“Keeping fit is a requirement of Ray Kelly's job as commissioner of the New York City Police Department. He has worked out since he was a teenager, and stints at the Police Academy and in Vietnam with the Marine Corps reinforced his commitment to physical fitness. ‘Exercise became something you had to do. I developed an unconscious need for it,’ he says. Mr. Kelly is the only person in the NYPD to go from police cadet to commissioner. He was at the helm of the department during the 1993 World Trade Center bombing, and is credited with building one of the most successful local counter-terrorism units in the U.S. ‘This is a full-time, total immersion job,’ Mr. Kelly says. ‘But I still need to make time to work out, whether that's at 6:30 a.m. or in the evening.’ On average, Mr. Kelly works out four days a week for at least an hour at a time. He devotes 30 minutes to cardio exercise -- a knee operation three years ago forced him to switch from running outdoors to using a treadmill -- and the rest to weightlifting. He jogs if his knee doesn't bother him, but most often he walks on the treadmill at a speed of 4.4 miles per hour with a slight incline Mr. Kelly learned the fundamentals of strength training during his Marine Corps service.