Muscles also tend to function in groups to accomplish specific movement. For example, the deltoid, biceps brachii, and pectoralis major all help flex the shoulder. Furthermore, many muscles are members of more than one group, depending on the type of movement being considered. For example, the anterior part of the deltoid muscle functions with the flexors of the shoulder, whereas the posterior past functions with the extensors of the shoulder. Members of agroup of muscles working together to produce a movement are called synergists. For example, the biceps brachii and brachialis are synergists in elbow flexion. Among a group of synergists, if one muscle plays the major role in accomplishing the desired movement, it is the prime mover. The brachialis is the prime mover in flexing the elbow. Fixators are muscle that hold one bone in place relative to the body while a usually more distal bone is moved. The muscles of the scapula act as fixators to hold the scapula in place while other muscles contract to move the humerus.