Muscles require oxygen carried by the blood. When the leg muscles do not get enough blood and oxygen, this can cause pain, cramping, fatigue, and/or discomfort in the leg muscles during walking or exercise. These symptoms are called intermittent claudication (IC). In more severe cases, tissues do not get enough blood and oxygen at rest, and pain may also be present when the legs are resting. Peripheral Artery Disease (PAD)is one of the most common causes of pain and disability in people between 55 and 75 years of age.