Quadratus lumborum

The quadratus lumborum, often shortened to QL, is a deep muscle on each side of the lower back. It runs from the top of the pelvis (the iliac crest and a ligament next to it) up to the lowest rib and to the side projections of the first four vertebrae of the lumbar spine. Its fibres together give it a roughly rectangular shape, which is where the Latin quadratus comes from (Kenhub).

Where is the quadratus lumborum?

Strictly, it is the deepest muscle of the back wall of the abdomen, and it is often mistaken for one of the back muscles. The long back muscles, the erector spinae, lie behind it and closer to the midline. The colon, the kidneys and the diaphragm lie in front of it. Its nerve supply comes from the 12th thoracic nerve and the first four lumbar nerves (Kenhub).

The position of the kidneys matters for symptoms: an ache in the back just under the ribs is not always muscular (see the last section).

What does the quadratus lumborum do?

• On one side: it bends the trunk sideways towards that side.
• On both sides: it helps extend the trunk and holds the 12th rib steady as you breathe in.
• Throughout movement: because it attaches to both the spine and the lowest rib, it helps stabilise the spine and the ribcage as the back moves (Kenhub).

Is a tight quadratus lumborum behind back pain?

The QL is a favourite explanation for a one-sided ache low in the back, the kind that builds through an afternoon at a desk. The usual story is that it becomes tight or knotted. When researchers have measured it, that is not what they found:

• Less stiff, not more. Using shear-wave ultrasound, researchers compared 40 people with chronic non-specific low back pain with 40 people without pain. The QL was less stiff in the people with pain, the opposite of what the authors expected from the trigger point idea. There was no difference between left and right, and the measurement was poor at telling the two groups apart (López-Redondo et al., 2025).
• Softer went with worse. In 76 people with chronic low back pain, the same team found that a softer QL went with higher pain intensity, more signs of a sensitised nervous system and poorer physical quality of life (López-Redondo et al., 2025).
• No difference in size or fat. In MRI scans of 102 older adults, those with chronic low back pain had more fat in the multifidus and smaller erector spinae than those without pain, but the QL did not differ between the groups (Sions et al., 2017).

These are small, cross-sectional studies, two of them from one research group, so they cannot show cause and effect. Still, they don’t support the idea that a tight QL is a common cause of low back pain. The feeling of tightness is real; it just may not come from a stiffer muscle.

What it means if you sit all day

We could not find studies that looked at the quadratus lumborum in office workers specifically. The general NHS advice for back pain applies: stay active, keep up your daily activities, and try exercises and stretches for back pain; walking, swimming, yoga and pilates may also help (NHS). Stretches for the lower back are shown on lower back stretches, the desk side of the problem is covered in lower back pain from sitting, and your seat in how to set up your office chair.

When to see a doctor

Ask for an urgent GP appointment or contact NHS 111 if pain in your back just under the ribs comes with a very high temperature or shivering, feeling sick, blood in your pee or pain when peeing: these can be signs of a kidney infection (NHS).

For back pain in general, see a GP if it hasn’t improved after a few weeks, is worse at night or you have lost weight without trying. Call 999 if it comes with numbness or weakness in both legs, loss of feeling around your genitals or bottom, or changes in bladder or bowel control (NHS). More in red flags.

Bavelu’s lower back sessions are designed and filmed by physiotherapists.