Athletes use caffeine strategically:
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.
Ganio said it is important to take the right dose, which shakes out to about three to six milligrams per kilogram of body mass. That is a lot of caffeine. An 80-kilo (176-pound) athlete taking six milligrams per kilogram would need 480 milligrams of caffeine.
“That’s four strong cups of coffee,” said Ganio. “If you can tolerate it, it seems to be the upper end of what you can have to improve performance.”
Since “cups of coffee” is a notoriously imprecise measure of caffeine, it may help to think of it this way: 480 milligrams would be six 8-ounce Red Bulls, two and a half NoDoz tablets, or two Extra Strength 5-hour Energy shots. A more moderate dose for a smaller athlete, say, a 65-kilo (143-pound) athlete taking three milligrams per kilo, is still an impressive amount of caffeine: equal to one NoDoz tablet, one 5-hour Energy shot, or two and a half Red Bulls. Even this amount of caffeine is difficult to obtain using caffeinated sodas like Coca-Cola. A 65-kilo athlete would need to chug nearly six cans of Coke at once to get a caffeine dose of three milligrams per kilogram.
Also, researchers found no evidence of dehydration from using caffeine.