A new study shows that cardiovascular strain begins at lower temperature and humidity levels than those that cause increases in the body’s core temperature and could inform revisions to safety guidelines and policies that help protect people during heat waves. Researchers will present their work this week at the American Physiology Summit, the flagship annual meeting of the American Physiological Society (APS), in Long Beach, California.
The study, which is part of the PSU Human Environmental Age Thresholds (HEAT) project led by W. Larry Kenney, PhD, FAPS, included 45 people in their 20s who slowly walked on a treadmill or performed activities simulating the minimal activities of daily living while inside environmental chambers that produced either warm and humid or hot and dry environmental conditions.
The researchers found that during minimal activity in warm and humid environments, cardiovascular strain increased when temperatures reached 95 degrees F and relative humidity was 65% while increases in core temperature occurred at 95 degrees and 73% relative humidity. During slow walking in warm and humid environments, cardiovascular strain increased at 95 degrees and 52% relative humidity while core temperature increased at 95 degrees and 58% relative humidity.
For hot and dry environments, cardiovascular strain rose at temperatures above 113 degrees F and 19% relative humidity while core temperature increased at 118 degrees and 17% relative humidity during minimal activity. During slow walking in the same conditions, increases in cardiovascular strain occurred at 104 degrees and 25% relative humidity and increases in core temperature occurred at 109 degrees and 22% relative humidity.
