These muscles are distinct in the abdomen, but in the thigh, they are usually indistinguishable, and so in that context, they are usually given a common name. They are occasionally labelled "dorsal hip muscles" or "inner hip muscles".
It is, however, a typical posture muscle dominated by slow-twitch red type 1 fibers, and is therefore susceptible to pathological shortening or contracture (especially in older people with a sedentary lifestyle) and requires regular stretching to maintain normal tone. Such shortening can lead to increased anterior pelvic tilt and lumbar lordosis (unilateral shortening), and limitation of hip extension (bilateral weakness).
The iliopsoas muscle is covered by the iliopsoas fascia, which begins as a strong tube-shaped psoas fascia, which surround the psoas major muscle as it passes under the medial arcuate ligament, 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.