What is the term for the muscle that acts as the main mover during an exercise?

The term for the muscle that acts as the main mover during an exercise is known as the agonist. When an exercise is performed, the agonist is the muscle primarily responsible for generating the force necessary to execute the movement. This muscle contracts and shortens while stabilizing the joint without excessive influence from other muscles.

For example, during a bicep curl, the biceps brachii is the agonist because it is responsible for flexing the elbow joint and lifting the weight. Understanding the role of the agonist is crucial as it helps in designing effective training programs by ensuring that the primary muscle groups are appropriately targeted for strength, endurance, or hypertrophy.

In contrast, the antagonist serves the opposite role by opposing the action of the agonist, providing balance and stability to the joint throughout movement, while the synergist assists the agonist by providing support or enhancing the movement. The term "isometric" refers specifically to a contraction where the muscle length does not change, which is not directly related to identifying the main mover in a dynamic exercise.