STRATAWBGT and heat safety: the Athletic Trainer's guide to modifying practice
Heat illness is one of the most predictable emergencies in sport, and one of the most preventable. Wet Bulb Globe Temperature (WBGT) is how you get ahead of it. This guide covers how to read it, what to change at each threshold, and what to do when it goes wrong.
If you take one thing from this guide, take this: air temperature alone will get an athlete hurt. A 90°F day at 40% humidity and a 90°F day at 80% humidity are two very different levels of risk, and only one number tells you the difference. That number is WBGT.
What WBGT actually measures
Wet Bulb Globe Temperature pulls together four things the body has to fight on a hot day: air temperature, humidity, radiant heat (direct sun, plus the heat coming back off the turf), and wind. The heat index only uses temperature and humidity, so it consistently underestimates the risk to an athlete standing on open turf in full sun. That is exactly why the military, OSHA, and the major sports-medicine bodies use WBGT.
A real WBGT reading comes from a device on-site, measured where the athletes actually stand, not from a weather app pointed at the nearest airport. Turf can run 10 to 20 degrees hotter than a shaded thermometer a mile down the road.
The activity-modification thresholds
These thresholds mirror the OHSAA 2025 heat policy, which is built on the NATA and Korey Stringer Institute (KSI) framework. Take a reading before practice and at least every 30 minutes once it starts, and modify the moment you cross a line.
| WBGT (°F) | Category | What to do |
|---|---|---|
| Under 79.8 | Low | Normal activity. Provide three separate 3-minute breaks each hour. Water available at all times. |
| 79.8 to 84.7 | Moderate | Three separate 4-minute breaks each hour. Remove helmets and equipment when the athlete is not in the drill. Monitor for early signs of heat illness. |
| 84.8 to 87.8 | High | Max practice 2 hours. Four separate 4-minute breaks each hour. Football limited to helmet, shoulder pads and shorts. Allow dry-shirt changes. Consider moving practice to a cooler time. |
| 87.9 to 89.8 | Very High | Max 1 hour of training with four separate 5-minute breaks inside that hour. No additional conditioning. No equipment. Dry-shirt changes. Strongly consider postponing. |
| 89.8 and up | Extreme | No outdoor workouts. No indoor workouts unless in an air-conditioned space. Have cold-water immersion on-site. Activate your Emergency Action Plan if anyone goes down. |
Your region changes the numbers
Athletes adjust to the climate they train in, so a school in Georgia and a school in Ohio should not be running the same thresholds. The Korey Stringer Institute publishes three regional zones:
- Zone 1: the cooler, northern states, with lower breakpoints.
- Zone 2: the central states, which is what the numbers above use, and the OHSAA default.
- Zone 3: the warmer, southern states, with higher breakpoints, because those athletes are more used to the heat.
The rule of thumb: you can always run stricter than your zone, never looser. Pick your region, then hold the line.
Preseason is the danger zone
The largest share of exertional heat-stroke deaths happen in the first few days of preseason, before athletes have adjusted to the heat and often when they are in the most equipment. Build an acclimatization plan, a slow ramp that gives the body time to catch up: phase equipment in over several days, cap two-a-days early, and treat that first week as the highest-risk week of the year. Because it is.
When it goes wrong: exertional heat stroke
Exertional heat stroke is survivable, but only with the right response, and it comes down to one principle: cool first, transport second.
Suspect it when core temperature climbs above 104°F and you see the brain start to misfire: confusion, collapse, aggression, loss of coordination. Get the athlete into cold-water immersion immediately and cool them to about 102°F before EMS transport. What saves the athlete is how fast you drop the core temperature, not how fast the ambulance arrives. Run your Emergency Action Plan at the same time.
This is why the extreme-heat protocol calls for a cold-water immersion tub, or the TACO (tarp-assisted cooling) method, on-site before anyone starts moving. In July, that tub is not optional equipment.
Stop doing this on a clipboard
Strata logs WBGT for your field, flags the exact activity modification for your region, and timestamps every reading it takes. If a decision is ever questioned, you are not defending a memory. You are showing the record. And it keeps logging even when the app is closed.
See it with your school's branding →Frequently asked
Is WBGT the same as the heat index?
No. The heat index uses only temperature and humidity. WBGT adds radiant heat from the sun and the effect of wind, which is why it is the standard for outdoor athletics. On open turf in full sun, the heat index will routinely tell you things are safer than they are.
How often should I measure WBGT during practice?
Before practice, and at least every 30 minutes once it is underway. Conditions move on you, especially as the sun angle shifts and clouds come and go, and the reading from two hours ago is not the one that matters now.
Can I just use a weather app?
Not for a safety decision. A regional forecast cannot see your actual field: the turf, the sun exposure, the pockets of shade all move the number up or down. Measure on-site, where the athletes are.
What is the single most important heat-stroke rule?
Cool first, transport second. On-site cold-water immersion down to roughly 102°F before EMS transport is what saves lives. How fast you drop the core temperature is the one variable that matters most.
Sources & further reading
- NATA Position Statement: Exertional Heat Illnesses. nata.org
- Korey Stringer Institute (KSI), University of Connecticut, heat-safety and WBGT guidelines. ksi.uconn.edu
- Gatorade Sports Science Institute (GSSI), heat and hydration research. gssiweb.org
- Your state athletic association heat policy (for example, OHSAA).