Roundtable on Preseason Heat Safety in Secondary School Athletics: Environmental Monitoring During Activities in the Heat.

OBJECTIVE: To develop best-practice recommendations using thermal indices to determine work-to-rest ratios and facilitate further implementation of environmental monitoring for heat safety in secondary school athletics in the United States. DATA SOURCES: A narrative review of the current literature on environmental monitoring for heat safety during athletics was conducted by content experts. A list of action-oriented recommendations was established from the narrative review and further refined using the Delphi method. CONCLUSIONS: Assessment of wet bulb globe temperature at the site of activity and throughout the duration of the event is recommended to assist clinicians and administrators in making appropriate decisions regarding the duration and frequency of activity and rest periods. Activity-modification guidelines should be predetermined and approved by stakeholders and should outline specific actions to be followed, such as the work-to-rest ratio, frequency and timing of hydration breaks, and adjustment of total exercise duration, equipment, and clothing. Furthermore, integration of exertional heat illness injury data with environmental condition characteristics is critical for the development of evidence-based heat safety guidelines for secondary school athletics. Athletic trainers play an essential role in conducting prospective injury data collection, recording onsite wet bulb globe temperature levels, and implementing recommendations to protect the health and safety of athletes.

Comparison of WBGTs over Different Surfaces within an Athletic Complex.

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.

Heat Policy Revision for Georgia High School Football Practices Based on Data-Driven Research.

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 (<27.8°C) to >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 (<27.80°C), 0.65 for WBGTs from 82.0°F (27.8°C) to 86.9°F (30.5°C), and 0.23 for WBGTs from 87.0°F (30.6°C) to 89.9°F (32.2°C). No HS/HE illnesses occurred in the POST period for WBGTs at >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.

Regional differences in exertional heat illness rates among Georgia USA high school football players.

Many high school associations in recent years are developing policies to improve player safety regarding exertional heat illnesses (EHIs). A question is whether states with diverse climates need multiple sets of guidelines with different activity modification thresholds. We examine this question in the state of Georgia, which has a diverse climate. Our study leverages a multi-year dataset of exertional heat illnesses (EHIs) among high school football players to test the hypothesis that EHI rates under similar wet bulb globe temperatures (WBGTs) will be greater among athletes in the cooler, northern region versus warmer, southern region of the state. The focus of this study is on a 3-year period (2012-2014) when uniform heat safety polices, including acclimatization and activity modification guidelines, were implemented across the state. Results show that athletes in the northern region acclimatize to cooler conditions. Almost 68% of practices have WBGTs < 27.8 °C (82 °F) compared to the southern region where athletes receive many times the exposures to hotter WBGTs in the 27.8-30.5 °C and 30.6-32.2 °C categories. In the post-acclimatization period, we observed statistically significantly (p < .05) greater EHI rates among athletes in the northern region of the state, even when controlling for meteorological conditions. Our findings suggest that differential acclimatization between football players in the northern and southern regions of the state is impacting EHI rates and that regional heat safety guidelines may be needed in Georgia and other states with similarly diverse climates.

Assessment of the Australian Bureau of Meteorology wet bulb globe temperature model using weather station data.

Exertional heat illnesses affect thousands of athletes each year and are a leading cause of death in sports. The wet bulb globe temperature (WBGT) is widely used as a heat stress metric in athletics for adjusting activities. The WBGT can be measured on-site with portable sensors, but instrument cost may provide a barrier for usage. Modeling WBGT from weather station data, then, presents an affordable option. Our study compares two WBGT models of varying levels of sophistication: the Australian Bureau of Meteorology (ABM) model which uses only temperature and humidity as inputs and a physically based model by Liljegren that incorporates temperature, humidity, wind speed, and solar radiation in determining WBGT outputs. The setting for the study is 19 University of Georgia Weather Network stations selected from across the state of Georgia, USA, over a 6-year period (2008-2014) during late summer and early fall months. Results show that the ABM model's performance relative to the Liljegren model varies based on time of day and weather conditions. WBGTs from the ABM model are most similar to those from the Liljegren model during midday when the assumption of moderately high sun most frequently occurs. We observed increasingly large positive biases with the ABM model both earlier and later in the day during periods with lower solar radiation. Even during midday, large (≥ 3 °C) underestimates may occur during low wind conditions and overestimates during periods with high cloud cover. Such differences can lead to inaccurate activity modification and pose dangers for athletes either by underestimating heat-related hazards or by imposing an opportunity cost if practice activities are limited by overestimating the heat hazard.

An Evaluation of Portable Wet Bulb Globe Temperature Monitor Accuracy.

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.

American football and fatal exertional heat stroke: a case study of Korey Stringer.

On August 1, 2001, Korey Stringer, a Pro Bowl offensive tackle for the Minnesota Vikings, became the first and to date the only professional American football player to die from exertional heat stroke (EHS). The death helped raise awareness of the dangers of exertional heat illnesses in athletes and prompted the development of heat safety policies at the professional, collegiate, and interscholastic levels. Despite the public awareness of this death, no published study has examined in detail the circumstances surrounding Stringer's fatal EHS. Using the well-documented details of the case, our study shows that Stringer's fatal EHS was the result of a combination of physiological limitations, organizational and treatment failings, and extreme environmental conditions. The COMfort FormulA (COMFA) energy budget model was used to assess the relative importance of several extrinsic factors on Stringer's EHS, including weather conditions, clothing insulation, and activity levels. We found that Stringer's high-intensity training in relation to the oppressive environmental conditions was the most prominent factor in producing dangerous, uncompensable heat stress conditions and that the full football uniform played a smaller role in influencing Stringer's energy budget. The extreme energy budget levels that led to the fatal EHS would have been avoided according to our modeling through a combination of reduced intensity and lower clothing insulation. Finally, a long delay in providing medical treatment made the EHS fatal. These results highlight the importance of modern heat safety guidelines that provide controls on extrinsic factors, such as the adjustment of duration and intensity of training along with protective equipment modifications based on environmental conditions and the presence of an emergency action plan focused on rapid recognition and immediate on-site aggressive cooling of EHS cases.

Exertional Heat Illness in American Football Players: When Is the Risk Greatest?

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.

The influence of ankle support on postural control.

Postural control assessments are commonly administered to athletes as part of a pre-season screening. Establishing a baseline level of function permits the clinician to compare post-injury results to normal functioning during the return to play decision-making process. In the athletic setting, follow-up tests may be completed on the sideline immediately following injury. We sought to examine the effect of commonly administered external ankle joint support on postural control using the balance error scoring system (BESS) and the NeuroCom sensory organization test (SOT). Nineteen volunteers free from balance issues completed three sessions with varied ankle support: bilateral prophylactic ankle taping, laced bracing device, or barefoot. Each session included an initial balance assessment on the BESS and SOT, a 20 min treadmill walk, and post-walk balance test. Fewer errors, indicating improved balance, were committed on the BESS during the barefoot condition than the braced ankle condition (p=0.044) at the pre-walk assessment. During the post-walk assessment, fewer errors were committed during the barefoot condition compared to the braced ankle condition (p=0.034) and the taped ankle condition (p=0.037). All ankle support conditions showed similar improvements in balance between the pre and post-walk assessments on the BESS (p<0.001) and SOT composite balance score (p=0.009). These findings indicate that ankle support devices may influence postural control on the BESS, but not on the NeuroCom SOT. Clinicians using the BESS as a balance assessment device at multiple time points should be consistent in the application of ankle support devices.

Exertional heat illness and environmental conditions during a single football season in the southeast.

CONTEXT: Recommendations for heat illness prevention provided by sports medicine associations do not always account for sex differences, specific age populations, regional environmental conditions, equipment worn during activity, or the athlete's size or preexisting level of fitness. OBJECTIVE: To evaluate the rate of exertional heat illness (EHI) among collegiate football athletes and to monitor environmental conditions during American football practice for a 3-month period. DESIGN: Epidemiologic study in which we reviewed the occurrence rates of EHI and wet bulb globe temperature readings during a 3-month period of American collegiate football practice sessions. SETTING: Five universities in the southeastern region of the United States. PATIENTS OR OTHER PARTICIPANTS: Collegiate football players at the 5 universities. MAIN OUTCOME MEASURE(S): Wet bulb globe temperatures were recorded from August through October 2003, at the beginning, middle, and end of each practice session. The EHIs were identified and recorded, and athlete-exposures (AEs) were calculated. RESULTS: A total of 139 EHIs and 33 196 AEs were reported (EHI rate = 4.19/1000 AEs). The highest incidence of EHIs was in August (88%, EHI rate = 8.95/1000 AEs) and consisted of 70% heat cramps (6.13/1000 AEs), 23% heat exhaustion (2.06/ 1000 AEs), and 7% heat syncope (0.58/1000 AEs). No cases of heat stroke or hyponatremia were identified. The highest risk of EHI occurred during the first 3 weeks of the study; mean wet bulb globe temperature declined significantly as the study continued ( P < .001). Temperatures in the final 5 weeks of the study were significantly cooler than in the first 5 weeks ( P < .05). CONCLUSIONS: Heat cramps were the most common EHI and occurred most often during the first 3 weeks of practice. Athletic trainers should take all necessary preventive measures to reduce the risk of EHI.