Portugal's Cristiano Ronaldo takes a water break during the 2014 World Cup soccer match between Portugal and the U.S. in Manaus, Brazil, on June 22. Siphiwe Sibeko/Reuters/Landov hide caption

itoggle caption Siphiwe Sibeko/Reuters/Landov

Ray Copeland, a football coach at Bishop McGuinness High School, puts his players through a workout in Oklahoma City in 2007. As is often the case in much of the U.S., the first day of high school football practice that year began in a heat wave. AP hide caption

itoggle caption AP

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

itoggle caption Murray Carpenter for NPR

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

itoggle caption Arnulfo Franco/AP