Ask an athletic trainer what worries them in late summer and heat will be near the top of the list. Practices start before school does, gym doors get propped open, and the kids want to push.
The thermometer on the wall doesn't tell the whole story. Humidity matters as much as temperature, because sweat only cools you when it can evaporate. On a muggy day it can't, and an athlete heats up faster than the air temperature would suggest. That's why coaches and trainers look at heat index or WBGT instead of temperature alone.
Heat index vs. WBGT
The heat index comes from the National Weather Service. It combines air temperature and relative humidity into one "feels like" number. It was built for shade and light wind, which makes it a good fit for indoor spaces like a gym or a wrestling room.
WBGT, short for wet bulb globe temperature, goes further. It also accounts for direct sun and air movement, so it's the better measure for an outdoor field in the afternoon. Some state athletic associations and school districts write their practice rules around WBGT, and others use heat index. Find out which one yours uses before you buy anything, and follow their current guidelines rather than a number you saw online.
One more thing to keep straight. The "wet bulb" reading on a psychrometer is not WBGT. The names sound alike, but WBGT adds a black globe reading for radiant heat, and you can't get there from a handheld humidity meter.
Putting the number where everyone can see it
For indoor spaces, we sell our own HIX1800 heat stress monitor. It mounts on the wall, measures temperature and humidity, and shows the heat index in 2-inch red LED digits you can read from more than 50 feet away. That's really the point of it. The coach running drills doesn't have to stop and dig out a meter, and the athletes can see the number too.
You set a high alarm, and when the heat index crosses it the display flashes and a buzzer sounds. There's also a 5 VDC output if you want to wire in an external strobe or siren for a big gym. It runs on a USB wall adapter, with an optional rechargeable battery for a few days away from an outlet.
It's an indoor instrument, though. Don't hang it in direct sun or take it out to the practice field. Outdoors in the sun you want a WBGT reading, and the HIX1800 isn't a WBGT meter.
For spot checks around a building, a handheld like the General Tools SAM990DW psychrometer reads temperature and humidity and gives you dew point and wet bulb in a few seconds. It's handy for walking the locker room, or for checking whether the field house is actually cooling down once the fans come on.
Making the readings count
A monitor only helps if somebody acts on it. Before the season starts, write down what changes at each level, such as when you add extra water breaks and when you shorten practice or move it. Post that plan where the coaches will see it. Then check the reading at the start of practice and again partway through, because a gym can warm up a lot in an hour.
Keep the instrument honest, too. Humidity sensors drift, so an annual calibration check is a good habit. Our in-house lab calibrates temperature and humidity instruments, and the RA form is on our calibration and repair page.
You'll find the HIX1800 in our heat stress collection, and more gear for trainers in the athletic training section. Questions? Call us at 800-390-0004. We're happy to talk it through.
