These Olympics could be the hottest yet. Here’s how athletes are preparing.

The 2021 Tokyo Olympics were the warmest in history. But the Paris Games could soon beat them to the title.

A report from June highlighted the potential health risks for athletes competing in this year’s Games in extreme heat. According to the report, published by the British Association for Sustainable Sport and Australian environmental organization Frontrunners, average temperatures in July and August in Paris have risen by an average of more than 5.5 degrees Fahrenheit since the last Olympics were 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. This is especially true for endurance events such as the marathon, race walking and triathlon, where many competitors compete for hours without rest.

“The best way anyone can prepare is to acclimatize,” said Dr. Carolyn Broderick, the Australian Olympic team’s medical director for the Paris Olympics. “But that means training in the heat — not just being in the heat,” she said.

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

In the final weeks of preparation for the Games, athletes structure their training schedules in this way.

The sweating out

For elite athletes, acclimating to the heat means moving to a hot and humid location, or simulating hot and humid training conditions at home by wearing extra layers of clothing or training in warm indoor areas.

Some teams have taken this strategy to the extreme: in preparation for the Olympic Games in Tokyo, the Belgian hockey team trained in a heat chamber at 49 degrees Celsius.

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

Two American runners that Mr. Eyestone is coaching for the Paris Olympic marathon, Conner Mantz and Clayton Young, spend 20 to 30 minutes in a sauna several days a week after their workouts. The practice can help trigger the physiological effects of heat acclimation, such as increased blood flow to the muscles, heart and skin, said Dr. Jason Zaremski, a sports medicine physician at the University of Florida.

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

Rory Linkletter, a marathoner representing Canada in Paris, also spends time in the sauna and overdresses during some of his runs. During a 10-mile recovery run in late June, he wore a black long-sleeved T-shirt in 82-degree weather.

“You’re an engine, and when the engine is hot, it burns faster, so it’s going to slow you down,” Linkletter said. “The most important thing you can do is train your body to be a little less affected by the heat.”

Stay calm

Adapting to the heat during 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 packs, wet towels and cool fluids during the 90-second breaks in tennis matches. Field hockey, rugby and soccer have less predictable breaks, but players can use similar strategies, she said.

Without those built-in rest periods, endurance athletes sometimes have to get creative about staying cool, as they can be particularly sensitive to the stresses of heat and humidity: Study 2023 Researchers of marathon runners and long-distance walkers evaluated the effects of the hot and humid conditions during the 2019 World Athletics Championships in Doha, Qatar.

Only one of the athletes in the study finished with a personal best, while the rest of them had finishes 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 prepare for such conditions and avoid overheating, endurance athletes try to keep their core temperature low before the competition begins and throughout the event.

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

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

Additionally, Mr. Eyestone says, some athletes bite into the balloon when it melts to drink some cold water or to sprinkle it over their bodies.

Once a race begins, many athletes try to cool themselves down with cold sponges and water splashes on their heads, necks and wrists. At the U.S. Olympic track and field trials in Eugene, Oregon, in late June, some runners splashed themselves with water during the women’s 10K race when temperatures hovered in the 80s.

Embrace it

Not all athletes fear the heat in Paris. Some sprinters and middle-distance runners even welcome 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, where 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 too worried either. “I’ve been practicing these things for the last few years,” he said. “Hopefully Paris is hot, because that will add a layer of bloodshed that I’m looking forward to.”