What joint action involves increasing the angle between two bones?

The action that involves increasing the angle between two bones is known as extension. This movement typically occurs in a way that straightens a joint and moves the bones further apart. For example, when standing up from a seated position, or raising the arms straight above the head, the angle at the joints increases—characteristic of extension.

In contrast, flexion refers to decreasing the angle between two bones, as seen when bending the elbow or knee. Abduction involves moving a limb away from the midline of the body, while adduction is the opposite action, bringing the limb closer to the midline. Understanding these actions is crucial for effectively teaching and conducting exercise classes, as it helps trainers demonstrate proper movement patterns and identify the specific muscle groups being engaged during various exercises.