Which of the following describes a movement that decreases the angle between body parts?

The movement that decreases the angle between body parts is known as flexion. This action typically involves bending a joint, bringing two body segments closer together. For example, when you bend your elbow, your forearm moves closer to your upper arm, resulting in a decrease in the angle at the elbow joint. Flexion occurs in various parts of the body, such as the knees, hips, and fingers, and is a fundamental movement in many physical activities.

In contrast, the other movements mentioned do not reflect this decrease in angle. Extension involves straightening a joint, thereby increasing the angle between body parts. Protraction refers to moving a body part forward, like pushing a shoulder forward, while retraction involves pulling a body part backward, such as bringing the shoulders back. Thus, flexion is the only term that correctly describes the action of decreasing the angle between body parts.