In an antagonistic muscle pair, what is the term for the muscle that contracts?

In an antagonistic muscle pair, the term for the muscle that contracts is "agonist." This muscle is responsible for executing the specific movement by shortening and pulling on the bone it is attached to. For example, when you perform a bicep curl, the biceps act as the agonist as they contract to lift the weight.

The agonist is crucial in initiating movement, while the opposing muscle, known as the antagonist, relaxes to allow this movement to occur smoothly. In a typical scenario, when the agonist contracts, the antagonist is in a relaxed state to prevent any resistance that could hinder the movement.

Additionally, the term "prime mover" often refers to the main muscle that performs an action, which in many cases is synonymous with the agonist. However, in the context of the question, the most straightforward and widely used term in muscle physiology for the contracting muscle is "agonist." Lastly, the term "synergist" refers to muscles that assist the agonist in movement but do not contract to create the primary action themselves.