It forms the lateral portion of iliopsoas, providing flexion of the thigh and lower limb at the acetabulofemoral joint.

[1] It proceeds across the iliopubic eminence through the muscular lacuna to its insertion on the lesser trochanter of the femur.

[1] Its fibers are often inserted in front of those of the psoas major and extend distally over the lesser trochanter.

[3] In open-chain exercises, as part of the iliopsoas, the iliacus is important for lifting (flexing) the femur forward (e.g. front scale).

In closed-chain exercises, the iliopsoas bends the trunk forward and can lift the trunk from a lying posture (e.g. sit-ups, back scale) because the psoas major crosses several vertebral joints and the sacroiliac joint.