At a small laboratory tucked away in a gleaming basketball arena, I’m running on a treadmill under lamps designed to mimic the heat of the sun.
It’s almost 92 degrees. Sweat is flying off my face. I’m hooked up to machines that are tracking my internal body temperature, heartbeat and other measurements I usually don’t think about.
“I’m starting to feel really hot,” I say to the researchers huddled nearby, watching my vital signs. “I’m sweating like crazy.”
For the researchers, it’s just another day at the heat lab at the Korey Stringer Institute, where they are working to understand the effects of a warming world on the human body.
“Sweat’s a good thing!” Rebecca Stearns, the institute’s chief operating officer and an academic expert in heat stroke, heat-related illnesses and athletic performance, tells me.
The lab, at the University of Connecticut, addresses a growing crisis. Deaths and illnesses related to heat exposure have increased sharply in recent years, as climate change pushes temperatures higher.
On average, heat kills more people each year than hurricanes, floods and tornadoes combined, according to the National Weather Service. And experts say those figures are likely undercounts.
The facility takes its name from a Minnesota Vikings offensive lineman who died from heatstroke in 2001, after training in stifling humidity and 90-plus-degree heat. Part of the Stringer family’s settlement with the National Football League provided funding for research to prevent heat illness .
As concerns mount over the effect of extreme heat on our bodies, the lab’s work has grown. After a major expansion this summer to double its capacity, it is now going beyond athletes to studying what hot temperatures do to the health of other heat-exposed groups, like military personnel or delivery-truck drivers.
“Everything is just perpetually getting hotter, but technology is also getting better. And we have strategies to study and try to overcome it,” said Douglas Casa, a professor at UConn and the institute’s chief executive officer. Workers, in particular, “are such a unique population,” he said, because of so many variables. Maybe they’re on medications or they have other health risks. “And they might be doing 12-hour shifts, not a two-hour practice.”
The lab, at first glance, it looks like a standard gym. There are a couple of treadmills, a stationary bike, a jumble of towels and water bottles.
But there are signs of something more. Solar radiation lamps. Large vents that can fill the room with hot or cold air. Rows of medical devices with wires and monitors.
That equipment is used to mimic heat conditions and to measure their effect on the human body. Temperatures in the room can be adjusted from minus 20 to 120 degrees Fahrenheit. Humidity from 20 to 90 percent. The lamps can recreate conditions from full cloud to full sun.
On the day of my visit, we were testing my heat tolerance under two scenarios. First, a relatively cool 70 degrees Fahrenheit and 60 percent humidity. Then, to test for heat, we kept humidity constant but raised the temperature to 93 degrees — essentially, replicating conditions that I recently had measured on a hot sidewalk near Times Square in New York.
For both scenarios, we also tested what would happen if I took a break to cool down with ice-cold towels.
In fact, there’s a cold water-immersion tank on standby, for heat-exertion emergencies. “But we never really have to worry about that, because we constantly are monitoring everybody,” Dr. Stearns says. “So it’s very hard to get to a scenario where it’s actually dangerous.”
The first step is a urine test to test for dehydration. Then I step onto a scale for a body-mass measurement. After that, my water bottle is weighed down to the milliliter, and from that point every sip of water is accounted for. I’m fitted with an internal thermometer and a heart monitor.
I also undergo a simple reaction test, tapping a series of lamps mounted on traffic cones that flash on and off. I’m supposed to hit them just when they flash pink. This tests the body’s ability to incorporate information in the brain, and then react to it, something that tends to be affected by extreme heat.
Breanna Black, a summer research fellow, holds up a chart and asks me how I’m feeling on a “rate of perceived exertion” scale. I point to “very light” exertion. That’s our base line.
I’m ready to go.
The team puts me on an easy workout program, four minutes of running at an easy 5-mile-an-hour pace, then a minute of walking. I repeat that cycle four times. At 70 degrees, it’s pretty easy. I’m hardly sweating.
Later I sit in a tub while Dr. Stearns covers me with ice-cold towels.
Then it’s time for the high-heat part of the test. The team cranks the room temperature up to 92 degrees. The radiation lamps on full blast, recreating the sun. They lent me a pair of sunglasses.
Researchers pay particular attention to a common measurement called the wetbulb globe temperature, she says, a measure of the heat stress that’s created by direct sunlight that takes into account the temperature, humidity, wind speed, sun angle and cloud cover.
Humidity is critical. “It gets harder for sweat to evaporate in humid environments, because the air is already saturated,” she says. “And when sweat drips off you, it doesn’t help. It has to actually evaporate off your skin in order to cool you.”
I feel fine for the first few minutes back on the treadmill, but then I start to sweat profusely. Soon my heart feels like it’s about to jump out of my chest.
But my vitals look fine, Dr. Stearns reassures me. “This is feedback, in terms of how your body is managing the heat load that we’re imposing on it,” she says.
The test would immediately end, she told me, if there were any signs of extreme heat exhaustion like dizziness, nausea, headache, muscle cramps or disorientation. Another red flag is an internal body temperature of more than 104 degrees Fahrenheit.
Because of the lab’s close monitoring, “we’re allowed to bring people right up to 104 degrees Fahrenheit, which is unique, because a lot of labs won’t let you bring people quite that high,” Dr. Stearns says.
“Then we could extrapolate,” she says. “If we continued, in the next 10 minutes you would be at perhaps 106, which is where you would start to see cell dysfunction and deterioration, where people tend to lose cognitive function.”
This time, the ice towels feel really good. I finish up. I’m tired, but I didn’t faint or feel nauseous. I held up.
It was time to examine my test results. And that introduced an unexpected twist: The importance of drinking enough water.
It turns out I’d arrived at the lab very dehydrated, and that had an outsized effect on how my body reacted to heat. Notably, my body temperatures were higher under the first, lower-heat, scenario — reaching 101.3 degrees — because of how dehydrated I had been at the start of testing.
But by the time we tested under higher temperatures, I’d drank more water, so my internal body temperature rose to just 100.9 degrees. A more standard result would have shown internal body temperatures soaring under a high-heat scenario.
The bottom line: Hydration countered the effects of extreme heat.
“I think we accidentally ended up testing for hydration,” says Robert Huggins, the lab’s president of occupational safety and athlete performance. “So you optimally hydrated, and recovered while you were exercising,” he says. “That’s actually amazing.”
There are signs my body was working harder to stay cool. At 92 degrees, I was sweating almost 2 liters an hour, almost five times my sweat rate at 70 degrees. And my cognitive capacities had slipped, making me 17 milliseconds slower to hit the flashing lights under the hotter scenario.
That’s an important lesson, Dr. Huggins says. “When you’re dehydrated, you can still be hotter than you need to be, even when you’re exercising in a cool environment.”
And under both scenarios, after taking a break, my body temperature dropped and then climbed more slowly. It turns out that cooling breaks really are an effective way of dealing with extreme heat.
There’s still a lot we don’t know about what extreme heat in a warming world will do to our bodies.
The lab’s work has contributed to more than 400 peer-reviewed scientific articles, including ones that looked at heat-exertion-related injuries and fatalities among workers. In recent years, the lab installed a box-lifting apparatus to recreate the heavy work that warehouse workers or delivery truck drivers and others do.
The lab has a growing number of corporate research partners, including UPS and Delta Air Lines as well as Mission, a company that makes cooling towels. It also works with the Department of Defense to study heat acclimatization.
The federal government is currently working on a rule to prevent heat-related illnesses and deaths in the workplace, the first of its kind. Put forward last summer by the Biden administration, the regulation would require employers to provide water and rest breaks when temperatures surpass certain levels.
In 2021, the lab led research that compiled a list of strategies to protect U.S. workers from heat. Among its recommendations are that job sites should have a designated rest, cooling and hydration center.
The lab still works with athletes, too. In the months before the U.S. women’s national soccer team headed to the 2020 Tokyo Olympics, players used the lab to prepare for the sweltering conditions they were expected to play in. “They were the most fit individuals that I’ve ever tested in my entire life,” Dr. Huggins said.
Heat can be a factor in even unexpected sports. “We’ve had ice hockey goalies in here. They can lose upward of three liters of fluid an hour.” It’s a reminder for everyone to pay attention to the temperature, he said.
And take frequent cooling breaks. And of course, drink water.
Hiroko Tabuchi covers pollution and the environment for The Times. She has been a journalist for more than 20 years in Tokyo and New York.
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