Sport Science
Wet-Bulb Globe Temperature (WBGT)
Wet-bulb globe temperature is a composite environmental heat stress index that accounts for temperature, humidity, solar radiation, and wind speed simultaneously. It is the most widely used standard for assessing heat risk in outdoor athletic settings and forms the basis of most state athletic association guidelines for practice modification and cancellation during hot weather. WBGT readings are more meaningful than air temperature alone because they capture the conditions that actually determine how effectively the body can cool itself, primarily the humidity and radiant heat that make sweating less effective.
How it differs from air temperature
A 95-degree day in dry desert heat and a 95-degree day in humid coastal conditions represent very different physiological challenges, but both show the same thermometer reading. WBGT captures that difference. High humidity reduces evaporative cooling from sweat, which is the primary mechanism by which the body sheds heat during exercise. Direct solar radiation adds heat load independent of air temperature. WBGT integrates all of these factors into a single number that more accurately reflects what an athlete’s body is actually experiencing.
How coaches use it
The National Athletic Trainers Association (NATA) and most state high school athletic associations publish WBGT-based activity modification guidelines. Typical thresholds: below 82 degrees Fahrenheit WBGT, normal activity; 82 to 87, increase rest breaks and monitor closely; 87 to 90, reduce intensity and duration significantly; above 90, consider cancellation or indoor alternatives. WBGT meters are available at various price points for programs that want real-time readings. Smartphone apps using regional weather data provide a reasonable approximation when a dedicated meter is not available. Coaches who work with outdoor athletes in summer should know their state association’s specific guidelines and have a heat emergency action plan in place before the first practice.
Related terms
Heat Acclimation · Load Management · Wellness Questionnaire · Readiness Score