Exercise physiologists have studied caffeine’s effects in nearly every iteration: Does it help sprinters? Marathon runners? Cyclists? Rowers? Swimmers? Athletes whose sports involve stopping and starting like tennis players? The answers are yes and yes and yes and yes. Starting as long ago as 1978, researchers have been publishing caffeine studies. And in study after study, they concluded that caffeine actually does improve performance. In fact, some experts, like Dr. Mark Tarnopolsky of McMaster University in Canada, are just incredulous that anyone could even ask if caffeine has a performance effect. "There is so much data on this that it’s unbelievable," he said. "It’s just unequivocal that caffeine improves performance. It’s been shown in well-respected labs in multiple places around the world."