Jul 2016 09

The muscles of the back - erector spinae

By: Dave Wheeler

How many muscles are there in the back?

If you exclude the neck & back of the shoulders, there are around 320... most of them nestled in between the vertebrae both sides of the spine.

In terms of the big muscles, the main one that "goes" and causes back pain is Quadratus Lumborum - the big square muscle at the base of your back either side of the spine.

The other really important back muscles, though, are the ones that run up either side the whole length of your spine: the erector spinae group.


The erector spinae group

There's actually no such muscle as erector spinae - the term refers to a group of muscles that snake together up the length of your back - from the sacrum at the back of your pelvis all the way up to the cranium in your skull.

The 3 muscles that make up the erector spinae group each side of your spine are:

  • Iliocostalis
  • Longissimus
  • Spinalis

They run outwards from the spine in that order - Iliocostalis-longissimus-spinalis. It's easy to remember the order I-L-S by using the mnemonic I Like Standing, which describes the main function of the muscle group.


The function of the erector spinae

The main function of the erector spinae group is to keep you upright.

The combined job of the Iliocostalislongissimus and spinalis together is to maintain posture.

Another function is to stop you falling over when you bend forward. Imagine bending over to pick up a pencil from the ground... your abdominal muscles contract to pull your trunk forward and to flex the spine - but once you've started bending forward the force of gravity should pull you forward so you end up face on the floor. It's the eccentric contraction of your erector spinae muscles that stop you falling forward.

Those same muscles also then themselves contract (normally, that is concetrically) to pull you back upright again when you stand up in the movement called extension of the spine.

Interestingly, the Iliocostalislongissimus and spinalis are also used when sitting - either keeping you upright, or if you're sitting hunched forward then stopping you falling forward onto your keyboard!

The muscles get used during a lot of sports: from Taekwon-Do, through rowing to gymnastics and weight lifting.


Back ache and the erector spinae muscles

The commonest way to injure the muscles of the erector spinae is poor lifting technique. Though injury of these muscles is nowhere near as common as injury of the quadratus lumborum in the lower back, it's still possible - especially if you've got relatively weak erector spinae in the mid (thoracic) back, which is common in cyclists and those with the flat back posture type.

The Iliocostalislongissimus and spinalis are used to stabilise the spine when the arms are raised either sideways (abduction) or forwards (flexion) - they become activated during the last 30 degrees of movement. Since all of these muscles of the erector spinae group connect down onto the base of the pelvis, if you lift your arms up high then there will be a bit of a pull in the lumbar region of your back.

So if you've got lower back ache - don't raise your arms up!


As ever, if you think I can help, give me a call.