Marathon Runners Are Training for a Hotter World

Jen Dimascio-Donohue was running seven miles near Cape Cod, Massachusetts, on a hot Fourth of July weekend. By 10 a.m., the temperature was already above 80°F. After finishing, she jumped into the ocean to cool off — and then went home and ordered a $234 cooling headband she had been putting off buying for months. She is one of many marathon runners changing their habits because of rising heat caused by climate change.

The headband Dimascio-Donohue bought is called the Omius. She had first noticed it when Olympic runner Sifan Hassan wore one while winning gold at the 2024 Paris Olympics. The band uses graphite blocks to pull heat away from the skin as water evaporates from it. Dimascio-Donohue rewets it every 30 minutes during her runs. She says it already feels worth the price — for her peace of mind, if nothing else.

Every marathon season, runners think carefully about things like which energy gels to eat and which shoes to wear. Now, heat has become something they can no longer ignore. Cities like New York, London, and Hong Kong have all seen extreme heat and humidity in recent years. High temperatures make it harder for the body to cool itself, which can hurt both safety and performance.

Coaches are no longer telling runners to just push through the heat. Instead, they are advising people to slow down, run during cooler parts of the day, and move indoors when needed. Running too hard in extreme heat can lead to heat exhaustion. In the worst cases, it can cause heatstroke, a dangerous condition that can damage the brain and other organs.

A popular coaching app called Runna found that 80% of its users change or skip runs because of hot weather. In America's Sun Belt — the hot southern states — that number rises to 92%. The app now uses local weather data to adjust a runner's suggested pace. The idea is to keep the training effort the same, even if the speed is lower. As Runna's lead coach Steph Kessell explains: 'Our bodies don't know pace, they know effort.'

Some runners are using saunas to help their bodies get used to the heat. Chris Dougé, who is training for the Chicago Marathon, visits the sauna three times a week. He says managing heat is 'significantly more important than the shoes I wear.' Scientists support this idea. Christopher Minson, a professor at the University of Oregon who studies how the body handles heat, says the human body has 'an incredible ability to adapt to heat.' He recommends that runners start heat training at least a month before a race.

The timing of the hottest part of the day has also shifted. Sports scientist Emma Kirk-Odunubi, based in London, says it used to peak between noon and 2 p.m. Now, extreme heat can last past 5 or 6 p.m. Runners in very hot cities, like Phoenix, Arizona, have long trained late at night for this reason. QuHarrison Terry, who is preparing to run seven marathons on seven continents in seven days, says the heat in Dallas has pushed his training to early evening.

Even the best preparation cannot control what the weather will be on race day. Fall marathons in cities like Berlin, Chicago, and New York have traditionally been run in cool conditions, with temperatures between 35°F and 55°F. But a recent study of 221 global marathons found that cool race-day weather is getting harder to find. In 2023, the Twin Cities Marathon in Minnesota was canceled because temperatures reached a record 92°F. Last year's Berlin Marathon saw temperatures of about 80°F — nearly 15 degrees hotter than normal for late September.

Race organizers are starting to make changes. The Cape Town Marathon moved from October to May to lower the risk of overheating. During the 2025 Los Angeles Marathon, runners were allowed to stop at mile 18 and still receive a finisher's medal when temperatures reached 88°F. Sports scientist Kirk-Odunubi worries that if races don't do more, runners may stop signing up — or even stop running outside — because they no longer feel safe.

Runners are also turning to new gear to stay cool. Stores like Fleet Feet in New York City have seen more interest in moisture-wicking clothing and high-electrolyte drinks. Nike developed a $150 shirt tested in climate chambers designed to copy extreme conditions. Other options range from $20 arm sleeves and $38 ice neck wraps to $149 shirts with a pocket in the back that can hold ice. The Omius headband, despite being the priciest option some runners try, was found in a scientific study not to actually lower the body's core temperature — but many runners still say it makes long runs feel more bearable, and experts note that feeling cooler can give you a mental edge on race day.