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The Body Has A Temperature-Triggered "Off Switch"

Exercising in the heat is rough. You sweat buckets, you get incredibly thirsty, and it feels like everything is harder than it should be. You also tire out faster. There's an interesting reason for that: once you hit a specific temperature, bodies call it quits—whether they're animals or humans.

Athlete in oxygen mask running on treadmill.

Heat Is The Achilles Heel

In 1984, Gabriela Andersen-Schiess represented Switzerland in the first women's marathon at the summer Olympics. The runner had numerous marathon wins under her belt, but in this event, something went wrong: when she entered the stadium to approach the finish, she was staggering, her left arm hanging limp and her torso twisted. She hobbled toward the finish line into the arms of waiting medics, who treated her for heat exhaustion.

Sports scientists have long sought to determine what exactly causes strong athletes to suddenly break down in the heat, and multiple studies have found something curious: both animals and humans tend to stop exercise at a distinct body temperature. For humans, that temperature was 104º F (40º C), no matter how much they cooled off beforehand, how quickly they stored heat, or how used they were to exercising in high temperatures. Further research has found that this temperature causes lower muscle activation in the brain and an increased perception of effort; that is, you think you're kicking it into high gear even though your brain is taking its foot off the gas.

How To Avoid The Off Switch

Luckily, a lab is the only setting where an athlete is forced to keep going at the same effort in the same unbearable temperature. In the real world, you can take a drink, pour cold water on your head, or slow down. It's also important to stay hydrated, since good hydration supports healthy blood flow, which is a critical element to avoiding heat exhaustion.

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