Psoas and iliopsoas: characteristics of the muscle

Psoas and iliopsoas: characteristics of the muscle

The iliopsoas, often called only psoas, is called “the muscle of the soul” and is the only one that connects the trunk to the legs. Due to its location and function it is an important support for our body and its health is crucial for the balance of the whole organism.


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  • What is psoas
  • Structure of the psoas
  • Psoas and internal organs
  • Breath regulation
  • Psoas, the muscle of the soul

What is psoas

The ileo-psoas muscle consists of two muscle bellies: 

  • the great psoas , which originates from the twelfth thoracic vertebra, from the first four lumbar vertebrae and from the related intervertebral discs, passes under the inguinal ligament and inserts into the lesser trochanter of the femur;
  • the iliacus , which originates from the iliac fossa and sacrum, passes under the inguinal ligament and inserts itself on the tendon of the great psoas.

There is also a small psoas muscle , which is located ventrally to the large one, but which may be missing in a large percentage of the population.

When the fixed point is the spine and the pelvis, it flexes, adducts and externally rotates the thigh ; while it flexes and participates in the lateral inclination of the trunk  when it has the femur as its fixed point.

It is often referred to as the deepest core of our body , because it guarantees movement, structural balance, support of the bone structure and joint function.

Structure of the psoas

The iliopsoas has an elongated shape , which crosses the lumbar region of the spine, passes through the pelvis and fits onto the femur. 

Due to its position and the fact that it is the only muscle that connects the trunk to the legs , it is in fact one of the most important and stressed in all activities : we use, and often overload, the iliopsoas when we run, when we go up or down the stairs, when we walk, but also when we are simply sitting on the sofa or in front of a desk.

Psoas and internal organs

In its long journey, the iliopsoas encounters and interacts with various organs , including the kidneys and ureters, the intestine , from the small intestine to the colon, the bladder and the reproductive system , especially the female. Furthermore, it is closely related to the activity of the diaphragm , the main respiratory muscle, which separates the thoracic cavity from the abdominal one.

This explains why tensions, stiffness or weakness of the psoas can cause problems in the whole surrounding area and how good breathing can beneficially affect this muscle, as well as, vice versa, bad breathing or postural habits can affect its functioning.

Some of the main consequences of a “contracted” psoas are:

  • low back pain ;
  • pain in the sacroiliac joint and pelvis;
  • tendon inflammation;
  • inflammation of the hip (bursitis, trochanteritis, arthrosis , etc.);
  • digestive problems or malfunction of the abdominal organs;
  • menstrual pains .

Breath regulation 

The psoas and the diaphragm meet at the solar plexus , home to a dense nervous and energetic network. Due to this connection, the psoas is a fundamental muscle not only mechanically and structurally, but also for the psychological well -being of the whole system. 


The autonomic nervous system , which has the function of ensuring homeostasis, that is the balance of the organism, is divided into: 

  • sympathetic system , often described as a fight or flight function, which determines the body’s responses to a situation of acceleration and activation;
  • parasympathetic system , which on the other hand deals with rest and digest responses, that is, the activities that guarantee digestive and rest functions.

A contracted psoas lives in a perennial state of alert , as if it were always ready to respond to the command to attack and escape, with everything that follows on a physiological level.

Breathing can also result , as a result, accelerated or blocked , thus giving rise to a vicious cycle whereby stress , fear or anxiety feed on and cause each other.

Psoas, the muscle of the soul

In the various oriental philosophies, the psoas is often called ” the muscle of the soul “, due to its very deep relationship with the condition of well-being or psychophysical imbalance and with the emotional sphere of the individual.

Preserving and guaranteeing the right degree of tone to this muscle is the key to obtaining very important benefits :

  • improve posture ;
  • improve the fluidity of movements ;
  • improve digestion and the functions of the abdominal organs;
  • decrease stress and anxiety levels ;
  • ensure good breathing and, consequently, good cardiac activity .

Many disciplines, including yoga , pilates and the Feldenkrais method , or treatments such as shiatsu and Thai massage , are useful for working on the psoas and training it correctly. And a happy psoas is sure to be a great ally for living a happy life!

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