Which muscle acts as an extensor in the human body?

The triceps muscle serves as an extensor in the human body primarily because its role is to extend the elbow joint. When the triceps contract, they pull on the ulna at the elbow, leading to the straightening of the arm. This action is crucial for various motions, including pushing and throwing, as well as overall arm stability.

In contrast to the triceps, the biceps muscle is categorized as a flexor because it bends the elbow when contracted, bringing the forearm closer to the shoulder. The deltoid muscle is primarily involved in raising the arm and does not function as a primary extensor. Lastly, the rectus abdominis, which is a muscle of the abdominal wall, aids in flexing the spine rather than extending it. Therefore, the triceps distinctly fulfills the role of an extensor in the upper limb.