Multifidus and Rotatores Deep Back Muscle Groups

Small back muscles pack a lot of posture power punch.

Deep intrinsic back muscles
Deep intrinsic back muscles. SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY/GETTY IMAGES

The multifidus and rotatores are two back muscles that belong to a group known as the deep layer of the intrinsic back muscles.

The back has a (potentially confusing) number of groups including an overall extrinsic layer that mainly moves the upper extremity and helps with breathing, plus an overall intrinsic layer, tasked with moving the spine itself. Inside each of these main layer divisions are more layers and/or muscle groups.

The superficial layer contains muscles with which you may be familiar like your lats, rhomboids or paraspinals (just to name a few.) But when we get into the intrinsics, and especially the deep layer of the intrinsics, we may be talking about muscles you’ve not heard of before. Let’s unpack.

The deep intrinsic layer belongs, as the name suggests, to the overall intrinsic layer. (The other intrinsic layers are the superficial and intermediate.) Also as the name suggests, the muscles in the deep intrinsic layer are the ones located most closely to the spine, when you compare them to the other back muscles.

Four muscles comprise the deep layer of the intrinsic back muscles. From superficial to deep they are the semispinalis, the multifidus, the rotatores and the interpinalis and intertransversii. This article is mainly concerned with the multifidus and rotatores.

Multifidus Muscles

The multifidus muscle is comprised of repeated bundles of short muscles that span just one single vertebral level each, and that are shaped like triangles.

These triangles are located on either side of the spine, attaching on the transverse and spinous processes. 

The multifidus is divided into parts that correspond with the main regions of your spine. These would be cervical (neck), thoracic (mid and upper back,) lumbar (lower back) and sacral (sacrum bone.) The muscle attaches onto all spinal vertebrae except the atlas, which is the first (and topmost) bone in your neck.

The job of the multifidus is to extend (think about arching) your spine. It also contributes to rotation (twisting) of the spine away from the side of the body on which they are located. And finally, the multifidus contributes to side bending, which is called lateral flexion.

The multifidus, like the rotatores and other deep back muscles, play a role in upright posture and spinal stability. According to Diane Lee, Canadian physiotherapist, the multifidus works in concert with your transverse abdominus (TA,) the deepest ab muscle in the body, and pelvic floor muscles (PFM) to stabilize your lumbar area — even before you add movement. Because of this subtle but important function of the multifidus, using imagery while lying in a supine position can help recruit the multifidus and help coordinate its action with the TA and PFM.

By the way, Lee says that when there’s low back pain, there tends to be a delayed reaction on the part of the multifidus, or it does not activate at all. And unless you do something to correct this, she adds, the physical dysfunction created by a sluggish or non-contributing multifidus will remain even after your pain goes away.

The multifidus also plays a role in sacroiliac joint stability, especially when you make big movements of the lower body such as climbing stairs, running, leg exercises and more.

Rotatores Muscles

Just below the multifidus lies the rotatores. Like the multifidus, the rotatores are small muscles located on either side of the spine. They are shaped like a quadrilateral and attach on the transverse process of the vertebrae. 

But unlike the multifidus, whose other attachment site is the spinous process, the rotatores insert on the lamina of the same vertebra. The lamina is a different part of the vertebral anatomy; it forms part of the bony ring that’s attached to the vertebral body. The spinous process, on the other hand, (as well as the transverse process) emanates from the bony ring in a projectile fashion.

Rotatore Action

The entire intrinsic layer of the back, including the rotatores (and, as discussed above, the multifidus,) produces spinal extension, and assists with lateral flexion (side bending) and rotation (twisting).

As a part of the team, the rotatores may contribute to these actions, but as you will see next, they also have a couple of other functions that distinguish them from their co-contractors.

First, the unique function of the rotatores is not well known. While they are grouped with all the other spinal extensor muscles (discussed above), because of their small size, they are at a mechanical disadvantage when it comes to actually producing any meaningful spinal motion. Instead, it is thought that the rotatores play a role in stiffening or stabilizing the spine.

Along with their likely contribution to spinal stabilization, the rotatores also serve as a sort of motion monitor, providing feedback about the precise location of the spinal bones they affect. A 1986 study published in the journal American Surgery found many more muscle spindles (nerve endings that sense your position, muscle tension and similar things) in the short rotatores (called rotatore brevis) than in the other spinal muscles. Because of this, the authors postulate that the role the rotatores likely play is more about your ability to sense the position of your low back and the degree of muscle tension or flexibility (called proprioception) than it is about actually moving that part of your spine.  

Source:

Kendall, F., McCreary, E. Provance, P. Muscles: Testing and Function. 4th edition. Williams & Wilkins. Baltimore, MD. 1993

Diane Lee & Associates. Training for the deep muscles of the core. Diane Lee & Associates website. http://www.dianelee.ca/article-training-deep-core-muscles.php

Moore, K., Dalley, A. Clinically Oriented Anatomy. Fifth. Edition. Lippincott, Williams & Wilkins. 2006. Baltimore. Philadelphia, PA

MacDonald. David A., Moseley, G. Lorimer, Hodgesa, Paul, W. The lumbar multifidus: Does the evidence support clinical beliefs? Review. Manual Therapy. 2006. http://bodyinmind.org/wp-content/uploads/McDonald-et-al-2006-Man-Ther-MF-review-paper.pdf

Nitz AJ, Peck D. Comparison of muscle spindle concentrations in large and small human epaxial muscles acting in parallel combinations. Am Surg.May 1986 . http://www.ncbi.nlm.nih.gov/pubmed/2422993

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