ACE Personal Trainer Practice Exam

Horizontal extension refers to a movement occurring in the horizontal plane, where a limb moves away from the midline of the body. This movement typically involves extending the arm or leg out to the side while it is parallel to the ground.

In the context of joint movements, horizontal extension can be most closely associated with abduction, which is defined as the movement of a limb away from the central axis of the body. For instance, when you lift your arms straight out to the side while keeping them parallel to the ground, you are performing horizontal extension or abduction at the shoulder joint.

Understanding that horizontal extension results in increased distance from the midline clarifies why abduction is the correct classification of this movement. While other options like adduction, flexion, and rotation describe different types of movements, they do not accurately represent the action of moving a limb in a horizontal direction away from the body.