The Quadratus Lumborum Muscle
The quadratus lumborum muscle is a unique part of our core. It’s an essential part of what connects our lower body to our upper body. It’s a necessary part of twisting, bending, and walking. Despite its important contributions to both static posture and functional movement, people are often unaware of where this muscle is located and unclear on exactly what it does. Read on for an introduction to the quadratus lumborum muscle.
Location
The quadratus lumborum, or QL for short, is actually two muscles. We have one on the right side of our body and one on the left. The name quadratus refers to the roughly square-shaped structure of this muscle, although it’s really more of a rectangle in most people. These two muscles lie deep within our body along the lumbar spine, which is what the name lumborum refers to.
Quadratus lumborum muscle attachments
Each of these two muscles has at least three distinct sets of fibers. There is one set of fibers that runs vertically from the crest of the ilium and the iliolumbar ligament to the 12th rib. A second set of fibers runs at a diagonal from the crest of the ilium to the transverse processes of the lumbar vertebrae. Those fibers typically attach to L1-L4, but there is variation from person to person.
Finally, there is a third set of fibers that run diagonally from the 12th rib to the transverse processes of the lumbar vertebrae. References vary on which specific lumbar vertebrae these fibers connect to, which highlights the variation in these attachments between individuals in the population. These fibers may, in some people, connect to the transverse processes of any of the lumbar vertebrae from L1-L5, but almost always include an attachment to L2, L3, and L4.
Muscle actions of the QL
Our quadratus lumborum muscles can act unilaterally, meaning one QL acts separately and differently from the other. Or, both QL can work together bilaterally, meaning that both QL are contributing to the same action. Additionally, as I’ve just explained, the quadratus lumborum has multiple fiber directions.
So, like other muscles with multiple lines of pull, different sets of fibers within the QL can potentially contribute to different actions. For these reasons, although our quadratus lumborum muscles are small, we can feel the effects of their contraction or resistance when twisting, side-bending, bending forward, and bending backward.
When acting unilaterally, our quadratus lumborum muscles can concentrically contract to contribute to lateral pelvic tilt (commonly called hip hiking) and lateral flexion of the lumbar spine. When acting bilaterally, they may contribute to extending the lumbar spine, but some anatomists suggest the QL muscles don’t create enough concentric force to be significantly involved in that action.
Anatomists do agree that these muscles generally don’t create a lot of concentric force. For that reason, their main action is stabilization and working with other muscles to stabilize, create, or resist movement. The quadratus lumborum muscles contribute to the stabilization of the lumbar spine, sacrum, and sacroiliac joints.
Relates the lower body and the upper body
Because this muscle is so central, it’s relevant to most kinds and directions of movement, and it is intimately related to the rest of the core of the body. It’s an essential part of relating the upper body to the lower body through its connections between the ribcage and spine to the pelvis. QL is one of several muscles that may respond by tightening as part of a larger compensatory strain pattern when there are patterns in the lower body that the upper body is adapting to, for example, a leg length difference. For similar reasons, QL may be part of back pain problems. However, back pain is complex and commonly does not have a single source.
Affects breathing
Finally, our quadratus lumborum muscles are related to breathing actions. Our QL muscles contribute to the position and stabilization of the 12th rib, which affects the support for the diaphragm. Additionally, some QL fibers are continuous with some fibers of the diaphragm and therefore have a more direct relationship on breathing.
Conclusion
The quadratus lumborum is a deep core muscle that runs along our lumbar spine and connects both to our 12th rib and the ilium of our pelvis. Its central location and multiple fiber directions mean that it affects a wide range of movements. Its action is essential for maintaining balanced static posture and for functional movements like walking.
References
Chaitow, L. and J. DeLany. 2011. Chapter 10: The Lumbar Spine. In Clinical Application of Neuromuscular Techniques – The Lower Body. Volume 2 (Second Edition). New York, NY: Churchill Livingstone Publishing.