noun, plural: antagonist muscles
There are muscles working together to produce and control movement. They may be grouped according to their action. They may be agonists, antagonists, or fixator muscles. The agonists are muscles that produce movements through their contraction and responsible for generating particular movements. The agonists are also called prime movers. They are typically the superficial muscles crossing the joint in motion, and are concentrically contracting or shortening the length of the muscle.1 The antagonist muscles, in contrast, are those that eccentrically contract. They relax in order to lengthen the muscle so that the agonists at the joint act accordingly and produce a particular movement. Antagonist muscles are those that interfere with the action of agonists. They are the superficial muscles that crosses the opposite aspect of the same joint as the agonist.1 Fixator muscles are those that act as stabilizers of a part of the body during the movement of another part, i.e. allowing the agonists to work effectively by stabilizing the origin of the latter.
1 Goodwin, J. (2012). Touch & Movement: Palpation and Kinesiology for Massage Therapists. NY, US: Cengage Learning, Inc. p.38.