The psoas is a long, powerful abdominal muscle located deep in the core of the body. It attaches to the front of the lumbar spine and extends down through the pelvis where it connects to the top of the femur (thigh bone). The psoas has the capacity to lengthen in two directions: up and forward as well as down and back, giving the body bounce and buoyancy as we stand, walk, and run – like an internal spring. Through the big toe, we engage the psoas, pressing off the ground and using gravity to find upward lift.
The psoas muscle is the primary flexor of the hip — in other words, its primary job is to bring the thigh towards the belly. When the psoas has elasticity, it also has the capacity for to lengthen, so the leg can flex upwards AS WELL as having the freedom to extend downwards and back — like a pendulum. When the leg is free to move in both directions, walking has momentum and running feels like flying. Watch a sprinter soar through the air, land, and spring upwards again — THAT is the working of a powerful psoas.
Sitting is a common form of hip flexion and since the psoas is a hip flexor it gets tighter the longer that we sit. Conversely, the more we stand upright and walk or run, the more we extend the hip and hence lengthen the psoas. The body will inevitably form and densify around the activities that we do most, and this explains why so many of us experience the manifestations of having short and tight psoas muscles.
The psoas, paired intimately with the nervous system, also acts as a protector of the body. As mammals, we instinctually go into a fetal posture when we fear harm, to protect our core and vital organs. This flexion of the core is often entirely unconscious, a visceral response that the body initiates through the autonomic nervous system, beyond our mental awareness or cognitive control. We now know that life experiences are held in our tissues, and the psoas in particular, responds to trauma by holding very tight.
Like everything in the body, one thing affects another, so when the psoas gets tight and holds the hip in flexion, the leg is not able to naturally extend away from the spine when we stand and behind us as we walk. This means the gluteus maximus — our primary glut muscle and hip extensor — can not do its job. The rotators of the hip get overworked trying to help out, swinging the leg around to move us forward, the thigh muscles get tighter as they partake in the constant hip flexion. In time, the lumbars are pulled continually forward by the tight psoas, and the low back starts to ache. And on it goes. Sound familiar? For many clients, freeing the psoas is necessary and powerful work that leads to a profound sense of liberation, release and expansion.