Psoas major muscle

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Psoas major muscle
Psoas major muscle11.png
Position of psoas major (shown in red)
Anterior Hip Muscles 2.PNG
The psoas major and nearby muscles
Latin Musculus psoas major
Origin Transverse processes of T12-L5 and the lateral aspects of the discs between them
Insertion In the lesser trochanter of the femur
lumbar branch of iliolumbar artery
Lumbar plexus via anterior branches of L1-L3 nerves
Actions Flexion in the hip joint
Antagonist Gluteus maximus
Gray's p.467
MeSH A02.633.567.825
TA A04.7.02.004
FMA 18060
Anatomical terms of muscle

The psoas major (/ˈs.əs/ or /ˈs.æs/,The word psoas comes from the Greek psoa meaning the “loin region.”) is a long fusiform muscle located on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It joins the iliacus muscle to form the iliopsoas.


The psoas major is divided into a superficial and deep part. The deep part originates from the transverse processes of lumbar vertebrae I-V. The superficial part originates from the lateral surfaces of the last thoracic vertebra, lumbar vertebrae I-IV, and from neighboring intervertebral discs. The lumbar plexus lies between the two layers.[1]

It is joined by the iliacus, psoas major forms the iliopsoas which is surrounded by the iliac fascia. The iliopsoas runs across the iliopubic eminence through the muscular lacuna to its insertion on the lesser trochanter of the femur. The iliopectineal bursa separates the tendon of the iliopsoas muscle from the external surface of the hip joint capsule at the level of the iliopubic eminence.[2] The iliac subtendinous bursa lies between the lesser trochanter and the attachment of the iliopsoas.[1]


Innervation of the psoas major is through the anterior rami of L1 to L4.


In less than 50 percent of human subjects,[1] the psoas major is accompanied by the psoas minor.

In animals[edit]

In mice, it is mostly a fast-twitching, type II muscle,[3] while in human it combines slow and fast-twitching fibers.[4]


As part of the iliopsoas, psoas major contributes to flexion in the hip joint. On the lumbar spine, unilateral contraction bends the trunk laterally, while bilateral contraction raises the trunk from its supine position.[5]

It forms part of a group of muscles called the hip flexors, whose action is primarily to lift the upper leg towards the body when the body is fixed or to pull the body towards the leg when the leg is fixed.

For example, when doing a sit-up that brings the torso (including the lower back) away from the ground and towards the front of the leg, the hip flexors (including the iliopsoas) will flex the spine upon the pelvis.

Owing to the frontal attachment on the vertebrae, rotation of the spine will stretch the psoas.

Clinical significance[edit]

Tightness of the psoas can result in lower back pain by compressing the lumbar discs.[6]

Racial Variation[edit]

Autopsy data show this muscle is thicker in blacks than whites, and that the presence of the psoas minor is also racially variant. [7]

See also[edit]

This article uses anatomical terminology; for an overview, see anatomical terminology.


This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

  1. ^ a b c Platzer (2004), p 234
  2. ^ Bojsen-Møller, Finn; Simonsen, Erik B.; Tranum-Jensen, Jørgen (2001). Bevægeapparatets anatomi [Anatomy of the Locomotive Apparatus] (in Danish) (12th ed.). pp. 261–266. ISBN 978-87-628-0307-7. 
  3. ^ Nunes, MT; Bianco, AC; Migala, A; Agostini, B; Hasselbach, W (1985). "Thyroxine induced transformation in sarcoplasmic reticulum of rabbit soleus and psoas muscles". Zeitschrift fur Naturforschung. Section C: Biosciences 40 (9–10): 726–34. PMID 2934902. 
  4. ^ Arbanas, Juraj; Starcevic Klasan, Gordana; Nikolic, Marina; Jerkovic, Romana; Miljanovic, Ivo; Malnar, Daniela (2009). "Fibre type composition of the human psoas major muscle with regard to the level of its origin". Journal of Anatomy 215 (6): 636–41. doi:10.1111/j.1469-7580.2009.01155.x. PMC 2796786. PMID 19930517. 
  5. ^ Thieme Atlas of Anatomy (2006), p 422
  6. ^ Akuthota, et all(2008). p 40
  7. ^ HANSON, P., MAGNUSSON, S. P., SORENSEN, H., & SIMONSEN, E. B. (1999). Anatomical differences in the psoas muscles in young black and white men. Journal of Anatomy, 194(Pt 2), 303–307. doi:10.1046/j.1469-7580.1999.19420303.x


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