Some people overcome the midday slump at work with caffeine. Shelly Fireman re-energizes by hopping on the elliptical machine in his office. Mr. Fireman, in his late 70s one of New York City’s most successful restaurateurs, puts in double workout sessions on most days. “I make time for it because I want to stay alive. And to stay alive I need to take away some of the stress in my life,” says Mr. Fireman, founder and chief executive of Fireman Hospitality Group, whose high-traffic Manhattan eateries include Bond 45, Brooklyn Diner, Red Eye Grill and most recently Florian.