All about the Psoas Muscle

The following blog on the psoas is generally aimed at our current Teacher Trainee group and forms part of the Teacher Training programme. Those who have already qualified and anyone with interest in anatomy may find this blog interesting. A thorough understanding of muscles and anatomy is not essential for all yoga teachers. An academic knowledge of the body doesn't create the ability to lead and teach which is a far more important skill for the yoga teacher to possess but I have found in my experience, that brushing up on my anatomy and keeping up to date with the latest research does help me offer my students a better rounded service. So if a student asks for a specific hip or lat stretch as an example, I have the knowledge to prescribe the correct posture. However at the same time, I would also agree if a yoga teacher said that overindulging in anatomy can create confusion and just complicate teaching. I guess its about balance. As is all things.

The subject of this in depth blog is the psoas. The psoas is a trendy muscle for yoga teachers to talk about over the past few years. I personally don't give it much attention as I prefer the whole body approach as opposed to breaking the body down into parts, but the increasing literature associating a tight psoas with back pain (Ellgen, 2015) means that this muscle continues to dominate discussions. The way the psoas links to the diaphragm (via fascia - connective tissue) also means a tight psoas may impair or restrict breathing (Koch, 2001). So lets look at the psoas in more detail.

The psoas is the largest muscle in cross section at the lower levels of the lumbar spine (McGill, 1988), the psoas is a long muscle (up to 16 inches) that lies on either side of the lumbar vertebral column. More specifically, it originates at the anterior (front) lateral (away from the midline) aspect of the lumbar vertebrae L5, joins the iliacus in the pelvis, and inserts at the lesser trochanter of the femur (upper thigh bone) (Ellgen, 2015). Although you can’t see your psoas muscle, it’s literally at the centre of most of your everyday movements, from walking or bending over to twisting and reaching. To view the main function of the psoas, think about walking up the stairs. Your psoas lifts the leg that allows you to take a step.

In conjunction with the other hip flexors, the psoas is primarily responsible for bringing the upper thigh toward the torso (see image below - left) or bringing the torso toward the thigh (see image below - right), depending on whether your legs or spine is stationary (Sajko, 2009).

In further yoga spiel, the psoas is the muscle responsible for Boat pose. Most people think this action is creating by the abdominals but if you pause to think for a moment, the back is straight, the abdominals (deeper abdominals anyway) contract to stabilise the spine, it's the psoas muscle that, when contracted, flexes the hip to lift the legs and create the final boat pose position (below).

Image used courtesy of Ray Long, Yoga Mat Companion 2: Forward Bends & Hip Openers (2010)

Now think of Hand-To-Toe Pose (Utthita Hasta Padangusthasana). In the image below, although subconsciously, it is the psoas that creates the action of lifting the knee into the chest and it continues to contract/work as I extend the foot away (or attempt to extend the foot away in my case). This is a hamstring stretch yes (for my left leg), but the psoas must work to maintain the integrity of the pose.

I am a far cry from looking like Claire Berhgorst in the finish pose, but oh well 😭 😭

Continuing on the yoga front, if the psoas works to flex or bend your hips, what action do we take to stretch this muscle? The opposite. Extension at the hip. Think lunge or back-bending.

Try to visualise the psoas muscles elongating as you bend backwards. Tight psoas muscles would inhibit your ability to perform some of the back bending yoga poses.

Images used courtesy of Ray Long, Yoga Mat Companion 3: Back Bends & Twists (2010)

The psoas is composed of slow-and fast-twitch muscle fibers, meaning it’s capable of both sustaining endurance activities at low levels of intensity and producing bursts of movement for a short duration (Ellgen, 2015). In about 50 percent of humans, the psoas major is also joined by a very thin muscle called the psoas minor.

Learn more about your psoas in this video by Dr Nabil Ebraheim.

The psoas is part of a larger muscle group called the 'hip flexors'. These include the rectus femoris and sartorius located on the front of your thigh, the tensor fasciae latae, which is part of your hip and upper thigh muscles, and the pectineus, adductor longus, adductor brevis, and gracilis, which are all part of your medial thigh (Ellgen, 2015). Although all classified as hip flexors, these muscles all appear to assist the psoas in lifting the leg up towards the chest to the point where the thigh is parallel to the floor (90 degress). Any further than parallel it is all psoas (Boyle, 2006). Active hip flexion is produced primarily by the psoas (Alter, 1996). The psoas muscle may also function as a lumbar spine stabiliser (Nachemson, 1966, Jemmett, 2004) but the subject of which secondary actions the psoas performs is a cause of much discussion. Dr Stuart McGill in his pioneering work in Toronto, Canada insists the psoas is simply a hip flexor (2016) and is not a stabiliser. Dr McGill also goes on to bust another common anatomy myth, that your psoas and iliacus join forces to create a super hip flexor muscle the ILIOPSOAS. Dr McGill says; "There is no such thing as an iliopsoas muscles!" (2016). Gasp! Dr McGill, who's work I have followed greatly in the past few years, insists that these two muscles are entirely separate. In his 2014 publication (Functional Anatomy of Yoga: A Guide for Practitioners and Teachers), David Kiel says the psoas and iliacus are generally grouped together as they share the same distal attachment and perform the same action. Eleine N. Marieb (1994 & 2014) also groups the psoas and iliacus together, as do many anatomy and physiology publications. Dr McGill however insists they shouldn't be grouped together as they are functionally different. Hmmm. Welcome to the wonderful world of anatomy, where one year you think you are making headway in your understanding of the human body and the next year you are questioning everything you know. Anyway, lets move on.

Some of the daily movements and exercises that involve the psoas include: • Walking • Climbing stairs • Running • Cycling • Sit-ups and crunches

Too much of the above activities can lead to an over worked and then ultimately a tight psoas muscle which can be a cause of back pain and compensatory problems (Ellgen, 2015). Liz Koch, author of The Psoas Book (2012), says, “The only muscle to connect your spine to your leg, the psoas influences everything from low back pain and anxiety to full-body orgasms and pure pleasure.” She goes on to say, “A tense psoas can disturb digestion, reproductive functioning and create a host of other aliments." In a summary of Liz's book, a tight or weak psoas has a profound effect on everyday movement and can contribute to pain, postural problems and muscle imbalances. When flexible and strong, it facilitates healthy functioning in daily movement, recreation, and exercise.

Do you have a weak psoas?

Lack of strength in the psoas isn't that common (in my own experience with clients and students anyway) as the psoas works so often without our awareness. There is still an exercise you can perform. The Shirley Sahrmann’s (2001) test for a weak psoas is pretty simple. In a single leg stance, pull one knee to the chest (image 1 below) and release (image 2 below). Inability to keep the knee above 90 degrees for 10 to 15 seconds indicates a weak psoas.

Compensation signs include: cramp, immediate backward lean (as below) to compensate or a large pelvic shift.

Do you have a tight psoas?

The Thomas Test (named after Dr. Hugh Owen Thomas 1834–1891 a British orthopaedic surgeon), helps to establish range of motion around the psoas (as well as the other associated hip flexors). In the video below I explain the concept of the Thomas Test (Clark, 2010).

Makes perfect sense. Right?

In Yoga we attempt to increase the flexibility of the psoas with our various lunge postures to try and minimise the risk of lower back which have been associated with a tight psoas muscle (Sajko, 2009, Ellgen, 2015). The theory being that if the psoas is tight, the lumbar intervertebral discs are stressed as the pelvis tilts anteriorly. This forward tilt of the pelvis also stresses the hamstring and gluteal muscles as they have to lengthen to compensate for the pelvis shift. So when you ask your body to walk or run the lower back muscles have to work even harder to make up for weaker hamstrings/gluteals. The Osteopathy Partnership in London (2016) say that ALL their patients with lower back pain have had a tight psoas. They say years of sitting at a desk will create tightness and nearly always lead to back pain.

From personal experience this isn't always true. I have had back pain nearly all my adult life and as I showed in my Thomas Test my psoas is not tight. Whilst its not exceptionally flexible it is not tight enough to create compensation patterns (that I am aware of). So back pain (lumbar) and a tight psoas are not always associated but there is an abundance of literature and arguments that suggest a tight psoas can be the source of back pain. Dr McGill (2016) advises us on applying caution when we train this muscle (in terms of strength) as there is substantial compression on the spine when the psoas is activated. A sit-up (which uses the psoas to flex) loads the spine with compressive loads that exceed guidelines (McGill 2016). Leg raises (even higher psoas activation) have been shown to compress the spine even higher than sit ups (McGill 2016). So constant sit-ups and leg-raises are more dangerous to long term spinal health than a tight psoas. McGill says in his research that those with a tight psoas have not always exhibited back pain. It is over working the psoas that is the cause. Better ease off on the ab workouts then. So, if the psoas is over-active and remains in a shortened state after exercise, would that suggest the lumbar spine would be be in a constant state of compression? Probably best to keep the psoas relatively flexible just in case. Right?

There are plenty of online articles about "awakening" the psoas and "releasing" the psoas etc, but lets keep it as simple as possible. If a tight psoas is linked to lower back pain, what are the best yoga stretches we can do for this muscle?

Personally, you can't go wrong with a basic lunge stretch and then work towards your backbend. The basic lunge posture demonstrated by your favourite yoga teacher below is simple yet very effective. In the pose, my right knee is behind the line of the hip going into hip extension (remember you are required to create the opposite action of hip flexion to create the stretch). I squeeze the backside of the back leg which sends a message to the back leg hip telling it to relax. I also gently contract the deep abdominal muscles to create support for my lower back as I don't want to arch the lumbar.

Looking at the image below, if I don't gently contract the deep abdominal muscles, my lumbar goes into hyper extension. This is especially uncomfortable for anyone who has suffered with back pain in the past. So don't look like the guy below, use your abdominals to protect your lower back. Your lunge/psoas stretch should look like the image above.

The mistake often made in the various stretches that target the psoas is an incorrect starting position. A few examples are given in the videos below.

You can stretch your psoas in a number of back-bending poses as they all take the hips into extension. Think wheel, bow, camel etc.

To finish the blog I leave you a few videos where yoga anatomist's Stuart Girling and David Kiel discuss the psoas and then a final summary from me.

Video 1.

Video 2.


Discussion regarding the psoas will no doubt continue as we reach new levels of understandings of the human body. There will also be countless arguments about the secondary actions of the psoas. We know for sure it flexes the hip (McGill, 2016) but what other movements it assists with are debatable. Are you thinking does it really matter? I would be inclined to agree with you. With a new raft of secondary so-called 'functions' of the psoas, will inevitably come a new raft of variations of poses created to target these functions but do we really need more? The art of hatha yoga has been so intelligently and artistically created for us, do we really need to create more poses and more variations using anatomy as a reason to justify our "creativity"? The basics of hatha yoga as taught to us by wonderful B.K.S Iyengar is a complete system that will target, stretch and fine tune all the muscles in your body. As a budding yoga teacher if you stick to teaching the fundamental poses (for example as taught by Iyengar or Pattabhi Jois), you can't go wrong.

So what was the purpose of this blog?

The purposes was to give you a fundamental understanding of your psoas. What does it do? Bend the hip. How do you stretch it? Extend the hip. So when a student asks you for your advice on how to stretch the hip-flexor, this basic understanding of that main hip flexor, the psoas, will give you the confidence to prescribe a few poses they can practice.

As always, if you have any questions, please feel free to ask. Email Link.

The blog forms part of our Teacher Training Programme. If you would like more information, please visit this link.

Additional reading:


1.Alter, Michael J, 1996. Science of Flexibility. 2nd ed. U.S: Human Kinetics (ADVANTAGE)

2.Bianca Elizabeth Machliss, Simon Andrew Borg-Olivier, 2016. Applied Anatomy & Physiology of Yoga. 1st ed. U.K: Yoga Synergy Pty Ltd; 1st edition (1 July 2016).

3.Boyle, Michael. 2006. Understanding Hip Flexion. Available at: understanding -hip- flexion- 2679.

4.Chila, Anthony G.; et al., eds. (2010). Foundations of Osteopathic Medicine. Published under the auspices of the American Osteopathic Association (3rd ed.). Lippincott Williams & Wilkins

5.Clare Frank, P., 2010. Assessment and Treatment of Muscle Imbalance by Phil Page, Clare Frank (2010). 1st ed. United Kingdom: B00NPNDGAA.

6.Ellgen, Pamela, 2015. Psoas Strength and Flexibility: Core Workouts to Increase Mobility, Reduce Injuries and End Back Pain. 1st ed. U.S: Ulysses Press; 1 edition (16 Feb. 2015).

7.Hugo, The Osteopathy Partnership. 2016. Look after your Psoas and your back pain. [ONLINE] Available at: [Accessed 30 August 2017].

8.Jemmett RS, Macdonald DA, Agur AMMan Ther. 2004 Nov; 9(4):203-10.

9.Kent Stuber, BSc, DC, MSc2, Sandy Sajko, BPHE, DC, MSc,, 2009. 2009 Dec; 53(4): 311–318. Psoas Major: a case report and review of its anatomy, biomechanics, and clinical implications, [Online]. 1, 1. Available at: [Accessed 27 September 2017].

10.Koch, Liz, 2012. The Psoas Book. 1st ed. U.K: B00YDKEGIA.

11.Kiel, David, 2014. Functional Anatomy of Yoga: A Guide for Practitioners and Teachers. 1st ed. U.K: Lotus Publishing (31 July 2014).

12.McGill SM, Patt N, Norman RWJ Biomech. 1988; 21(4):329-41.

12.McGill, Dr. Stuart, 2016. Low Back Disorders-3rd Edition with Web Resource: Evidence-Based Prevention and Rehabilitation. 3rd ed. U.S: Human Kinetics Australia P/L; 3rd edition (10 Jan. 2016).

13.Nachemson AActa Orthop Scand. 1966; 37(2):177-90

14.National Academy of Sports Medicine, (., 2013. NASM Essentials Of Corrective Exercise Training. 2nd ed. U.S: Jones and Bartlett Publishers, Inc; Revised ed. edition (25 Jun. 2013).

15.National Academy of Sports Medicine, (., 2016. NASM Essentials Of Personal Fitness Training (National Academy of Sports Medicine). 5th ed. U.S: Jones and Bartlett Publishers, Inc; 5th Revised edition edition (23 Jun. 2016).

16. Nicpon-Marieb, Elaine, 2014. Human Anatomy and Physiology (The Benjamin/Cummings series in the life sciences). 3rd ed. U.K: Benjamin-Cummings Publishing Company, Subs of Addison Wesley Longman, Inc; 3rd Revised edition edition (30 Nov. 1994).

17.Sahrmann PT PhD FAPTA, Shirley, 2001. Diagnosis and Treatment of Movement Impairment Syndromes, 1e. 1st ed. U.K: Mosby (12 Sept. 2001).

18.Sajko S (2009) “Psoas Major: a case report and review of its anatomy, biomechanics, and clinical implications”. J Can Chiropr Assoc 53: 311-318.

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