From Phoenix heat to Tokyo humidity: ASU facility supports elite marathoner
Jess McClain trains in the Clinical Research Services environmental chamber at the Health Futures Center in northeast Phoenix. McClain spent four sessions in the chamber acclimating to the high temperatures and humidity that awaited her at the World Athletics Championships in Tokyo on Sept. 14. Photo by Billy Hollander/ASU
Any runner worth their salt will tell you: nothing new on race day.
That’s why elite marathoner Jess McClain visited Arizona State University's Core Research Facilities before securing an eighth-place finish at the 2025 World Athletics Championships women’s marathon on Sept. 14 in Tokyo.
A Brooks-sponsored runner based in Phoenix, McClain is accustomed to desert heat but less familiar with the stifling humidity she faced in Tokyo. Race conditions were grueling: low- to mid-80s temperatures combined with high humidity.
To prepare, McClain trained in Clinical Research Services' environmental chamber, where she acclimated to heat and humidity from Aug. 26 to Sept. 4.
“I do think the chamber helped on race day. Because I spent four sessions in the chamber and had six full days in Tokyo to adjust to the time change and conditions, I feel like the weather on race day wasn't something that affected me mentally,” said McClain, who secured her top-10 finish with a time of two hours, 29 minutes and 20 seconds — a sub-six-minute-per-mile pace.
“My ‘A’ goal was top five, but after the long trip home and a lot of reflection, I am super proud to come away as the eighth best female marathoner in the world in 2025,” McClain said. “My Team USA teammate and I took the lead in the race pretty early on, which was not necessarily the plan going in, but it was really fun to lead a high-caliber marathon for the first time in my career. It definitely made me hungry for more, and the experience I gained competing on the world stage is invaluable!”
Ellie Iwersen, a clinical exercise physiologist at Clinical Research Services, said McClain trained on a treadmill under simulated race-day conditions. Over four sessions, staff progressively raised the chamber’s temperature and humidity — from 86 degrees Fahrenheit and 60% relative humidity to 89.6 degrees and 80% relative humidity.
“We did progressive environmental acclimation, so we started a little bit lower and then built up each day, that way her body could take a moment to get used to it,” Iwersen said..
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Team USA marathoners Jess McClain and Susanna Sullivan speed toward the finish on Sept. 14 in Tokyo. Sullivan finished in fourth place and McClain in eighth.
Photo by Lauren Nemeroff/Flow State Creative
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Jess McClain smiles as she cruises toward a top-10 finish at the 2025 World Athletics Championship in Tokyo on Sept. 14. She said her training in the ASU environmental chamber at the Health Futures Center in northeast Phoenix ultimately helped her on race day.
Photo by Lauren Nemeroff/Flow State Creative
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Ellie Iwersen, a clinical exercise physiologist at Clinical Research Services, applies a sweat patch to Jess McClain in the environmental chamber. As McClain ran, staff collected sweat samples, which Brooks Running principal physiology researcher Bridget Sopeña analyzed to measure sodium and electrolytes loss — data that informed McClain's race-day fueling strategy.
Photo by Billy Hollander/ASU
The chamber, installed at the Health Futures Center in January, can replicate environments ranging from 39.2 to 109.4 degrees and 20-90% humidity.
The ASU staff also worked with Brooks Running principal physiology researcher Bridget Sopeña to conduct sweat testing. As McClain ran, staff collected sweat samples, which Brooks analyzed to measure sodium and electrolytes loss — data that informed her fueling strategy.
“We’ve had a lot of researchers use the chamber, but not to the degree that Jess did,” said Veronica Martinez, Clinical Research Services director. “This goes to show what we can offer to athletes at this level.”
Beyond athletic performance testing — such as VO2 max, cardiopulmonary exercise testing and resting metabolic rate — Clinical Research Services also provides imaging, phlebotomy, nutrition services and clinical spaces for human research.
For more information on Clinical Research Services and how to access the environmental chamber and other facilities, contact [email protected] or visit Core Research Facilities.
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