Quadratus Lumborum

coreMusculus quadratus lumborum

The quadratus lumborum is a thick square muscle deep in your lower back, running from the top of your pelvis to your lowest rib. It bends you sideways and stops you being bent sideways.

The quadratus lumborum sits deep at the back of the abdomen, on each side of the lumbar spine and behind the internal organs. It runs from the back of the pelvis up to the lowest rib, with additional attachments onto the sideways projections of the lumbar vertebrae along the way. It is roughly square, which is what its name says.

One side alone bends the trunk toward that side. With the ribcage held still it works the other way instead and lifts the hip on that side — the movement that happens on the swinging leg during walking, which is one of the reasons it works constantly without anyone noticing.

Its most common job in a gym is resisting rather than producing. Carry a heavy weight in one hand and your trunk wants to bend toward it; the quadratus lumborum on the other side is what stops that happening. A single-arm carry is essentially a direct exercise for it.

It also has a role in breathing. It holds the twelfth rib down so that the diaphragm has something firm to pull against, which makes it an accessory muscle of respiration as well as a trunk muscle.

It is often referred to as a cause of one-sided lower back pain, and it sits in exactly the region people point to. Whether it is responsible in any particular case is a clinical question and not one a website should answer.

Training notes

Suitcase carries are the best single exercise for it: a heavy weight in one hand, walking, staying upright. The muscle on the opposite side works isometrically the whole way, which is precisely its job.

Side planks and side bends also load it, the first isometrically and the second through a range. Both train the obliques at the same time, which is convenient rather than a compromise — the two work together in every side-bending movement.

It also works hard during heavy deadlifts and squats, stabilising the lumbar spine against sideways deviation. Any asymmetry in a lift is a demand on it.

Because it is a one-sided muscle, unilateral work matters more here than almost anywhere else. Loading only a dominant side is easy to do and easy to miss.

Anatomy

Origin
  • Iliolumbar ligament and the adjacent posterior part of the iliac crest
Insertion
  • Inferior border of the twelfth rib
  • Transverse processes of the first to fourth lumbar vertebrae
Actions
  • Laterally flexes the lumbar spine to the same side
  • Elevates the ilium when the thorax is fixed
  • Fixes the twelfth rib during inspiration
  • Resists contralateral lateral flexion under asymmetric load
  • Assists lumbar extension when both sides act together
Innervation
Anterior rami of T12–L4

Quadratus lumborum lies in the posterior abdominal wall, deep to the erector spinae and separated from it by the middle layer of thoracolumbar fascia. It arises from the iliolumbar ligament and adjacent iliac crest and passes upward and slightly medially to the twelfth rib, giving slips to the transverse processes of the upper four lumbar vertebrae.

Acting unilaterally it laterally flexes the lumbar spine; with the thorax fixed the same contraction elevates the ipsilateral ilium. Bilateral action contributes to lumbar extension, though this is secondary to the erector spinae. Much of its functional load is eccentric and isometric, resisting lateral flexion toward the opposite side.

Its attachment to the twelfth rib gives it a respiratory role: it fixes the rib against the upward pull of the diaphragm during inspiration, and it is accordingly classed among the accessory muscles of respiration.

Its innervation from the anterior rami of T12–L4 places it with the muscles of the posterior abdominal wall rather than with the intrinsic back muscles, which are supplied by posterior rami — the same distinction that separates it from the erector spinae lying superficial to it.

Under load

It is loaded most directly by unilateral carrying, where it resists lateral flexion toward the loaded side for the duration of the carry.

Lateral flexion under load — side bends — trains it through a range, and it acts with the ipsilateral obliques in doing so.

It is active during bilateral heavy lifting as a stabiliser of the lumbar spine against asymmetric deviation, which makes unilateral loading a more specific stimulus than bilateral work.

Exercises

No exercise in the library names Quadratus Lumborum yet. Nothing has been invented to fill the gap — a false reference costs more than an absent one.

Antagonists

Synergists