Quadratus Lumborum: Definition, Function & Innervation

Instructor: Dan Washmuth

Dan has taught college Nutrition, Anatomy, Physiology, and Sports Nutrition courses and has a master's degree in Dietetics & Nutrition.

Did you know that the quadratus lumborum muscle is often considered both an abdominal AND back muscle? Learn why this is, as well as other great information about this muscle, in this lesson.

Quadratus Lumborum

Go ahead and feel your quadratus lumborum muscle...

If you are like most people, you have no idea where this muscle is located. However, you are about to learn exactly where this muscle is found. Just follow these simple steps:

  1. With your fingers, find your iliac crest (hint: it's the top of the hip bone located in your lower back)
  2. Now move your fingers about 1-2 inches above this bone

Congrats, you have just found your quadratus lumborum muscle! (Yes, it was that easy.)

The quadratus lumborum muscle is located at the back of the abdominal wall, near the lower back.

Quadratus Lumborum: Definition

The quadratus lumborum muscle is the body's deepest abdominal muscle, located at the very back of the abdominal wall. In fact, the quadratus lumborum muscle is so far back in the abdominal wall that it is often considered a back muscle (a point reiterated by the fact that you found your quadratus lumborum muscle by feeling your lower back).

The name of this muscle comes from the Latin words quadrus, which means square, and lumbus, which means loin. Therefore, the name quadratus lumborum simply means square loin, a reference to the shape and location of this muscle. The quadratus lumborum muscle is also very think and takes up a lot of space in the abdominal cavity.

Quadratus Lumborum: Function

There are several functions of the quadratus lumborum muscle. These include:

  • Maintaining correct posture by stabilizing the vertebral column and the pelvic bone
  • Back extension: bending the back backwards
  • Side flexion: bending the back to each side
  • Stabilizing the 12th rib (the lowest rib) during forced exhalation

Interestingly, the quadratus muscle is a common source of lower back pain, especially when someone sits with bad posture all day at a desk job. Since this muscle functions to maintain correct posture of the spinal column and pelvis, it works extra hard when a person sits with improper posture. This constant effort by the quadratus lumborum to maintain correct positioning of the spine and pelvis can lead to the muscle becoming overworked, irritated, and painful.

One of the functions of the quadratus lumborum muscle is side flexion, which allows a person to bend to their sides.
side bend

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