What is defined as extension in relation to joint movement?

Extension in relation to joint movement refers to an unbending movement that increases the angle at a joint. When a joint is extended, the body parts on either side of the joint move away from each other, leading to a straightening motion. For example, when you straighten your arm from a bent position, you are extending the elbow joint, which increases the angle between your forearm and upper arm.

Understanding this definition clarifies the nature of movements like extension in contrast to other joint actions. Flexion, which is the opposite of extension, reduces the angle at a joint, as seen when bending the elbow. The other options highlight different aspects of joint movement but do not accurately define extension. For instance, rotation around a fixed axis does not describe either flexion or extension specifically. Thus, the correct definition accurately captures the essential aspect of extension, which is critical in understanding the range of motion in human anatomy.