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Study shows heat acclimation program can improve athletes' performance

College of Health Solutions professor finds brief intervention can make a difference in competition

black and white close-up of person's chest with sweat on it

March 30, 2021

The time for the mercury to begin creeping toward the triple digits in the Valley is nigh. And when it does, the sudden transition from pleasant warmth to serious heat can wreak havoc on the body.

But one Arizona State University researcher has determined that it’s possible to mitigate the effect of rising temperatures on physical performance with just a little preparation. In a recently published study, College of Health Solutions Assistant Professor of nutrition Floris Wardenaar found that a five-day heat acclimation program improves heat stress indicators while maintaining exercise capacity.

In the study, a group of 14 athletes were divided evenly into one control group and one intervention group. Participants from each group were pair matched based on gender (four female pairs and three male pairs) and body composition for comparison.

Both groups performed two physical capacity tests outdoors during the middle of the summer, one at the beginning of the study period and one at the end. The test asked participants to run as much distance on a 400 meter track as they were able to within 12 minutes to assess their exercise capacity.

After the initial capacity test, participants in the control group performed no additional exercise for five consecutive days, while those in the intervention group performed 60 minutes of biking in a hot (approximately 95 degrees Fahrenheit), temperature-controlled environment each day for the same five consecutive days.

Participants’ temperature, skin temperature and heart rate were continually monitored throughout. Following the five-day intervention period, participants also performed a heat stress test.

Researchers found a nonsignificant but practical difference between the physical performance of those in the control group and those in the intervention group, with the latter showing a 3% increase in physical capacity compared to the former’s 2% decrease. Additionally, a 4% difference in participants’ physical capacity was noted during the heat stress test, in favor of the intervention group.

“We didn't see a significant difference between groups, but there was a practical difference,” Wardenaar said. “They were hiking almost 500 meters more, which is really substantial, and they were doing it with a lower heart rate and with a relative lower core temperature. So all the markers went toward the right direction; they became more efficient in warmer, more stressful conditions, which could potentially make a difference in competition.”

While the study was limited to athletes who were already partially acclimatized to the Arizona heat – meaning they live in the state year-round – Wardenaar said the results are more or less applicable to anyone who trains regularly.

One interesting aspect to note is the role humidity plays in heat acclimatization: the more humid it is, the harder it is for the body to release heat compared to times of the year when it is drier.

So for athletes who train throughout the summer, engaging in a heat acclimatization program during the months of June and July, when it is still relatively dry in Arizona, will help them to get through the rest of the summer as it becomes more humid.

For the same reason, a heat acclimatization program would also be beneficial to athletes recovering from injury who may not be able to begin training until part of the way through the summer.

As for those of us who prefer to leave high stakes physical competition to the experts, Wardenaar said just being outside for a while can help the average person acclimate. So if you have to be outside during the summer and you want to be able to bear the brunt of the heat a bit better, he recommends spending 30 to 45 minutes outdoors each day, while properly hydrating, for a couple of weeks to get to a point where you can better function in the desert climate.

“Most of us, when we go out in the summer, we go into the garage and straight into the car, then straight into another garage or car park and back into the AC,” he said. “So there's almost no heat exposure. You need exposure to be acclimated.”

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