Pronation is a normal motion of the foot in which the arch drops down and the ankle and leg turn in. Pronation is important for the body to accommodate to uneven ground and provide shock absoption when the heel hits the ground. When excessive pronation occurs, the arch stretches out too much and the leg rotates in too much, both which may cause muscles and tendons to work too hard and even cause them to stretch out too much. When under pronation (also known as supination) occurs, the foot becomes very rigid and there is a reduction of shock absorption.