As climate change reshapes the way humans live outdoors, it’s affecting the way they play, too. That includes runners, who may find themselves in harm’s way on a warming planet.

They pursue a sport that esteems grit and suffering in pursuit of improvement. Experts told The Associated Press that can be a recipe for heatstroke as the frequency of dangerously hot days in the continental U.S. is expected to grow by roughly one-third by mid-century.

Here are some takeways from AP’s reporting on running, racing and the hazards of heat:

The average human body temperature is 98.6 degrees or 37 Celsius. That’s only 7 degrees Fahrenheit - or 4 Celsius - away from catastrophic damage. (AP Video: Donavon Brutus)

Heatstroke is a dangerous illness associated with extreme heat

Exertional heatstroke happens during exercise when the body can’t properly cool, rising above 104 degrees (40 Celsius) and triggering a central nervous system problem such as fainting or blacking out.

Muscles can break down, releasing proteins that damage kidneys. The lining of the digestive system may weaken and leak bacteria. Brain cells may die. It can damage organs and ultimately kill a victim.

There’s an effective and simple treatment

When runners suffer heatstroke, getting them into a tub of ice water is the best way to quickly cool them. And it needs to happen fast, with quick diagnoses to treat runners on the spot. Medical staff need rectal thermometers to gauge temperature when skin can be deceptively cool.

Read more Runners are used to toughing it out. A warming climate can make that deadly

Douglas Casa is director of the University of Connecticut’s Korey Stringer Institute, named for the Minnesota Vikings lineman who died of heatstroke in training camp in 2001. He’s been researching athletes and exertional heatstroke for some three decades.

“I can’t guarantee everything that is going to happen in the future,” Casa said. “But based on over 3,000 cases we’ve tracked, if someone’s temp gets under 104 within 30 minutes of the presentation of heatstroke, no one has ever died.”

How are races doing at protecting runners?

It’s a mixed bag that’s typically related to the size of a race and its resources. Casa says many races don’t have the resources or expertise to offer the right lifesaving care.

One that does is the Falmouth Road Race in Falmouth, Massachusetts, a popular, long-running and big race that’s run in August on the shore of Cape Cod. The summer setting and the 7-mile distance make Falmouth a magnet for heatstroke — it’s just long enough for runners to really heat up, and short enough that many of them are pushing hard.

But Falmouth has enough people, equipment and experience to handle lots of cases. The race’s medical director has documented so many of them — nearly 500 over more than two decades — that the race has attracted researchers.

That’s a big difference from small local races that Casa says might have an ambulance, or a nurse, but no significant medical tent ready for heat.

One runner’s experience

Carolyn Baker was about to turn 60 last summer when she ran Falmouth. She had done it several times before and was cruising as she neared the final mile, looking around for friends.

Then she collapsed — a moment she doesn’t remember. Her family members rushed to the medical tent where volunteers had taken Baker and plunged her into an ice bath, with her internal temperature nearly 107 degrees (41.6 Celsius).

Baker regained consciousness in the ice bath, which lowered her temperature to safe levels. She was eventually able to go home, though she felt weak and took a while to fully recover.

Baker was determined to finish the race, so she went back a week later to run the final mile with her husband there to record it. This year, she was back at Falmouth again — and finished safely.

Racing may slightly increase the chances a runner will suffer from a rare event like heatstroke or cardiac arrest, but doctors say it’s almost certainly healthier to show up anyway.

“Runners and athletes are at reduced risk of having not only cardiac arrest, but all forms of heart disease compared to non-runners,” said Dr. Aaron Baggish, a professor at the Université de Lausanne and former medical director of the Boston Marathon.

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