UM Studies Prepping Soldiers for Extremes of Altitude, Heat, Cold

Peak performance: UM’s Walter Hailes, who studies the effects of extreme altitude on human performance, stands atop Mount Everest in spring 2022. (Courtesy of Walter Hailes)
Pictured outside the center’s environmental chamber are (left to right) Robert “Trey” Coker, Brent Ruby, Dustin Slivka and Walter Hailes.
Researchers at UM’s Montana Center for Work Physiology and Exercise Metabolism study the outer limits of human fitness and endurance. Pictured outside the center’s environmental chamber are (left to right) Robert “Trey” Coker, Brent Ruby, Dustin Slivka and Walter Hailes. (UM photo by Ryan Brennecke)

By Cary Shimek, UM News Service

MISSOULA – Last year University of Montana scientist Walter Hailes was on top of the world – literally. An experienced climbing guide, he summited Mount Everest, enjoying spectacular 360-views of the highest mountains on Earth.

Hailes said the memory is hazy. Even with sufficient oxygen, the mind plays tricks at that ultimate altitude. He can’t precisely remember how long they lingered on top. Maybe a half hour? But it was wonderful up there: sunny, little wind and a balmy (for Everest) -25 F.

“It was perfect,” Hailes said. “I even took my gloves off to take pictures.”

Hailes often works with high altitudes at UM. He is part of the Montana Center for Work Physiology and Exercise Metabolism (WPEM), which recently earned $9 million in grants from the U.S. Air Force and Army to investigate ways to improve the performance of service personnel working in extremes of altitude, heat and cold. A big part of the work is to understand any differences in how male and female bodies deal with such challenges.

The center is directed by Brent Ruby, a former Ironman triathlete who has long studied the limits of human endurance among wildland firefighters, soldiers and athletes. The center’s modern WPEM exercise lab was tacked onto McGill Hall in 2007 and includes a 10-by-10 climate-controlled environmental chamber. WPEM also employs a series of solar-powered Airstream trailers as mobile labs for fieldwork.

“We’ve been doing lab and field-based research funded in part from the U.S. military since 1996,” Ruby said. “We’ve shown we can work faster and much cheaper, and we are a lot more flexible in how we can get these big projects done. It’s also challenging to do these projects with service personnel, so we find surrogate populations.”

The scientific stand-ins for America’s elite military personnel usually are super-fit male and female athletes. Ruby said they are working on a heat adaptation study that will be done in their campus lab. An altitude-adaption study already launched last summer at Hawaii’s Mauna Kea volcano. Another cold and physical stress study will happen in Alaska.

Getting more data on females during these projects will be groundbreaking.

“I would say 90% of the data out there is with 18- to 24-year-old men,” said Robert “Trey” Coker, another WPEM researcher. “There is a huge gap in knowledge when it comes to energy expenditure, how muscles maintain their resiliency in these environments and what happens when you add ridiculous amounts of physical activity.”


The WPEM environmental chamber can crank to 120 F. Researcher Dustin Slivka said the military wants strategies to help personnel of both sexes adapt quickly to extreme heat. During a seven-day study, research subjects will go into the heat chamber. One group will come in once a day for an hour and a half. Another group will come in three times a day for shorter sessions.

“We are trying to see what is the best strategy to get them to a heat-tolerant level that’s the most efficient,” Slivka said.

They will monitor the subjects with skin and rectal monitors. (Slivka said rectal is the gold standard for this type of work.) They also use swallowed thermostat pills that provide temperature data to a watch over a 24-hour period.

“We have found in a previous study that women do acclimate differently than men,” he said. “This has made some researchers say, ‘Hey, we have to be more careful with females in the heat.’ But some of our data suggests women may be better at acclimating to heat than men. Female body cycles already require them to deal with more temperature changes than men, and we are investigating what is different about females that may allow them to acclimate better than men.

“Anytime the data doesn’t look like men, some assume it’s worse. But we think that those with that interpretation should be cautioned. We’ll learn more.”


What does extreme cold exposure do to overall energy expenditure in combination with physical activity, and is it different between the sexes? UM will investigate this during two upcoming endurance races in Alaska and the Yukon.

The Alaska Mountain Wilderness Ski Classic is an unsupported cross-country ski race lasting five to seven days that crosses an icy mountain range. The Montane Yukon Arctic Ultra is 430 miles of skiing, biking or hiking that is marginally supported over 12 to 14 days. Temperatures can plunge to -50 F and colder. Only about 20 extreme athletes do each race, and usually half of those sign up to be studied by UM’s Coker and his crew. The athletes agree to provide regular urine samples as they compete.

“It’s easy to store urine at that temperature – it freezes pretty quick,” Coker said. “We will have them drink a harmless stable isotope that is like a tracer bullet. This labels their hydrogen and oxygen. The hydrogen comes off in a predictable way, but the oxygen changes in proportion to energy expenditure. The method helps us trace metabolically what is taking place in real time.”

Ruby said they have used the isotope-tracing technique on other projects but never before in an extreme cold environment.

“It’s underrepresented in the literature,” he said.


Most U.S. military bases are located at sea level. During the War in Afghanistan, troops would fly from places like Florida to forward operating bases at 9,000 feet, where they would carry heavy loads on missions to heights at 14,000 feet with few days to acclimate.

“We don’t want them presenting with acute mountain sickness or pulmonary edema and all the other bad things that can happen to them,” Slivka said.

In summer 2022, WPEM conducted experiments in Hawaii. Research subjects from Missoula (elevation 3,200 feet) slept at 9,000 feet and then took daily hikes on the slopes of Mauna Kea, which rises to almost 14,000 feet.

Everyone slept with a tent over the bed, with half getting extra oxygen pumped into the tent and half getting normal room air. Hailes said their working hypothesis is that those with boosted oxygen will sleep and perform better atop the volcano.

“The big negative is that maybe those people won’t acclimate as well because they are not getting as much time with lower blood oxygen,” he said. “They are spending nine hours in a tent with oxygen, so maybe it hampers their long-term acclimation. Maybe we’ll find it's better to suffer for three days, and then you perform better than those who didn’t suffer.”

As the studies progress, UM will provide strategies that should help the military achieve peak performance for its personnel – male or female – no matter the environment.

Upcoming UM research will study the implications of loads and environmental and nutrient stress on protein synthesis and muscle metabolism. The work may improve performance among military personnel, extreme athletes and others.


This story was originally published in Vision magazine 2023.

Contact: Dave Kuntz, UM director of strategic communications, 406-243-5659,; Dustin Slivka, WPEM chief scientific officer, UM associate professor, 406-243-2389,