Final answer:
The Triceps brachii muscle is responsible for extending the forearm at the elbow, counteracting the biceps brachii muscle which bends the arm. It plays an essential role in pushing movements and is vital for arm straightening actions like pressing weights overhead.
Step-by-step explanation:
The action of the highlighted muscle, Triceps brachii, is to extend the forearm at the elbow. When the triceps brachii contracts, it works in opposition to the biceps brachii, which is responsible for bending the arm. The triceps brachii is known as an extensor muscle, and during its contraction, it increases the angle between the ulna and the humerus, effectively straightening the arm.
The triceps brachii connects to the upper arm and the forearm through tendons, allowing the arm to extend. This muscle is critical for pushing movements and is actively engaged in activities like pressing a weight overhead or during the straightening phase of a push-up.
Moreover, understanding the role of the triceps brachii is essential for analyzing movements in various physical activities and for designing targeted exercise routines to strengthen this muscle group.