We often hear of the psoas as a hip flexor, and it is, but did you know that the psoas is also a paraspinal muscle? The psoas originates from five lumbar vertebrae, meaning it plays an important role in back health. The psoas connects the upper body to the lower body, making it a player in many essential functions and movements. Evolutionarily, our ambulatory ancestors were able to walk, run and sit due to the psoas! The psoas also connects the superficial body to the deep body, and the front of the body to the back of the body.

Often when we use the word “psoas” we’re referring to a combination of two muscles: the iliacus and the psoas major. Together these two muscles are better known as the iliopsoas muscle.

What does the iliopsoas do?

The rumors are true - the psoas is a hip flexor! In this function, it works to bring the leg forward, and in toward the chest as well as externally rotating the femur (turning the toes out like a ballerina). As a paraspinal muscle, the psoas helps to laterally flex the spine (side bending) and is essential for correct standing or sitting lumbar posture and stability of the hip joint. The psoas also helps stabilize the SI joint, and is connected through fascia to the pelvic floor, deep core muscles, and the diaphragm.

Where exactly is the psoas?

The psoas attaches to the spine at vertebrae T12-L4 (the mid- to lower back), crossing a total of eight joints before heading slightly forward to drop over the front of the pubic bone and attach to the femur. Thus, the iliopsoas can play an important role in posture by supporting the natural curve of the spine, or pulling on the spine to increase or decrease the natural curve of the low back.

The psoas and low back pain

The musculature that connects the spine and hip joint, and the balance between those muscles can come into play in cases of low back pain. However, low back pain is complex. “Psoas” may have recently become a buzzword, but we can’t assume that the psoas muscle is the key to resolving low back pain. There are many possible explanations and solutions, which is why it’s important to talk to a doctor about your low back pain!

Interestingly, low back pain, anxiety, and mood disorders are “widely studied and closely related.” All of these conditions involve the activation of the central nervous system’s ‘fight-or-flight’ reaction. The psoas major is involved in the complex neural network of the mind-body experience and the reactive stress system. There’s some evidence that the psoas is involved in PTSD occurrence and may be used in PTSD relief.