Physical activity based on stretching movements, which are designed to increase the range in which a person can bend and stretch his or her joints, muscles, and ligaments. Exercises that stretch the muscles may also help relieve certain kinds of pain: lower back pain may b alleviated or prevented by stretching the hamstring muscles (at the back of the thigh) and the lower back muscles; calf cramping may be prevented by regularly stretching the calf muscles. With age, the muscles weaken and the joints become less flexible. Flexibility training can help overcome these aspects of aging.