Introducing the Psoas Muscle

Hip Flexor and Stabilizing Muscle

Mike Harrington/Getty Images

The psoas muscle is a key part of core fitness. Take a look at where it is, what it does, and how to keep it healthy. To answer another common question, it is pronounced so-ass.

Location of the Psoas Muscle

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.

The psoas is not like many of the familiar surface muscles. You can't see it, and most people can't flex or release it on demand as you 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.

How the Psoas Moves You

The psoas is traditionally considered a hip flexor. Hip flexors are muscles that bring the trunk and leg closer together. It is also a posture stabilizing muscle and 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, the psoas muscles are tight and overworked in many people—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 you constantly. It is unable to return to a neutral position from which it could respond with flexibility to the shifts of the 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.

Working With the Psoas Muscle

Fitness trends put more attention on the core and people are taking a deeper look at the breadth of influence of the psoas. 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 decades. She describes this nerve-rich core muscle as a messenger of the central nervous system. 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 in an article in Pilates Digest:

"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."

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. They see their job as one of creating ideal conditions for the psoas to do its 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 you do in Pilates, gives the psoas the opportunity to be the flexible and 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. That's something you can do right now.

2 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Rauseo C. The rehabilitation of a runner with Iliopsoas tendinopathy using an eccentric-biased exercise – a case report. Int J Sports Phys Ther. 2017;12(7):1150-1162. doi:10.26603%2Fijspt20171150

  2. Clevland Clinic. Psoas Syndrome.

Additional Reading
  • Calais-Germain B. Anatomy of Movement. Seattle: Eastland Press; 2014.

By Marguerite Ogle MS, RYT
Marguerite Ogle is a freelance writer and experienced natural wellness and life coach, who has been teaching Pilates for more than 35 years.