The wet bulb globe temperature is similar to the heat index in that it's a way to quantify the impact of the heat on our bodies. There are a few key differences, though, in how these measurements are taken.
The heat index is a value of how hot it feels outside when combining the air temperature and relative humidity based on measurements taken in the shade. This is why it can be a better generalization for a region on a hot day.
Wet bulb globe temperatures, though, factor in the air temperature, humidity, winds, sky condition, and sun angle to get a final value. That's why the wet bulb globe is a better estimate for real-time heat risk for a specific location and time of day.
The UIL has listed specific precautions for high school athletes based on the wet bulb globe temperature. If the value is between 82 and 86.9 degrees, it's expected there to be at least three separate rest breaks of at least four minutes during an hour-long practice. From 87 to 90 degrees, the above standards carry over, and the maximum practice time should be limited to two hours. From 90.1 to 92 degrees, the maximum practice time is limited to an hour, and there must be a 20-minute rest break.
If the wet bulb globe temperature is equal to or above 92.1 degrees, outdoor practice should be cancelled altogether. That's because the heat poses an extreme risk. There are also additional measures put in place for football athletes practicing with or without pads and helmets. And just like the heat index, the wet bulb globe temperature can vary during the day, giving coaches and staff an idea as to what time of day will be safest to practice outdoors.
Another important note on the wet bulb globe temperature is that the final value will be lower than the air temperature, which is opposite of the heat index value. Something to keep in mind when assessing heat risk using the wet bulb globe temperature.