What is the term used to describe the action of increasing the angle of a joint?

The term that describes the action of increasing the angle of a joint is indeed extension. When a joint undergoes extension, two connected bones move away from each other, resulting in a straightening of the joint. This action is commonly observed when you straighten your arm or leg from a bent position.

For example, when you perform a motion that involves lifting your arm straight up above your head, you are extending the shoulder joint. This increase in the angle allows for greater movement and flexibility in various activities and exercises, making it a fundamental concept in both anatomy and physical therapy practices.

Understanding the distinction between extension and other movements like flexion, which decreases the angle, or abduction and adduction, which involve movements away from or toward the midline of the body, is crucial for the effective assessment and performance of physical therapy techniques.