Technically the psoas major is not a hip flexor in the traditional sense of flexion. Flexion in the body is when two body parts are brought closer to one another. The psoas major is the most important muscle in the body for a number of reasons.
- It is the muscle most responsible for holding us upright when standing correctly. The psoas major created the lumbar curve of the spine when we came up to stand from all fours- and it is this curve that allows us to be upright with the help of the psoas and other muscles.
- The psoas is the muscle that walks us through life. With every correct step we take the brain tells the psoas to move the leg forward.
- The psoas is the warehouse for the body’s fear and trauma. The body is meant to process energetic stimuli both good and bad—and then let go of the nervous energy that is created in the never ending search for balance or homeostasis. When the nervous energy gets stuck in the body it tends to reside in the psoas.
I often refer to the psoas as a hip flexor because of the connection between flexion and our fear response. When we fear we flex; when we fear too much we stay flexed. This condition of staying flexed is what keeps the nervous energy that gets stuck in the body in the psoas.
But technically the psoas shouldn’t flex. In a happy and healthy body the psoas should always lengthening. The quadriceps muscle of the leg is a hip flexor. When engaged it extends the knee and draws the thigh closer to the trunk. Many people mistakenly think that their quadriceps muscle is the main muscle for walking but that job falls to the psoas.
The way it works is that rather than flexing the leg forward at the command of the brain the psoas should swing the leg forward. Swinging is much different that flexing. For the psoas to work this way though, the body must be functioning at a high level with loose joints and long muscles. Very often tightness in the hip joint or the lower restricts the psoas from swinging let alone flexing and then walking leaves the psoas major behind and the physical action of moving forward is accomplished by compensatory muscles.