4.1 Heat Illness Prevention & WBGT Monitoring
Key Takeaways
- Wet-bulb globe temperature (WBGT = 0.7Tw + 0.2Tg + 0.1Td) is the preferred environmental measure; heat index omits radiant load and wind and is not the NATA activity-modification standard.
- NATA 2015 Table 5: WBGT <82.0°F normal activity with ≥3 rest breaks of ≥3 min; 82.0–86.9°F discretion and ≥3 breaks of ≥4 min; 87.0–89.9°F max 2 h with equipment limits; 90.0–92.0°F max 1 h, no pads, 20 min rest; >92.1°F cancel outdoor workouts.
- Heat acclimatization is typically 7–14 days; the first 2–3 days use reduced intensity and equipment, and the first 2–3 weeks of preseason carry the highest exertional heat-illness risk.
- Exertional heat stroke requires central-nervous-system dysfunction plus a high core temperature (typically >40.5°C / 105°F); rectal temperature is the gold-standard field measure—oral, axillary, tympanic, forehead, and temporal readings must not be used to rule it out.
- On-site cold-water immersion capability is a prevention/preparedness requirement at high-risk events; full stroke treatment is Domain 3, but policy without a ready tub is an incomplete plan.
Practice Analysis, 8th Edition (PA8) Domain I, task 0105, asks the athletic trainer (AT) to monitor environmental conditions and respond with activity modification, equipment changes, and emergency preparedness before an athlete collapses. Task 0104 (optimize wellness) shares the same chapter because hydration, sleep, and fitness are heat-illness risk factors. Exertional heat stroke (EHS) treatment—cold-water immersion (CWI), “cool first, transport second,” and return-to-play after laboratory clearance—belongs mainly in Domain 3. This section is prevention and recognition thresholds, with a brief pointer to why a tub must already be on the sideline.
Why Heat Still Kills Athletes
The Korey Stringer Institute (KSI) notes that most American-football EHS deaths (~65%) have occurred in August, and more than half of reported deaths occurred during morning practices when humidity was high—not only on the hottest afternoon. Humidity blocks evaporative cooling, which is the body’s primary heat-loss method during exercise. Pads, helmets, poor fitness, acute illness, and unacclimatized athletes multiply that load. Prevention is a written, rehearsed policy: measure the environment, change work-rest and equipment, identify high-risk athletes, guarantee fluid and shade access, and stage cooling equipment before the first whistle.
WBGT Versus Heat Index
Wet-bulb globe temperature (WBGT) is the preferred environmental measure in the National Athletic Trainers’ Association (NATA) 2015 position statement on exertional heat illnesses (Casa et al., Journal of Athletic Training, 50(9):986–1000). The equation weights the factors that actually drive heat strain:
WBGT = 0.7Tw + 0.2Tg + 0.1Td
- Tw = wet-bulb temperature (evaporative capacity / humidity)
- Tg = globe temperature (radiant heat from sun, turf, and stadium surfaces)
- Td = dry-bulb (ambient air) temperature
The National Weather Service heat index uses only air temperature and relative humidity and assumes shade and light wind. It underestimates stress in full sun, on dark turf, and in full pads, and it does not include wind that could help evaporation. KSI and NATA both treat WBGT as the standard for activity-modification tables. Place a WBGT device at the venue 15–20 minutes before activity (NFHS/KSI practice), recheck when conditions change, and tighten restrictions if the reading rises mid-practice. Guidelines must be region-specific (Grundstein et al., 2015): a 90°F afternoon in Louisiana is not the same physiologic shock as the first 90°F day in Maine.
NATA 2015 Table 5 — Activity and Rest-Break Guidelines
| WBGT (°F) | Activity and rest-break guidelines |
|---|---|
| <82.0 | Normal activities. Provide ≥3 separate rest breaks of minimum 3 min each during the workout. |
| 82.0–86.9 | Use discretion for intense or prolonged exercise. Watch at-risk players carefully. Provide ≥3 separate rest breaks of minimum 4 min each. |
| 87.0–89.9 | Maximum practice time = 2 h. Football: helmet, shoulder pads, and shorts only. All protective equipment off for conditioning. All sports: ≥4 separate rest breaks of minimum 4 min each. |
| 90.0–92.0 | Maximum practice = 1 h. No protective equipment. No conditioning. Provide 20 min of rest breaks during that hour. |
| >92.1 | No outdoor workouts. Cancel or delay until a cooler WBGT reading. |
Rest breaks belong in shade or a designated cooling zone, with helmets off and enough time for every athlete to drink. Work-to-rest ratios must match both WBGT and intensity (NATA recommendation 12). Access to fluids is continuous, not only at a coach’s whistle (NATA recommendation 4).
Heat Acclimatization: Physiology Versus Policy Calendars
Heat acclimatization is the physiologic adaptation to repeated exercise-heat exposure, typically over 7 to 14 days (NATA recommendation 2). Adaptations include expanded plasma volume, earlier and more copious sweating, more dilute sweat, lower exercising heart rate, and lower core and skin temperatures. If not maintained, benefits decay within about 3 weeks. The first 2–3 weeks of preseason—especially in equipment-intensive sports—are the highest-risk window. The first 2–3 days should use reduced intensity, duration, and equipment.
Do not confuse physiologic acclimatization (7–14 days) with a governing-body practice calendar. NCAA and secondary-school football heat-acclimatization policies (NATA 2015 Figure 1; Casa et al. 2009 secondary-school guidelines) typically phase equipment as:
| Days | Equipment and session structure (typical football policy) |
|---|---|
| 1–2 | Helmets only; one practice per day; field time commonly capped near 3 hours (including warm-up, conditioning, and cool-down). |
| 3–5 | Helmets and shoulder pads; still single sessions in the first five days. |
| 6+ | Full pads and contact may begin; double-practice days are restricted (not consecutive; total practice time on a two-a-day is commonly ≤5 hours with hours of rest between sessions). |
A team that “did one hot practice in full pads on day 1” is not acclimatized. Sick athletes (fever, gastroenteritis, viral illness, extensive rash) should not practice in the heat until recovered and then should be watched closely (NATA recommendation 3).
Differential: Five Conditions the Exam Will Mix
Exercise-associated muscle cramps (EAMCs) are painful, involuntary contractions during or after exercise. NATA notes that “heat cramps” is a technically inappropriate popular term: cramps are not caused by a high core temperature, can occur in cool conditions, and have mixed proposed mechanisms (fatigue/neuromuscular control, large sweat sodium losses, dehydration). Immediate care is rest and passive stretching; sodium-containing fluids help when a whole-body sodium deficit is suspected. Distinguish from exertional sickling (sickle cell trait): a sickling collapse is often a painful, slump-to-the-ground event without the twitching prodrome of EAMC and is a medical emergency, not a stretch-and-drink timeout.
Heat syncope is orthostatic dizziness or a brief faint in unfit or unacclimatized people who stand in the heat or change posture suddenly, often in the first 5 days of heat exposure, before blood volume expands. Rectal temperature is relatively low (<39°C). Rule out cardiac syncope. Care: shade, elevate legs, cool the skin, rehydrate.
Heat exhaustion is inability to continue exercise in the heat from cardiovascular insufficiency, energy depletion, and central fatigue. Core temperature is usually <40.5°C (105°F). Sweating is typically heavy. Cognition may be mildly off (headache, dizziness) but profound CNS dysfunction is absent—that finding pushes the diagnosis toward EHS. Same-day return is not recommended.
Exertional heat stroke is the medical emergency: CNS dysfunction (confusion, irritability, collapse, seizures, combativeness, coma) plus a high core temperature, typically >40.5°C (105°F). Skin is usually hot and wet (unlike classical heat stroke in the elderly, which may be dry). If CNS dysfunction is present and rectal temperature is slightly under 40.5°C because of delay or passive cooling, still treat as EHS. Survival depends on how long the brain stays above the critical threshold—not on how dramatic the first number looked.
Exercise-associated hyponatremia (EAH) is serum sodium <135 mmol·L⁻¹ during or within 24 hours of activity (NATA fluid-replacement position statement, 2017). It is typically caused by overdrinking hypotonic fluid (including sports drinks) plus impaired free-water clearance—not by “not drinking enough.” Athletes may gain weight during the event. Early symptoms (headache, nausea, malaise) overlap heat illness; later signs include swollen hands/feet, worsening headache, confusion, seizures, and noncardiogenic pulmonary edema. EAH is not treated with more water. Mild cases: withhold fluids until the athlete urinates; severe encephalopathy requires hypertonic saline under advanced medical care. Giving free water to a seizing, puffy endurance athlete because “it looks like heat stroke” can be fatal.
| Feature | EAMC | Heat syncope | Heat exhaustion | EHS | EAH |
|---|---|---|---|---|---|
| Core temperature | Not the cause | Relatively low (<39°C) | Usually <40.5°C | Typically >40.5°C / 105°F | Often normal or low |
| CNS | Alert | Brief faint, then lucid | Mild change | Profound dysfunction | Can be profound (seizure) |
| Body mass | Variable | Variable | Usually loss | Usually loss | Gain or no loss |
| First action | Stop, stretch | Shade, legs up | Shade, rest, oral fluids | Rectal temp + CWI (Domain 3) | Stop hypotonic fluids |
High-Risk Athletes and Equipment Modifications
Identify and watch: prior heat illness, sickle cell trait, low fitness, high body mass, lack of acclimatization, current illness or fever, sleep loss, hypohydration, and medications or supplements that impair thermoregulation or increase heat production (stimulants, diuretics, anticholinergics, some ADHD medicines, and unregulated “fat burners”). NATA discourages dehydrating or thermogenic supplements (recommendation 13). Equipment modifications follow Table 5: remove pads for conditioning, helmets off on breaks, shorts and T-shirts when WBGT climbs, and cancel rather than “push through” above 92.1°F.
Aim to keep body-mass loss <2% from pre- to post-session and keep morning urine pale; do not gain weight during exercise (that is an EAH warning, not a hydration victory).
Rectal Temperature and Why a Tub Must Already Exist
Rectal temperature is the clinical gold standard for suspected EHS (NATA recommendation 8; strength A). Oral, axillary, tympanic, forehead-sticker, and temporal-artery devices are not valid after intense exercise in the heat and can read deceptively “normal.” Exam trap: using an oral temperature to “rule out” heat stroke in a collapsed, confused athlete. If rectal thermometry is not immediately available and EHS is suspected from CNS findings and the setting, start cooling—do not wait for a gadget.
When conditions warrant, a cold-water or ice tub and ice towels must be on site (NATA recommendation 7). That is a prevention/preparedness requirement: you cannot invent a 150-gallon immersion station after collapse. Full CWI technique (water about 1.7–15°C / 35–59°F, stir continuously, remove at rectal 38.9°C / 102°F, goal to cool below 102°F within 30 minutes of collapse) is Domain 3. Remember the slogan that makes the tub policy non-negotiable: EHS is 100% survivable when recognized and cooled immediately. A heat policy without a ready tub is a paper policy.
A lineman collapses on day 2 of August preseason. He is confused and combative. A coach obtains an oral temperature of 99.4°F and says heat stroke is ruled out. What is the most appropriate next action?
Which statement correctly describes environmental monitoring and NATA activity modification for heat?
A football program wants a heat-acclimatization and preparedness plan that matches NATA recommendations. Which plan is correct?