Sarah Piampiano holds two energy gels, one with caffeine and one without, as she runs in this year's Ironman World Championship. Murray Carpenter for NPR hide caption

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Murray Carpenter for NPR

Caffeine Gives Endurance Athletes A Third And Fourth Wind

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Lance Armstrong competes in the Ironman Panama 70.3. triathlon in Panama City, Panama. Arnulfo Franco/AP hide caption

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Arnulfo Franco/AP

Triathletes begin the 1,500-meter swim (just under 1 mile) in the Hudson River as part of last year's New York City Triathlon. Two race participants died during this year's swim portion. Dario Cantatore/Getty Images hide caption

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Dario Cantatore/Getty Images