Final answer:
When Bobby performed curls, his biceps brachii acted as the agonist muscle contracting to flex the forearm, while his triceps brachii served as the antagonist muscle, which relaxes during the bicep contraction.
Step-by-step explanation:
When Bobby performed curls, his biceps brachii and the triceps brachii served as agonist and antagonist muscles respectively.
The biceps brachii is a two-headed muscle that plays a significant role in the movement of both the shoulder and elbow joints. It is responsible for flexing the forearm, assisting in its supination, and flexing the arm at the shoulder joint. On the other hand, the triceps brachii serves as the extensor muscle of the forearm. During a curl exercise, when the biceps contracts to lift the weight, the triceps must relax to allow this movement. This coordinated action between the two muscle groups is essential for smooth and controlled motion.
Understanding the role of these muscles in exercises like curls underscores the complexity and coordination involved in human movement. The biceps brachii and triceps brachii are perfect examples of how muscles work in pairs: while one contracts (biceps as the agonist), the other relaxes (triceps as the antagonist), demonstrating their function in facilitating the bending and extending of the elbow joint.