Psoas major muscle

The Psoas major is a long fusiform muscle placed on the side of the lumbar region of the vertebral column and brim of the lesser pelvis.

Origin
It arises:
 * (1) from the anterior surfaces of the bases and lower borders of the transverse processes of all the lumbar vertebrae
 * (2) from the sides of the bodies and the corresponding intervertebral fibrocartilages of the last thoracic and all the lumbar vertebrae by five slips, each of which is attached to the adjacent upper and lower margins of two vertebrae, and to the intervertebral fibrocartilage;
 * (3) from a series of tendinous arches which extend across the constricted parts of the bodies of the lumbar vertebrae between the previous slips; the lumbar arteries and veins, and filaments from the sympathetic trunk pass beneath these tendinous arches.

Insertion
The muscle proceeds downward across the brim of the lesser pelvis, and diminishing gradually in size, passes beneath the inguinal ligament and in front of the capsule of the hip-joint and ends in a tendon; the tendon receives nearly the whole of the fibers of the Iliacus and is inserted into the lesser trochanter of the femur.

A large bursa which may communicate with the cavity of the hip-joint, separates the tendon from the pubis and the capsule of the joint.

Function
It forms part of a group of muscles called the hip flexors, whose action is primarily to lift the upper leg towards the body when the body is fixed or to pull the body towards the leg when the leg is fixed.

For example, when doing a sit up that brings the torso (including the lower back) away from the ground and towards the front of the leg, the hip flexors (including the iliopsoas) will flex the spine upon the pelvis.

Significance in Western Cuisine
Based on the anatomy and physiology of a cow, this muscle is the tenderloin, and tends not to be called upon to do a lot of work, thus it remains underdeveloped, resulting in a cut of meat that is known as the most tender. It forms the basis for several succulent dishes, including chateaubriand, filet mignon and Beef Wellington.

Other meat cuts in this area of the cow's body include the sirloin and the top sirloin.

Arts, Spirituality
Often of high significance in practice such as yoga, pilates, martial arts etc.

Being the only actual muscular connection between body and legs, makes efficient and controlled usage of this muscle very important in terms of finding ones strength, balance, and grounding.

Most forms of lunge will engage and stretch the psoas. Half- and full-lotus positions both stretch and elongate the psoas muscle and hip flexors in general.

Essential for proper lumbar, sacral and spinal support, alignment and control.