The Complex Low Back
The low back is a frequent source of complaints. Pain, tension, and dysfunction in the lower back area are all common reports heard by doctors, physical therapists, and bodyworkers. So, why is this area of our body such a magnet for discomfort? In this article, we’ll explore the answer to that question. We’ll look closer at the anatomy of the low back, how it comes together, and see why it could complicate movement and posture.
What is the low back?
There is no official anatomical region called the lower back. Different people may mean different things when they say low back. Generally, though, if we refer to the low back, we would include the tissues and structures within the lumbosacral region. That is, all the tissues and structures on and around the lumbar spine and sacrum.
Bones
The lumbar area of the spine spans a section of five vertebrae from L1 to L5. The sacrum is a single triangular bone just inferior to the lumbar spine. When we’re young, the bones that eventually fuse to become the sacrum are five individual vertebrae. The most inferior of the lumbar vertebrae, L5, articulates with the top of the sacral bone. On each side, our sacrum articulates with the two sides of our pelvis, where the sacrum meets the ilium at the sacroiliac joints. These bony structures and the soft tissue that connects to them loosely define the area that we might consider our lower back.
Muscles
Most superficially, we have the erector spinae muscles and the thoracolumbar aponeurosis. Deep to the erector spinae and attaching to the vertebrae, you’ll find the transversospinales group, including the multifidus and rotatores. Those muscles are often considered part of our core because they are located deep in the body. They are found right up along the spine. Also attached to the lumbar vertebrae are the quadratus lumborum and psoas major, two more muscles that are part of our core. More inferior in the low back region, we have piriformis, gluteus maximus, the coccygeus muscles, and some fibers from the iliacus, which all attach to the sacrum.
The low back is a criss-cross of muscles and associated fascia in several layers and reaching from all directions. Some muscles on the front of our body reach around to the low back or have indirect fascial connections to the lower back. Muscles like the internal and external obliques and the transverse abdominis don’t attach directly to the lumbar spine or sacrum, but could still contribute to a pull on that area indirectly. This is one reason that the low back can show up as an area where we feel pain or tension, even if the source of that tension is not in the lower back itself.
This is why tight abdominals can create compression of the discs by reducing the lumbar curve. Or, a tight psoas muscle can contribute to an increased lordotic curve and an anterior pelvic tilt. Even tension from muscles on the side, such as obliques, can contribute to hiking up a hip or pulling one side of the rib cage down.
Actions in the low back
Movement in the area of the low back happens in the spine, the sacroiliac joints, and to some degree, at the hip joints. The available directions and amount of movement at each of these joints influence what kind of movement is or is not available to us.
The sacroiliac joints, or SI joints, are small, uniquely shaped joints that do only a tiny amount of movement. The hip joints, of course, are ball-and-socket joints that allow the pelvis to move in many directions over our legs. The bone shape of the lumbar vertebrae and the specific way that they glide at the facet joints make the lumbar spine flex and extend much more easily than side-bend or twist.
What influences ease of movement in our lower back?
By looking at all the directions of pull on the low back from the muscles we’ve covered and the influence in all directions by multiple sets of joints that move this area, you get a sense of how complex this area really is. All of these structures and tissues influence movement and tension in the lower back.
You could think of the low back like the section of a big city where multiple interstate highways intersect. There are roads going in every direction, lanes beginning and ending at various points, and multiple on and off-ramps that appear along the way. The combination of all of these potential interactions allows for both the adaptability of this area where our lower and upper body meet. It also creates a seemingly endless potential for compensations if any parts of this whole are tight, injured, or dysfunctional.
The balance of muscle tension between all the different muscles and their associated fascia affects the ease of movement in the low back. And, although there are muscles crossing the low back and supporting it from multiple directions, movement is also restricted by the available movement at the joints in this region. The interrelationship between what kind of movement the joints allow and the tension of the myofascia that further allows or restricts movement leads to the kind of complex situation we have at the low back.
Conclusion
There are many possible reasons for pain and dysfunction in the lower back. The specific details are out of the scope of our topic here. In the big picture, the complex situation created by the number of muscles, joints, and other myofascial structures that relate to each other in the low back makes it vulnerable to potential compensations and dysfunction.