American Board of Surgical Assistants (ABSA) Orthopedic Practice Test

The action that increases the angle between body parts is known as extension. An extensor muscle is primarily responsible for this action, which typically occurs in various joints throughout the body, such as the elbow and knee.

For instance, when extending the arm at the elbow, the angle between the forearm and the upper arm increases, which illustrates the fundamental concept of extension. In the case of the leg, when kicking it backward, the angle at the hip joint and the knee increases.

This differentiates the action from flexion, which decreases that angle, as seen when bending the elbow or knee. Meanwhile, abduction refers to movement away from the midline of the body, while adduction involves movement toward the midline. These actions also change angles in certain joints, but they do not primarily focus on increasing the angle between body parts in the same sense as extension does.