Make the switch to morning workouts by setting your alarm a half hour earlier than usual and immediately turning on a lamp (light signals your brain to be alert). "For the first few days, just get up and start your morning routine," says Rikki Charles, owner of Fitness Guru studio in New York City. "After a week, the wake-up time will seem normal and you'll feel with it enough to exercise." If mornings are a mad rush
Squeeze in a workout at the end of the day. "If the sun is still shining, move it outdoors," Charles says. "When darkness sets in, work out in a bright room." (Gyms with glaring fluorescent lights qualify.) Wrap it up at least two hours before bedtime, otherwise you may have trouble falling asleep.