AS is a type of arthritis that usually affects the spine but can also affect other joints. It is inflammation of the joints that can cause more bone to be formed and a possible fusion of joints to occur. It causes joint pain and stiffness and can cause chronic discomfort at many levels of the spine and extremities. Regular daily exercise is an integral part of any AS treatment program. Exercise can help improve posture and flexibility and decrease pain. Most people with AS feel much better with an exercise program that is designed by a properly trained physical therapist.