With the m. iliacus and m. psoas minor, the m. psoas major (PM) forms part of the m. iliopsoas. As the m. psoas minor is missing in 50% of individuals [9], it will not be dealt with further. Figure 1 presents an overview of the iliopsoas muscle. The PM arises from the lateral aspects of
the lumbar vertebral bodies and discs, and with smaller fascicles from the transverse processes. With the iliacus muscle, the PM converges towards the iliopubic eminence and, curving backwards along the inner side of the hip joint, inserts with a common tendon on the lesser trochanter
of the femur.
According to anatomical textbooks [9, 18], the PM
1. Flexes the lumbar spine (LS) and bends it laterally
2. Powerfully flexes the femur and rotates it a little outwards,and
3. If the femora are fixed, flexes lumbar spine and pelvis.