How Hot Is Too Hot to Hold a Marathon?

Climate change is creating dangerous conditions for road racing.

Last Tuesday, USATF announced that the Olympic Marathon Trials—the race to determine which marathoners will represent the USA at the Paris Olympics in 2024—will start at noon on February 3, 2024 in Orlando, FL. Almost immediately, the platform formerly known as Twitter erupted: 

“In this history of marathoning has a marathon ever been held in the middle of the day in 90 degree humid weather? Is there any precedence for this even being safe?” Sara Hall, who broke the American record in the half marathon back in 2022, wrote. 

For what it’s worth, at that time of year, Orlando’s average temperature is a high of 75°F and a low of 54°F, with humidity at around 74 percent. It’s not ideal, especially at noon—the ideal marathon temp is between 46°F to 59°F, a 2019 study published in PLOS One determined after analyzing nearly 50 years of finishes at the Boston Marathon. But climate change has eradicated the idea of “normal” temperatures, and there’s a good chance the temperate could climb into the 80s.  

Case in point: It was 73°F in Los Angeles at the 2016 Olympic Marathon Trials, conditions that caused Shalane Flanagan to become dehydrated to the point where she collapsed over the finish line to earn third place (and a spot on Team USA).

OK…so the athletes will just need to train for that kind of heat, right? Sure, as much as that’s possible in the dead of winter. “We’ll heat prep for it but even training in Orlando in January probably won’t be warm enough. Don’t need perfect weather just want safe!” Emily Sisson, who currently holds the American record in the marathon, said in response to Hall’s Tweet (are they still Tweets?). 

It’s an interesting choice to hold such an important race in the middle of the day, especially when marathoners typically race in the morning. At the Tokyo Olympics in 2021, due to the heat and humidity, the race was moved an hour earlier, to 6 a.m., for runners’ safety (in case you forgot how hot it was, here’s a reminder via bronze medalist Molly Seidel). Paris in August is also expected to be warm during the Olympics, but both the men’s and women’s marathons are starting at 8 a.m. local time.

The reasoning: a live broadcast on NBC. “They want that time for optimal tv viewership, to grow the sport!” Des Linden, who represented Team USA in the marathon in 2012 and 2016, wrote. “Nobody cares about time during a qualifying race. Top 3 or bust. And you’re indeed correct ANY given day someone can be overcome by heat — 7am, 9am, noon — so why not pick the optimal tv time?” (Linden was also unfazed by the later start time, saying “Warmer temps should slightly minimize the pace of super shoes and reward smart racing.”)

Running does have a media problem, in that it doesn’t get the same kind of exposure as football, basketball, baseball, even F1. An optimal TV slot could be a boon to the sport, drawing in new fans. But is that worth putting athletes at risk? 

Because it’s not just the pros who will be at risk in the bigger picture. There’s a reason most major marathons aren’t held in the summer: Racing long distances in that kind of heat is bad for your body—the heat elevates your core body temperature before you even start moving, which directs blood away from your working muscles and to your skin to cool you down; that makes maintaining paces harder and, if you push those paces, puts you at risk for heat exhaustion and heat stroke. 

When researchers looked at body temperature data from 108 marathoners and racewalkers who competed in temperatures ranging between 85 and 91°F, with relative humidity between 46 and 81 percent, they found that they were, on average, 13 percent slower than their personal best times, and their core temperature had increased by an average of 2.7° over the course of the races, a study in the Journal of Applied Physiology reported. At the finish line, every athlete recorded a core temperature of over 100°, and 16 percent topped 104°.

But excessive heat isn’t just happening in the summer anymore. Last year during the New York City Marathon—which took place on November 5—temperatures reached 75° in Central Park, making it the city’s hottest marathon since the race was moved from October to early November in 1986. The reason it was moved back in ‘86? “In the hope that cooler weather, and thus more impressive times, would be achieved,” the New York Times reported. (I thought nothing could top the 2021 Chicago Marathon, where temperatures reached 81° and the humidity was 84%, but NYC was worse.)

A high of 75° sounds balmy, and it is—for spectators (bless my non-running friend who texted me “looks like perfect running weather!” the night before the race). As a runner, it felt so bad that I had to scale back my pace by over 90 seconds per mile, and had to start alternating walking and running at mile 10 because I thought I might pass out or puke. Fortunately, I didn’t do either, but Brazilian athlete Daniel do Nascimento, who was leading the race until he dramatically collapsed at mile 21, wasn’t so lucky. 

It was also unseasonably warm at the Brooklyn Half Marathon—the largest half marathon in the U.S.—in May 2022, where one person died and 15 were hospitalized when temperatures reached the high 80s and the relative humidity reached 97 percent during the city’s first May heat advisory in 16 years. 

In 2019, forty-three percent of elite endurance athletes did not prepare for expected hot conditions, blaming the cost and availability of suitable equipment and facilities, and 83 percent were ignorant of heat-related material that could aid their health and performance, a 2023 study by World Athletics found. Can you imagine what those numbers are like for normal people? 

If the governing bodies of the running world aren’t taking into account how the heat affects professional athletes, what does that mean for amateur runners? The reality is, summer is getting hotter and lasting longer. The average summer temperature in the past five years has been 1.7° warmer than it was from 1971 through 2000, according to a Washington Post analysis, and, on average, high-heat days arrived at least a week earlier, on average, than 50 years ago, a Climate Central study found. Summer is slowly bleeding into spring and fall, bringing with it potentially dangerous conditions (including heat waves, heat domes, and wildfire smoke) for runners.

At the very least, these types of events need contingency plans for abnormal conditions: How hot is too hot to run? At what temperature, humidity percentage, and dew point do races adjust their starting time to avoid putting athletes in danger? It’s OK to plan for the average temperature conditions, but there needs to be a back-up plan in place in case of abnormal temperatures (which seem to be more of the norm these days). 

There is precedent for races changing their dates and times, like the New York Marathon moving from late October to the first weekend of November. The Boston Marathon started at noon until 2007, when it was pushed up to 10 a.m. And there’s an opportunity here for the USATF to set an example for those big fall and spring races by prioritizing athlete health.

“@usatf needs to be prepared to tape delay,” Sisson wrote. “Not sure what temp cutoff should be to move it but at noon sun will feel strong.”  Aliphine Tuliamuk, who won the 2020 Olympic Marathon trials in Atlanta and competed on Team USA at the 2021 Olympics, wrote “If truly @usatf @USOPC_CEO values athletes’ safety then changing the start times shouldn’t be an issue. We the athletes plus the public all need to speak up. What’s the logic behind a noon marathon in Orlando? Is tv/fan THE factor & greater than human health? NO!”

If it feels like the response to the Trials is a lot of yelling about the “what ifs,” well, you’re not wrong. But given the realities of climate change, I do think it’s fair for athletes to ask why they’re being subjected to a scenario that may put them at risk—especially when a clear back-up plan hasn’t been put forward. It’s not that these athletes aren’t tough enough. It’s about setting them (as well as all the recreational runners who emulate them) up for success.

the rundown

Nike Ultrafly
I feel like I’ve been waiting for this shoe for the better part of a year, and I finally got to run in it this past week. It’s as good as I’d hope it would be, with a full ZoomX midsole (which is wrapped in fabric to protect the foam) and a slightly flexible carbon plate to better handle uneven terrain. The other big selling point is the Vibram outsole—a first for Nike—which finally delivers reliable grip and also helps stabilize the midsole foam. I did find the upper, which is made from Vaporweave, to be a little unstable and my ankles suffered for it, which I did not love. And I will never understand why a brand would make a white trail shoe. But I liked how responsive this felt underfoot—there was plenty of cushioning without sacrificing ground feel, and while it may not be a trail-ified Vaporfly, it’s definitely my favorite trail shoe from the brand.

Therabody RecoveryTherm Cube
Who wants to go through all the trouble of immersing themselves in hot and cold tubs for contrast therapy? Therabody’s RecoveryTherm Cube ($149) isn’t quite a replacement for that kind of immersive treatment, but it does offer contrast therapy in a compact, wearable package. The Cube can heat up to 109°F and cool down to 46°F, and it comes with two straps that allow you to wear it pretty much anywhere on your body. In my testing, I found it worked best as an arm or leg wrap versus a shoulder sling or belt, or when I just held it to a specific area that was bothering me. Obviously, you’re not getting the same kind of immersive treatment as you would in a tub, but I thought this was a neat solution for replacing ice packs and warm compresses.

Courtney Dauwalter on the Ali On the Run Podcast
This was such a delightful listen on a recent long run, partly because Dauwalter seems like the chillest professional runner out there and partly because of the easygoing rapport between her and Ali. I really appreciated Dauwalter’s openness in discussing how bad Hard Rock felt from step one—anyone who’s ever come back to running too fast after a race will appreciate her perspective. Her lack of interest in course records (despite setting them) and finish time was also really refreshing, and I loved that what motivates her instead is this fear of finishing a race and wondering “what if?” I’m going to take that mindset into my next marathon.

Mental Health Issues Are Common In Ultra-Endurance Runners
Here’s your weekly reminder that exercise isn’t therapy and may actually lead to less than ideal mental health: In a 2023 study published in Sports Medicine, researchers looked at studies involving approximately 3,670 ultra-endurance runners and determined that between 32 and 62.5 deal with eating disorders, 11.5 to 18.2 percent battle exercise addiction, and 18.6 percent suffer from depressive symptoms. Woof. The researchers said “high-quality studies are needed to examine underlying factors and find preventative strategies,” but in the meantime, if you’re using running to run away from your problems, maybe you should talk to someone.

“How Food Affects the Mind, As Well As the Body,” The Economist
Nutrition is something that’s been top of mind for me lately, because it turns out I’ve been drastically underfueling basically since the day I started running. A friend forwarded this article to me, and its focus on nutritional psychiatry was kind of mind-blowing. I know that what you eat can have a direct effect on your mental health—mostly because when I eat healthy, I feel way better than when I eat like a college freshman—but the author’s breakdown of how nutritional science is still so damn hard to figure out really hit home. If you’re someone who struggles with food and mental health, I highly recommend reading this.