Which action is primarily performed by the triceps brachii?

The triceps brachii primarily performs the action of extending the elbow. This muscle is located on the posterior aspect of the upper arm and consists of three heads, which originate at different points on the shoulder and upper arm. When contracted, the triceps brachii pulls on the olecranon process of the ulna, leading to the extension of the elbow joint.

This action is crucial for movements such as pushing, throwing, and any other activities that involve straightening the arm. Understanding the function of the triceps brachii highlights its role in various physical activities, where elbow extension is essential for force generation and movement efficiency.

The other options focus on different actions that are not primarily associated with the triceps brachii, as flexion of the elbow is primarily the role of the biceps brachii, abduction of the shoulder is mainly facilitated by muscles such as the deltoid, and medial rotation of the shoulder is typically accomplished by the subscapularis and other rotator cuff muscles.