Which term refers to the movement that decreases the angle of a joint?

The term that refers to the movement that decreases the angle of a joint is flexion. This movement typically occurs in hinge joints like the elbow or knee, where bringing two surfaces closer together reduces the angle between them. For instance, when you bend your arm at the elbow, this movement is a clear example of flexion as it decreases the angle between the forearm and the upper arm.

In contrast, extension is the opposite movement, where the angle of the joint increases. Dorsiflexion refers specifically to moving the foot upwards at the ankle, and adduction describes the movement of a limb toward the midline of the body. These movements do not involve the direct action of decreasing the angle between two body parts from a joint, which is the defining characteristic of flexion. Thus, flexion is the correct term that captures the essence of decreasing the angle of a joint.