It was the heat wave over the Fourth of July weekend that finally pushed Jen Dimascio-Donohue to hit the ¡°checkout¡± button on an item that had been sitting in her cart for months.
After an 11-kilometer run in Massachusetts, with temperatures above 27 degrees Celsius by 10 a.m., she jumped into the ocean off Cape Cod to cool down.
¡°I came home and ordered it immediately,¡± she says. ¡°I felt, ¡®I¡¯ve reached my boiling point. Literally.¡¯¡±
¡°It¡± was a $234 cooling headband called Omius.
Dimascio-Donohue, who¡¯s training for the New York City Marathon, had been eyeing it since watching Sifan Hassan wear one while winning gold at the 2024 Olympics in Paris. The New York-based project manager says the band has ¡°already paid for itself in my sanity,¡± and she¡¯s since worked it into her regular runs, rewetting it every 30 minutes or so to refresh the cooling effect.
Every marathon season, runners like Dimascio-Donohue strategize about more than just how many miles a week to train. They focus on details that can make or break race day: which nutrition gels they can tolerate, which shoes work best for their feet. Climate change has become a variable they can¡¯t ignore.
New York City¡¯s frequent heat waves, London¡¯s extended dry spell and Hong Kong¡¯s record-breaking summer have all brought the kind of high temperatures and humidity that make it harder for the body to cool itself. Training through miserable weather has long been a rite of passage for marathoners, but today¡¯s extremes are affecting training schedules and race days in ways that can affect safety and performance.
Instead of telling them to just push through, trainers are advising runners to adjust their pace, run during cooler times of the day and move indoors if need be. The alternative: heat exhaustion, and in extreme cases heatstroke, a potentially life-threatening condition that can damage the brain and other organs.
The coaching app Runna found that 80% of its users adapt or skip their runs because of hot weather; in America¡¯s Sun Belt, that figure rises to 92%. It introduced a heat-adaptation update that uses local weather data to adjust a subscriber¡¯s pace, helping them maintain the same training effort they would on a cooler day.
As Steph Kessell, lead coach for Runna explains, the body has to work much harder to cool itself in high temperatures.
¡°If done correctly,¡± she says, ¡°adjusting training sessions and reducing the pace of a run during hotter conditions means the same training benefit is experienced as running at a quicker pace on a cooler day. Our bodies don¡¯t know pace, they know effort.¡±
Physiological realities
The approach reflects an increasing emphasis from exercise scientists on training the body to cope with heat stress. Chris Douge, a business developer from New York who¡¯s training for the Chicago Marathon on Oct. 11, has incorporated visits to the sauna three times a week. Managing the heat, he says, is ¡°significantly more important than the shoes I wear.¡±
He adds: ¡°I consider training for the heat equivalent to training for hills on a course.¡±
There is a physiological basis to this approach, says Christopher Minson, a professor of human physiology at the University of Oregon who studies exercise and thermoregulation. The human body has ¡°an incredible ability to adapt to heat,¡± he says, and many of these changes are protective. ¡°By far the best thing a runner can do in terms of safety and performance is to get acclimated to the heat.¡±
Minson suggests athletes start at least a month in advance of a race, but ideally make some heat exposure a regular part of their training routine. This could include a post-training sauna or hot tub, scheduling low-effort training during the warmer part of the day and doing some training in a heated room. He says athletes shouldn¡¯t use critical training sessions, such as interval days, for heat exposure.
Another factor for runners to consider is how the peak heat window has shifted, says Emma Kirk-Odunubi, a sports scientist and running coach in London. ¡°It used to be that 12 to 2 p.m. was the hottest time, but now that¡¯s extending all the way past 5 or 6 p.m. sometimes, and people are needing to readjust their schedules completely.¡±
This is why athletes in the unrelenting heat of Phoenix have long been night owls.
QuHarrison Terry, who¡¯s gearing up for the Great World Race, a series of seven marathons on seven continents in seven days in November, says the heat and humidity in Dallas, where he lives, have moved his training toward early evening.
¡°It feels like it¡¯s getting cooler as you go, versus morning runs, where it just keeps getting hotter the longer you¡¯re out there,¡± says the venture capitalist and tech entrepreneur.
In Hong Kong, where heat has long been a challenge for outdoor sports, Sylvia Lour, a telecommunications strategist, says the problem has become more pronounced in recent years. During her training for the Berlin Marathon, she skipped group runs that started at 8:45 a.m. on exposed routes, when the sun and heat can be too much.
Organizational shifts
Still, even the best preparation can¡¯t account for the weather on race day. Traditionally, runners could count on cool conditions for the fall marathons in Berlin, Chicago and New York, with low humidity and temperatures around 2 C to 13 C. But a recent Climate Central analysis of 221 global marathons suggests these cooler race days are already becoming harder to find.
Andrew Pershing, who worked on the analysis as the nonprofit¡¯s chief program officer, points to the cancellation of the Twin Cities Marathon because of extreme heat in 2023. Temperatures reached a record-setting 33 C in Minneapolis and St. Paul; organizers moved it to later in the year.
Last year¡¯s Berlin Marathon also experienced an unseasonal high of about 27 C. That¡¯s 8.3 degrees hotter than normal for late September, Pershing says, an increase ¡°made at least two times more likely by climate change.¡±
¡°The reality is that the risk of heat affecting performance or safety will continue to increase year after year for most races,¡± says Pershing.
Race organizers are responding in different ways.
The Cape Town Marathon moved from October to May to reduce overheating risks, while in February, the Los Angeles Marathon allowed runners to stop at Mile 18 and still get a finisher medal when temperatures climbed to 31 C. The changes reflect a broader question of how much responsibility race organizers bear for heat safety.
Kirk-Odunubi, who has spent her London summer working toward the Sydney Marathon on Aug. 30, says these conversations and adjustments will have to extend beyond major marathons to shorter events. Otherwise, she worries, runners may simply start avoiding races ¡ª or running outdoors altogether ¡ª because they no longer feel safe in the heat. She recalls receiving worried messages in the run-up to the April 26 London Marathon, despite that not traditionally being a hot time of the year.
Cooling gear
Since runners can¡¯t control race-day weather, another approach has been to try to make the heat more manageable. At Fleet Feet¡¯s Columbus Circle store in New York, employees have noticed increased interest in moisture-wicking and cooling apparel, as well as high-electrolyte drink mixes, capsules and chewable tablets.
On streets around the city, Nike¡¯s ACG Radical Airflow shirt, with its distinctive gradient-knit design, offers a visible example of how performance brands are responding. Developed and tested at Nike¡¯s Sports Research Lab, the $150 shirt was evaluated in climate chambers designed to mimic extreme conditions; professional trail runner Caleb Olsen wore a prototype when he won the 100-mile (161-km) 2025 Western States Endurance Run. There¡¯s also Aero-FIT, a fabric designed to aid in cooling that was first seen in players¡¯ kits at the World Cup this summer.
Cooling technology ranges from relatively simple gear to more specialized products. There are $20 Adidas arm sleeves made with the brand¡¯s Climacool fabric, $38 Lululemon ice neck wraps and $62 Oiselle racerback tanks made with Brrr¡ã, a cooling performance fabric. At the higher end, you¡¯ll find $149 Raide RaceTech T-shirts that has a stow pocket at the back that can also hold ice, turning the shirt into a portable cooling system.
And then there¡¯s that Omius headband, which uses graphite blocks to pull heat away from the skin as water evaporates. For Dimascio-Donohue, who plans to wear it on race day, the effect is unmistakable: ¡°It feels like you have an ice pack strapped to your forehead.¡±
¡°When you cool that area, you feel it more than if you cool another area, like the arm,¡± says Omius founder Gustavo Cadena, given the forehead¡¯s high concentration of sweat glands and thermal receptors.
But there¡¯s an important distinction between feeling cooler and actually lowering the body¡¯s core temperature. A peer-reviewed study of the Omius headband found that the local cooling didn¡¯t translate into a whole-body or performance benefit during a 5-kilometer time trial in hot, humid conditions. Cadena acknowledges the limitation: ¡°It¡¯s very difficult to actually change the core temperature of the body¡± when cooling such a small area, he says.
This seems to match the experience of some runners who use it, such as Johnny Del Balso, a triathlete in Grand River, Ohio, who purchased one recently.
It ¡°works OK, but nothing groundbreaking,¡± he says. Del Balso still plans to use it for hot races and training, because it has a ¡°noticeable effect¡± in making long runs more tolerable ¡ª even if, he says, ¡°it¡¯s only mental.¡±
Still, as better heat management becomes another performance advantage, perception alone can make a difference, says Kirk-Odunub, provided there¡¯s been physiological preparation as well.
¡°If in your head you¡¯re like, ¡®I¡¯m wearing lighter clothing, that¡¯s going to help me breathe¡¯ ¡ª psychologically, you¡¯re going to gain an advantage from that.¡±
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