Football
- Highest risk in American sport. Pads and a helmet block evaporation over most of the body surface.
- Preseason runs in August, when heat and zero acclimatization overlap.
- See football WBGT for equipment-adjusted thresholds.
Exertional heat stroke is one of the leading causes of sudden death in sport, and it is close to entirely preventable. The prevention begins with knowing the actual heat load, which is why wet bulb globe temperature has become the standard across athletics rather than air temperature or the heat index.
The reason is specific to sport. Athletes exert themselves in direct sun, often in equipment that traps heat, frequently when they have just arrived from an air conditioned summer and have no acclimatization at all. Every one of those factors is invisible to the heat index and visible to WBGT.
88°FRed flag: cut hard training sharply
90°FBlack flag: cancel outdoor practice
Days 1-5When most heat illness actually happens
80°FHave cold-water immersion ready from here up
Practice modification by WBGT
The widely adopted athletic activity guidelines. Individual state associations publish their own numbers, usually within a degree or two of these.
| WBGT | Practice | Breaks | Equipment |
|---|---|---|---|
| Under 82.0°F | Normal activity | 3 per hour, 3 minutes | Normal |
| 82.0 to 86.9°F | Normal, monitor at-risk athletes closely | 3 per hour, 4 minutes | Normal |
| 87.0 to 89.9°F | Maximum 2 hours | 4 per hour, 4 minutes | Helmets and shoulder pads only |
| 90.0 to 92.0°F | Maximum 1 hour, no conditioning | 20 minutes of breaks within the hour | No protective equipment |
| Above 92.0°F | Cancel or move indoors | — | — |
How the risk differs by sport
The same reading is not the same risk across a campus. Equipment, intensity and surface do most of the work.
Cross country and track
- Minimal equipment, but sustained maximal effort for extended periods.
- Often run on open roads and tracks with no shade and significant radiant load from the surface.
Soccer, field hockey and lacrosse
- Continuous running with limited substitution in many formats.
- Synthetic turf can sit 40 to 60°F above air temperature and radiates into every player on it.
Marching band and drill
- Rehearses on asphalt lots in full sun with uniforms and instruments.
- Frequently excluded from athletic heat policies despite comparable or worse exposure.
The acclimatization period is the dangerous part
Most exertional heat illness in athletics happens in the first three to five days of preseason, not on the hottest day of the year. A heat acclimatization period exists to spread that load, and it is the single highest-value thing a program does.
- Days 1 to 2: one practice per day, maximum three hours, helmets only for football, no contact.
- Days 3 to 5: one practice per day, maximum three hours, helmets and shoulder pads, contact limited to blocking sleds and dummies.
- Days 6 onward: full equipment permitted, and double practice days may begin.
- On a double practice day, the two sessions are separated by at least three continuous hours of rest, and a double day is never followed by another double day.
- Walk-throughs do not count as practice, as long as no conditioning or equipment is involved and they stay separated from practice by three hours.
These are the widely adopted NATA-derived guidelines. Your state association's version governs; most are close to this.
What actually prevents heat illness
The reading tells you the environment is dangerous. These are the things that change the outcome once you know.
Unrestricted fluid access
Water available at all times, not only at scheduled breaks. Withholding water as discipline has killed athletes.
Cold-water immersion on site
A tub, water and ice, ready before practice starts from roughly 80°F WBGT. Cooling first, transport second, is what survives heat stroke.
Breaks that are real
In shade, with helmets off and fluids in hand. A break spent standing in the sun listening to coaching is not a break.
A culture of speaking up
Athletes hide symptoms when toughness is the measure. The program has to make reporting normal and costless.
Warning signs of heat illness
Heat stress shows up before it becomes an emergency. Anyone on site should speak up immediately on any of these:
Dizziness or lightheadedness
Nausea or vomiting
Chills or goosebumps in the heat
Severe or throbbing headache
Confusion or out-of-character behavior
Stumbling, cramping or collapse
When in doubt, cool first and call for help. Collapse or confusion in the heat should be treated as possible exertional heat stroke: begin cold-water immersion immediately and call 911. Cooling comes before transport.
A sports WBGT app for the sideline
The WBGT app was built for exactly this: a trainer or coach who needs the number quickly, in Athlete mode, with the practice guidance attached, and a forecast so a four o'clock session can be moved before anyone travels to it.
- Live WBGT at your field or any city
- Hourly and 14-day forecasts to schedule practice
- Athlete mode with practice modification guidance
- Flag level, color-coded, at a glance
WBGT is estimated from weather data with the peer-reviewed Liljegren model. Where a policy requires on-site measurement, use the app for planning and as a cross-check alongside your instrument.
Common questions
What WBGT is too hot for sports practice?
Most athletic guidelines cancel outdoor practice above 92°F WBGT and require significant modification from 87°F: helmets and shoulder pads only, two hours maximum and four breaks an hour. Your state association's numbers govern.
What is a good WBGT app for sports?
You want live WBGT for your actual field rather than a regional forecast, an athlete-specific threshold set rather than a generic one, and an hourly forecast so practice can be rescheduled in advance. The free WBGT app does all three.
Who should take the WBGT reading at practice?
Your policy should name a specific role, usually the athletic trainer, with authority to modify or stop activity. The reading should be taken at the practice site about 15 minutes before activity and repeated every 30 minutes, and every reading logged.
Does WBGT apply to indoor sports?
It can. Indoor WBGT uses a different weighting with no solar term, and a hot gym with poor ventilation and high humidity can reach concerning values. Wrestling rooms and un-air-conditioned gyms are the usual cases.
How is WBGT different from the heat index for sports?
The heat index assumes shade and light wind, which describes almost no athletic practice. WBGT includes direct sun and actual wind, so it reflects conditions on an open field. See WBGT vs heat index.
Related WBGT guides
Know the real heat number
Real-time WBGT, flag levels and forecasts. Free on iPhone.
