Athlete and trainer Ryan Fischer collapsed after a competition-winning workout gave him heat stroke.
He said pacing workout intensity and getting enough electrolytes in the heat can help prevent issues.
A sports researcher said humidity, sunlight, and wind can all play a role in heat risk during exercise.
He suffered heat stroke during a CrossFit regional competition in 2012, and said he would have been seriously hurt if medics hadn't acted quickly.
"I definitely felt like I was going to die," he told Insider.
Fischer said he vividly remembers the event — three rounds of 50 squats, 40 pull-ups, and 30 shoulder-to-overhead repetitions with the squat difficulty increasing from back squats to front squats to overhead squats, with decreasing weight.
He said he didn't notice anything was wrong during the grueling workout until symptoms like dizziness and hot flashes hit.
Conditions were brutal — the sun was beating down on the athletes competing on black asphalt, and the barbell and pull-up rig were black, absorbing even more heat, he said.
"Everything you touch is hot, it's hot outside, it's just so uncomfortable, but it meant everything to me, so I wasn't holding back on anything. I was going hard and it was hot so it wasn't a big deal."
Fischer won the event with a record-setting time, but immediately collapsed and had to be taken off the field in a stretcher, treated with IVs and ice packs. He recovered quickly and was able to continue the competition.
Since then, he said he's felt more anxious about working out in sweltering conditions, is more careful to avoid overexertion, stay cool, and get enough electrolytes.
Be prepared for the weather
Not just heat but also factors like humidity, wind, and exposure to direct sunlight, are included in a metric called "wet bulb globe temperature" used to measure heat stress, according to Sean Langan, an associate research director at the University of Connecticut's Korey Stringer Institute who specializes in heat injury prevention.
Get enough salt and other electrolytes
Fischer said the biggest change he's made to his training after heat stroke is prioritizing high-quality salt and electrolytes.
"When you're sweating a ton, you need to replenish that salt," Fischer said.
Drinking lots of water during exercise without adding electrolytes can dilute your body's supply, leading to a condition called hyponatremia, with symptoms like nausea and confusion.
Cover up when possible
Getting out of the sunlight, either into the shade or by wearing loose, lightweight, and breathable clothing can help you stay cool, according to Fischer.
Big, floppy hats are popular at the CrossFit Games for a reason, he said, offering great protection from direct sun.
Pace yourself in the heat
Heat injuries can happen to outdoor athletes in many different sports, Langan said.
"When you exercise, you get metabolic heat production, so when you combine with hot environments, your risk is going to go up," Langan said.
But high-intensity workouts like CrossFit or HIIT can crank up your heart rate and body temperature quickly.
"It's like a magnifying glass on you because the intensity is higher," Fischer said.
Unless you're competing, your safest bet when exercising in hot weather is to avoid all-out effort, sticking to a steady pace that will get you results without unnecessary risks, according to Fischer.
"There's no reason to hit it 100%, get your workout in, get your sweat in, and get out of there," he said.
If high-intensity is necessary, he recommends doing short, repeated intervals of three to five minutes at a time, with rest in between.
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