Final answer:
Extension is the straightening of a joint, resulting in an increase of angle between the bones.
Step-by-step explanation:
Extension is the straightening of a joint, resulting in an increase of angle between the bones. It is the opposite of flexion, which is the bending of a joint and decreases the angle between the bones.
For example, straightening your arm after bending it at the elbow is an example of extension. Similarly, moving the leg forward after bending it at the knee is also an example of extension.