Richard Kessinger loves to hit the gym. But some days he needs a little something to get him pumped up for his weightlifting routine.
"You might be a little bit sore. You might be tired. You might have had too many beers the day before," says Kessinger, 23, of Arlington, Va. "So you might start putting up a set and you get a few reps in and you're like, 'I'm not feeling this. I can't keep going.' "