Lower BackSource-checked

Quadratus lumborum

Pronunciation: kwah-DRAY-tus lum-BOR-um

For beginners

A deep side-of-the-low-back muscle that bends you sideways and helps keep your pelvis level, for example when you carry a heavy bag in one hand.

Show the advanced explanation

Because it links the pelvis, spine, and lowest rib, it is active both as a mover (lateral flexion) and, especially bilaterally, as a spinal and pelvic stabilizer during loaded standing tasks.

Structure & function

Location: A deep, quadrangular muscle on either side of the lumbar spine, between the lowest rib and the top of the pelvis.
Origin: Iliac crest.
Insertion: Twelfth rib and transverse processes of the lumbar vertebrae.
Main action(s): Laterally flexes the trunk to the same side; helps extend the lumbar spine; stabilizes the twelfth rib during breathing; on both sides together, helps stabilize the pelvis and low back.
Joint(s) crossed: Lumbar intervertebral joints
Movement plane: frontal
Innervation: Subcostal nerve and lumbar plexus branches (T12–L4)
In daily movement: Side-bending, hiking a hip while walking, and steadying the pelvis when standing on one leg.
In exercise: A key stabilizer in single-leg and carrying exercises (e.g., a suitcase carry), resisting unwanted side-bending.
Commonly confused with: Deep and hard to feel directly, so its stabilizing role is often overlooked compared to the more visible erector spinae.
Common misconceptions: It is not a 'core ab' muscle — it lies in the back, not the front abdominal wall.

Exercises that use this muscle

As a secondary / stabilizer

Romanian Deadlift (secondary)
Bird-Dog (secondary)

⚠ Safety note

A common site of low back tightness/spasm with prolonged sitting or asymmetric loading; persistent or radiating pain needs assessment.

Sources

“The quadratus lumborum laterally flexes the vertebral column and stabilizes the lumbar spine and twelfth rib.”

Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 11.4 Axial Muscles of the Abdominal Wall, and Thorax and the Deep Back

Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19

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