How much can the body actually adapt?<\/p>\n
While you can train your body to respond better in the heat, it has limits. Race organizers often rely on guidelines based on the wet-bulb globe temperature (WBGT) index<\/a>, which accounts for temperature, sun angle, cloud cover, wind speed, and humidity, to determine when conditions become unsafe. In fact, P\u00e9riard and fellow researchers found<\/a> that over one-quarter of all endurance running events were held in moderate, high, or extreme heat.<\/p>\n One of the biggest factors that influences humans\u2019 ability to regulate is humidity.\u00a0 As it rises, the risks of heat-related illnesses increase. When the air is already saturated with water vapor, sweat can\u2019t evaporate as effectively, limiting the body\u2019s ability to cool itself. That\u2019s why a 90-degree day with high humidity can be more dangerous than a much hotter, drier environment. One ongoing study<\/a> by researchers at Penn State found that the safety threshold for young, healthy adults (without heat acclimation) is around 87 degrees Fahrenheit at 100 percent humidity.<\/p>\n But not everyone reacts the same to the heat, either. Jessica Mee<\/a>, an environmental physiology researcher at the University of Worcester, studies how men and women respond differently to heat training. Some of her research<\/a> suggests women have a lower heat tolerance than men and may benefit from longer periods of acclimation, but the evidence is still evolving.<\/p>\n