Context: Knowledge about the specific environmental and practice risks to participants in American intercollegiate football during preseason practices is limited. Identifying risks may mitigate occurrences of exertional heat illness (EHI). Objective: To evaluate the associations among preseason practice day, session number, and wet bulb globe temperature (WBGT) and the incidence of EHI. Design: Descriptive epidemiology study. Setting: Sixty colleges and universities representing 5 geographic regions of the United States. Patients or Other Participants: National Collegiate Athletic Association football players. Main Outcome Measure(s): Data related to preseason practice day, session number, and WBGT. We measured WBGT every 15 minutes during the practice sessions and used the mean WBGT from each session in the analysis. We recorded the incidence of EHIs and calculated the athlete-exposures (AEs). Results: A total of 553 EHI cases and 365 810 AEs were reported for an overall EHI rate of 1.52/1000 AEs (95% confidence interval [CI] = 1.42, 1.68). Approximately 74% (n = 407) of the reported EHI cases were exertional heat cramps (incidence rate = 1.14/1000 AEs; 95% CI = 1.03, 1.25), and about 26% (n = 146) were a combination of exertional heat syncope and heat exhaustion (incidence rate = 0.40/1000 AEs; 95% CI = 0.35, 0.48). The highest rate of EHI occurred during the first 14 days of the preseason period, and the greatest risk was during the first 7 days. The risk of EHI increased substantially when the WBGT was 82.0°F (27.8°C) or greater. Conclusions: We found an increased rate of EHI during the first 14 days of practice, especially during the first 7 days. When the WBGT was greater than 82.0°F (27.8°C), the rate of EHI increased. Sports medicine personnel should take all necessary preventive measures to reduce the EHI risk during the first 14 days of practice and when the environmental conditions are greater than 82.0°F (27.8°C) WBGT.

Context: : Wet bulb globe temperature (WBGT) is the gold standard for assessing environmental heat stress during physical activity. Many manufacturers of commercially available instruments fail to report WBGT accuracy.Objective: : To determine the accuracy of several commercially available WBGT monitors compared with a standardized reference device.Design: : Observational study.Setting: : Field test.Patients or Other Participants: : Six commercially available WBGT devices.Main Outcome Measure(s): : Data were recorded for 3 sessions (1 in the morning and 2 in the afternoon) at 2-minute intervals for at least 2 hours. Mean absolute error (MAE), root mean square error (RMSE), mean bias error (MBE), and the Pearson correlation coefficient (r) were calculated to determine instrument performance compared with the reference unit.Results: : The QUESTemp° 34 (MAE = 0.24°C, RMSE = 0.44°C, MBE = –0.64%) and Extech HT30 Heat Stress Wet Bulb Globe Temperature Meter (Extech; MAE = 0.61°C, RMSE = 0.79°C, MBE = 0.44%) demonstrated the least error in relation to the reference standard, whereas the General WBGT8778 Heat Index Checker (General; MAE = 1.18°C, RMSE = 1.34°C, MBE = 4.25%) performed the poorest. The QUESTemp° 34 and Kestrel 4400 Heat Stress Tracker units provided conservative measurements that slightly overestimated the WBGT provided by the reference unit. Finally, instruments using the psychrometric wet bulb temperature (General, REED Heat Index WBGT Meter, and WBGT-103 Heat Stroke Checker) tended to underestimate the WBGT, and the resulting values more frequently fell into WBGT-based activity categories with fewer restrictions as defined by the American College of Sports Medicine.Conclusions: : The QUESTemp° 34, followed by the Extech, had the smallest error compared with the reference unit. Moreover, the QUESTemp° 34, Extech, and Kestrel units appeared to offer conservative yet accurate assessments of the WBGT, potentially minimizing the risk of allowing physical activity to continue in stressful heat environments. Instruments using the psychrometric wet bulb temperature tended to underestimate WBGT under low wind-speed conditions. Accurate WBGT interpretations are important to enable clinicians to guide activities in hot and humid weather conditions.

Context: Interscholastic heat policies for football have not been evidence based. Therefore, their effectiveness in mitigating exertional heat illness has not been assessed.Objective: To discuss the development of the Georgia High School Association heat policy and assess the effectiveness of revised guidelines.Design: Descriptive epidemiology study.Setting: Georgia high schools.Patients or Other Participants: Interscholastic football players in grades 9 through 12.Main Outcome Measure(s): Heat syncope and heat exhaustion (HS/HE) illness rates (IRs) were calculated per 1000 athlete-exposures (AEs), and relative risk (RR) was calculated as a ratio of postpolicy (POST) IR divided by prepolicy (PRE) IR.Results: A total of 214 HS/HE cases (172 PRE, 42 POST) and 341 348 AEs (178 230 PRE, 163 118 POST) were identified. During the first 5 days of the PRE period, approximately 50% of HS/HE illnesses occurred; HS/HE IRs doubled when practice sessions increased from 2 to 2.5 hours and tripled for practices ≥3 hours. The HS/HE IRs in the PRE period increased from 0.44/1000 AEs for wet-bulb globe temperatures (WBGTs) of <82°F (2.0/1000 AEs for WBGTs from 87°F (30.6°C) to 89.9°F (32.2°C). The RRs comparing PRE and POST policy periods were 0.29 for WBGTs of <82.0°F (90°F (>32.3°C).Conclusions: Results from the PRE period guided the Georgia High School Association to revise its heat and humidity policy to include a mandated 5-day acclimatization period when no practices may exceed 2 hours and the use of WBGT-based activity-modification categories. The new policy reduced HS/HE IRs by 35% to 100%, depending on the WBGT category. Our results may be generalizable to other states with hot and humid climates similar to that of Georgia.

Many athletic governing bodies are adopting on-site measurement of the wet-bulb globe temperature (WBGT) as part of their heat safety policies. It is well known, however, that microclimatic conditions can vary over different surface types and a question is whether more than one WBGT sensor is needed to accurately capture local environmental conditions. Our study collected matched WBGT data over three commonly used athletic surfaces (grass, artificial turf, and hardcourt tennis) across an athletic complex on the campus of the University of Georgia in Athens, GA. Data were collected every 10 min from 9:00 a.m. to 6:00 p.m. over a four-day period during July 2019. Results indicate that there is no difference in WBGT among the three surfaces, even when considered over morning, midday, and afternoon practice periods. We did observe microclimatic differences in dry-bulb temperature and dewpoint temperature among the sites. Greater dry-bulb and lower dewpoint temperatures occurred over the tennis and artificial turf surfaces compared with the grass field because of reduced evapotranspiration and increase convective transfers of sensible heat over these surfaces. The lack of difference in WBGT among the surfaces is attributed to the counterbalancing influences of the different components that comprise the index. We conclude that, in a humid, subtropical climate over well-watered grass, there is no difference in WBGT among the three athletic surfaces and that, under these circumstances, a single monitoring site can provide representative WBGTs for nearby athletic surfaces.

Exertional heat illness poses a significant risk for workers, athletes, and military personnel participating in outdoor activities during hot weather. An important component of heat safety is to monitor environmental conditions through heat stress indices like the wet bulb globe temperature (WBGT) and adjust activity as conditions get progressively hotter. Traditionally, on‐site (OS) WBGT measurement devices are used, but phone applications (PAs) offering WBGT estimates have emerged as a potential alternative. However, there is little information on how closely PA‐derived WBGTs match OS measurements to guide decision‐making. This study compared the PA‐derived Zelus WBGT estimates with OS measurements from Kestrel 5400 devices and their impact on activity modification categorization. A 2‐month observational study collected 1,056 paired (OS and PA) WBGT measurements from 26 high schools across 11 states in the United States and over diverse surfaces (artificial turf 53%, natural grass 44%, others 3%). WBGT values were categorized using regional activity modification thresholds to account for local acclimatization. Our findings indicated that while exhibiting high correlation (r = 0.89), PA WBGTs were on average about 1°C cooler, with differences of 2–3°C at higher WBGTs. Findings were similar for both grass and artificial turf surfaces. Further, significant discrepancies were observed in WBGT‐based activity modification categories, with the PA more frequently indicating lower modification categories compared to OS devices, especially in hotter conditions. In light of these findings, the PA requires further validation prior to its adoption as a replacement for OS measurements.

Exposure to solar radiation significantly elevates heat stress during outdoor physical activity, increasing the risk of exertional heat illness. This study quantified the operational impact of a permanent, full-coverage shade pavilion on wet-bulb globe temperature (WBGT) and evaluated how shade-induced cooling modifies activity-restriction thresholds in a recreational sport setting. In Athens, Georgia, USA, we collected 309 paired sun–shade observations across a wide, representative range of humid subtropical summer conditions, comparing a sun-exposed grass field with the shaded pavilion area. WBGT values were classified according to Georgia High School Association (GHSA) heat-safety guidelines. The pavilion reduced WBGT by an estimated 4.1°C relative to the sun-exposed grass site under mean observed meteorological conditions, although the magnitude of this cooling varied with sky cover, with larger reductions under sunnier skies. In full sun, only 36% of observations fell into the no modification category, and 15% reached the most restrictive thresholds. Under the pavilion, 96% of observations required no modification, and none reached the highest activity restriction categories. These shifts in activity-modification categories translate into substantially longer durations of unrestricted activity under the pavilion, corresponding to approximately 6.7 versus 2.5 h during a standardized 9 a.m. to 4 p.m. period in shaded and sun-exposed areas, respectively. These findings demonstrate that permanent shade infrastructure can serve as an effective heat mitigation tool for schools, parks, and municipalities. The exact reductions in WBGT and associated changes in activity modification decisions, however, may vary depending on the specific shade structure design and regional climate setting.