11 ways to prevent heat exhaustion during a workout

Stay cool—and safe—in the blazing summer heat or your hot gym with these essential health tactics.

HANGING OUT IN the heat is pretty uncomfortable, but working out in the heat can be downright dangerous.

“In hot (and especially humid) environments, we dissipate heat by physiological cooling mechanisms, including sweating for heat loss via evaporation,” explains Elaine Choung-Hee Lee, Ph.D., associate director of Human Performance Laboratory at the University of Connecticut. “When you’re unable to dissipate enough heat to cool the body, that’s when you might experience heat exhaustion, heat-related illness, or, in extreme cases, heatstroke.”

Heat exhaustion will sideline you for a day or so, but heatstroke can be fatal—so it’s not really something to take lightly. And whether you’re working out in the great outdoors or at your un-air-conditioned CrossFit box, you run the risk of overheating. Here’s how to ensure you don’t run too hot—and how you can recover if you do.

1. Know the signs of heat exhaustion

Heat exhaustion is uncomfortable, but it’s also the first alarm bell to warn you it’s time to slow down and cool off. If you push past this, you enter the territory of heat illness, and then potentially the ultra-dangerous condition of heatstroke—so you need to know what those alarm bells look like.

The primary force behind heat exhaustion centers around your cardiovascular system—it has to shuttle blood not just to your muscles to support the physical work of exercise, but also to your skin to help keep you cool, explains Michael Sawka, Ph.D., professor of physiology at Georgia Tech.

When you heat up, your blood pressure is so high, your heart starts to race, you feel faint, and you feel exhausted before you normally would. “You can’t sense a high core temperature, but wet skin and a high heart rate are signs of thermal discomfort,” he adds.

And here’s the slightly alarming reality: Heat exhaustion is a possibility any time your skin temperature exceeds 81°, which, for all intents and purposes, is whenever the air is 81° or higher, according to Sawka.

Signs you’re passing the threshold of heat exhaustion onto something more dangerous: cold and clammy skin, nausea, dizziness and fainting, pale skin, heavy sweating, headaches, decreased coordination, chills, and irritability.

“It is challenging because many of these may merely be signs of working hard and challenging your body, but many of these together with the context of working in a hot environment can signal that the athlete should back off activity,” Lee adds.

2. Hydrate like crazy

Drinking water before and during a workout is always important, but during the summer it’s absolutely crucial. Hot temps already put a strain on your system, but being dehydrated reduces your blood volume, increasing its thickness and making it even harder to continue proper blood flow, Sawka explains. Because your heart can’t pump blood as efficiently, dehydration will boost your heart rate and increase balance and coordination issues.

On top of this, dehydration prevents your body from cooling itself, since less water means less sweat, Lee says. Not only do you want to go into the workout well-hydrated, but you want to continue to hydrate throughout the circuit and after, Lee adds.

And even though it sounds unnecessarily intense, consider measuring your water loss to know you’re hydrating enough: “If an athlete has an unusually high sweat rate, he can even lose up to 4 or 5 liters of water over hours of exercise,” Lee says. Weigh yourself before and after a grueling workout in the heat. Losing 1kg of mass during a workout is equivalent to about 1 liter of water, and you want to rehydrate 150%, so you’d aim to drink 1.5 liters of water over the course of recovery and into the next day, she explains. Even just doing this once will give you a sense of your sweat rate and water recovery needs.

3. Seek out heat

The single best thing you can do to avoid heat exhaustion, other than hydrate properly, is actually to head straight for it and work out in the heat. Why? While your body’s initial reaction to high temps is to essentially freak out—skyrocketing your heart rate, sweating buckets—it then becomes more efficient at managing blood flow and core temperature, as well as sweating and conserving sodium.

“It’s similar to strength or endurance training—you’ll adapt faster if you exercise in the heat versus just sitting in it, and the fitter you are the quicker you adapt,” Sawka says. He was part of a 2015 study in Sports Science Exchange that determined most people acclimatize to heat and subsequently feel overheated less often after working out for just a week or two for 90 minutes in hot conditions. It doesn’t have to be crazy hot either—85° is enough to drive up your body temperature, he adds. 

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