Piampiano uses Clif Shot Blocks, which are “kind of like gummy bears,” when it is easier to chew. She also has several energy gels—which have the consistency of thick honey and come in foil pouches—to use during the run. Throughout the day, she tries to take about 300 calories per hour and augments that with increasing doses of caffeine.

“As you get further into the marathon, your energy supplies are depleted and you just really start suffering; that’s why I start increasing the amount of caffeine I take. At the end of the marathon, you need that energy kick,” she said. And Piampiano said caffeine is an essential tool for an elite triathlete. “It’s critical, particularly if you want to perform and have any success at the top level.”

Like Piampiano, most of the super-fit endurance athletes at Kona used caffeine—but not everyone was on board.

Peter Vervoort, a physician from Belgium, has studied caffeine in athletes in Antwerp. He said for many athletes in his studies, doses of 200 to 350 milligrams were not helpful, especially in hot weather. He also competed in the Ironman and told me, “I’m not using caffeine. I do use Coca-Cola in the last 20 kilometers. But that’s caffeine in very small doses.” He said it’s actually getting hard to avoid caffeine on the race course. “There are more and more gel companies which only make gels with caffeine. So it is difficult.” Vervoort is an outlier. Most researchers have come to a different conclusion about caffeine’s ergogenic effects.

While in Kona, I tracked down Matthew Ganio, an exercise physiologist at the University of Arkansas Department of Health, Human Performance, and Recreation, and Evan Johnson, a University of Connecticut doctoral candidate. They have collaborated on caffeine research and were in Hawaii to study the effects of the triathlon on athletes’ physiology.

Ganio is soft-spoken but unequivocal about caffeine’s benefits for athletes. In 2009, Ganio and his colleagues published a systematic review of 21 studies on caffeine in timed performance. Most of the researchers looked at subjects cycling, but some also studied running, rowing, and cross-country skiing, and most of the tests were in the 15-minute to two-hour range. Looking across all the results, Ganio found consistent improvements in performance.

The improvements can be substantial, he told me, often as much as 3 percent. To put that into context, a 3 percent improvement would mean an 18-minute boost in a 10-hour race. Eighteen minutes was all that separated the top eight finishers in both the men’s and women’s pro races at Kona.

“There is always going to be some variability—some people won’t see as much of an effect as others; some people will see a large effect,” Ganio said. “Some people may not like it as much, or it may impair their performance a little bit. But on average, it does improve performance.”