It’s fairly well-established that older people’s exercise performance suffers more in hot weather than that of younger athletes. According to new research, the decline in ability to handle the heat can start as early as age 40, and gets more significant with age.
For the study, 85 men age 20 to 70 did four 15-minute bouts of stationary cycling in a hot, dry chamber (35 degrees Celsius, 20% relative humidity). They rested 15 minutes between each short ride. Researchers measured the men’s total heat loss and whole-body sweat rates while the men rode and rested. Greater heat loss and whole-body sweat rate mean doing a better job at dissipating the heat generated by exercise, which in turn should allow for better performance in the heat.
As expected, the youngest men (ages 20 to 31) had the highest rate of heat loss and sweating, and the oldest men (ages 56 to 70) did the worse job at bodily cooling.
What most surprised the researchers was that with each short bout of cycling, more of the middle-aged men started to suffer in the heat. By the second ride, the participants age 50-55 were starting to sweat less (i.e., store more heat). By the fourth short ride, those in the 45-49 age group were also significantly less, and even those in the 40-44 age group were showing signs of being less able to deal with the heat than the younger riders.
These findings were consistent throughout the study participants, regardless of their cardiovascular fitness (as measured by VO2 max), body surface area or body-fat percentage.
“[A]ge was the only variable to significantly correlate with whole-body sweat rate,” the researchers wrote. “This would suggest that when the stimulus for sweating is equal for all participants … ageing may have a larger influence on whole-body heat loss capacity than the fitness level or specific physical characteristics of the individual.”
The researchers concluded that middle-aged and older adults might therefore have an increased risk of heat-related illness when working hard in hot weather.
The study was published in the online journal PLoS One.
