Ilipsoas muscle is divided into iliopsoas muscle and psoas major muscle. The psoas major provides important vertical stability for the lumbar spine. At this point, we know two aspects of stabilizing the lumbar spine, psoas major and intra-abdominal pressure. The two will compensate each other, and the most important area to maintain human stability is pelvic chain, including transverse abdominis, multifidus, diaphragm and pelvic floor muscle. These four muscles are activated at the same time to keep the trunk stable and transmit strength.