When the body heats up during exercise, it copes in several ways. There are involuntary systems, such as sweating that help it cool off, and voluntary measures, such as dousing with cold water or wearing (and switching) hats filled with ice, as American Galen Rupp did every five kilometers during the Rio 2016 Olympic marathon. (He won a bronze medal.) Voluntary actions are known as “thermal behavior.”
When it comes to men and women, it appears that not all thermal behavior is the same, during exercise or after, in cooling down. Women seem to need more cooling than men, according to a study, which is “the first to highlight sex differences in thermal behavior,” said author Nicole Vargas, a postdoctoral fellow in exercise and nutrition sciences at the University at Buffalo’s school of public health.
The study was small, but its findings could have an impact on ways to prevent heat injuries, inspire improved designs in sports clothing and commercial cooling products, and in other areas. Information about thermal behavior also could help athletes deal with heat waves, common due to climate change.
“The manner in which men and women tolerate and respond to these perceived changes may have implications not just for apparel manufacturing, but potentially for improving athletic performance, particularly in endurance and heat-related activities,” said Michael Jonesco, a sports medicine specialist at Ohio State University’s Wexner Medical Center. He was not involved in the study.
Vargas and her colleagues believe the study also could prove clinically useful in caring for the elderly and those suffering from certain diseases such as multiple sclerosis.
“We know that the elderly and individuals with MS have altered thermoregulatory patterns, which consist of both a reduced ability to sweat, thereby trapping more heat in their body, and attenuated perceptual cues pertaining to thermal stimuli, so they may not sense the need to cool themselves when necessary,” Vargas said. Thus, it’s important to study thermal behavior in these groups to determine whether it could help with their symptoms, “or at least improve their levels of thermal comfort,” she said.
In the study, the scientists had 10 men and 10 women in their early 20s exercise at low intensity — about 65 revolutions per minute — on a stationary bicycle for one hour while watching a nature documentary. Each subject had access to a custom-made dual tubing system that was in direct contact with the back of their neck.
One set of tubing contained water at 93.2 degrees that flowed constantly across their necks. The other set had liquid at minus-4, but also a valve that could control the flow. Researchers told participants to open the valve, thereby releasing the flow of extremely cold liquid, whenever they felt their neck had become uncomfortably warm during exercise. They could turn the valve off and on as needed. Researchers monitored them through the exercise and for one hour after exercising, telling them to keep their neck temperature comfortable during recovery.
The women wanted more cooling than the men, despite similar overall changes in body temperature, and used the cold liquid more often as evidenced by the women’s more frequent use of the antifreeze liquid while exercising. Vargas theorizes that women have more subcutaneous fat than men, as well as greater perceptual responses to temperature changes.
What was especially striking, however, was what scientists saw during recovery or cool-down. After a vigorous workout or competition, most athletes take the time for a cool-down (also sometimes called a warm-down), an easy exercise that allows the body to return to a resting state. After a hard run, for example, a cool-down might involve a slow jog or walk. (Not to be confused with a warm-up, an exercise that prepares the muscles for a more vigorous workout.)
During the cool-down, skin temperature in men fell gradually and returned to normal within an hour. In women, however, skin temperature fell more rapidly, returning to normal within 10 minutes. Logically, this should have reduced the need for neck cooling in women; but the women in the study continued to release the cold liquid, perhaps because their core temperature (the body’s internal temperature, that is, the temperature of their circulating blood) remained elevated, Vargas said.
The scientists studied young healthy men and women and did not take into account hormones or menopause in the women, thus “it would be remiss to conclude that there aren’t other factors involved,” Vargas said, conceding that “considering the wealth of knowledge surrounding impaired temperature regulation during and post menopause, it is likely that these findings would differ greatly for women in these categories.”
Further research should include these women, she said.
Edward Laskowski, co-director of the Mayo Clinic Sports Medicine, who also was not involved in the study, said he found the results surprising. “I would have thought that women would be making themselves warmer instead of cooler — for example, guys always want to lower the air conditioner, and women raise it,” he said.
Because the study sample was small, Laskowski said it would be difficult to extrapolate the findings to a larger population. Nevertheless, he said, “it points out some interesting trends, and, as the authors point out, it can provide the foundation for future studies that look at thermal response in disease states, such as multiple sclerosis.”
Both elite and recreational athletes engage in thermal behavior, although elite athletes probably have a better understanding of their limits and their ability to push their bodies to extremes, Vargas said. “Nevertheless, we often see elite athletes coming off the field, or running by a water station and dousing themselves with water on a hot day, in an attempt to cool themselves,” she said.
Vargas said she believes that a better understanding of thermal behavior during sports — with the goal of improving thermal comfort — potentially could provide competitors with a performance edge. “Athletes who perform multiple bouts of high intensity exercise, which result in compounding increases in core temperature, may benefit greater from recovery periods that utilize cooling modalities, and females may benefit even more,” she said.