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The Deep Core Muscles Behind Back Pain: Multifidus and Transversus Abdominis

Written by Ifije Ohiorhenuan, MD, PhD — Board-Certified Spine Surgeon. Last updated 2026-06-20.

Two muscles that get a lot of attention

In the world of core exercise for back pain, two muscles come up again and again: the lumbar multifidus (deep muscles running along the spine) and the transversus abdominis (a deep, corset-like abdominal muscle). Both help stabilize the spine during movement, and both behave differently in people with chronic low back pain.

Understanding what actually happens to these muscles — and what does not — helps explain why deep-core training is emphasized, and why it is not a magic switch.

What changes in chronic back pain

Imaging studies (ultrasound and MRI) consistently find that people with chronic low back pain tend to show, compared with pain-free people, smaller paraspinal and multifidus muscle size, more fatty infiltration within those muscles, and reduced or altered activation of the deep stabilizers.[1, 2, 3, 4, 5]

A careful note: these are findings reported across studies. No single study proves that one person’s back pain was caused by all of these changes at once, and it is often unclear whether the muscle changes came first or developed as a response to pain and reduced activity. The direction of cause and effect is genuinely uncertain.

Can exercise reverse these changes?

Partly. Core stabilization training can increase multifidus size and reduce fatty infiltration in some studies. But this is also where the evidence gets messy and where honesty matters:

  • Some trials show core stabilization produces greater muscle change than conventional physiotherapy.[6, 7]
  • Other trials report no statistically significant difference between groups in multifidus cross-sectional area, even when both groups improve.[8, 9]

So “exercise rebuilds the multifidus” is too strong. A fairer statement is that exercise can improve deep-muscle size and quality in some people, but the effect is inconsistent and not always better than other active treatment.

The structure-symptom disconnect

Here is the part patients find most surprising: changes in muscle size do not reliably track with how much better you feel. People can improve clinically without a measurable change in muscle cross-sectional area, and muscle changes do not guarantee pain relief.

This is actually liberating. It means you do not need a perfect MRI-measured multifidus to get better. Pain relief comes from a combination of factors — movement confidence, control, conditioning, and load tolerance — not just one muscle’s thickness.

How these muscles are assessed

Clinicians can measure transversus abdominis and multifidus thickness reliably with ultrasound, and real-time ultrasound biofeedback during exercise can help people learn to activate the deep muscles and may improve multifidus size; its correlation with pain and disability reduction, where studied, has been on the weaker side.[10, 11, 12, 13, 14]

Bottom line

The multifidus and transversus abdominis are real targets of core training, and chronic back pain is associated with changes in them. Exercise can partly reverse those changes, but inconsistently — and crucially, muscle size and symptoms do not move in lockstep. Train these muscles as part of restoring control and confidence, not as a number to perfect.

References

This guide draws on the following studies and reviews. Much of this literature is observational or abstract-level, and several findings are mixed, so they are described here as associations rather than proof. The numbered markers in the text show which sources support each point.

  1. Fortin M, Macedo LG. Multifidus and paraspinal muscle group cross-sectional areas of patients with low back pain and control patients: a systematic review with a focus on blinding. Phys Ther. 2013;93(7):873-88.
  2. Kalichman L, Carmeli E, Been E. The Association between Imaging Parameters of the Paraspinal Muscles, Spinal Degeneration, and Low Back Pain. Biomed Res Int. 2017;2017:2562957.
  3. Kjaer P, Bendix T, Sorensen JS, et al. Are MRI-defined fat infiltrations in the multifidus muscles associated with low back pain? BMC Med. 2007;5:2.
  4. Hodges PW, Danneels L. Changes in Structure and Function of the Back Muscles in Low Back Pain: Different Time Points, Observations, and Mechanisms. J Orthop Sports Phys Ther. 2019;49(6):464-476.
  5. Danneels LA, Vanderstraeten GG, Cambier DC, et al. CT imaging of trunk muscles in chronic low back pain patients and healthy control subjects. Eur Spine J. 2000;9(4):266-72.
  6. Guo X, Song W, Zhao L, et al. The effect of lumbar stabilization and stretching exercises on pain, disability, and characteristics of the lumbar paraspinal muscles in chronic nonspecific low back pain: a randomized controlled trial. J Orthop Surg Res. 2026;21(1).
  7. Karagiannopoulou V, Meirezonne H, De Greef I, et al. The effects of exercise therapy on lumbar muscle structure in low back pain: A systematic review and meta-analysis. Ann Phys Rehabil Med. 2025;68(5):101988.
  8. Güler MA, Demirdel E, Gezer İA, et al. Effect of core stabilization exercises on lumbar multifidus morphology and functional outcomes in chronic non-specific low back pain: a randomized controlled trial. BMC Musculoskelet Disord. 2025;27(1):83.
  9. Danneels LA, Vanderstraeten GG, Cambier DC, et al. Effects of three different training modalities on the cross sectional area of the lumbar multifidus muscle in patients with chronic low back pain. Br J Sports Med. 2001;35(3):186-91.
  10. Teyhen D, Koppenhaver S. Rehabilitative ultrasound imaging. J Physiother. 2011;57(3):196.
  11. Nabavi N, Mosallanezhad Z, Haghighatkhah HR, et al. Reliability of rehabilitative ultrasonography to measure transverse abdominis and multifidus muscle dimensions. Iran J Radiol. 2014;11(3):e21008.
  12. Gibbon KC, Debuse D, Hibbs A, et al. Reliability and Precision of Sonography of the Lumbar Multifidus and Transversus Abdominis During Dynamic Activities. J Ultrasound Med. 2017;36(3):571-581.
  13. Sarafadeen R, Ganiyu SO, Ibrahim AA, et al. Lumbar stabilization exercise with and without real-time ultrasound imaging biofeedback in chronic low back pain patients: a randomized controlled trial. Sci Rep. 2025;15(1):36975.
  14. Sarafadeen R, Ganiyu SO, Ibrahim AA. Effects of spinal stabilization exercise with real-time ultrasound imaging biofeedback in individuals with chronic nonspecific low back pain: a pilot study. J Exerc Rehabil. 2020;16(3):293-299.

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This article is educational and does not replace individualized medical advice. Exercise recommendations should be tailored to your diagnosis and abilities; if your back pain is severe, persistent, radiates into the leg, or comes with numbness, weakness, or bowel or bladder changes, seek evaluation from a qualified clinician before starting or continuing a program.