Muscle Spotlight: Psoas and Iliacus

One set of muscles which are often exceedingly tight due to the fact that most in our modern society sit for long periods of time are the psoas and iliacus (sometimes called the iliopsoas because they share a common insertion point and perform identical actions). The psoas muscle (the “p” is silent, so that it is pronounced sō-ăz) originates at the bodies and transverse processes of the last thoracic vertebra (T12) and the first four lumbar vertebrae (L1-L4). It inserts at the lesser trochanter of the femur. The iliacus muscle originates at the iliac fossa all along the anterior aspect of the ilium (or all along the inner top of the pelvic bone, in laymen’s terms) and inserts, just like the psoas, at the lesser trochanter of the femur. In terms of actions, both muscles flex the hip (bring the thigh towards the abdomen) and can assist in externally rotating it.

(Fun fact! Only about 40% of the population has a psoas minor in addition to the psoas major. It actually has the exact opposite action of the psoas major, but since that particular action – upward rotation of the pelvis – is not one that is commonly used in bipedal movement, it is a largely insignificant muscle in those that possess it.)

 Image borrowed from "Trail Guide to the Body, Third Edition" by Andrew Biel.

Image borrowed from "Trail Guide to the Body, Third Edition" by Andrew Biel.

Due to their location deep in the abdominal cavity and below layers of other tissues, these muscles can be extremely difficult to access; but it is not impossible to do so and can be very useful depending on the client’s issues. A therapist may find, for instance, that the psoas is so tight that it is causing excessive lordosis (curvature of the lumbar spine) and accompanying low back pain issues. While most clients would be very surprised to have a therapist locate and release a muscle deep in their abdomen for an issue they are feeling with their low back, it is a powerful technique to try, along with working on the other muscles commonly associated with low back pain. Clients themselves can also be taught to regularly stretch the psoas and iliacus, especially if their life or work situations leave them sitting for long hours at a time, as this will help prevent them from becoming too tight in the first place. Practicing such stretching techniques for these muscles as well as the abdominal muscles can provide better posture and significant relief from back pain.