It is important to include flexibility training with your exercise program because it helps relieve contractures. Contractures are joints that remain partially contracted even when they’re not in use. As a result, this shortens muscles around the joint making it less strong and unable to absorb the shock and stress of movement. Contractures also cut of circulation to a muscle decreasing its supply of oxygen and nutrients, and allowing waste products to build up in muscle cells.
(Source: Nelson, et. al. Strong Women and Men Beat Arthritis. G.P Putnam’s Sons. New York: 2002)