The psoas major is a muscle of greater strength and area in the lumbar muscles of the human body, and its location is in the deeper layers of the lumbar region, which cannot be touched in the back of the human body, but may be touched in the deeper layers of the abdomen. The upper end of the psoas major muscle as a whole is at the level of the lower edge of the 12th thoracic vertebra, and the lower end is at the level of the upper edge of the 5th lumbar vertebra, and the two psoas major muscles are on the two sides of the lumbar vertebra, and have been downward with the iliacus muscle to form a bundle of tendons connected to the femur. When the human body to do a kick step action or thigh force against the abdominal action, is the contraction of the psoas major muscle control, but also allows the legs to do the internal eight foot action, psoas major muscle can also be involved in completing the forward flexion of the spine action. The psoas major muscle is mainly innervated by the lumbar nerves, especially the 2nd-4th lumbar nerves, which are the main nerves controlling the psoas major muscle. Patients with lumbar disc herniation who have symptoms of lumbar pain may have pain in the psoas major muscle caused by stimulation of the nerve.