what is fixator muscle
4. Fixator: The fixator in a movement is the muscle(s) that stabilises the origin of the agonist and the joint that the origin spans (moves over) in order to help the agonist function most effectively. In the bicep curl this would be the rotator cuff muscles, the âguardians of the shoulder jointâ.. Agonist: The agonist in a movement is the muscle(s) that provides the major force to complete the movement. Because of this agonists are known as the âprime moversâ. In the bicep curl which produces flexion at the elbow, the biceps muscle is the agonist, as seen in the image below.