What does the term "antagonist" refer to in muscle movement?

The term "antagonist" in muscle movement refers to a muscle that lengthens during an action, specifically when the opposing muscle (the agonist) contracts. In a typical movement, when the agonist muscle contracts to produce movement, the antagonist muscle relaxes and allows this motion to occur, often returning to its resting length or being actively lengthened. This relationship helps facilitate controlled and balanced movement. For example, when you flex your arm at the elbow, the biceps (agonist) contracts and shortens, while the triceps (antagonist) lengthens to enable that movement.

Understanding this concept is key in biomechanics and functional movement because the interaction between agonist and antagonist muscles is crucial for smooth and coordinated actions, as well as for protecting joints from excessive strain.