All about the Psoas muscle

All about the Psoas muscle

(It’s a silent “P” – pronounce it “soas”).

What’s a psoas?

Our two psoas muscles sit either side of our lower spines. They connect the base of the spine to the thigh bones. This means they play a huge role in movement – and so much more, as we’ll find out in this article. 

<Yawn> Why are we talking about this?

Because they connect to the lower spine, they obviously influence it. This is a big deal for Yoga teachers, because lots of people have lower back issues. But important research from twenty years ago shows that we’ve misunderstood how the psoas affects the lower spine. Most Yoga teachers are not aware of this research. Your Yoga teacher might be trying to help your back and in fact making it worse.


This article has been prepared to help Yoga teachers better understand the psoas and how to interact with it through movement and breath, in order to improve health. The article is just a little technical, but each technical term will be explained, so read on even if you’re not a Yoga teacher. It might help you better understand how to care for – or even fix – your own back.


Courses at Yogafurie Academy are based on the latest learnings from anatomy and science. We continually update them as the knowledge base changes. You can be assured that Yogafurie has always taught the content you’re about to read to our future teachers.

Some info about the psoas

Let’s start with a picture:

…and from the side:

Let’s break down the diagrams. What are they saying?


  • There are two psoas muscles – one left, one right.
  • Each psoas grows from the lower back obliquely down to the front of the pelvis, crosses the crest of the pubes and attaches to the inside of the thigh bone.


Here’s a bit more detail:


  • The psoas joins to several vertebrae in the lower back – for part of its length, it follows the path of the lumbar spine.
  • The diaphragm muscle – the main muscle of breathing – has attachments in the same areas. Some researchers state that the fibres of the diaphragm and psoas blend together, supporting (or ruining) the relationship between breathing and walking.

What does it do?

Current dogma is that the psoas is a hip flexor muscle – it’s believed that the psoas helps bring the front of the thigh and the belly closer to each other (that’s what hip flexion means). However, this view was challenged around 20 years ago and today, a growing number of researchers agree that it acts as a stabiliser instead. 

Imagine trying to balance a vertical pole of the palm of your hand. To keep it upright, you sometimes have to move left, sometimes right, sometimes forwards, sometimes back. The psoas has several attachments to the spine on both left and right sides and braces across the pubes on its way to the femur. It can exert a multi- directional influence on the base of the spine. The diagram to the left gives a schematic representation – one could imagine the different “layers” of muscle subtly repositioning different levels of vertebrae.

Remember also that muscles can change the tension they exert without changing length – adjustments to the integrity of the lower spine really could be quite subtle. By determining the position of the lower spine, the psoas effectively controls the quality of overall body posture as a whole. 

This is profound and we need to pause to let it sink in. Poor posture accelerates wear and tear and leads to unnecessary energy consumption supporting off-axis weight. Short term fatigue and long term exhaustion can result from an unresponsive psoas. Body language is also clearly affected: if the upright stance is simply not available, then there will be a prevailing air of burden in the presentation of the body. That burden is felt in the off-axis weight but probably does not register consciously until that off-axis load results in injury. Meantime, the way people approach changes because the person they are approaching looks burdened. 


Furthermore, there is an important nerve plexus embedded in the surface of the fascia enwrapping the psoas. (Fascia is a body-wide tissue bed: it grows around and in between each of the individual elements of the body. It creates different spaces for the different tissues to grow in, and provides a protective wrapper for each.) 


The autonomic nervous system is the set of nerves that regulate involuntary processes like heart rate, blood pressure etc. The lumbar plexus enables and controls movement of the lower body and has autonomic fibres. It forms a bridge between the instinctive management facility and the active, conscious actuation of intention. Should the underlying psoas be unwell, badly positioned, moving poorly etc then there will be an impact, however subtle, on the lumbar plexus.

Is it working?

Clearly, the psoas is extremely important for physical, mental and emotional health in varying degrees. You can get an estimate of how it’s doing by looking at a person’s posture in profile:

Lumbar lordosis (lower back jutting in too much) is the Yoga teacher stance: many teachers have this presentation through years of back bending based on the wrong advice they were given at training courses. Thoracic kyphosis (upper back jutting out too much) is the office worker’s stance: having to sit in a chair to make a living can result in a cascade of collapsing compensations through the back. For both body types, attention to what the psoas is doing will improve posture. Let’s look in a bit more detail:

These three images are in the same order: from left, good posture (“straight” back), thoracic kyphosis, lumbar lordosis. On each, the red line traces the line of good posture. Points to note:


  • Good posture this position is called neutral for the hips. The middle of the hip (where you can feel the bony lump at the side – where the thigh bone joins the pelvis) is below the middle of the shoulder.
  • Kyphosis – the hips have gone forwards, the lower spine has gone back. We say that the hip is extended, because the line between the front of the belly and the thigh is straighter. The lower back is starting to round outwards – the lower back is in flexion.
  • Lordosis – the hips are going backwards, the lower spine has moved forwards. The hip is in flexion, because the line between the front of the belly and the thigh has now got a steeper angle in it. The lower back is in extension, because the bones are rounding inwards.

If all is well, the psoas will elongate and fall back towards the spine in hip flexion (when the thigh and belly get closer together). This is not what is taught on anatomy courses or on most Yoga teacher training,, but think about it: it must be true. The psoas crosses the pubic rim, then drops towards the thigh bone. When you’re upright, it makes a significant angle at the pubic bone. When the upper psoas attachments move forward – when the leg and belly get closer (flexion), that angle changes and softens. At least, that’s what happens if the psoas is well. 


The well, lengthening with each movement of flexion, psoas will help maintain the right distance between the lower vertebrae, regardless of body position. If the lumbars have moved forward – as in the case of lordosis – then there’s something wrong. Remember that lordosis is a flexion of the hip. Similarly, if the lumbars move backwards (kyphosis) then the hip has gone into an unnatural extension. All of this points to the psoas’ role as a stabiliser. When things go wrong, people develop an unhelpful pelvic tilt. 


Why would the psoas “stabilise” the pelvis in a tilted position? And what happens to the psoas when it does that? There are multiple muscles around the pelvis and lots of internal organs in it, each wrapped individually in fascia, with all the wrappings growing around and sometimes through each other. Any of them can have a problem, any of the wrappings can be a bit stiff and dried out and impinge on the ones around. There’s no single answer as to why this happens. But, the body wants to be well. The body knows how to be well. Wise and informed movement and manipulation can trigger the body to adjust its internal environment – to “stabilise” in a more functional place.

The buddy…or the enemy?

Anatomy offers a very simple model of how muscles work in pairs to get things done. For instance, to straighten your leg you extend through your quads (called the agonists) and let go through your hamstrings (called the antagonists).


Conventional wisdom is that the glutes (medius and maximus) are the antagonists for the psoas. However, that’s based on the notion of psoas as a hip flexor. With our new knowledge of the psoas, we could ask – what else can affect pelvic tilt? You may have guessed it – the rectus abdominis.

From the diagram, it’s quite clear that this group can create lift at the pubis and depression of the mid to lower ribs. And so we can see the problem with much of our modern approach to exercise. There’s an emphasis on exercises that shorten the rectus repeatedly – crunches etc. The body always grows to use: if I repeatedly shorten a tissue, it will understand that there is a need to be shorter in that area. 


What happens? One the one hand, the ribs depress, which degrades breath. The breath rate might have to increase to compensate. Also, the muscle of breathing (the diaphragm – shown below) is locked down. The body will have to find space for the air elsewhere – probably the upper chest. Short breaths in the upper chest…is stress breathing. On the other hand, the pubic bone is drawn up. This is an example of how the psoas can be asked to stabilise in an aberrated position.

The Yoga problem…

Discussion of the rectus above highlighted one way that (well intentioned) movement practice can result in significant issues. Our Yoga postures can also become part of the problem if we are not aware of how to interact with the body through movement. Here we’ll discuss the simple forward fold. 


There are lots of forward folding postures. There are standing postures where we bend at the hips and take the chest towards the legs. There are sitting postures where we do the same – or even ones where we lie down and do this.


The issue is that people put their lower spine into extension in an effort to “do the posture”. See the image below.

In the picture above, the practitioner arches her back inwards. Do you have the sense of doing that, right before you dive down into the forward fold? It’s quite common in Yoga class: I see it a lot. When the teacher gives the instruction to come into a forward fold, people often start the movement by lifting the tail. Next time you hear the instruction, can you forward fold directly, without first flaring the tail back?


If the hamstrings aren’t fully competent then it can help to start as shown because lifting the tail pre-tensions the hamstrings. The hamstrings lengthen and bear a large fraction of bodyweight in this position. Pretensioning puts additional length in and activates some of their strength before the load is applied. The person above has moved her hips back to fold forward: this is usually a sign that the hamstrings are still just a little tight. They’re not ready to lengthen easily, so the body finds the movement by taking the hips backwards.Nex time you do this, can you enter without taking the hips back – even if that means not going as deep as you usually do?


How does the body lift the tail backwards? One of the muscles involved (unless there’s an injury or some other cause of inhibition) is the quadratus lumborum (QL).

This muscle links the back of the pelvis to the base of the rib cage. Some researchers claim that there are fibres from the spine to the lower ribs, and from the hip to the spine also. Repeatedly shortening this muscle (eg for forward folding) will again tell the body that shortness is needed there. The body will comply and shorten the tissues, contributing to a tilt of the pelvis. The psoas can then stabilise the aberrated hip position.

Self test

Here’s a simple diagnostic to check the overall functioning of your psoas.


  • Lie on your back and extend your legs along the ground.
  • Keeping the feet landed, draw the legs back by bending the knees upwards.
  • Does the waistline fall back? 


If the answer is yes: This indicates that as the lower end of the coccyx (tail) turns under, the lower back is free to fall back. The psoas itself is falling back as the flexion begins and the rectus abdominis will too, because it has nothing to resist against from its partner, the psoas. This movement alone – if things are working – can relax and decompress the spine.

I had to push my back onto the floor

This is the average situation. Most people have some dysfunction in the psoas on one or both sides. There are a number of simple exercises and movements that you can use to begin the retraining process, and they will be presented in a future blog.


It’s impossible for some people to drop the waistline backwards, even if they try to push it downwards with muscular effort. If this describes you, then don’t worry – your body can be retrained. But for now you need to be careful with exercises labelled as “core work”.

Where it is, it isn’t

The body is an amazing piece of bioengineering. Computers are very one way: there is an input and there is an output. The body is multidimensional: you can go in through the output to create the input, so to speak. In terms of what we’ve discussed here, it’s not as simple as saying that a tight rectus causes one psoas issue and a tight QL causes the other. There will be other factors, other muscles at play and the problem will grow through all of them simultaneously.


  1. This isn’t how an anatomy book would define the terms flexion and extension – but it gives you the right idea. Don’t worry too much about the terminology, just think about the shapes. And have a look at the people in your life. You can begin to recognise how people carry themselves.

  2.  The article referenced earlier does a good job of explaining how shear and strain forces would damage the psoas if it really was a major hip flexor. 

  3. It’s a rather oversimplified view: there’s always more than two muscles involved, and you aren’t letting go through the antagonists but in fact decelerating the movement. 

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