The psoas, also referred to as the “muscle of the soul”, is the most significant structural & postural muscle in the body. It effects posture, balance, breath, energy, & movement. Understanding the actions & associated movements of the psoas can help deepen our understanding of bandha by utilizing the muscle to create feelings of lift & lightness. The psoas crosses, & therefore influences, a total of nine joints as it attaches our upper body to our lower body. It is a powerful hip flexor as seen in navasana & utthita hasta paddagusthasana yoga poses. Secondary actions of this muscle are external rotation & abduction of the hip.
The psoas is comprised of the psoas major, psoas minor (which only about half of people have), & the iliacus. The psoas major & iliacus are often referenced together as the iliopsoas muscle because their distal ends merge together in one common tendon & therefore create the same action of flexion & external rotation in the hip. The psoas major has finger-like attachments on the lateral section of the mid & lower vertebrae of the spinal column. The muscle then drapes in front of the pubic bone (to each corresponding side) & attaches to the lesser trochanter of the femur (where the iliacus also attaches). The flat, broad, proximal attachment of the iliacus lines the inside of the pelvic bowl (the ilium).
If the upper section of the psoas is tight, it will flex the spine by pulling down & forwards on the lower thoracic & upper lumbar areas of the spine, thereby decreasing the space between the lower ribs & the pelvis. If the lower section of the psoas is tight, it creates spinal extension through an anterior tilt of the pelvis, increasing the lordotic curve by pulling on the lumbar section of the spine.