Final answer:
The triceps are considered the agonist during exercises that involve extending the forearm at the elbow joint, such as during a triceps extension. This muscle is the prime mover in this action, contracting to straighten the arm.
Step-by-step explanation:
In an exercise where the triceps are considered the agonist, such as during the triceps extension, the triceps brachii muscle principally works to extend the forearm at the elbow joint. This muscle is the prime mover for this action, contracting to straighten the arm and countering the action of the biceps muscle, which acts to flex the elbow. The triceps muscle, also known as an extensor, works opposite the biceps, acting as the primary muscle during elbow extension exercises.
When discussing muscle movement dynamics, the term agonist refers to the muscle that is primarily responsible for generating a specific movement. Conversely, the antagonist muscle moves in opposition to the agonist. In the case of elbow extension, the triceps is the agonist and the biceps is the antagonist.
In everyday life, certain muscle groups may be utilized more than others. However, specific exercises are designed to target less frequently used muscles, like the triceps, to achieve a balanced strength across muscle groups.