Positive Health Online

The 'p' right in the middle of this strange looking word is a silent letter, so one pronounces the whole thing ill-e-o-so-as. This curious name refers to a group of three muscles: the iliacus, the psoas major and the psoas minor. Psoas comes from the Greek 'the muscles of the loins'; ilio comes from the Latin iliacus 'of or pertaining to the flank, or to the ilium or hip-bone'.

It sounds rather obscure but it starts to make sense when you know that the psoas runs from the front of the lumbar spine to the top of the thighbone. By virtue of its attachments it is supposed to have twelve actions. But, even in our days of sophisticated technology such as electromyography, there is still a lot of controversy about some of these actions. Is it, for example, an internal rotator of the thigh or an external one, or can it do both actions? I would hate to add to the confusion and so will stick prudently to what is fairly certain, even though it might not be well publicised knowledge.

In the sagittal plane, it is clear that the iliopsoas is a flexor of the hip joint - the main one. In walking, it swings the leg forward.

In the standing posture, if the fixed point is the lumbar spine, a tight psoas will pull the pelvis forward, giving rise to a common mal-posture characterised by an undue extension of the hip joint with the development of the transverse furrow of the buttock or gluteal fold. This furrow is a skin fold which depends on the degree of extension of the thigh on the trunk - the more the hip joint is extended due to the forward displacement of the pelvis, the deeper, longer and more defined the gluteal fold will be.

On the other hand, if the fixed point is on the thighbone, a tight iliopsoas will increase the lumbar lordosis (lower back concavity).

Boris J Dolto has compared the course of the psoas muscle with the strings passing above the bridge of a cello. In our bodies, the bridge is the pubic bone which acts like a natural pulley. This anatomical particularity complicates things a bit. If the two attachments are fixed, then, due to the pubic bone's pulley, the pelvis is retropulsed (pushed backwards) while some lumbar vertebrae are pulled forward, thus creating a shearing force. It has been hypothesised by the College of Reconstruction Posturale that, in this situation, the shortening of the psoas could be at the origin of spondylolisthesis, a condition where one vertebra slips forward or backward in relation to an adjacent vertebra.

Arthur A Michele wrote about what he termed the 'iliopsoatic syndrome': "the potential of destruction that lies in the power of the iliopsoas". According to him, "...any and all defects of the spine and the hip joint structures should be evaluated in terms of disturbance of function of the iliopsoas, a hitherto unrecognized prime mover, in the aetiology of those defects." Sir Colin Mackenzie in The Action of Muscles writes that "there is no muscle in the body whose action is of more diagnostic significance than that of the psoas magnus of man."

Yet, if you were to ask most people what the iliopsoas is, not many would know what you are talking about. Only those who deal with living muscles and movement will be acquainted with this deep muscle, but even here a lot of misconceptions can be found. Thus, in his excellent book Walking, Casey Meyers writes: "have you ever heard of anybody who had a pain in the iliopsoas? Me neither." Sadly, pain in or from the psoas is not rare, but it is frequently misdiagnosed.  

There are two main reasons why the iliopsoas is frequently the source of much mischief. The first one is that it forms, with the diaphragm, a muscular chain - a group of overlapping muscles which always ends up hypertonic, in other words too short and tight. The iliopsoas is no exception. And, when too tight, it becomes a serious source of pain, distortions and malfunction. A tight iliopsoas is one of the main causes of the ubiquitous back pain. But it can also lead to abdominal pain and, due to its linkage with the diaphragm, it can sometimes cause difficulty in breathing, especially in the standing posture.

The second reason has to do with evolution which made us bipedal animals. Have you ever eaten beef tenderloin or fillet? If you have, then you have eaten a piece of meat cut from the psoas major muscle that belonged to domestic cattle. Because these animals walk on all fours they are called quadrupeds. In quadrupeds the spine is horizontal and the hind limbs are at roughly right angles with it. In this anatomical configuration, the psoas runs in a straight line. The adoption of the erect posture specific to humans brought the lower limbs in line with the trunk. This posture could not have been attained without elongation of the psoas which is forced, in this position, to bend round the front rim of the pelvis. To allow for this major stretch, the lower back has to arch. Our lumbar curvature (lordosis) is a necessity which was imposed by the psoas muscle which hasn't lengthened enough to allow for a straight lumbar spine.

Looked at in the context of evolution, our upright habit is a fairly recent one, one which can quickly become uncomfortable and painful when the psoas muscle loses its elasticity. The Mezieres' method offers an original and efficient approach to restoring it to its normal length.

References
Arthur A Michele. Iliopsoas, Development of Anomalies in Man, Charles C. Thomas, Illinois. 1962.
Sir Colin Mackenzie, The Action of Muscles, H.K. Lewis & Co. Ltd. 1930.
Casey Meyers. Walking, a Complete Guide to the Complete Exercise, Random House Australia Pty Ltd. 1992.