Is the Wet-Bulb Globe Temperature (WBGT) Index Relevant for Exercise in the Heat?

Heat-related risk at Paris 2024: a proposal for classification and review of International Federations policies

Several International Federations (IFs) employ specific policies to protect athletes' health from the danger of heat. Most policies rely on the measurement of thermal indices such as the Wet Bulb Globe Temperature (WBGT) to estimate the risk of heat-related illness. This review summarises the policies implemented by the 32 IFs of the 45 sports included in the Paris 2024 Olympic Games. It provides details into the venue type, measured parameters, used thermal indices, measurement procedures, mitigation strategies and specifies whether the policy is a recommendation or a requirement. Additionally, a categorisation of sports' heat stress risk is proposed. Among the 15 sports identified as high, very high or extreme risk, one did not have a heat policy, three did not specify any parameter measurement, one relied on water temperature, two on air temperature and relative humidity, seven on WBGT (six measured on-site and one estimated) and one on the Heat Stress Index. However, indices currently used in sports have been developed for soldiers or workers and may not adequately reflect the thermal strain endured by athletes. Notably, they do not account for the athletes' high metabolic heat production and their level of acclimation. It is, therefore, worthwhile listing the relevance of the thermal indices used by IFs to quantify the risk of heat stress, and in the near future, develop an index adapted to the specific needs of athletes.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Does choice of outdoor heat metric affect heat-related epidemiologic analyses in the US Medicare population?

Outdoor air temperature is associated with increased morbidity and mortality. Other thermal indices theoretically confer greater physiological relevance by incorporating additional meteorological variables. However, the optimal metric for predicting excess deaths or hospitalizations owing to extreme heat among US Medicare beneficiaries remains unknown.

Methods

We calculated daily maximum, minimum, and mean outdoor air temperature (T), heat index (HI), wet-bulb globe temperature (WBGT), and Universal Thermal Climate Index (UTCI) for populous US counties and linked estimates with daily all-cause mortality and heat-related hospitalizations among Medicare beneficiaries (2006-2016). We fit distributed-lag nonlinear models for each metric and compared relative risks (RRs) at the 99th percentile.

Results

Across all heat metrics, extreme heat was statistically significantly associated with elevated risks of morbidity and mortality. Associations were more pronounced for maximum daily values versus the corresponding minimum for the same metric. The starkest example was between HImax (RR = 1.14; 95% confidence interval [CI] = 1.12, 1.15) and HImin (RR = 1.10; 95% CI = 1.09, 1.11) for hospitalizations. When comparing RRs across heat metrics, we found no statistically significant differences within the minimum and maximum heat values (i.e., no significant differences between Tmax/HImax/WBGTmax/UTCImax or between Tmin/HImin/WBGTmin/UTCImin). We found similar relationships across the National Climate Assessment regions.

Conclusion

Among Medicare beneficiaries in populous US counties, daily maximum and mean values of outdoor heat are associated with greater RRs of heat-related morbidity and all-cause mortality versus minimum values of the same metric. The choice of heat metric (e.g., temperature versus HI) does not appear to substantively affect risk calculations in this population.

Heat stress in horses: a literature review

Healthy adult horses can balance accumulation and dissipation of body heat to maintain their body temperature between 37.5 and 38.5 °C, when they are in their thermoneutral zone (5 to 25 °C). However, under some circumstances, such as following strenuous exercise under hot, or hot and humid conditions, the accumulation of body heat exceeds dissipation and horses can suffer from heat stress. Prolonged or severe heat stress can lead to anhidrosis, heat stroke, or brain damage in the horse. To ameliorate the negative effects of high heat load in the body, early detection of heat stress and immediate human intervention is required to reduce the horse's elevated body temperature in a timely manner. Body temperature measurement and deviations from the normal range are used to detect heat stress. Rectal temperature is the most commonly used method to monitor body temperature in horses, but other body temperature monitoring technologies, percutaneous thermal sensing microchips or infrared thermometry, are currently being studied for routine monitoring of the body temperature of horses as a more practical alternative. When heat stress is detected, horses can be cooled down by cool water application, air movement over the horse (e.g., fans), or a combination of these. The early detection of heat stress and the use of the most effective cooling methods is important to improve the welfare of heat stressed horses.

Using Wet Bulb Globe Temperature and Physiological Equivalent Temperature as Predicative Models of Medical Stress in a Marathon: Analysis of 30 Years of Data From the Twin Cities Marathon

OBJECTIVES

: Assess the relationships between wet bulb globe temperature (WBGT) and physiologic equivalent temperature (PET) at the start of a northern latitude marathon and their associations with medical stress and transfers to the emergency room (ER) when the race environment is unexpectedly warm, and participants are not acclimatized.

DESIGN

: Retrospective review.

SETTING

: Twin Cities Marathon from 1990 to 2019.

PARTICIPANTS

: Runners competing in the Twin Cities Marathon.

INDEPENDENT VARIABLES

: Start WBGT (prospectively collected) and PET (retrospectively calculated).

MAIN OUTCOME MEASURES

: Marathon race starters and finishers and race day medical data (eg, medical stress, number of medical encounters, and number of ER visits).

RESULTS

: The mean WBGT was 7.4°C (range -1.7°C to 22.2°C), and the meant PET was 5.2°C (range -16.7°C to 25.9°C). PET was not determined to be a significant predictor of medical stress (P = 0.71); however, a significant quadratic association between WBGT and medical stress was found (P = 0.006). WBGT (P = 0.002), but not PET (P = 0.07), was a significant predictor of the number of ER visits.

CONCLUSIONS

Start WBGT was a better predictor of medical stress and ER visits than PET at the Twin Cities Marathon over a 30-year period. The start WBGT may be a better tool to predict race day environment medical safety.

Wet-Bulb Globe Temperature, Universal Thermal Climate Index, and Other Heat Metrics for US Counties, 2000-2020

Epidemiologic research on extreme heat consistently finds significant impacts on human morbidity and mortality. However, most of these analyses do not use spatially explicit measures of heat (typically assessing exposures at major cities using the nearest weather station), and they frequently consider only ambient temperature or heat index. The field is moving toward more expansive analyses that use spatially resolved gridded meteorological datasets and alternative assessments of heat, such as wet-bulb globe temperature (WBGT) and universal thermal climate index (UTCI), both of which require technical geoscientific skills that may be inaccessible to many public health researchers. To facilitate research in this domain, we created a database of population-weighted, spatially explicit daily heat metrics - including WBGT, UTCI, heat index, dewpoint temperature, net effective temperature, and humidex - for counties in the conterminous United States derived from the ERA5-Land gridded data set and using previously validated equations and algorithms. We also provide an R package to calculate these metrics, including gold-standard algorithms for estimating WBGT and UTCI, to facilitate replication.

Earlier Boston Marathon Start Time Mitigates Environmental Heat Stress

PURPOSE

This study aimed to compare the wet bulb globe temperature (WBGT) index and other environmental parameters between early and late Boston Marathon race start times from 1995 to 2016.

METHODS

Environmental data from 1995 to 2016 (excluding 1996) were used to compare two identical time frames using the 0900-1300 h start versus the 1100-1500 h start. This included the WBGT, dry bulb (Tdb), black globe (Tbg), wet bulb (Twb), solar radiation, relative humidity, and air water vapor pressure. To make comparisons between start times, the difference in the area under the curve (AUC) for each environmental variable was compared within each year with a Wilcoxon signed rank test with a Holm-Bonferroni correction.

RESULTS

AUC exposures for WBGT (P = 0.027), Twb (P = 0.031), Tdb (P = 0.027), Tbg (P = 0.055), and solar radiation (P = 0.004) were reduced with an earlier start, whereas those for relative humidity and air water vapor pressure were not. Overall, an earlier race start time by 2 h (0900 vs 1100 h) reduced the odds of experiencing a higher flag category 1.42 times (β = 0.1744, P = 0.032).

CONCLUSIONS

The 2007 decision to make the Boston Marathon start time earlier by 2 h has reduced by ~1.4 times the odds that runners will be exposed to environmental conditions associated with exertional heat illness.

An investigation into environmental variables influencing post-race exertional heat illness in thoroughbred racehorses in temperate eastern Australia

Exertional heat illness (EHI) is a syndrome that occurs when metabolic heat production from muscular contraction exceeds the rate at which it can be dissipated. Core body temperature rises to critical levels, causing hyperthermia and central nervous system dysfunction. Best practice for the prevention of EHI centres around early detection, rapid response and aggressive cooling. Advance planning enables risk mitigation measures. The more that is known about EHI in horses, the better prepared those in the positions of responsibility can be to anticipate events in which the risk of EHI may be elevated. This prospective, observational study investigated environmental risk factors associated with the occurrence of EHI. From 2014 to 2018, the number of horses exhibiting the symptoms of post-race EHI was recorded at 73 convenience sampled race meetings. Of the 4809 starters, the signs of EHI were recorded for 457. Thermal environmental data were measured and included ambient temperature, radiant heat, vapor pressure (humidity) and wind speed (WS). Mixed linear regression models were computed to assess the associations between the occurrence and incidence of post-race EHI and the four thermal environmental variables. The analysis showed that vapor pressure and WS had the largest effects on the occurrence of post-race EHI. The major limitations were that the race meetings selected were convenience sampled according to attendance by the first author and individual horse data were not available. EHI is influenced by a complex interaction of independently acting environmental variables, but warm, windless, humid days are most likely to result in the cases of EHI.

Understanding occupational heat exposure in the United States and proposing a quantifying stress index

PURPOSE

Millions of workers exposed to the outdoor environment are extremely susceptible to extreme heat. Although several articles analyzed heat-related illnesses, injuries, fatalities at the country level, few investigated regional and state statistics especially for OSHA Region 4 and the state of Alabama, U.S, which we explored in this study.

METHODS

We studied the number of heat-days over 90 °F (32.2 °C) heat-index within our study area, analyzed heat-related injury and illnesses to calculate their incidence rate during 2015 to 2019, observed the nature of such incidents, their monthly occurrence, and incidence trend over average air temperature. We conducted a comparative analysis of heat-related fatalities between construction and all industries. The existing heat regulations by OSHA and some state agencies have also been summarized.

RESULTS

We observed the highest mean, maximum heat-days and injury-illness rate in the south and southeast part of Region 4; increase in incidence rate from 0.03 in 2017 to 0.28 per 10,000 employees in 2018 for the contiguous U.S; highest injury-illness rate (HIR) in OSHA Region 1, 4 and 6; highest HIR in Lee, Montgomery, Mobile and Madison counties of Alabama; 34.7% (construction) and 31.3% (all industries) of all cases experiencing nonclassifiable heat-light effects; high fatalities in construction industry with a trend of 1 death/5 years; increased mortality in all occupations with 1 death/2.4 years. We also proposed a Heat-Stress Index (HSI) as a routine heat-stress measure on jobsite.

CONCLUSION

The findings from this research and the proposed index can help in understanding heat-related risk at a regional level and implementing workplace interventions.

Meteorological Risks in Doha 2019 Athletics World Championships: Health Considerations From Organizers

The Doha 2019 IAAF World Championships represent a challenge for athletes, workforce and spectators who could compete, work or attend under likely extreme meteorological conditions. This short article summarizes the methodology used by the IAAF and the Local Organizing Committee doctors to analyze and reduce risks, while complying as much as possible with existing recommendations or policies. The main steps to be completed are identification and description of weather-related risks, description and whenever possible testing of all their possible mitigation measures during test events, revision of these risks once mitigation implemented, and finally drafting a contingency plan for remaining exceptional and impactful occurrences. Such risk management methodology could apply to other sports, ideally from the host city selection to the delivery of the competitive event.

A Comprehensive Model for Estimating Heat Vulnerability of Young Athletes

Current methods for estimating heat vulnerability of young athletes use a heat index (HI) or a wet bulb globe thermometer (WBGT), neither of which fully include the environmental or physiological characteristics that can affect a person’s heat budget, particularly where activity occurs on a synthetic surface. This study analyzed and compared the standard methods, HI and WBGT, with a novel and more comprehensive method termed COMFA-Kid (CK) which is based on an energy budget model explicitly designed for youth. The COMFA model was presented at the same time to demonstrate the difference between a child and an adult during activity. Micrometeorological measurements were taken at a synthetic-surfaced football field during mid-day in hot environmental conditions. Standard methods (HI and WBGT) indicated that conditions on the field were relatively safe for youth to engage in activities related to football practice or games, whereas the CK method indicated that conditions were dangerously hot and could lead to exertional heat illness. Estimates using the CK method also indicated that coaches and staff standing on the sidelines, and parents sitting in the stands, would not only be safe from heat but would be thermally comfortable. The difference in thermal comfort experienced by coaches and staff off the field, versus that experienced by young players on the field, could affect decision making regarding the duration and intensity of practices and time in the game. The CK method, which is easy to use and available for modification for specific conditions, would lead to more accurate estimates of heat safety on outdoor synthetic surfaces in particular, and in sports with a high prevalence of heat illness such as football, and should be considered as a complementary or alternative preventive measure against heat.

Diverse Effects of Thermal Conditions on Performance of Marathon Runners

Heat exposure affects human performance in many ways. Both physiological (i.e., glycogen sparing, oxygen uptake, thermoregulation) and biomechanical mechanisms (i.e., contact time, knee flexion, muscle activity) are affected, hence reducing performance. However, the exposure affects persons differently. Not all athletes necessarily experience an identical thermal condition similarly, and this point has been overlooked to date. We analyzed endurance performances of the top 1000 runners for every year during the last 12 New York City Marathons. Thermal conditions were estimated with wet-bulb globe temperature (WBGT) and universal thermal climate index (UTCI). Under identical thermal exposure, the fastest runners experienced a larger decline in performance than the slower ones. The empirical evidence offered here not only shows that thermal conditions affect runners differently, but also that some groups might consistently suffer more than others. Further research may inspect other factors that could be affected by thermal conditions, as pacing and race strategy.

Is Physiological Equivalent Temperature (PET) a superior screening tool for heat stress risk than Wet-Bulb Globe Temperature (WBGT) index? Eight years of data from the Gothenburg half marathon

BACKGROUND

The Wet-Bulb Globe Temperature (WBGT) index is a common tool to screen for heat stress for sporting events. However, the index has a number of limitations. Rational indices, such as the physiological equivalent temperature (PET) and Universal Thermal Climate Index (UTCI), are potential alternatives.

AIM

To identify the thermal index that best predicts ambulance-required assistances and collapses during a city half marathon.

METHODS

Eight years (2010-2017) of meteorological and ambulance transport data, including medical records, from Gothenburg's half-marathon were used to analyse associations between WBGT, PET and UTCI and the rates of ambulance-required assistances and collapses. All associations were evaluated by Monte-Carlo simulations and leave-one-out-cross-validation.

RESULTS

The PET index showed the strongest correlation with both the rate of ambulance-required assistances (R²=0.72, p=0.008) and collapses (R²=0.71, p=0.008), followed by the UTCI (R²=0.64, p=0.017; R²=0.64, p=0.017) whereas the WBGT index showed substantially poorer correlations (R²=0.56, p=0.031; R²=0.56, p=0.033). PET stages of stress, match the rates of collapses better that the WBGT flag colour warning. Compared with the PET, the WBGT underestimates heat stress, especially at high radiant heat load. The rate of collapses increases with increasing heat stress; large increase from the day before the race seems to have an impact of the rate of collapses.

CONCLUSION

We contend that the PET is a better predictor of collapses during a half marathon than the WBGT. We call for further investigation of PET as a screening tool alongside WBGT.

Heat-related issues and practical applications for Paralympic athletes at Tokyo 2020

International sporting competitions, including the Paralympic Games, are increasingly being held in hot and/or humid environmental conditions. Thus, a greater emphasis is being placed on preparing athletes for the potentially challenging environmental conditions of the host cities, such as the upcoming Games in Tokyo in 2020. However, evidence-based practices are limited for the impairment groups that are eligible to compete in Paralympic sport. This review aims to provide an overview of heat-related issues for Paralympic athletes alongside current recommendations to reduce thermal strain and technological advancements in the lead up to the Tokyo 2020 Paralympic Games. When competing in challenging environmental conditions, a number of factors may contribute to an athlete's predisposition to heightened thermal strain. These include the characteristics of the sport itself (type, intensity, duration, modality, and environmental conditions), the complexity and severity of the impairment and classification of the athlete. For heat vulnerable Paralympic athletes, strategies such as the implementation of cooling methods and heat acclimation can be used to combat the increase in heat strain. At an organizational level, regulations and specific heat policies should be considered for several Paralympic sports. Both the utilization of individual strategies and specific heat health policies should be employed to ensure that Paralympics athletes' health and sporting performance are not negatively affected during the competition in the heat at the Tokyo 2020 Paralympic Games.

Thermal comfort along the marathon course of the 2020 Tokyo Olympics

The Olympic Games will be held in Tokyo in 2020 and the period will be the hottest period of the year in Japan. Marathon is a sport with a large heat load, and it is said that the risk of heat stroke rises more than other sports activities. The thermal environment of the 2020 Tokyo Olympic marathon course is analyzed by using wet-bulb globe temperature (WBGT) and Universal Thermal Climate Index (UTCI) map of the center area of Tokyo. The change due to the place, the effect of the shadow of the building, and the position on the course was analyzed from the distribution of WBGT and UTCI in the short-term analysis of sunny day from August 2 to August 6, 2014. To make the distribution map, we calculated distributions of sky view factor and mean radiant temperature of the 10 km × 7.5 km analyzed area in the center of Tokyo. Distributions of air temperature and humidity are calculated from Metropolitan Environmental Temperature and Rainfall Observation System data, which is a high-resolution measurement network. It was possible to incorporate the local variation of temperature and humidity of the analyzed area. In the result, the WBGT is about 1 °C lower and the UTCI is about 4-8 °C lower in the shadow of buildings from 9:00 to 10:00 than in the sunny side. As a cooling method, making a shadow is a relatively effective method. The variation along the course considering the distribution of meteorological data within the area is about 0.5 °C WBGT and 1 °C UTCI range. If we allow the error of this range, one-point meteorological data can be applied for the estimation along the course. Passing the right side (left side in the case of return) of the course could keep the accumulated value slightly lower along the course in the morning because the marathon course roughly runs from west to east and buildings' shadow is on the relatively right side (south side). But practically, the effect of changing the position on the course was small. The long-term analysis on the degree of risk for each hour was also carried out by using one-point data of the first 10 days of August from 2007 to 2016. The risk increased rapidly after 8:00. It will be safer if the marathon race is finished before 9:00 or if the race is held after 19:00.

Heat stress assessment in artistic glass units

Heat stress in glass industry is mainly studied in large and highly mechanized manufacturing Units. To the contrary, few studies were carried out in small factories specialized in hand-made products. To stress the need of combined objective and medical surveys in these environments, this paper deals with a simultaneous climatic and physiological investigation of working conditions in artistic crystal glass factories in Tuscany (Italy). The microclimatic monitoring, through a continuous survey has been carried out in early spring. The main physiological parameters (metabolic rate, heart rate, tympanic temperature and water loss) were measured over the whole shifts. The results show that, despite the arduousness of the working conditions, the heat stress levels are physiologically tolerable. The predictions made using the PHS model at the Analysis level described in ISO 15265 agree closely to the observed values, validating the use of PHS model in these conditions. This model was then used to analyse what is likely to be the situation during the summer. It is concluded that the heat constraint will be very high and that some steps must be taken from the spring to monitor closely the exposed workers in the summer and take measures to prevent any heat accident.