Spinal ErectorsErector Spinae

backErector spinae

The erector spinae are the columns of muscle running either side of your spine that straighten your back and stop it rounding under load. They are what is working when a deadlift stays flat.

The erector spinae is not one muscle. It is three vertical columns on each side of the spine — iliocostalis nearest the ribs, longissimus in the middle, and spinalis closest to the spine — each made of overlapping bundles that span a few vertebrae at a time and stack the whole way up the back. What we model here is the thoracic and lumbar part of that system, the part that runs from the pelvis to the upper ribs and does the work people mean when they say lower back.

Because it is a stack of overlapping bundles rather than a single strap, it has no single origin or insertion. The bottom of the system arises from a broad tendon over the sacrum and the back of the pelvis; from there, slips leave and rejoin the column at every level, attaching to ribs and to the bony projections of the vertebrae above. Any single origin or insertion given for the erector spinae is a summary of a range.

Its everyday job is to hold you upright, and its job under load is to refuse to bend. When you pick something heavy off the floor, the weight is trying to fold you forward; the erectors are what keeps the spine in one shape while the hips and knees do the lifting. In a back extension or a good morning they are also the muscle actively straightening you up, but far more of their working life is spent resisting movement than producing it.

This is the muscle group people mean by lower back, and the source of a widespread confusion: a lower back that feels tired after deadlifts and a lower back problem are not the same thing, and only one of them is a training question. This site does not give injury advice — that is a conversation for a professional.

Training notes

The erectors are trained by every heavy compound lift long before they are trained by anything aimed at them. Deadlifts, squats, rows and carries all load them hard, and for most people that is genuinely enough. Direct work is worth adding when the lower back is what fails first in those lifts rather than as a matter of routine.

When it is added, back extensions and good mornings are the direct options, and both reward a light load and a full range far more than a heavy one through a few inches. The muscle spans a long distance and the range where it lengthens under load is the useful part.

Its endurance matters more than its peak strength. In a set of deadlifts, the erectors are holding one position for the whole set rather than contracting once, so sets that stay under tension for a while suit them better than heavy triples. Carries — anything held while you walk — train that quality without adding a movement to recover from.

One common misreading: rounding of the upper back during a heavy pull is often described as the erectors being weak, when the immediate cause is that the load exceeded what any position could be held against. The distinction matters because the response is different — one is trained, the other is loaded differently.

Anatomy

Origin
  • A broad common tendon from the sacrum, the posterior iliac crest, and the spinous processes of the lumbar and lower thoracic vertebrae
  • Additional slips arise segmentally from ribs and transverse processes along the column
Insertion
  • Ribs and the transverse and spinous processes of vertebrae above, each fascicle spanning several segments
  • The thoracolumbar portion modelled here reaches the upper ribs and upper thoracic spinous processes
Actions
  • Extends the vertebral column
  • Resists flexion of the trunk under load, working eccentrically and isometrically
  • Side-bends the trunk to the same side when acting unilaterally
  • Contributes to controlling rotation of the trunk
Innervation
Posterior rami of the spinal nerves, supplied segmentally along the length of the column

The erector spinae is a composite. Three columns lie side by side on each side of the spine: iliocostalis most laterally, attaching to ribs; longissimus in the middle, the longest of the three; and spinalis most medially, running between spinous processes. Each column is further divided by region, and what is modelled here is the thoracolumbar part — iliocostalis lumborum, iliocostalis thoracis, longissimus thoracis and spinalis thoracis. The cervical divisions are excluded.

Because each column is built from overlapping fascicles that span a few segments and then hand over to the next, no single origin or insertion describes it. Inferiorly the whole mass springs from a broad common tendon over the sacrum and posterior ilium; from there, slips leave and rejoin at every level. Any stated attachment is the endpoint of a range.

Its innervation follows the same segmental pattern: the posterior rami of the spinal nerves supply it level by level rather than by a single named nerve. This is one of the features that distinguishes true intrinsic back muscles from the superficial muscles that migrated to the back during development and are supplied by anterior rami.

Functionally the three columns act together. Bilaterally they extend the spine; unilaterally they side-bend it. Under load most of their work is isometric and eccentric — maintaining a position against a flexing moment rather than producing movement.

Under load

It is loaded heavily and indirectly by any lift where the trunk is held against a forward-bending moment: deadlifts, squats, bent-over rows, loaded carries. Direct work adds to that rather than replacing it.

Its demand is predominantly one of endurance and position-holding. Sets held under tension for extended periods match how it works better than brief maximal efforts.

Back extensions and good mornings load it through active extension rather than isometric holding, which is a different and complementary stimulus, and both reward moderate loads through a full range over heavy loads through a short one.

Exercises

Antagonists

Synergists