Buried deep within the core of your body, the psoas (pronounced “so-az”) affects every facet of your life, from your physical well-being to who you feel yourself to be and how you relate to the world. A bridge linking the trunk to the legs, the psoas is critical for balanced alignment, proper joint rotation, and full muscular range of motion. In yoga, the psoas plays an important role in every asana. In backbends, a released psoas allows the front of the thighs to lengthen and the leg to move independently from the pelvis. In standing poses and forward bends, the thighs can’t fully rotate outward unless the psoas releases. All yoga poses are enhanced by a released rather than shortened psoas. (When you reverse your orientation to gravity in inversions, however, the psoas must be toned as well as released to maintain proper spinal stability.)
To locate this powerful muscle, imagine peeling your body like an onion. The first layer is the skin; next come the abdominal muscles in front and the massive muscles of the sides and back. One layer deeper lay the intestines and another layer of back muscles. Continue peeling each layer until just before you reach your skeletal core: There in the center of your inner universe rest the psoas muscles. One on each side of the spine, each working independently yet harmoniously, the psoas attaches to the side and toward the front of the 12th thoracic vertebra and each of the lumbar vertebra. Moving through the pelvis without attaching to bone, the psoas inserts along with the iliacus muscle in a common tendon at the top of the femur.
A healthily functioning psoas provides a sensitive suspension bridge between the trunk and the legs. Ideally, the psoas guides the transfer of weight from the trunk into the legs and also acts as a grounding wire guiding the flow of subtle energies. Working properly, the psoas functions like the rigging of a circus tent, stabilizing your spine just as guy wires help stabilize the main pole of the big top.
In addition, the psoas provides a diagonal support through the trunk, forming a shelf for the vital organs of the abdominal core. In walking, a healthy psoas moves freely and joins with a released diaphragm to continuously massage the spine as well as the organs, blood vessels, and nerves of the trunk. Working as a hydraulic pump, a freely moving psoas stimulates the flow of fluids throughout the body. And a released, flowing psoas, combined with a stable, weight-bearing pelvis, contributes to the sensations of feeling grounded and centered.
Excerpt from Yoga Journal Article The Psoas Is: by Liz Koch