The psoas is the muscle that links your lower back to your leg. You have one on each side of your body, with 10 attachment points at the lumbar spine (sides of the vertebrae and intervertebral disks too) and just one attachment point on the inside of the femur. There is a psoas major and a psoas minor; the latter is present in about half the population. In this article, the psoas refers to the psoas major as a pair.
The psoas lies very deep inside the belly, under a network of nerves (the lumbar plexus) and layers of connective tissue and is therefore very difficult to palpate. It is not a muscle that works hard - just like the tender loin in beef, it does very little work, so it is the tenderest part, as you can physically see when taking part in dissection or cadaver studies. It's a postural muscle and will respond in accordance to the positions you keep it in most frequently.
What does the psoas do?
Does it flex the hip? Yes in the sense that it can pull your leg towards you, but only by rounding your lower back. The hinge is the lumbar spine, not the hip.
Does it tilt your pelvis? Yes, it can bring the lower part of your pelvis (pubic symphysis) towards the most prominent part of your pelvis at the front (ASIS).
Does it thrust your ribcage? Yes, it does take your ribs forward. It's not the psoas, it's you taking the psoas there without realising - you might take it there when trying to appear straighter, taller, slimmer!
Does it stabilise your spine? Considering the amount of attachment sites on the spine (10 on each side), it does make sense that the psoas has this role!
It can also prevent your pelvis from twisting relative to your ribcage.
It can be chronically contracted on one side only, making it seem that you have a shorter leg, but if your ribcage is poking out on the same side, then it's likely that the psoas is involved.
It is important that the psoas is free from tension, so the spine, the pelvis and the hips can articulate freely and smoothly. This goes a long way towards a body free from lower back, groin, pelvis, hip and knee pain.
How does the psoas get tense?
The psoas adapts its shape in response to your movement habits. The closer you bring the bottom attachment to the top attachments and the longer you spend in this position, the tenser the psoas will be. Think of how your lower back and hips feel when standing upright after a long car or plane journey or a long bike ride? Stiff!
Spending too much time with the two attachments of the psoas close to each other resets its resting length. It creates an imbalance between flexor and extensor muscles, with pain and injury not far behind as you end up taking this shape to your walking and running, extending at the spine instead of extending at the hip. Ouch.
If your lower back is rounded and you have lost your natural lumbar curve (left photo), your psoas is not at its optimal length.
If your ribs are sticking out when lying on your back (top picture right) and you can curl your fingers up under your ribcage, your psoas is not at its optimal length - meaning that it not releasing back at its longest length.
This simple observation is not enough to o assess a tight psoas objectively. To assess the spinal curve created by a tense psoas, you need to look at the forward displacement of the vertebrae highest on the spinal attachment as well as various degrees of extension and flexion in the lumbar spine.
What causes psoas issues?
Spending most of your day (and night!) at the same angle of flexion at the hip - often 90 degrees as measured between pelvis and thigh bone (femur). Think sitting, cycling, rowing, treadmill walking, stepper and other gym machines, etc. The default resting position of your psoas in theses cases is in flexion, rather than anatomically neutral (neither flexion, nor extension but centered).
What are some potential solutions?
In my training as a soft tissue therapist, I learned some hands-on therapy to "release" the psoas but I stopped doing this several years ago because I realised (both as therapist and client) that the effects were short-lived, which was confirmed by many clients who spent a fortune on quick fix treatments with various other health practitioners for very little benefit and often with a great deal of pain ("brute force" as reported to me by a client, and some bruising for another). Not only is the psoas difficult to access for massage and trigger point therapy, it is also risky as you might press on something other than the muscle. It often feels uncomfortable for the therapist and/or the client. Muscle Energy Techniques (a technique involving contraction of the psoas against resistance to better relax it) may appear effective, but the relief will be temporary as you go back to your old habits and the psoas never recovers its full resting length.
Your physio, personal trainer or yoga/pilates teacher will almost certainly offer you some exercises involving hip extension, which may seem like a sensible approach. The trouble is that these do very little to reduce the excessive tension in the psoas. Again, the effects of your stretches will be temporary as you might spend, at best, 30 minutes of extension for many hours of accumulated flexion. Some yoga poses might make your psoas issue worse by "feeding" the rib thrusting habit - think back-bends. Some pilates exercises might also increase tension in your psoas by increasing tension in the abdominals or the glutes; fighting tension with tension rarely works in my experience. You might be able to bring your ribcage down towards your pelvis by contracting your muscles but as soon as you relax, your true shape will re-appear and should be addressed rather than hidden. You might be able to strengthen your glutes by doing lots of static exercises but if you can't use your glutes as you go about your daily life, you don't have functional glutes that engage naturally as needed, with just the right amount of contraction for the task.
Instead of manual therapy and extension exercises, consider replacing hip flexion activities, such as treadmill walking, cycling and rowing, by walking combined with some corrective exercises to restore length and strength in all the muscles in your body and full range of movement in all your joints; so eventually you will be able to walk with hip extension, your glutes and hamstrings engaging naturally and happily with every step. Consider also gradually reducing your sitting time, sitting better (check out the first exercise in my taster balance class) and changing your sitting position often, when there is no choice but to sit.
To restore the natural resting length of your psoas, learn a method of slow, passive self-release. Once you get it, it will save you a lot of pain and a lot of money! And it's easy and pleasant to do in your daily life.
Additionally, when you're well on your way to a happier psoas, consider adding a few gentle psoas stretches and lengthening exercises, such as lunges, paying special attention to ways you might "cheat", by rib thrusting for example, which adds slack in the psoas and reduces the effectiveness of the exercises.
This is what your body looks like when your psoas is at its natural, resting length (photo above) - back of the legs resting fully on the floor and front ribs on the same horizontal line as the pelvis, the back of the ribcage completely resting on the floor, with no gap.
Once you can relax in this anatomically neutral position, you can start recovering ranges of hip extension and hip flexion.
Note that if you can't lie flat on the ground, you won't be able to stand upright either. There will be some spinal compression somewhere.
The photo above shows the position I get clients into when they come for a private session and it invariably feels good! To achieve this passive self-release of the psoas, all you need to do is to anchor the bottom attachment of the psoas down and bolster your shoulders and head, until you find the resting length of your psoas. The amount of bolstering will depend on the state of your psoas and on how much tension you are holding.
How important is the psoas?
It is no more or less important than the other 600+ muscles in your body! Every single muscle in your body has important functions, some of which may be surprising to you. For example muscles are part of your cardiovascular system (pumping blood back to the heart) and of your lymphatic system (which eliminates waste, cleaning up any debris). A muscle that is in a state of chronic contraction needs attention, as it won't be fulfilling its important roles of circulating blood and lymph, to keep you as healthy as you should be.
It is worth noting that the psoas is part of a whole system of muscles and connective tissue. You cannot look at a muscle in isolation. You cannot think that one exercise, one position will sort all your ills. When the psoas is chronically contracted, it's always a good idea to look at the other muscles it has a close connection to - rectus femoris, iliacus, quadratus lumborum, diaphragm, intercostals, tensor fascia latae, rectus abdominis, pelvic floor muscles, etc.
Muscles don’t exist in isolation. Muscles contract and relax in combination with other muscles and connective tissue. Proper pelvic position is established by chains of muscles working together, so a whole-body approach is the most sensible approach.
For more guidance on the psoas passive self-release and other corrective exercises, consider subscribing to the Virtual Treatment Room.
For more information (and a break from the screen!), listen to this podcast between biomechanist Katy Bowman and psoas specialist Liz Koch.