Psoas Major

20th January 2014

Psoas Major has long been a topic for discussion and has been an area of interest for Kinetic Control for many year. We have a popular online module by Mark Comerford: Psoas Major Uncovering the Evidence.


Kinetic Control has developed a unique muscle classification system and presents a classification of muscles functional roles in terms of function, characteristics and dysfunction - see Chapter 2 in text Kinetic Control: The Management of Uncontrolled Movement.

  • Local Stability Muscles: increase muscle stiffness to control segmental motion / translation
  • Global Stability Muscles: generate force to control range of movement - of particular importance is eccentric control - they are the brakes!
  • Global Mobility Muscles: generate torque to produce range of joint movement - they are the accelerator!


Koen Schoolmeesters, our tutor Belgium and Holland has been looking at some recent literature on Psoas Major. 


Psoas is often considered as a problem muscle that is often short and overactive, but Kinetic Control has considered the muscle function based on the anatomical location and structure, biomechanical potential, neurophysiolgy and consistent and characteristics changes in the presence of pain and pathology and believes there is considerable support of it's primary function as a movement controller (stabiliser)  for the hip joint as well as for the lumbar spine.


In 2010 Hu et al showed bilateral activity of Psoas during an unilateral ALSR.  The contralateral psoas will not be flexing the hip but is acting bilaterally to actively control the lumbar spine in the frontal plane.

Our clinical experience  is that the Psoas muscle is rarely shortened (except in kypho-lordotic postures) but is more subject to inhibition and/or lengthening (especially in sway back postures). Efficient rehabilitation of Psoas is directed at addressing cognitive motor control retraining and efficient low threshold recruitment.

Kinetic Control considers the differences in anatomy and function of the iliopsoas complex:

  • Iliacus muscle,
  • Psoas Anterior (from anteromedial aspects of T12/L1 to L4/5 discs and vertebral bodies)
  • Psoas Posterior (from anteromedial aspect of lumbar processes transversus).  



In several recent studies of Rachel Park et al the activity of these different regions of Psoas Major was investigated in painfree subject (Park et al 2012, 2013) and in subject with LBP (Park et al 2013).
In the following blog posts we present a summary and clinical interpretation of the results of these interesting studies.


Hu e.a., 2010, Is the Psoas a hip flexor in the active straight leg raise ?, European  Spine Journal

Park R, Tsao H, Cresswell AG, Hodges P, 2012, Differential Activity of Regions of the Psoas Major and Quadratus Lumborum during Submaximal Isometric Trunk Efforts, J. Orthopaedic Research Febr:311-318

Park R, Tsa H, Claus A, Cresswell AG, Hodges P,  2013(a), Changes in regional EMG-activity of the Psoas major and Quadratus Lumborum with voluntary trunk and hip tasks and different spinal curvatures in sitting,  JOSPT 43(2):74-82

Park R, Tsao H, Cresswell AG, Hodges P,  2013(b), Changes in direction-specific activity of Psoas Major and Quadratus Lumborum in people with recurring back pain differ between muscle regions and patient groups,  Journal of electromyography and kinesiology 23 :734-740

Keywords: Review 2014