Erector spinae

The erector spinae is a group of long muscles that run up either side of the spine, from the pelvis to the skull. In the lower back they form the two ridges of muscle you can feel beside the spine. Their main jobs are to straighten the back and to control it as you bend.

Where is the erector spinae?

It is made of three columns on each side, lying between the spinous processes in the middle of the back and the angles of the ribs (TeachMeAnatomy):

• Iliocostalis, the outer column, which attaches to the ribs and the side projections of the neck vertebrae.
• Longissimus, the middle and largest column, which reaches all the way up to the mastoid process behind the ear.
• Spinalis, the inner and smallest column, which runs along the spinous processes and reaches the back of the skull.

All three share one tendon at the bottom, anchored to the lower thoracic and lumbar vertebrae, the sacrum and the back of the pelvis. Underneath them lies a deeper layer of short muscles that includes the multifidus. They are supplied by small branches of the spinal nerves at each level (TeachMeAnatomy).

Anatomists class them as intrinsic back muscles, the only ones considered true back muscles. The more superficial muscles over them, such as the trapezius and rhomboids, mainly move the shoulders and neck (Henson et al., 2023).

What does the erector spinae do?

Working on both sides at once, it extends the spine and the head, which is what straightens you up. Working on one side, it bends the spine to that side (TeachMeAnatomy). It runs the whole length of the thoracic spine and the lower back.

It also controls bending forward. At the bottom of a full forward bend, the back muscles normally go quiet. This is called the flexion-relaxation phenomenon (Gouteron et al., 2022).

What happens to the erector spinae when you sit?

How you sit changes how hard these muscles work. In a study of 22 pain-free people, sitting upright by lifting the chest made the thoracic part of the erector spinae work harder than an upright posture that came from tilting the pelvis. The chest-lifted posture also used less of the lumbar multifidus, about as little as slumped sitting did (O’Sullivan et al., 2006). In other words, “sit up straight” is not one posture, and some versions of it keep these muscles working hard.

It is widely believed that slouching causes back pain. A review of 41 systematic reviews found no consensus that particular postures or prolonged sitting cause low back pain, although associations were reported (Swain et al., 2020). Physiotherapy researchers have questioned the “sit up straight” message for the same reason (Slater et al., 2019). Chair height and support are covered in office chair setup.

How are the erector spinae linked to back pain?

• They often don’t switch off. In people with long-term non-specific low back pain, the flexion-relaxation response is altered, with the back muscles staying active at full bend, in about 55% of cases. The studies varied a lot, so that figure is uncertain (Gouteron et al., 2022). It is not clear whether this causes pain or follows it.
• Their strength matters with age. Strength and endurance of the back extensors are important for upright posture, and weakness of these muscles is one of the factors proposed behind an increasing thoracic kyphosis in older age (Roghani et al., 2017).
• Exercise has the best evidence. A Cochrane review of 249 trials found moderate-certainty evidence that exercise therapy reduces pain in chronic low back pain compared with no treatment, usual care or placebo (Hayden et al., 2021).

The erector spinae come up most often in lower back pain from sitting and a rounded upper back. The hip flexors at the front of the hip are the other muscles often blamed for back pain from sitting. For how back pain tends to behave over time, see Will back pain go away on its own?

When should you see a doctor?

See a GP if back pain hasn’t improved after a few weeks of home care, if it doesn’t improve with rest or is worse at night, if it is worse when you cough, sneeze or poo, if you have lost weight without trying, or if your back has changed shape or has a lump. Ask for an urgent GP appointment or contact NHS 111 if you feel hot, shivery and unwell, or the pain is severe and getting worse quickly. Call 999 or go to A&E if back pain comes with numbness, tingling or weakness in both legs, loss of feeling around the genitals or anus, changes in bladder or bowel control, or chest pain, or if it started after a serious accident (NHS).

Stretches and mobility work for the muscles along the spine are part of Bavelu’s lower and upper back sessions, designed and filmed by physiotherapists.