During our Cultivating the Core class this week, a discussion of the postural muscles came up. I mentioned how the psoas muscle was the hidden performer in our core strength and stability. And, because it plays such a large role in many of our yoga postures, I promised to address it in our Friday Focus this week.
Pronounced “so az” (the letter p is silent), the psoas is the only muscle that connects the upper body to the lower body. Basically, it is fundamentally responsible for your posture and regarded as the most important skeletal muscle in the body.
Technically, the psoas is made up of two muscle groups, the minor and the major psoas. The major psoas is attached all along the lumbar spine and travels deep from the back of the body to the front of the body where it inserts on the inside of the femur (or thigh) bone. 
The minor aspect, being smaller and nearly function less (since we are now an upright standing species), joins the top of the lumbar spine to the inside of the pelvis.
To make things more complicated the psoas is also part of a larger muscle group called the iliopsoas which includes the iliacus. It stretches from the iliac crest (top of the hip) to the femur. Together the three muscles are integral to hip movement.
Needless to say the psoas’ involvement in body function is immeasurable. Physically, it is essential to our balance, critical to healthy alignment and a major stabilizer. It functions along with many other muscle groups to move the hips, lumbar spine, and legs.
Within the subtle body, the psoas is credited as the mover of energy and related to the actions of the third chakra. Because it is located so deeply within the body, the psoas is also known to be linked to the nervous system and many emotional functions.
Want to Learn More?
Here is an excellent book for you to explore: The Vital Psoas Muscle Although it is only 128 pages long, it is filled with valuable information regarding anatomy/function and the emotional/spiritual qualities of the psoas.