Spotlight on the Psoas Major (PM)
What the Evidence Tells Us
4 Min
Mahmoud Saad
Anatomy
Not just a hip flexor. The PM has complex attachments to the lumbar spine, diaphragm, transversus abdominis, pelvic brim, and pelvic floor. Evidence suggests anterior and posterior fasciculi with distinct innervation and functions.
Biomechanics
Its main job isn’t big spinal or hip movements—it’s axial compression, adding stiffness and resisting shear. It also contributes to a neutral lumbar lordosis and influences SIJ mechanics.
Neurophysiology
EMG shows the iliacus is the main hip flexor, while PM plays a stabilizing role for the spine, pelvis, and hip during movement.
Dysfunction
In low back pain (LBP), PM demonstrates segmental atrophy and inefficient recruitment patterns, especially during low-threshold stability exercises.
Clinical Implications
Time for a reality check!
Physio Educators
Stop using the term “iliopsoas.” It’s outdated. Update your PowerPoints. Update your lectures. Evidence is clear—there’s no excuse to keep teaching old concepts.
Clinicians
- Do you still rely on high-threshold training only (speed, load, resistance) without addressing low-threshold control?
- Example: neutral lumbar spine with pressure biofeedback
- Example: vertical shortening of the femoral head into the acetabulum
- And let’s be honest—why are we still needling the Psoas? Social media hype doesn’t equal best practice. A flashy video with buzzwords doesn’t make it evidence based.
”The psoas major is not just a mover—it’s a stabilizer with a precise role in spinal and pelvic mechanics.
The references
Anatomy
- Bogduk N, Pearcy M, Hadfield G 1992– Anatomy and biomechanics of psoas major. “Clinical Biomechanics” 7:109–119 (Although titled with biomechanics, this paper contains foundational anatomical description)
- Gibbons SGT 2005a — Anatomy and functional relations of psoas major.
- Gibbons SGT, Whalen B 2003-Computed tomography imaging of posterior psoas major. Proceedings of the 52nd Annual Conference of the Newfoundland and Labrador Association of Medical Radiation Technologists. St John’s, Newfoundland (Imaging study focused on anatomical structure)
- Yoshio M, Murakami G, Sato T et al 2002. The function of the psoas major muscle: passive kinetics and morphological studies using donated cadavers. “Journal of Orthopaedic Science” 7:199–207 (Morphological study on cadavers) AMAZING PAPER
Biomechanics
- Focus: Papers that study the mechanical function, forces, and stability role of the psoas major.
- “Andersson E, Oddsson L, Grundstrom H et al 1995″The role of the psoas and iliacus muscles for stability and movement of the lumbar spine, pelvis and hip.
- “Scandinavian Journal of Medicine, Science and Sports” – 5:10–16 (Focus on stability and movement – biomechanical roles)
- “Bogduk N, Pearcy M, Hadfield G 1992” — Anatomy and biomechanics of psoas major. ‘Clinical Biomechanics’ 7:109–119 (Title explicitly states biomechanics as a key focus)
- “Gibbons SGT 2004” — A hypothetical link between psychosocial factors, pain and sensory motor function using a biomechanical model of psoas major. ‘MSc Thesis in Health Ergonomics, University of Surrey, UK’ (Proposes a biomechanical model)
- “Gibbons SGT, Pelley B, Molgaard J 2001” –Biomechanics and stability mechanisms of psoas major. ‘Proceedings of the Fourth Interdisciplinary World Congress on Low Back Pain. 9–11 November, Montreal, Canada’ (Title explicitly states biomechanics and stability)
- “Nachemson A 1968” — The possible importance of the psoas muscle for stabilisation of the lumbar spine. ‘Acta Orthopaedica Scandinavica’ 39:47–57 (Early hypothesis on a biomechanical stabilising role)
- “Santaguida PL, McGill SM 1995” — The psoas major: a three-dimensional geometric study. ‘Journal of Biomechanics’ 28:339–345 (Biomechanical modeling study)
- “Yoshio M, Murakami G, Sato T et al 2002” — The function of the psoas major muscle: passive kinetics and morphological studies using donated cadavers. *Journal of Orthopaedic Science* 7:199–207 (Includes passive kinetics, a biomechanical focus)
Neurophysiology
- Gibbons SGT, Holmes MWR, Grandy C et al 2005 — Altered hip and trunk muscle recruitment in subjects with chronic low back pain during a specific exercise for the psoas major muscle.
Pathology
- Bachrack RM, Nicelorra J, Winuk C 1991 — The relationship of low back pain to psoas insufficiency. *Journal of Orthopedic Medicine* 13(2):34–40 (Links a muscle problem to a pain state)
- Barker KL, Shamley DR, Jackson D 2004 –Changes in the cross sectional area of multifidus and psoas in patients with unilateral back pain. *Spine* 29(22):E515–E519 (Investigates morphological changes (atrophy) linked to pain)
- Dangaria T, Naesh O 1998 — Changes in cross-sectional area of psoas major muscle in unilateral sciatica caused by disc herniation. *Spine* 23(8):928–931 (Investigates morphological changes due to a specific pathology).
- Gibbons SGT, Comerford MJ, Emerson P 2002a –Rehabilitation of the stability function of psoas major. *Orthopaedic Division Review* Jan/Feb: 7–16 (Focuses on rehabilitating a dysfunctional muscle).
- Gibbons SGT, Holmes MWR, Grandy C et al 2005 –Altered hip and trunk muscle recruitment in subjects with chronic low back pain during a specific exercise for the psoas major muscle. *Submitted* (Investigates altered motor control in a pathological pain population)