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Tuesday, June 6, 2023


Brent Brookbush

Brent Brookbush


Human Movement Science & Functional Anatomy of the:


by Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS

Psoas Image – Gray’s Anatomy 20th Edition via Bartleby.com


  • Origin: Ventral surfaces of the transverse processes of all lumbar vertebrae, sides of the bodies and corresponding intervertebral disks of the last thoracic and all lumbar vertebrae, and the membranous arches that extend over the sides of the bodies of the lumbar vertebra (11) Occasionally reference is made to a psoas minor with and origin on the vertebral body of T12 and fusing with the psoas major approximately the level of the femoral head. The psoas minor is not present in everyone.
  • Insertion: Lesser trochanter of the femur
    • The psoas is bordered posteriorly by the deepest layer of the thoracolumbar fascia and quadratus lumborum , enveloped by fascia arising from the deep layers of the thoracolumbar fascia, and abutting the peritoneum anterioly. The superiorly the fibers of the psoas extend past the diaphragm and invest in the arcuate ligament and inferiorly they pass just anterior the pubic ramus, posterior to the inguinal ligament and lateral to the fascial structure known as the iliopectineal arch.
    • Palpating the psoas major is a skilled palpation. With your partner lying supine, flex their hip and knee into hook-lying (crunch) position. Place your leg under their leg so they can completely relax. With finger pads over finger pads palpate an inch or so medial to the ASIS (between naval and ilium). Allow your fingers to slowly depress in the direction of the lumbar spine (slight medial inclination) as they exhale. Make small gentle hook like motions to help overlying tissue re-position and to improve your chance of "hooking" the psoas. You can be assured you are on the psoas by having the individual flex their hip and feeling for a contraction when you believe you have reached the target tissue. If you do not feel a contraction start the palpation over. Most importantly be careful. There are many sensitive structures in this area - feeling a pulse (the abdominal aorta or common iliac artery), causing tingling (femoral nerve), causing a sensation of needing to urinate (pressure on the bladder), or causing GI symptoms (nausea, hunger, bowel motility) are all signs that you are likely compressing and or impinging upon sensitive tissues (14). See image and warning about Self-administered release techniques toward the end of this article.
  • Nerve: The anterior fibers are innervated by the femoral nerve via the lumbar plexus, arising commonly from nerve roots L2 & L3, and may be segmentally innervated by nerves from T12 to L4. The posterior fibers (those arising from the ventral aspect of the transverse process) are commonly innervated by ventral rami (18).

Psoas passing inferiorly in-front-of the pubic ramus, behind the inguinal ligament and lateral to the iliopectineal arch - http://nadiyogi.com/wp-content/uploads/2012/05/psoas.jpg



  • Primary hip flexor with iliacus to 90°. Above 90° the psoas and iliacus become the sole hip flexors as the rectus femoris , TFL , and adductors become actively insufficient. The Psoas may become the sole hip flexor during the last 20 -30° of hip flexion, as even the iliacus is likely actively insufficient.
  • External rotation of the hip (some texts also list the psoas as a weak abductor)

Lumbar Spine:

  • Lumbar spine contralateral rotation, lateral flexion to the same side, and increases lumbar lordosis (lumbar extension).
  • Special Considerations: With a fixed pelvis and femur the psoas may reverse its role at the lumbar spine and contribute to lumbar flexion.


  • By acting on the lumbar spine the psoas may contribute to sacral flexion. Because the psoas has no attachment to the ilium this would result in sacral nutation (sacral flexion and relative posterior rotation of the pelvis). For more on sacral motion check out this article - Sacroiliac Joint Motion and Predictive Model of Dysfunction

Psoas being enveloped by fibers arising from the thoracolumbar fascia and bordering the peritoneum.

Frontal plane view of the Psoas - Note it's proximity to both the common iliac artery superiorly, and it proximity to the lower abdominal region inferiorly. Who would have thought that an illustration from 1918 would answer the question - "Why do I feel leg raises in my lower abs?"

Psoas Image – Gray’s Anatomy 20th Edition via Bartleby.com

Integrated Function:

  • Stabilization: Hip and lumbar spine
  • Research by Bogduk suggests that the psoas may act as two separate muscles, with the posterior fibers originating on the costal surface of the transverse process playing a larger role in stabilization of the spine, and the more anterior fibers, having a larger moment arm and capacity to move the spine (17). Further, this division is also innervated separately (as mentioned above). Research is needed to confirm that the muscle the anterior and posterior fibers can be recruited separately.
  • Eccentrically Decelerates:
    • Hip extension and internal rotation (possibly adduction)
    • Lumbar spine rotation, lateral flexion, and kyphotic forces
    • Posterior pelvic tilt
  • Synergists: The psoas is a unique muscle - the only muscle to cross from lumbar spine to hip. It's synergists in hip flexion are the iliacus, TFL , rectus femoris , gluteus minimus , and adductors (primarily the pectineus) Interestingly, the psoas and iliacus are the only hip flexors that may contribute to external rotation force. The TFL, anterior adductors and gluteus minimus are strong internal rotators.
  • The psoas may act synergistically with the lumbar flexors or extensors  to decrease or increase the lumbar lordosis depending on the relative "fixation" of the pelvis; however, based on preliminary findings by McGill, the psoas muscle will only play a role in motion of the spine when accompanied by an intent to flex the hip (15).
  • Synergistic Dominance: The psoas may become synergistically dominant when core dysfunction leads to inhibition of the intrinsic stabilization subsystem ; however, there is growing evidence to support that the psoas may also be the victim of inhibition. Many marquee professionals have noted a level of weakness that implies the muscle is "under-active"; that is - although short/overactive structures will often test weak; the weakness "felt" when testing the psoas was greater than what is generally "felt" when testing a muscle that is short/over-active. Janda noted that although both short and long muscles may test weak, long muscles are about a 1/3 weaker than short muscles (1). A rationale for a long inhibited psoas with a concurrent short overactive iliacus is discussed in Sacroiliac Motion and Predictive Model of Dysfunction  (see SI joint dyskinesis below). You may also consider "Differential Diagnosis of Psoas Under-activity…." below.
  • The real cause of "tight" hamstrings (Biceps Femoris , Semitendinosus and Semimembranosus ): The hamstrings are often implicated as short and tight; however, taking a look at the "Overhead Squat Assessment Solutions Table, " "Lumbo Pelvic Hip Complex Dysfunction, " "Sacroiliac Joint Dysfunction ," and common activity of the "Deep Longitudinal Subsystem, " would indicate that these muscles are actually long, but over-active. Although it is tempting to stretch "tight" hamstrings, it is counter productive to increase the length of a muscle that is in a lengthened position during static and dynamic postures. Releasing the hamstrings may prove beneficial, but to improve length of these structures we must optimize pelvic position. With this goal in mind, stretch the short and over-active hip flexors (Hip Flexor Flexibility ) to return the pelvis to a neutral position and reduce the amount of strain created by the dysfunctional position. In essence, you can think of the hip flexors, psoas and pelvis as winding the hamstrings into a long and tight position; just as the tuners of a guitar act to "wind-up" guitar strings. Most often, release and stretch of the the hip flexors will improve hamstring extensibility - Try it.

Lumbar Plexus - Grey's Anatomy - 20th Edition via bartleby.com


  • Lumbar Spine: The psoas contributes to anterior translation, torsion, and compression of the lumbar vertebrae. Of these, the psoas can contribute the most force to compression, which is sometimes referred to as "vertical stabilization" (18). Further the psoas creates anterior shear on the lumbar spine, a force that can only be mitigated by the often under-active Intrinsic Stabilization Subsystem . Despite the importance of this vertical load (compression), it should be noted that the combination of arthrokinematic forces created by the psoas are the same combination of forces that are often cited in reference to the etiology of lumbar disk deformation and injury, especially those related to posterior or posterior/lateral herniation.
  • Hip: May contribute to superior glide of the femoral head.

Lateral Arcuate Ligament - http://classconnection.s3.amazonaws.com/33/flashcards/602033/jpg/diaphragm_lumbar_attachments1314562001703.jpg

Fascial Integration:

  • Origin on the lumbar spine -
    • The psoas invests with the lateral arcuate ligament and the left and right crus of the diaphragm (18). This may imply a functional relationship between the psoas with the diaphragm and the Intrinsic Stabilization Subsystem .
    • Further, the psoas may be influenced by forces applied to the anterior longitudinal ligament - for example reflex inhibition, resulting from mechanoreceptors activation via the stretching force on the anterior longitudinal ligament during end range spinal extension. The anterior longitudinal ligament also invest in the fascia of the pelvic floor, along with the psoas on the brim of the ilium, reinforcing the idea that the psoas may play a role in stabilization along with the Intrinsic Stabilization Subsystem .
  • Origin on the Lesser Trochanter -
    • The most obvious fascial connection exists between the psoas and iliacus which share a common tendon.
    • The psoas may share some fascial slips with the vastus medialis at the anterior rim of the lesser trochanter and the most medial aspect of the intertrochanteric line; however, this seems rather unlikely given the relative level of activity adopted by each.
    • The nearly continuous line of insertion from psoas and iliacus to pectineus, does strengthen the argument made for the pectineus as a hip flexor. An argument that already had some validity due to portions of the muscle being innervated by the femoral nerve.

Insertions on Femur - Gray's Anatomy via wikipedia.com

May Contribute to the Following Impairments:

  • Knee Pain
    • Patellar tendonitis (Jumper’s Knee)
    • Lateral knee pain (Runner’s Knee)
    • Hamstring tendonitis
    • Generalized knee pain
  • Sacroiliac Joint Pain and Dysfunction
  • Hip Pain
    • Impingement Syndrome (FAI)
    • Lesser trochanteric bursitis
    • Ischial tuberosity bursitis
    • Generalized hip pain
    • Groin pain
    • Groin strain
  • Lumbar spine pain
    • Low back pain
    • Excessive lordosis
    • Functional scoliosis
    • Lateral shift of lumbar spine
  • Trigger points may be felt as lower abdominal pain.

The presence of a unilateral psoas minor and clearly visible psoas major - http://www.scielo.cl/fbpe/img/ijmorphol/v30n1/art24_f2.jpg

Behavior in Postural Dysfunction:

This muscle has a tendency toward adaptive shortening and over-activity, but may be long and underactive depending on the compensation pattern (posture) adopted. We find altered activity in lumbo pelvic hip complex dysfunction and sacroiliac joint dysfunction. For more information on these predictive models of dysfunction click on the link below:

In the model above the psoas is short and overactive when an individual adopts an anterior pelvic tilt. The psoas is often referred to as the primary cause of an anterior pelvic tilt; as it will contribute to both an excessive lumbar lordosis and hip flexion (the composite joint actions of an anterior pelvic tilt); however, this is likely an overstatement as the force created by all lumbar extensors and hip flexors will have a greater impact on pelvic position than the psoas with it's primarily vertical arrangement. Regardless, this does create a gap in our repertoire of exercise as the psoas cannot be easily (or safely) released using self-administered techniques. If the psoas is determined to be the cause of dysfunction than referral to a skilled manual therapist is essential for a return to optimal performance.

Check out this "Workshop Snippet" where I describe the scenario above and the daily activity that contributes to this dysfunction:

In the predictive model of Sacroiliac Joint Dysfunction (SIJD) (discussed in the article above) the psoas is long and under-active on the side opposite the dysfunction. Motor behavior that is exactly opposite to the scenario discussed above. In this case the psoas must be "activated" and "integrated" for a return to optimal lumbo pelvic hip complex function. As my assessment skills and understanding of the SI Joint continue to evolve I am beginning to believe that SIJD is actually more common than an anterior pelvic tilt alone. Although it takes some specific manual and self-administered techniques to improve SI joint arthrokinematics, for the purposes of this article, the tonicity and adaptive length change this implies is more important. Could it be that the psoas is inhibited and "dominated" by the iliacus, similar to the way the hamstrings become dominant in extension for inhibited glute complex?

Preliminary studies also seem to be pointing in the direction of a long/under-active psoas, with potential atrophy and deconditioning of the posterior fibers in individuals with unilateral disc herniation and sciatica. It would seem that those fibers innervated by the herniated segment showed significant atrophy on the side of dysfunction, with some atrophy in the segments above and below. This scenario, seems very similar to available research on the neurophysiology and morphology of the lumbar multifidus in individual with low back pain. In reviewing my model of sacroiliac joint dysfunction, you may note that sacral dysfunction is almost always unilateral and includes rotation that imposes uneven forces on the lumbar spine. This prelimanary research does seem to support my hypothesis, that the psoas is under-active on one side.

Signs of Altered Length/Tension and Tone:

  • Overhead Squat Assessment:
  • Single Leg Squat:
    • Excessive Forward Lean - Short/Overactive
    • Turn Out - Short/Overactive (potential Long/Under-active on opposite side)
  • Goniometry(Indication of restriction and over-activity):
    • Hip Internal Rotation < 45° w/ muscular end feel (capsular end feel may still imply psoas tightness, but in conjunction with other structures (TFL, posterior capsule, etc.)
    • Hip Extension < 15°
  • Special Tests for Psoas Tightness:
    • Thomas Test
  • Palpation of Psoas
    • Tenderness (indication of over-activity)
    • Trigger points (indication of over-activity and chronic postural dysfunction)

Differential Diagnosis of Short Hip Flexors, but an Under-active Psoas:

Overhead Squat Assessment: Asymmetrical Weight Shift

  • Overhead Squat Assessment: Asymmetrical Weight Shift
  • Single Leg Squat: Knee Bows In or Torso Turns In
  • Goniometry: Decreased Internal Rotation
  • Modified Thomas Test: Negative or Minimal
  • Manual Muscle Testing: Marked decrease in strength in last 20 degrees of hip flexion, or a loss of active hip flexion ROM
  • Palpation (Most Important) - No marked increase in tissue density in the psoas, this may be compared to the neighboring iliacus

Trigger Point Map for Psoas:

  • Note: Manual techniques are he only safe and effective way to address this muscular dysfunction

Trigger Point Map of Psoas - www.triggerpoints.net

Specific Test for Psoas/Iliacus Extensibility:

Modified Thomas Test

Specific Techniques for the Psoas:

Static Hip Flexor Stretch:

Active Hip Flexor Stretch:

Dynamic Hip Flexor Stretch:

Releasing the Psoas

Unfortunately the psoas is buried underneath the lower portion of the rectus abdominis and is in close proximity to some very sensitive structures (Namely, the common iliac artery and branches of the lumbar plexus and femoral nerve.). Although, I have seen individuals use a softball to release their own psoas (lying on belly), I believe this is best left to the skilled hands of a manual therapist. It may be safe for a manual practitioner to palpate the psoas and then have the client/patient re-create the sensation using a softball, but without physical confirmation that the intended structure has been located, it is hard to justify the risk that may be associated with regular (2-3 minutes per side/most days of the week) pressure and tension placed on arteries, nerves, and internal organs.

Signs of impinging on sensitive structures during manual or device assisted release:

  • feeling a pulse (pressure on the abdominal aorta or common iliac artery)
  • causing tingling (pressure or stretch of the femoral nerve),
  • causing a sensation of needing to urinate (pressure on the bladder)
  • causing GI symptoms such as nausea, hunger, bowel motility (impingement or stretching of the intestine)

Manual Release of Iliacus and Psoas:

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  1. Phillip Page, Clare Frank Robert Lardner Assessment and Treatment of Muscle Imbalance: The Janda Approach © 2010 Benchmark Physical Therapy, Inc., Clare C. Frank, and Robert Lardner
  2. Dr. Mike Clark & Scott Lucette, “NASM Essentials of Corrective Exercise Training” © 2011 Lippincott Williams & Wilkins
  3. Donald A. Neumann, “Kinesiology of the Musculoskeletal System: Foundations of Rehabilitation – 2nd Edition” © 2012 Mosby, Inc.
  4. Michael A. Clark, Scott C. Lucett, NASM Essentials of Personal Training: 4th Edition, © 2011 Lippincott Williams and Wilkins
  5. Leon Chaitow, Muscle Energy Techniques: Third Edition, © Elsevier 2007
  6. Tom Myers, Anatomy Trains: Second Edition. © Elsevier Limited 2009
  7. Shirley A Sahrmann, Diagnoses and Treatment of Movement Impairment Syndromes, © 2002 Mosby Inc.
  8. David G. Simons, Janet Travell, Lois S. Simons, Travell & Simmons’ Myofascial Pain and Dysfunction, The Trigger Point Manual, Volume 1. Upper Half of Body: Second Edition,© 1999 Williams and Wilkens
  9. Cynthia C. Norkin, D. Joyce White, Measurement of Joint Motion: A Guide to Goniometry – Third Edition. © 2003 by F.A. Davis Company
  10. Cynthia C. Norkin, Pamela K. Levangie, Joint Structure and Function: A Comprehensive Analysis: Fifth Edition © 2011 F.A. Davis Company
  11. Florence Peterson Kendall, Elizabeth Kendall McCreary, Patricia Geise Provance, Mary McIntyre Rodgers, William Anthony Romani_, Muscles: Testing and Function with Posture and Pain: Fifth Edition © 2005 Lippincott Williams & Wilkins_
  12. Andrew Biel, Trail Guide to the Human Body: 4th Edition, © 2010
  13. Carolyn Richardson, Paul Hodges, Julie Hides. Therapeutic Exercise for Lumbo Pelvic Stabilization – A Motor Control Approach for the Treatment and Prevention of Low Back Pain: 2nd Edition (c) Elsevier Limited, 2004
  14. Craig Liebenson, Rehabilitation of the Spine: A Practitioner’s Manual, (c) 2007 Lippincott Williams & Wilkins
  15. Stuart McGill, Low Back Disorders: Second Ediction © 2007 Stuart M. McGill
  16. Robert Schleip, Thomas W. Findley, Leon Chaitow and Peter A. Huijing. Fascia: The Tensional Network of the Human Body. (c) 2012 Elsevier Ltd.
  17. Bogduk N., Pearcy M, Hadfield G. Anatomy and biomechanics of the psoas major. Clinical Biomechanics 7:109-119
  18. Andrew Vleeming, Vert Mooney, Rob Stoeckart. Movement, Stability & Lumbopelivic Pain: Integration of Research and Therapy (c) 2007, Elsevier Limited

© 2012 Brent Brookbush

Questions, comments, and criticisms are welcome and encouraged.