Definition:
"Extensor surface" is an anatomical term used to describe certain areas of the body. A body part flexes when it bends, and extends when it straightens. The parts of the skin that touch when a joint bends are called the flexor surfaces. The parts of the skin on the opposite side of the joint are called the extensor surfaces.
For Example:
The flexor surface of the arm is the inner arm - when you bend your elbow, the skin of the inner forearm and inner upper arm touch. The extensor surface of the arm is the outer arm - obviously the extensor surfaces cannot touch, but they are located on the side of the joint that extends.The flexor surface of the leg is the back of the leg, and the extensor surface of the leg is the front of the leg.
