Define Extension.

• A. Rotating around the joint
• B. Increasing the angle of the joint
• C. Decreasing the angle of the joint
• D. Stabilizing the joint

Answer: (B)

Extension is the movement that increases the angle between two bones at a joint. Think of straightening a bent elbow or knee—the angle inside the joint becomes larger as you move toward a more extended position. This is the action described by "increasing the angle of the joint," which is why that option is correct.

Rotating around the joint refers to turning the bone orientation without necessarily changing the straight-ness of the limb in the same two-bone angle, so it isn’t extension. Decreasing the angle corresponds to flexion, like bending the elbow. Stabilizing the joint means keeping it from moving rather than changing the angle.