Which muscle is referred to as the antagonist?

The term "antagonist" refers to a muscle that opposes the action of another muscle, which is typically referred to as the agonist or prime mover. In a movement scenario, while the agonist is responsible for producing the desired action, the antagonist works to counterbalance or moderate that movement. This is essential for coordinating smooth and controlled movements, preventing excessive motion, and allowing for the necessary range of motion.

For example, when you flex your elbow, the biceps brachii acts as the agonist, and the triceps brachii serves as the antagonist by relaxing to allow the movement, and then contracting to straighten the arm after the movement is completed. This relationship between agonist and antagonist muscles is crucial for maintaining stability and control during physical activity. The other options represent different roles that muscles play in movement and stabilization but do not define the antagonist's specific function of opposing an action.