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Introducing: The Psoas Muscle


Updated June 06, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Pilates instructor in Studio sitting on matt infront of a mirror doing Pilates.
Mike Harrington/Digital Vision/Getty Images

Everyone is talking core fitness these days, and there may be no muscle more core than the psoas muscle (pronounced so-as). In this article we take a look at where the psoas muscle is and what it does, as well as consider various approaches to the health of the psoas muscle.

The psoas is not like many of the surface muscles we are familiar with. We can't see it, and most of us can't flex or release it at will as we might a quad or bicep. It is a deep muscle, involved in complex moves and communications through the core and lower part of the body.

Where the Psoas Is
The psoas major is a large muscle that attaches at the bottom of the thoracic spine (T12) and along the lumbar spine (through L4), then runs through the pelvic bowl, down over the front of the hip joint, and attaches at the top of the femur (thigh bone). It is the only muscle connecting the spine to the leg.

How the Psoas Moves Us
The psoas is traditionally considered a hip flexor. Hip flexors are muscles that bring the trunk and leg closer together. Also a posture stabilizing muscle, the psoas assists in straightening the lumbar (lower) spine. Finally, in actions where one side contracts and not the other, the psoas aids side-bending. It is important to note that the psoas muscle works by eccentric contraction, lengthening along the front spine rather than shortening on exertion.

Since the psoas is a muscle of flexion, exercises that incorporate those kinds of moves are said to strengthen it. When the leg is in a fixed position, the psoas helps flex the torso. Pilates roll up would be an example of such a move. When the torso is fixed, the psoas helps bring the thigh to the torso, as in Pilates knee folds exercise. However, for most of us, our psoas muscles are tight and overworked as it is - a situation often leading to back pain, particularly low back pain in the area where the psoas has so many attachments.

Psoas Stretches
Poor habits of posture and muscle alignment, and sometimes over-training, create conditions where the psoas is required to stabilize us constantly, and is unable return to a neutral position from which it could respond with flexibility to the shifts of spine, pelvis, and leg. Lunge exercises are the most popular exercises to stretch the psoas. However, exacting alignment is required or lunges are of little use with regard to the psoas.
Learn a standing lunge

Working with the Psoas Muscle
As fitness trends put more attention on the core, and people take a deeper look at the breadth of influence of the psoas in particular, some very different views of the best ways of working with the psoas muscle have come to light. Liz Koch has been teaching about the psoas for 30 years. She describes this nerve-rich core muscle as as a messenger of the central nervous system, and she challenges the idea that the psoas' main function is as a hip flexor at all.

Koch describes the many levels of understanding the psoas this way:

It tells a story about an essential midline called the primitive streak from which everything emerges. Within this paradigm the psoas grows out of the human midline and is a messenger of the central nervous system; integral to primary reflexes, neurological proprioception, and personal integrity.
Pilates Digest, September 8, 2009

Koch is not alone in her thinking. Many in Pilates and movement arts are promoting a new respect for the sensitivity and intelligence of the psoas muscle. We are seeing our job as one of creating ideal conditions for the psoas to do it's job - at which it is already a sophisticated expert - rather than attempting to train or interfere with the psoas itself. Focusing on good posture and proper alignment in movement, as we do in Pilates, gives the psoas the opportunity to be the flexible, responsive, bridge between the spine and lower body that it can be.

As a first step, Liz Koch recommends adjusting your posture so that you are truly sitting up on your sit bones. I bet you can do that right now.

Read my in-depth interview with Liz Koch: Does the Psoas Speak Pilates?

The Anatomy of Movement, Calias-Germain
The Psoas is NOT a Hip Flexor, Koch, 2009
The Psoas Muscles and Abdominal Exercises for Back Pain, Gold, 2004

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