The Psoas is:
If you guessed C, you're correct. 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.)
Whether you suffer from a sore back or anxiety, from knee strain or exhaustion, there's a good chance that a constricted psoas muscle might be contributing to your woes. Getting in touch with this deeply buried muscle can be humbling at first. You may discover that you've been doing many poses by contracting your core, instead of relying on your skeleton for support and allowing your more peripheral muscles to organize around a toned but flowing and spacious center. But if you persevere, psoas work can add new insight, openness, and stability to your practice. Though your psoas may not be as easy to sense as your biceps or hamstrings, improving your awareness of this crucial muscle can greatly enhance your physical and emotional health.
Along with improving your structural stability, developing awareness of your psoas can bring to light fears long locked in the body as unconscious physical tension. Intimately involved in the fight or flight response, the psoas can curl you into a protective fetal ball or flex you to prepare the powerful back and leg muscles to spring into action. Because the psoas is so intimately involved in such basic physical and emotional reactions, a chronically tightened psoas continually signals your body that you're in danger, eventually exhausting the adrenal glands and depleting the immune system. As you learn to approach the world without this chronic tension, psoas awareness can open the door to a more sensitive attunement to your body's inner signals about safety and danger, and to a greater sense of inner peace.
Meet Your Psoas
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 lie 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.