Multifidus

The multifidus is a deep muscle that lies right against the spine, under the larger back muscles. It is made of many short bundles rather than one long strap, and it is most developed in the lower back. Its main job is to stabilise the spine (TeachMeAnatomy).

Where is the multifidus?

It belongs to the deepest layer of back muscles, the transversospinales, together with the semispinalis, which lies over it, and the small rotatores beneath it. It lies under the erector spinae. Its origin is broad: the sacrum, the back of the pelvis, the shared tendon of the erector spinae, small bony bumps on the lumbar vertebrae and, higher up, the side projections and joints of the thoracic and neck vertebrae. Each bundle climbs two to four vertebrae and attaches to a spinous process, the bony point you can feel down the middle of your back. It is supplied by branches of the spinal nerves at each level (TeachMeAnatomy).

What does the multifidus do when you sit?

Studies in pain-free people show how posture changes its work. In 20 healthy adults, the lumbar multifidus, along with the internal obliques, was less active in slumped sitting and in “sway” standing than in upright postures (O’Sullivan et al., 2002). In 22 people, sitting tall by lifting the chest used less lumbar multifidus than sitting tall by rolling the pelvis forward, about as little as slumping did (O’Sullivan et al., 2006).

Less activity in a slumped posture is not proof of harm. A review of 41 systematic reviews found no consensus that sitting or particular postures cause low back pain (Swain et al., 2020).

What happens to the multifidus in back pain?

• It can shrink on the painful side. Using ultrasound in 26 people with acute or subacute one-sided low back pain, researchers found the multifidus on the painful side about 31% smaller, but only at one level, which matched the level of symptoms in 24 of them. The size difference did not track how bad the pain was (Hides et al., 1994).
• Smaller size is linked with pain. A review of 25 studies found evidence that a smaller lumbar multifidus goes with low back pain, and in men predicted it up to a year ahead. Evidence on fat inside the muscle was conflicting (Ranger et al., 2017).
• Early specific training looked promising. In 39 people with a first episode of acute low back pain, those given exercises for the multifidus and a deep abdominal muscle had fewer recurrences: 30% against 84% after one year, and 35% against 75% after two to three years. The trial was small and the follow-up was by telephone questionnaire (Hides et al., 2001).
• But targeted exercise is not better than other exercise. A Cochrane review of 29 trials with 2,431 people with chronic non-specific low back pain found that motor control exercise, which trains the deep trunk muscles, worked better than minimal intervention but not better than other forms of exercise. The authors suggested choosing exercise by preference, cost and safety (Saragiotto et al., 2016).

So the multifidus does change in back pain, but you don’t need to single it out. The bird dog, which Bavelu’s physiotherapists include to strengthen the deep muscles around the spine, is one example: see bird dog exercise.

The multifidus in the neck

There is a multifidus in the cervical spine too. In an ultrasound study, people with chronic neck pain had a stiffer cervical multifidus than people without pain, but the stiffness was not linked with how severe their pain or disability was (Valera-Calero et al., 2025).

For more on the bigger picture, see the lumbar spine and lower back pain from sitting.