Studies at the University of Alabama worked with men and women in their 60s and 70s. Under supervised weight training programs they developed muscles that had a mass and strength of people 20 to 30 years younger. Unlike younger men and women who can build new muscle fibers, with age a portion of the muscle fibers in older people dies. The remainder of the muscle fibers suffer from shrinkage do to underuse. However these remaining fibers do respond and will grow with proper and consistent training. Progressive weight training until the muscle are exhausted seems to be the way to go.