What does the term "flexion" reverse?

The term "flexion" refers to the bending movement that decreases the angle between two parts of the body, typically occurring at joints. The opposite movement to flexion is "extension," which increases the angle between body parts, essentially straightening the joint. For example, when you bend your elbow, you are performing flexion; when you straighten it back out, you are performing extension. This direct relationship establishes why flexion reverses extension, making this answer the correct choice.

In contrast, the other movements mentioned—abduction, adduction, and elevation—refer to different types of movements. Abduction describes moving a limb away from the midline of the body, while adduction involves moving it back towards the midline. Elevation refers to moving a body part superiorly, such as shrugging the shoulders. These movements do not directly relate to the bending and straightening of joints that define flexion and extension.