This Olympics Could Be the Hottest Yet. Here’s How Athletes Are Preparing.

The Tokyo Olympics in 2021 were the hottest in history. But the Paris Games could soon edge them out for the title.

A June report highlighted the potential health risks for athletes competing in extreme heat at this year’s Games. According to the report, which was published by the British Association for Sustainable Sport and the Australian environmental organization Frontrunners, the average temperatures during July and August in Paris have increased by an average of more than 5.5 degrees Fahrenheit since the Olympics were last held in Paris, in 1924.

Training for the Olympics is now as much about athletes’ ability to handle the heat as it is about strength and speed. That’s especially true for endurance events like the marathon, race walk and triathlon, where many competitors will compete for hours without breaks.

“The best way a person can prepare is acclimatization,” said Dr. Carolyn Broderick, the medical director of the Australian Olympic team at the Paris Olympics. “But that involves training in the heat — not just being in the heat,” she said.

It can take two to three weeks of heat training to fully adjust, Dr. Broderick said, but some of the effects can be seen in the first seven days. At that point, athletes should notice a lower sweating threshold and a lower heart rate for the same level of exertion.

In the final weeks of preparation before the Games, here’s how athletes are structuring their heat-training plans.

Sweat it out

For elite athletes, getting comfortable in the heat can involve moving to a hot and humid location, or simulating hot and humid training conditions at home by wearing extra layers or training in warm indoor spaces.

Some teams have taken that strategy to the extreme: To prepare for the Tokyo Olympics, Belgium’s field hockey team trained in a heat chamber set to 122 degrees Fahrenheit.

Ed Eyestone, a two-time Olympic marathoner and a track and field and cross-country coach at Brigham Young University, competed at the 1988 Games in Seoul and the 1992 Games in Barcelona. Both marathons became races of attrition in warm, muggy weather. “When Olympic sites are chosen, they typically do not take into account the best places for marathoners,” Mr. Eyestone said. He now specifically prepares his collegiate and Olympic athletes for hot and humid conditions.

Two American runners that Mr. Eyestone is coaching ahead of the Olympic marathon in Paris, Conner Mantz and Clayton Young, have been spending 20 to 30 minutes in a sauna after workouts several days a week. This practice can help kick-start the physiological effects of heat acclimation, such as increased blood flow to the muscles, heart and skin, said Dr. Jason Zaremski, a sports medicine doctor at the University of Florida.

For some runs, Young wears an outfit that Mr. Eyestone compared to both a “marshmallow suit” and “hazmat suit.” It’s made from a non-breathable fabric, Mr. Eyestone said, and Young wears it over whatever other layers he’s put on that day.

Rory Linkletter, a marathoner who will be representing Canada in Paris, is also spending time in the sauna and overdressing during some of his runs. On one 10-mile recovery run in late June, he wore a black long-sleeved T-shirt in 82-degree weather.

“You are an engine, and if the engine is hot, it burns faster, so it’ll slow you down, Linkletter said. “The No. 1 thing you can do is train your body to be a little less bothered by the heat.”

Stay cool

Adjusting to the heat in training is only part of the equation. Athletes must also experiment with tactics that keep them cool and hydrated during competition.

Dr. Broderick, who is also the chief medical officer for the Australian Open, recommends interventions such as ice towels, wet towels and cool fluids in the 90-second breaks during tennis matches. Field hockey, rugby and soccer have less predictable breaks, but players can use similar strategies, she said.

Without those built-in periods of rest, endurance athletes sometimes have to get creative about staying cool, as they can be particularly affected by the strain of heat and humidity: In a 2023 study of marathoners and long-distance race walkers, researchers evaluated the effects of the hot and humid conditions at the 2019 World Athletic Championships in Doha, Qatar.

Only one of the athletes in the study finished with a personal best, while the rest of them had finishing times that were 3 and 20 percent slower than their best times. Dozens of runners — 25 percent of the men’s field and 41 percent of the women’s field — dropped out of the marathon.

To brace for such conditions and prevent overheating, endurance athletes work to keep their core temperature low before the competition begins, and aim to keep it down during the event.

Ice vests are a popular pre-race tool, allowing athletes to warm up their limbs without overheating their core.

Mr. Eyestone adds another low-tech cooling method to his arsenal: frozen balloons, the size of baseballs, for athletes to hold during warm-up routines. “I give them an ice balloon that they will hold in their hands and pass back and forth,” he said. Cooling the palms can help lower the body’s temperature, Dr. Zaremski said.

Plus, as the balloon melts, Mr. Eyestone said, some athletes bite into it to drink some cool water or drizzle it over their body.

Once a race begins, many athletes try to cool themselves with cold sponges and splashes of water on their head, neck and wrists. At the U.S. Olympic Track and Field trials in Eugene, Ore., in late June, some runners splashed water on themselves during the women’s 10-kilometer race, when the temperature was in the low 80s.

Embrace it

Not all athletes are dreading the heat in Paris. Some sprinters and middle-distance runners are even welcoming it.

“All I know is heat,” Trevor Bassitt, a 400-meter hurdler, said in an interview before the final round of his event at the Olympic trials in Eugene, in which he qualified for Paris. Bassitt trains in Gainesville, Fla., and has taped his fingers during practice so he doesn’t burn his hands on the hot track.

Linkletter, the Canadian marathoner, isn’t all that worried either. “I’ve been practicing these things for the last couple of years,” he said. “Hopefully Paris is hot, because it will add a layer of carnage that I look forward to.”