The psoas major and the rectus abdominis muscles have an important relationship inside the body even though they don’t literally work together. Muscles relate to each other in many different ways. Sometimes they work in opposition—for .
De Quervain's Syndrome: Tendons of the Extensor Pollicis Brevis and Abductor Pollicis Longus muscles. Both provide radial abduction, as opposed to palmar abduction.The tendons run, as do all of the tendons passing the wrist, in synovial sheaths.