The Opinionated Psoas, Part 1

By Thomas Myers

Illustrations by Andrew Mannie

Originally published in Massage Bodywork magazine, February/March 2001.
Copyright 2003. Associated Bodywork and Massage Professionals. All rights reserved.

The psoas is a fascinating muscle. I joke with my students that when they go to visit the Rolf Institute, after they light a candle on the altar to Ida Rolf, they will have to go over and light another stick of incense at the altar to the psoas muscle. Not a word of truth in it, of course. One of the things that drew me to Rolfing in the first place was its warm-hearted and clear-headed resistance to orthodoxy; but Dr. Rolf and Rolfing(R) did have a lot to do with putting the psoas on the bodywork map. Not that she was alone in worshipping this muscle; various dance teachers have gotten excited about it, and one yoga teacher even wrote a book devoted solely to the psoas.1

There are a couple of reasons why the psoas was not on the map 25 years ago when I first took up bodywork -- out of sight and out of mind. Out of sight because it is deep in the body, and does not show up on a chart of the surface muscles. Out of mind because every function the psoas performs can be duplicated by one or more of these surface muscles. It is also difficult to feel inside yourself unless your attention is specifically called to it, and even then it can take some sustained effort. A quarter century ago, the response in most physiotherapy, medical and even massage circles to "psoas" was "so what?"

Things have changed. Last year, I was teaching a workshop in a city noted for its medical work, in a facility that did sophisticated assessments for workers' compensation and athletic injuries. The physiotherapist in charge linked nearly everything he saw to the psoas. Spinal twist? Must be the psoas. Leg length discrepancy? Let's check the psoas. Radiculopathy in the neck? You guessed it -- the psoas was responsible.

FIG. 1 - The psoas is in a unique position, with many important neighboring structures.
There are also a couple reasons why the psoas has climbed the charts to be a hit on almost everyone's list: centrality and connection. The psoas links top to bottom, inside to outside, axial to appendicular, and breathing to walking, to name some of the major connections it makes. The psoas provides part of the root support for the diaphragm (as we will see later) and definitely provides the highest and most important initiation of walking. It's at least an arguable opinion the legs start at T12-L1, and the psoas begins the division into "two-ness" which culminates in our bipedal walking.

The neighbors of the psoas are also very influential -- the hip joints, lumbar spine, sacrolumbar junction, thoracicolumbar junction, kidneys, adrenals, iliac arteries, solar plexus, lumbar plexus (which lies within the psoas) and, of course, diaphragm. See Fig. 1.

The psoas arises at the top from numerous small attachments on the lateral side of the body and the front side of the transverse processes of the five lumbar vertebrae and the 12th thoracic. All these individual slips gather together to run down and forward to the iliopectinial ridge, right over the front of the hip joint, and then down and back to the lesser trochanter on the inside corner of the "7" shape of the femur. It is widely agreed the psoas is a hip flexor. From there on out, there is a lot of controversy about its other functions, and its role in posture and everyday movement.

As a devotee of the psoas, I have lived with these competing ideas for 25 years, breathed in a number of other people's ideas, and breathed out a few of my own.2 It is important for the reader to understand that the following set of ideas about the psoas are entirely untested in the halls of science, except they work, clinically, for me (and for my students, or so they say).

Over the next few installments, we are going to examine several issues: 1) What is the action of the psoas at the hip joint in terms of medial and lateral rotation?, 2) What is the action of bilateral contraction of the psoas on the lumbar spine?, 3) What is the effect on the spine of unilateral contraction of the psoas?, and 4) What other muscle complexes can take over from the psoas? Once again, caveat emptor: these are just ideas, opinions designed to make you think. As you read, believe and incorporate only what works in your own experience.

Fig. 2A - When you look from the side, it is clear the psoas, by going over the lip of the ilium in front of the hip joint on its way to the femur, must be a hip flexor.

Is Psoas a Hip Flexor?
Let's first look at the action of the psoas at the hip. Looking from the side, we can see how it goes forward from the lumbars to the pelvic rim, and then back again to the femur. Given where the fulcrum of the hip joint lies, it is difficult to escape the idea the psoas is a hip flexor (Fig. 2A). Once you are familiar with finding the belly or the tendon of the psoas, the experience of feeling it flash into tightness every time the hip is flexed is also a convincing argument.

Ida Rolf, in her book on Rolfing3, states, "In normal balanced (hip) flexion, the psoas does not shorten, does not bulge forward; it lengthens and falls back within the abdomen." This is one of those illogical (she calls it that herself in the very next sentence) statements that Dr. Rolf often made which later turned out to be right. But this one I cannot figure out or make it conform with my experience. Whether I have my client supine or sitting, whenever I ask for hip flexion (as in "raise your knee to take your foot off the ground"), I feel the psoas leap forward, tightening into my hand. In fact, it is my principle way of reassuring myself where I am on the psoas.

FIG. 2B - In Ida Rolf's conception, the proper balance between the rectus abdominis and the psoas muscle would allow the psoas to 'fall back' within the body (right). Whether or not that is true, it is most certainly the case that an overly short psoas produces strain against the rectus from within and compression between the lumbar vertebrae (left).
There is the phenomenon of the belly falling back in trunk flexion on the legs (which amounts to the same change in bony relationships as hip flexion on the trunk). In what I would recognize as "proper" movement in a forward bend, the contents of the belly seem to fall back against the lumbar spine in trunk flexion. And it is true that if the belly contents bulge out during a forward bend, the possibility of lumbar binding and compression seem to increase (Fig. 2B). But in this movement, essentially a standing person looking closely at their knees, active contraction of the psoas is not required, it is simply a matter of eccentric contraction (a controlled letting go) of the hip extensors like the hamstrings, since the person essentially falls forward into gravity in a controlled manner. This passive movement of the psoas, however, does not seem to me to confirm what Dr. Rolf was asserting above.

In the matter of the psoas as a hip flexor, I am afraid, since I can't make her statement either make sense logically or fit my experience, that I must abandon my favorite teacher in favor of the more traditional view, as expressed by nearly everyone else, that the psoas is designed to flex the hip when it contracts.4

Okay, so it is a hip flexor, but what else is it? Looking at the psoas from the front, we can see it goes up and in from the hip, so it could possibly participate in adduction; but it is so vertical that I doubt its contribution to this action is significant. Turning our attention to its action in medial and lateral rotation, though, the situation becomes a little trickier.

Is Psoas a Medial or Lateral Rotator?
This question is worth answering, for this simple reason -- if you see a client with a strong medial rotation of the femur (pigeon-toed), should you work to release the psoas? Or should you perform such a release on the client with the strong lateral rotation (duck-footed)?

Rolf weighs in on this issue also: "In thus inserting on the medial side of the femur (the rotator inserts more laterally), the psoas major can function as a medial rotator of the thigh, balancing external rotators."5 Once again, this is a contrarian view, since most texts list the psoas as a lateral rotator. Let's examine both arguments.

FIG. 2B - In Ida Rolf's conception, the proper balance between the rectus abdominis and the psoas muscle would allow the psoas to 'fall back' within the body (right). Whether or not that is true, it is most certainly the case that an overly short psoas produces strain against the rectus from within and compression between the lumbar vertebrae (left).
First, let us look at some other muscles which perform these two tasks. The lateral rotators of the hip -- like my favorite, the obturatur internus -- work by pulling back on the greater trochanter, rotating the ball in the socket. Because the greater trochanter is obviously on the outside edge of the bone, this muscle and its neighbors clearly have the leverage to perform the movement, and clearly contract when lateral rotation is produced.

The tensor fasciae latae muscle, which produces medial rotation among other movements, pulls forward on the front of the trochanter, pulling the femur into medial rotation, likewise rotating the ball in the socket. You can feel this for yourself by putting your finger or thumb just below and outside of your anterior superior iliac spine (ASIS), and then turning your knee in. No matter whether you are sitting, standing or lying, you will feel this muscle bulge and tighten when you medially rotate the leg on the trunk.

Now let us consider the argument for the psoas as a lateral rotator. The psoas attaches distally to the inside of the femur to the lesser trochanter, which is toward the posterior part the upper femoral shaft (Fig. 3). Tape string or a ribbon to the lesser trochanter of a loose femur -- if you have access to one, or imagine it if not -- and pull up and forward on the string. The femur will spin like a top into a lateral rotation. The image is roughly equivalent to how the biceps tendon goes onto the radius, and likewise spins the radius like a top (see the column on the biceps in Massage Bodywork, Oct/Nov 2000). If you don't have a femur handy, reach down between your legs, grab the inner seam of your trousers and pull up -- doesn't your leg want to rotate laterally? No less an authority than Frank Netter tacitly makes this argument in his illustration on the psoas, a version of which is given in Fig. 3. Is this not pretty convincing?

FIG. 3 - The argument for the psoas as a lateral rotator, redrawn from Netter's Atlas of Human Anatomy, page 352. But is the axis of rotation the same as the axis of the femoral shaft, as he implies?
But so is the counter-argument. Here's the problem with the supposition in the preceding paragraph: it assumes the femur spins around the axis of the shaft of the femur (the dotted line in Fig. 3). When the biceps spins the radius, the proximal end of the radius is rounded and straight, so the bone as a whole can and does spin along its long axis. If you followed the experiment above, you can indeed tape a "psoas" onto the lesser trochanter, turn the bone medially to wind the string around the bone, and indeed spin the femoral shaft laterally when you pull on it. But the proximal end of the femur is not straight, it turns a sharp corner from the femoral shaft onto the femoral neck and head. The head is not free to spin; it is firmly fixed into the socket of the acetabulum. When you spin the femur along the axis of its main shaft, the ball part of it has to move in a way it could not possibly move when it is fixed in the hip joint. The big problem with the argument for the psoas as a lateral rotator is simple, compelling, but not immediately obvious -- the axis of rotation of the femur is not the same as the axis of the shaft itself.

The action of a muscle is dependent not only on the placement of the muscle's attachment to the bone, but also on the relation of that attachment to the mechanical axis (MA) of that bone's movement. The MA needs to be drawn from the proximal bearing point to the distal one, and then the movements considered as working around that axis. If we examine the MA of the femur, we see it runs not along the shaft of the femur, as Fig. 3 assumes, but on a line drawn from the bearing point of the hip joint to the bearing point below (Fig. 4). If we assume the lower bearing point of the femur is in the middle of the knee joint, and we draw such a line, we see the line of the MA passes way medial to the shaft of the femur. If this is the case, the psoas attachment to the lesser trochanter is outside this line. Since the psoas pulls to the front from this point, it will, like the tensor fasciae latae, necessarily act as a medial rotator of the femur on the hip bone. Can you see it would draw the lesser trochanter forward and in a narrow inward arc, while the greater followed with a greater arc? So the psoas is a medial rotator, yes? And a complete stretch for the psoas should involve hip extension and lateral rotation, not extension and medial rotation as many professionals recommend, right?

FIG. 4 - The mechanical axis of femoral rotation does not pass through the long axis of the shaft of the femur, as implied in Fig. 3, but along a line between the hip joint and the lower point of rotation, drawn here through the middle of the knee joint.
Well, we are not quite done with it yet. Netter is clearly wrong in drawing the axis along the shaft of the femur, but are we right (in our attempt to justify Ida Rolf's statement) in drawing this MA of rotation from the center of the hip to the center of the knee joint? Is that actually the axis of rotation of the femur? The answer is "it depends." Depends on what? When the knee is extended, the femur and the lower leg rotate together. Straighten your knee and try to rotate the femur without rotating the lower leg. You can't. If you put your heel on the floor (when your knee is extended and locked), then the MA is between the top of the hip joint and the heel. If you put your toe on the floor, then the MA is between the hip and the toe. If you take the foot off the floor and rotate the leg, then the axis of rotation changes again, to a line running between the hip joint and the center of gravity of the leg as a whole. Bend your knee with your foot on the floor and the axis changes again, because some 30 degrees of rotation is possible between the femur and the tibia in a flexed position. In other words, the MA of rotation in the femur is variable depending on your position, the mass of your upper and lower leg, and the physics of the whole situation.

FIG. 5 - Leg with mechanical axis more outside the knee.
If we draw the MA to pass through the center of mass of the leg as a whole, it seems to pass more laterally than the line we drew in Fig. 4 (see Fig. 5). If the line passes this way (which is admittedly presumptive and not necessarily always the case), then the MA of rotation passes right over the distal insertion of the psoas at the lesser trochanter. If and when this is the case, then the entire iliopsoas muscle has no rotational component at all -- it tends to produce neither medial rotation nor lateral rotation.

Perhaps we could show with myography (difficult in such a deep muscle) that in some given individual in some given situation, the psoas fires to help produce either medial or lateral rotation. But by now we should be clear the placement of the lesser trochanter, protruding medial and posterior from the shaft of the femur, acts by design to maximize the action of the iliopsoas as a hip flexor, and to minimize its action as a rotator in either direction, because it approximates the (variable) MA of rotation. Whatever minor role it may play, the contribution of the psoas to either direction of rotation will be negligible compared to the medial and lateral rotators which attach to the greater trochanter.

So the psoas as a medial or lateral rotator? 'Fuhgeddaboudit' -- it is a hip flexor for sure, but we6 hope to have convinced you it is not responsible for significant postural contribution to either side of rotation.

Next installment, we will turn our attention to another set of untried theories about the action of the psoas on the spine.

Thomas Myers, Certified Advanced Rolfer(R), LMT, NCTMB, studied directly with Drs. Ida Rolf and Moshe Feldenkrais, and has practiced integrative bodywork for more than 25 years in a variety of cultural and clinical settings. Myers directs Kinesis, Inc. which develops and runs training courses internationally for manual and movement therapists. He served as a founding member of the NCBTMB, and as chair of the Rolf Institute's Anatomy faculty. His articles have appeared in a number of magazines and journals, and a book is now underway on his "Anatomy Trains" Myofascial Meridians approach. Myers retains a strong interest in perinatal and developmental issues around movement. His practice in Boston combines structural integration, physiological rhythmic sensitivity and movement. He lives, writes and sails on the coast of Maine.

1. Koch, L, 1997, The Psoas Book, 2nd ed, Guinea Pig Publications, ISBN 0965794407.
2. This and the columns following depend on ideas gratefully received from Rolfers Robert Schleip (lecture notes on the adductors and psoas, first published in Rolf Lines, Nov. 1998, and available at, Michael Murphy (notes for a workshop on the psoas, not published), and Michael Morrison ("Further Thoughts on Femur Rotation and the Psoas," Rolf Lines, Fall 1999, available on Any failure to convey their ideas accurately is entirely my own.
3. Rolf, Dr. I.P., Rolfing; Dennis Landman , 1977 (San Francisco), p116. Published by the Rolf Institute: 800/530-8875.
4. For example: Basmajian, John, Grants Method of Anatomy, 8th ed, p 264; and Luttgens, Kathryn, Kinesiology, 7th ed, p 153.
5. Rolf, Ida, Rolfing, 1977 Dennis Landman Pub, p 170.
6. Once again, I would like to acknowledge the contributions of Rolfers Michael Murphy, Robert Schleip and Michael Morrison to this discussion, as well as numerous students and practitioners who have struggled with this vexing conundrum.

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