Reveille is 0400 at the home of the chairman of the Joint Chiefs of Staff, Adm. Mike Mullen. In the predawn, we hear, the Pentagon boss hits the gym to lift weights and swim, explaining how the 6-foot-1 U.S. Naval Academy grad stays buff. Spokesman Capt. John Kirby says: "The chairman believes strongly in the power of physical fitness to reduce stress and improve one's health and well-being. He sees it very much as a readiness issue and is dedicated to making it a part of his life." Mullen's more into fitness than sweat. "He is less concerned about maintaining a given weight than he is in general fitness," adds Kirby. And he wants to lead by example. Kirby says Mullen "believes that all members of the military should maintain appropriate fitness levels, regardless of their rank or age." Of course, it's easy for the skipper. A member of the class of 1968, he played four sports and still finds time for golf and fly-fishing.