November 9, 2015

What’s so special about Psoas?

Psoas is a deep lumbo-pelvic muscle that can curl us into the protective fetal position or quickly engage to hurl us forward in a run. There are fascinating articles out there on the emotional role of this muscle, but I’m here to talk about its biomechanics in yoga asana.

Psoas is a multi-articulate or multiarticular muscle — one that crosses multiple joints. In anatomic terminology “Articulate” refers to a joint, a part of the body that “articulates”. 

Articular, according to the dictionary, means this:  :consisting of segments united by joints :jointed <articulate animals>”

Most muscles cross one joint. Some cross two. Occasionally a muscle will not cross a classic joint at all (like the muscles that raise your eyebrows ). These muscles are not multiarticular.

I think a lot about one muscle, psoas, because it connects so many moving parts. A sustainable Psoas is crucial to treating low back, sacroiliac, pelvis, hip and even knee or shoulder dysfunctions.

Psoas is perhaps the most central multi-articulate muscle, and (I believe) the winner for “most joints crossed.” (Some of the joints it crosses are: multilevel facet and intervertebral joints, SI joint, hip joint, you could even count the pubic symphysis because of its power to separate that joint).

^ This is what makes it so very special in dynamic movement.


Anatomy of Psoas Major

You have two psoai (the plural form — I had to look that up!), one on each side.

Psoas major stems from the sides of the weight-bearing portion of multiple vertebrae (the vertebral bodies). Some fibers attach to the intervertebral discs and to the anterior portion of the transverse processes of at least 5, maybe 7 vertebra.

In plain speak: psoas attaches to all the lower front-side spine.

Specifically, fibers stem from T12 (the lowest thoracic vertebra), and L1-L4 (the upper 4 out of 5 lumbar vertebrae) and the discs in between.

Fascinatingly enough, there is slight anatomic variability between individuals so sometimes Psoas has fibers coming off of T11, and occasionally L5 as well.

(Also, for clarity, I’m referring to psoas major. There is a psoas minor, but it is absent in many people.)

Psoas is shaped like a long, skinny curved fan — the kind of human-powered fan you would hold in your hand. It tapers from all the connecting points above (“superiorly” in anatomic language) to connect below (inferiorly) to one spot via a shared or “common” tendon with another nearby hip flexing muscle, iliacus.

 The lower attachment point, where the “iliopsoas” tendon attaches, is the inner upper thigh bone (the lesser trochanter of the femur).

Actions of Psoas Major

The main job of psoas is flexing the hips on a stationary spine (marching, climbing stairs). But it also flexes the spine when the legs are stationary (as in a sit-up or hurling yourself out of bed).  And it assists external rotation of the hips, which will turn your toes out.

Psoas in Yoga Asana

Psoas is involved in thousands of poses or transitions that could show up on the yoga. Essentially, it is present in any standing pose that involves lifting a leg. Hasta Pandangustasana is the classic one. 

In vinyasa, from plank, this muscle helps you curl your knee to your nose, or set your foot between your hands. When lying on your back, simply bringing the knees to your chest involves psoas contraction. The transition from paschimottonasana to savasana also involves what’s called an eccentric (or negative) contraction of psoas.

How psoas shows up in dysfunction

Confusingly, reduced pliability in psoas may contribute to a hyperextended (excessively curved shape in the) lower back — primarily via the lower or posterior fibers.

Or it could contribute to a posteriorly tilted pelvis if the upper and anterior fibers are overly-taut.

Re-read the last two statements, and gaze at the image below to really absorb that complexity:



Tightness, trigger points or general myofascial restrictions in Psoas are one of the reasons you might have difficulty internally rotating your thighs in some yoga asana (like the outstretched leg in supta hasta padangusthasana –basic supine hamstring stretch).

And psoas strengthening is sometimes confused as core strengthening. Leg lifts and lowers while on your back: psoas.  Navasana or boat pose: it’s a Psoas  pose!

This is not to say that psoas is not involved in our core strength, but it is not considered part of our classic “Core Container”. The core container — a topic for another post — maintains steady intraabdominal pressure, keeps our intervertebral discs happy and juicy and sustains a healthy respiratory diaphragm as well as pelvic floor.

Over-reliance on psoas, without training the abdominal musculature can cause all sort of problems, precisely because psoas crosses so many joints.

As you engage psoas in the future — flexing your hips while standing, or curling your spine while your legs stay stationary — pay close attention to the engagement of the entire “corset” of muscles around your abdomen.

Psoas needs the whole team to play along.

Love yoga anatomy? We do too!

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