Quadratus lumborum: what does it do and how do you train it?

Where is the quadratus lumborum?

You have one on each side of your lower back. It starts at the top of your pelvis and runs up to your lowest rib: in 6 dissected cadavers, about half its bundles acted on the 12th rib, and the rest on the lumbar vertebrae (Phillips et al., 2008). In 18 others, it attached to the outer edge of their transverse processes, the small bony wings on each side of the vertebra (Barker et al., 2007).

Its bundles vary a lot in number and size, from one person to the next and even from one side to the other (Phillips et al., 2008).

What does the quadratus lumborum do?

When one shortens, your torso leans toward it: that’s lateral flexion of the trunk. In 9 adults, fine-wire electrodes placed in its two layers found both more active when bending the torso sideways; the back layer was also active when straightening the back (Park et al., 2013). Its sideways force is modest: in a model built from the dissections, it exerts no more than 10% of that of the spinal erectors and multifidus (Phillips et al., 2008).

But when a load pulls you to one side, it stops you from leaning. During a very heavy yoke carry, a strongman event, the hip didn’t have the strength to hold the pelvis on its own: muscles like the quadratus lumborum made up for it by holding the torso and pelvis sideways (McGill et al., 2009). In 4 young adults, it worked at 74% of its max on average during heavy lifts, with a barbell up to 70 kg (154 lb) (McGill et al., 1996).

Why does carrying in one hand load your back more?

In 6 young men walking with buckets, a spine model fed by electrodes, force plates and motion tracking calculated the load on the low back: with 30 kg (66 lb) in one hand, over 2,800 newtons of compression; with 15 kg (33 lb) in each hand, 1,570, or 44% less; and even with 30 kg in each hand, less than with 30 kg in one (McGill et al., 2013).

The load pulls your torso toward it: to keep you upright, the muscles on the other side pull back. In 5 men carrying a bag on their left shoulder, the sideways effort at the low back shifted to the right (DeVita et al., 1991). In 27 adults, a dumbbell held in the right hand made the trunk muscles on the left work harder, abs and back, and vice versa; the quadratus lumborum wasn’t measured (Paek et al., 2022).

And as these muscles pull, they squeeze your spine: on the yoke carry, the highest spine load came from the weight plus the strong contraction of the trunk muscles (McGill et al., 2009). With a load in each hand, the two sides balance out.

On stairs too, the same load, 20% of body weight, carried on one side demanded more sideways effort at the low back than split between both hands (Wang and Gillette, 2018). This is about carrying: in 30 adults, lifting and lowering with one hand compressed the spine less than with two, but sheared it more sideways (Weston et al., 2020).

Which exercise works the quadratus lumborum?

The side plank: in 4 young adults, it was more active there than the other muscles measured, and the authors recommend it to train this muscle (McGill et al., 1996). In 13 men, fine-wire electrodes placed in its two layers tracked 14 kinds of plank: it worked hardest in the side plank with the top leg raised (Oshikawa et al., 2020).

If you can’t bear weight on your elbow, lifting your torso while lying on your side on a 45° bench worked it as much as a side plank, in 20 men, measured with surface electrodes (Choi et al., 2020).

That’s activity, not growth: no study has yet measured which exercise makes the quadratus lumborum grow.