscle mass restricts the range of motion in this direction. Spondylolisthesis occurs with some regularity in young hyper-flexible gymnasts and other athletes who repeatedly experience spinal overextension.

This is an excellent example of a situation where excessive “flexibility” is just not helpful. When loaded under the bar, your spine needs to be kept in rigid normal anatomical extension, and not overextension. If you are hyper-flexible, do not confuse these two positions, and do not fail to make your abs do their job of limiting spinal extension from the anterior.