The psoas major originates along the outer surfaces of the vertebral bodies of T12 and L1–L3 and their associated intervertebral discs.

The inferior portion below the inguinal ligament forms part of the floor of the femoral triangle.

Together with the iliac fascia, it continues down to the inguinal ligament where it forms the iliopectineal arch which separates the muscular and vascular lacunae.

[4] It is a typical posture muscle dominated by slow-twitch red type 1 fibers.

It can cause pain in the low or mid back, SI joint, hip, groin, thigh, knee, or any combination.

[citation needed] Iliopsoas muscle is a common site of bleeding in patients who are undergoing blood anticoagulation.