Anatomy of the psoas The psoas muscle is a long, ribbon-shaped muscle that starts at your lower back, and runs down through your pelvis where it joins the iliacus and connects to the top of your thigh bone (lesser trochanters). You can’t talk or work on the psoas muscle without also mentioning the iliacus. Together, these muscles are known as the iliopsoas muscle and they form the strongest of the hip flexor muscles while also supporting your spine. #anatomy | YOGABODY