Which action would result from flexion at the elbow joint?

Flexion at the elbow joint specifically refers to the action of decreasing the angle between the forearm and the upper arm. This action is commonly known as bending the arm. When flexion occurs, the forearm moves closer to the upper arm, which leads to a reduction in the angle at the joint. This movement is fundamental in various activities, such as lifting objects or performing exercises like curls.

The other choices represent different types of movements that do not involve flexing the elbow. For instance, straightening the arm indicates extension at the elbow, lifting the arm sideways involves shoulder abduction, and rotating the forearm pertains to movements such as pronation or supination. Understanding these terms highlights the specific nature of flexion as a movement that brings two body parts closer together at the joint.