Researchers with the U.S. Army Research Institute of Environmental Medicine are tracking down risk factors and biomarkers of soldiers who are more resilient to heat-related illnesses in a new study, according to a Pentagon news release.

“Heat illnesses pose a serious threat not just to individuals, but also to units and deployability, and they impose a significant financial cost as well,” said Gabrielle Giersch, a research physiologist with the Research Institute of Environmental Medicine’s thermal and mountain medicine division. “We don’t have a lot of data on the factors that contribute to the onset of heat illness or optimal recovery time.” 

Exertional heat stroke, which is a severe heat illness characterized by a high body temperature and altered mental state, like disorientation or loss of consciousness, affected almost 500 active-duty troops in 2024 alone, according to Pentagon data.

This latest study aims to improve criteria for when soldiers can return to duty after they experience a heat-related illness through identifying risks and understanding how risk factors affect soldiers, Giersch said.

Earlier this year, Giersch and her team had 24 soldiers assigned to 1st Battalion, 145th Aviation Regiment, at Fort Rucker, Alabama, participate in a 5-mile run and an 8-mile ruck march. Participants served as the study’s control group and provided blood and urine samples, and their heart rate, skin temperature and core temperature were monitored.

“The core temperature data showed that several people reached high temperatures without experiencing any symptoms of [exertional heat stroke] and cooled off very quickly, which gives us a very good indication that we have a really good control group to identify what individuals who don’t become heat illness casualties look like relative to those who do,” she said.

The team hopes to include participants from elite groups, including Rangers and special operations volunteers, since they are more likely to experience heat-related illnesses while training. The goal is to publish the team’s findings next year.

Beyond interest from soldiers who participated, the study will have a lasting impact on the Army’s ability to understand heat-related illnesses and shape policy decisions.

“There is so much intrinsic value for the volunteers in this study,” Giersch said. “People were constantly coming up to me and asking what their core temperature was, when we’d have their blood data and similar questions. They want to see the papers when they get published and learn how our study impacts policy. They really want to make life better for their future battle buddies, whether they know them or not. That makes it all worthwhile.”