Medically reviewed by Kimberly Brown, MD Fact checked by Khara Scheppmann The iliopsoas muscle is the major flexor of your hip joint. It’s made up of two muscles: the iliacus, the psoas major.

Psoas major vs. minor muscles. The psoas minor is another muscle in your core. It starts at the cartilage that connects the last bone in your mid-spine and the first bone in your lower spine.