- The psoas major of the iliopsoas attaches from the anterolateral bodies and discs of T12-L5 and transverse processes of L1-L5 to the lesser trochanter of the femur.
- The iliacus of the iliopsoas attaches from the internal surface of the ilium to the lesser trochanter of the femur.
- Both the psoas major and iliacus flex and laterally rotate the thigh at the hip joint.
- Both the psoas major and iliacus anteriorly tilt the pelvis at the hip joint.
- The psoas major also flexes, laterally flexes, and contralaterally rotates the trunk at the spinal joints.
NOTE: Depending on the posture of the lumbar spine, the psoas major can extend the lumbar spine instead of flex it. Specifically, if the lumbar spine is hyperlordotic (in greater extension), then the line of pull of the psoas major (or much of the psoas major) passes behind the mediolateral axis for flexion/extension and the psoas major becomes an extensor in the sagittal plane.