Which of the following movements refers to an increase in the angle between body parts?

The movement that refers to an increase in the angle between body parts is known as extension. This term specifically describes the action of straightening a joint, which increases the angle between two bones or body parts, effectively moving them away from each other. For instance, when you extend your arm, you are straightening it at the elbow, which causes the angle at that joint to increase.

In contrast, flexion refers to the bending of a joint, decreasing the angle between the body parts involved. Retraction involves moving a structure backward, often used in the context of the shoulder blades moving towards the spine, while adduction refers to moving a limb towards the midline of the body. Understanding these terms is crucial in many medical and anatomical discussions, particularly when describing movements in physical therapy or anatomy classes.