The psoas major (/ˈsoʊ.əs/ or /ˈsoʊ.aes/ ,æs the word psoas comes from The greek psoa meaning “the loin.”) region is a long fusiform muscle located on the side of the lumbar region of the vertebral column and brim of the lesser. pelviss part of the iliopsoas, psoas major contributes to flexion in the hip joint. On the lumbar spine, unilateral contraction bends the trunk laterally, while bilateral contraction raises the trunk from its supine position.