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Heat Illness in Sport and Exercise

Heat illness - defining the problem

What is heat illness?

Heat illness refers to a spectrum of disorders that can be caused by excessive or prolonged exposure to heat, particularly when exercising. Even in temperate conditions, heat illness may occur in those exercising vigorously for more than 45 minutes. As air temperature and relative humidity rises, the risk of heat illness is further increased. However, it is not just environmental temperature that is important, over-exertion, prolonged sun exposure or working out in a poorly ventilated space can also contribute to the body’s inability to dissipate excess heat. If left untreated (i.e., cooling mechanisms remain ineffective, exercise continues) body temperature will continue to rise beyond the body’s ‘healthy’ limits which will lead to progressive functional decline, both physical and cognitive.

Hyperthermia

Hyperthermia is an abnormally elevated body core temperature that results when the rate of heat gained by the body is greater than the rate of heat loss. A body temperature of 40°C or higher is considered potentially life threatening.

In response to a change in activity level and environmental conditions, our bodies initiate a series of processes that act to maintain internal (core) body temperature within a narrow range, around 37°C. This temperature regulation in humans (thermoregulation) is orchestrated by the hypothalamus in the brain, based on sensory information that detects heat gained by the body and heat lost to the environment. These involuntary processes allow the skin and limbs to vary in temperature while keeping the core body temperature as stable as possible. In the case of an elevation in body temperature (hyperthermia), heat loss mechanisms, such as increasing cardiac output, vasodilation (widening) of the skin’s blood vessels and sweating, are activated to maintain thermal homeostasis (stability or balance).

Exercise-induced hyperthermia

When we exercise, our body converts metabolic energy into mechanical and thermal energy in order to produce movement. Approximately 75% of this energy is liberated as heat, making humans relatively inefficient and heavily reliant on heat loss through evaporative means [source: muscle efficiencyWikipedia, (accessed 11 January 2018)]. As air temperature and body temperature rise, the potential for heat exchange between the skin and the environment is reduced. Furthermore, sweating increases as core body temperature rises until 39°C, when maximal sweat rates are achieved. The body’s inability to cope under enduring exertional heat-related stress can cause significant discomfort and impair exercise performance.

Thermoregulatory fatigue can occur at core temperatures around 40°C, irrespective of starting core temperature. The rate (i.e. how quickly) of heat storage is the main limiting factor in exercise performance. The body usually slows down (i.e. fatigue sets in) so that thermal failure can be avoided.

While the human body can tolerate small fluctuations (2-3˚C) in temperature, progression towards a critically high body temperature results in increasing symptom severity—from cramps to exhaustion and finally heat stroke—which can be life threatening. When highly motivated athletes, who are accustomed to pushing themselves to the extent of their physical limits, fail to heed crucial warning signals, this already unfortunate event may become a tragedy.

Heat exhaustion

Is a condition of fatigue caused by prolonged exposure to high temperatures, particularly when combined with high humidity and strenuous activity.

A person suffering from heat exhaustion will generally have a core body temperature of less than 40°C, with no neurological symptoms. People who suffer from heat exhaustion usually recover rapidly with assistance.

Exertional heat stroke (EHS)

Severe cases of heat-stress can lead to heat stroke, which is a life-threatening medical emergency. EHS can occur in previously healthy people, usually when exercising in hot and humid climates. It should be noted that heat exhaustion does not necessarily precipitate EHS. Although relatively rare, EHS is a more serious condition brought about, again, by the body’s inability to dissipate heat to the surrounding environment.

Event officials should be specifically trained to recognise EHS and begin aggressive treatment in order to prevent further decline. Early diagnosis and appropriate management may improve the outcome for the participant and reduce any risk of injury or permanent organ damage. Although there is no universal definition for this illness, the accepted diagnostic criteria for EHS are central nervous system (CNS) dysfunction (e.g. delirium, coma) and internal (core) body temperature greater than 40°C.

As the difference between heat exhaustion and heat stroke is not always obvious, athletes who have collapsed following exercise should be actively cooled according to the guidelines. Most importantly, if in doubt, treat for heat stroke. If the person remains seriously ill, confused, vomiting, or shows signs of altered consciousness call an ambulance and seek medical help.

Collapse

Participants who collapse after exercise are likely suffering from a post-exercise drop in blood pressure (postural hypotension); the body’s overriding response to defence in maintaining the blood flow to the brain. A collapse as a result of heat-illness during exercise is a sign of heat-stroke.

Organ damage to liver, kidney, muscle and heart—the progression of heat stroke to multi-organ failure is the consequence of a delicate balance between acute physiologic alterations, direct cytotoxicity of heat and the balance between pro- and anti-inflammatory responses.

Prevalence

There are currently limited reliable data sources on the occurrence of heat-related illness, exertional heat stroke, or episodes with complications that result in death in Australia. There is some information available from research conducted in the United States which indicates that heat-related illness is one of the leading causes of death and injury among college and high school athletes.

Extreme weather events

Heat waves kill more people than any other natural hazard experienced in Australia. In 2009, a two-week heat wave in South Australia and Victoria caused at least 150 deaths and may have contributed to more than 370 deaths. Between the years 1803 and 1992, at least 4287 people died in Australia as a direct result of heat waves. Classical heat stoke is more characteristic of heatwaves, affecting the elderly, the very young, and those without adequate resources or means to escape the heat. However, those more physically capable who try to keep up their exercise regimen or play in a previously scheduled competition during phases of high heat load, are more likely to suffer from exertional heat stroke.

Although not specifically related to heat illness it is also important to note that during heat waves, particularly in Australia, bush fires may also become a significant risk and may exacerbate other heat related conditions. In December 2019, in response to unprecedented levels of smoke pollution from bush fires across the country the Australian Institute of Sport (AIS) developed a position statement on Smoke Pollution and Exercise to provide guidance and leadership specifically for the Australian high performance sport system.

Access to resources
Where possible, direct links to full-text and online resources are provided. However, where links are not available, you may be able to access documents directly by searching our licenced full-text databases (note: user access restrictions apply). Alternatively, you can ask your institutional, university, or local library for assistance—or purchase documents directly from the publisher. You may also find the information you’re seeking by searching Google Scholar.

Additional resources

  • Exertional Heat Illness: A Clinical and Evidence-Based Guide, William M. Adams John F. Jardine (eds.), Springer, (2019). Provides clinicians, scientists and students with a comprehensive overview of exertional heat illness. Specifically, it addresses the prevention, recognition, treatment, and care of the various medical conditions that fall within the realm of exertional heat illness.
  • Heat Stress in Sport and Exercise: Thermophysiology of Health and Performance, Julien D. Périard and Sébastien Racinais (eds.), Springer, (2019). The book is designed to provide a flowing description of the physiology of heat stress, the illnesses associated with heat exposure, recommendations on optimising health and performance, and an examination of Olympic sports played in potentially hot environmental conditions. Includes sport-specific chapters including: football/soccer, Australian football and rugby; American football; tennis; athletics; cycling; open-water swimming; and, triathlon and ultra-endurance events in tropical environments.
  • Smoke Pollution and ExerciseAustralian Institute of Sport, (December 2019). Bushfire smoke can pose a health risk to athletes. The health impact of bushfire smoke can vary based on an individual’s current health status and previous medical conditions. Current public health advice is aimed at high-risk groups, including people over 65, children 14 years and younger, pregnant women and those with existing heart or lung conditions. However, athletes involved in high performance sport can also be at higher risk while performing high intensity prolonged exercise outdoors and additional caution should be taken.
  • AIS advises athletes to be alert to smoke haze, media release, Australian Institute of Sport, (19 December 2019). Australian Institute of Sport (AIS) Chief Medical Officer Dr David Hughes has cautioned athletes to be vigilant regarding air pollution levels in bushfire-affected regions, and to adjust their training plans accordingly.
  • Extreme Heat: When Outdoor Sports Become RiskyClimate Central, (21 August 2019). Climate change’s impact is being felt throughout the world of sports as these extreme heat events become more common. On high heat index days, sports and heat become a dangerous mix. According to the Center for Disease Control, heat-related illnesses are the leading cause of death or disability among high school athletes. During hot, humid weather, sweat cannot evaporate as easily from the skin, so athletes are at greater risk of developing  illnesses such as heat exhaustion and heat stroke - the latter being potentially fatal. With an estimated 8 million high school athletes across the U.S., late summer is the time when many head back to football, soccer, field hockey, or track and field practice—and when parents, guardians and coaches need to be vigilant about the potential risk for exertional heat illnesses.
  • Lives increasingly at risk from ‘angry climate’, media release, Climate and Health Alliance, (4 March 2013).
  • Management of exertional heat stroke: a practical update for primary care physicians, Edward Walter and Kiki Steel, British Journal of General Practice, Volume 68(668), pp.153-154, (2018). The number of cases of EHS appear to be on the rise; this may be due in part to increasing numbers of athletes participating in endurance events each year. Running USA estimates that 25 000 runners completed a marathon in the US during 1976; by 2016, this had grown to 507 600; similarly, the number of runners completing a half-marathon is estimated to have risen from 303 000 in 1990 to 1 900 000 in 2016. However, the incidence may also be rising; the US military has reported an eight-fold increase in the rate of hospitalisation from EHS, from 1.8 to 14.5 per 100 000 soldiers, over a 20-year period.
  • ‘This Was Preventable’: Football Heat Deaths and the Rising Temperature, James Bruggers, Inside Climate News, (20 July 2018). Most states rank poorly on heat safety for their high school football players. Too many teens have paid the price, and temperatures are only getting worse. Includes information from the United States relating to which States take heat risk seriously for high school sports (i.e. by mandating heat safety measures).
  • Heat Illness and Endurance Athletes: The Science of Staying Safe When It Gets Hot, Corrine Malcolm, Trainright.com, (accessed 6 January 2020). Many experienced endurance athletes are well versed in hydration and cooling strategies, but as a community it is crucial for all athletes to understand the signs and symptoms of heat illness, how to prevent it, and how to help athletes suffering from it.
  • NATA Offers 10 Tips to Prevent Heat Illness and DehydrationNational Athletic Trainers' Association [USA], (5 July 2018). Many parts of the country are experiencing extreme heat this summer, but for the most part, outdoor activities continue as planned. Young athletes participating in summer and pre-season sports are particularly susceptible in July and August. To guard against heat illnesses and dehydration, the National Athletic Trainers’ Association offers these important recommendations.
  • Annual survey of football injury research 1931-2018, Kristen L. Kucera, David Klossner, Bob Colgate, Robert C. Cantu, National Centre for Catastrophic Sport Injury Research (US), (15 February 2019). Report includes a specific section on Heat Stroke which highlights that since 1995, 64 football players have died from heat stroke (47 high school, 13 college, 2 professional, and 2 organised youth). Ninety percent of recorded heat stroke deaths occurred during practice. During the most recent five year period from 2014-2018 there was an average of 2.2 heat stoke deaths per year compared to 3.2 per year during the previous five year period 2009-2013.
  • Catastrophic sports injury research: 34th Annual Report [Fall 1982 - Spring 2018], Kucera K, Cox L and Cantu R, National Centre for Catastrophic Sport Injury Research (US), (3 October 2019). This report summarises 36 years of data, covering over 2,686 incidence of catastrophic sports-related injuries in US high schools and colleges. From July 1, 2017 to June 30, 2018 there were a total of 99 catastrophic injuries/illnesses captured by NCCSIR among high school and college organized sport participants. Of these 15.2% were heat-related.
  • The exceptional heatwave of January-February 2009 in south-eastern AustraliaAustralian Bureau of Statistics, Feature Article, Catalogue Number 1301.0, Year Book Australia, 2009-10 (2010).
  • Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors, and diagnosis, Francis G O'Connor and Douglas J Casa, UpToDate, Wolters Kluwer, (last updated 12 November 2018; literature review current through December 2019). Includes information on the epidemiology, risk factors, thermoregulation in the heat, determining risk, basic types and clinical presentation, differential diagnosis, and summary and recommendations relating to exertional heat illness.
  • Recent trends in and preparedness for extreme weather eventsEnvironment and Communications References Committee report to the Australian Senate, (August 2013). Australia has long been a land of weather extremes, 'a sunburnt country…of droughts and flooding rains'. However, recent extreme weather events have raised questions about whether the patterns and nature of these events are changing. Submission to the inquiry were recieved from the Climate and Health Alliance, among others.
  • Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors, and diagnosis, Francis G O'Connor and Douglas J Casa, UpToDate, Wolters Kluwer, (last updated 12 November 2018; literature review current through December 2019). Includes information on the epidemiology, risk factors, thermoregulation in the heat, determining risk, basic types and clinical presentation, differential diagnosis, and summary and recommendations relating to exertional heat illness.
  • Sport & Climate Impacts: How much heat can sport handle?, Menzies L, The Climate Institute, (2015). Sport is embedded in the lives of Australians, its culture and economy. As with other aspects of Australian life, sport is starting to feel the impact of climate change. This report synthesises recent research on the physical impacts of extreme weather and analyses sport’s vulnerability and resilience. This report finds that most sports are struggling to cope, especially at the local level. Heat policies are often ambiguous and may vary at state, national and international level, with ambiguity about their application. Duty of care thresholds vary within and across sports from 32°C to 41°C. The CSIRO and the Bureau of Meteorology predict the number of days over 35°C across the nation will increase significantly by the end of the century. Hot days will increase 2.5 times in Adelaide, treble in Melbourne and Hobart, quadruple in Sydney, be six times higher in Canberra and 20 times higher in Brisbane. In Perth, for more than two months out of a given year, the mercury will soar over 35°C, as it will for 10 months in Darwin.
  • Epidemiology of exertional heat illness among U.S. high school athletes, Kerr Z, Casa D, Marshall M and Comstock R, American Journal of Preventative Medicine, Volume 44(1), pp.8-14, (2013). Although most exertional heat illnesses occurred in football, athletes in all sports and all geographic areas are at risk. Because exertional heat illness frequently occurs when medical professionals are not present, it is imperative that high school athletes, coaches, administrators, and parents are trained to identify and respond to it. Implementing effective preventive measures depends on increasing awareness of exertional heat illness and relevant preventive and therapeutic countermeasures.
  • The Epidemiology and Management of Exertional Heat Illnesses in High School Sports During the 2012/2013–2016/2017 Academic Years, Zachary Y. Kerr, Susan W. Yeargin, Yuri Hosokawa, Rebecca M. Hirschhorn, Lauren A. Pierpoint and Douglas J. Casa, Journal of Sport Rehabilitation, (February 2019). Recent data on exertional heat illness (EHI) in high school sports are limited yet warranted to identify specific settings with the highest risk of EHI. American football continues to have the highest overall EHI rate although the high competition EHI rate in girls’ cross-country merits additional examination. Regional differences in EHI incidence, coupled with sport-specific variations in management, may highlight the need for region- and sport-specific EHI prevention guidelines.
  • Epidemiology of Exertional Heat Illnesses in National Collegiate Athletic Association Athletes During the 2009–2010 Through 2014–2015 Academic Years, Susan W. Yeargin, Thomas P. Dompier, Douglas J. Casa, Rebecca M. Hirschhorn, and Zachary Y. Kerr, Journal of Athletic Training, Volume 54(1), pp.55-63, (2019). Athletic trainers reported Exertional heat illnesses (EHIs) to the NCAA Injury Surveillance Program. Only EHIs sustained during a sanctioned practice or competition were included. The EHI rate, specific diagnoses, and number of emergency transports were measured. Football players continue to experience the most EHIs; however, EHIs can potentially occur in all NCAA sports. Continued emphasis on preseason EHI policies and institution-specific environmental guidelines is needed to address EHI rates.
  • Exercise in the Heat for Children and Adolescents. Statement from the Commission for Pediatric Sports Medicine, German Society for Sports Medicine and Prevention, Lawrenz, W., German Journal of Sports Medicine, Volume 70, pp.265-268, (November 2019). › Exertional heat illness in children and adolescents is preventable by different measures. There should be sufficient time for recovery between repeated exercise bouts. Children and adolescents should drink sufficient quantities regularly and provide for sun protection of head and skin. During all athletic events in the heat with participation of children and adolescents, trained personnel and facilities capable of effectively treating all forms of heat illness, should be readily available on site.
  • Exertional Heat Stroke Management Strategies in United States High School Football, Kerr Z, Marshall S, Comstock R and Casa D, American Journal of Sports Medicine, Volume 42(1), pp.70-77, (2014). Preseason exertional heat stroke events, which are likely to be fatal if untreated, were reported by one fifth of all athletic trainers in high school football programs. The standard of care is (and should be) to treat proactively; therefore, treatment is not a perfect proxy for incidence. Nevertheless, there is an urgent need for improved education and awareness of exertional heat stroke in high school football. Areas of improvement include the greatly increased use of rectal thermometers and immersion in ice water.
  • Heat illness among high school athletes: United States, 2005-2009, Yard E, Gilchrist J, Haileyesus T, Murphy M, Collins C, McIlvain N and Comstock R, Journal of Safety Research, Volume 41(6), pp.471-474, (2010). During 2005–2009, the 100 schools sampled reported a total of 118 heat illnesses among high school athletes resulting in ≥ 1 day of time lost from athletic activity, a rate of 1.6 per 100,000 athlete-exposures, and an average of 29.5 time-loss heat illnesses per school year. The average corresponds to a weighted average annual estimate of 9,237 illnesses nationwide. The highest rate of time-loss heat illness was among football players, 4.5 per 100,000 athlete-exposures, a rate 10 times higher than the average rate (0.4) for the eight other sports. Time-loss heat illnesses occurred most frequently during August (66.3%) and while practicing or playing football (70.7%). No deaths were reported.
  • Heat stress incidence and matchplay characteristics in Women's Grand Slam Tennis, Matthew T.Smith, Machar Reid, Stephanie Kovalchik, Tim Wood, Rob Duffield, Journal of Science and Medicine in Sport, Volume 21(7), pp.666-670, (July 2018). An association between higher estimated WBGT and medical callouts (heat and non-heat related) was evident, with an increased call rate >32 °C WBGT, despite no heat-related retirements. As estimated WBGT increased, the number of winners and net approaches were reduced, while double faults increased, particularly >30 °C WBGT. Accordingly, the manner in which female players manage and play in the heat during women’s Grand Slam tennis appears to change at ≈30 °C WBGT.
  • Heat stress incident prevalence and tennis matchplay performance at the Australian Open, Matthew T.Smith, Machar Reid, Stephanie Kovalchik, Tim Wood, Rob Duffield, Journal of Science and Medicine in Sport, Volume 21(5), pp.467-472, (May 2018). Increased estimated WBGT increased total match doctor and trainer consults for heat related-incidents, post-match heat-related consults (>32 °C) and cooling device callouts (>28 °C). However, few matchplay characteristics were noticeably affected, with only reduced net approaches and increased aces evident in higher estimated WBGT environments.
  • High Thermoregulatory Strain During Competitive Paratriathlon Racing in the Heat, Ben T. Stephenson, et.al., International Journal of Sports Physiology and Performance, (2019). Paratriathletes face significant thermal strain during competition in the heat, as evidenced by high Tc, relative to previous research in able-bodied athletes and a high incidence of self-reported heat illness symptomatology. Differences in the Tc profile exist depending on athletes’ race category and wetsuit use.
  • The impact of different environmental conditions on cognitive function: A focused review, Taylor L, Watkins S. Marshall H, Dascombe B and Foster J, Frontiers in Physiology, Volume 6, (6 January 2016). Extreme environments; such as heat, hypoxia, and cold, can alter human cognitive function due to a variety of psychological and/or biological processes. This review provides updated knowledge regarding the effects of extreme environmental stressors on cognitive function and their biological underpinnings. This review discuss: (1) the current state of knowledge on the effects of heat, hypoxic and cold stress on cognitive function; (2) the potential mechanisms underpinning these alterations, and; (3) plausible interventions that may maintain cognitive function upon exposure to each of these environmental stressors. The available evidence suggests that the effects of heat, hypoxia, and cold stress on cognitive function are both task and severity dependent. Complex tasks are particularly vulnerable to extreme heat stress. Both simple and complex task performance appear to be vulnerable at even moderate altitudes; and cold stress also appears to negatively impact both simple and complex task performance.
  • Risk of heat illness in men and women: A systematic review and meta-analysis, Robert M.Gifford, et.al., Environmental Research, Volume 171, pp.24-35, (April 2019). The rate of HI was significantly increased in men compared with women. Risk for HI might be conferred by psychological and behavioral factors rather than physiological ones. Further research is required to delineate which groups are at greatest risk, leading to the development of mitigation strategies against HI.
  • Sport-related exertional heat illness hospitalisations in Victoria, Australia: Incidence and trend over 11 years, S.McMahon & L.Fortington, Journal of Science & Medicine in Sport, Volume 22(Supplement 2), pp.S68, (October 2019). Sport-related EHI hospitalisation data with specific age, gender and sport characteristics can be used as a guide to develop EHI policies, and decision making on EHI risk mitigation and prevention. These data support specific age-related risks and therefore the specific participation characteristics for these age groups should be addressed in prevention measures. Fewer than expected cases were identified, particularly when considered the ratio of ED presentations relative to hospital admissions, leading to questions on the adequacy of data capture in this source. Alternative methods to measure annual changes should be considered.
  • The Application of Heat Stress to Team Sports: Football/Soccer, Australian Football and Rugby, Katie Slattery and Aaron J. Coutts, in 'Heat Stress in Sport and Exercise: Thermophysiology of Health and Performance', Julien D. Périard and Sébastien Racinais (eds.), Springer, pp.181-202, (7 March 2019). This chapter addresses how an added heat stress affects football, Australian football and rugby players during both training and competition. Although these sports are typically played in the cooler winter months, players can still be exposed to hot conditions and this may affect health and performance. It is therefore important to understand how an increased thermal load influences the tactical, technical, physical and psychological constructs that contribute to team sport performance.
  • Crawling to the finish line: why do endurance runners collapse? Implications for understanding of mechanisms underlying pacing and fatigue, St Clair Gibson A, De Koning J, Thompson K, Roberts W, Micklewright D, Raglin J and Foster C, Sports Medicine, Volume 43(6), pp.413-424, (2013). This review provides a comprehensive theoretical understanding of collapses that occur during exercise as a result of postural hypotension, caused by hyperthermia and other conditions. This paper identifies the sequence of dynamic changes in posture and gait, termed the ‘Foster collapse positions’, which might serve as a protective mechanism in the event that the athlete is highly motivated enough to continue their effort to reach the finish line, in the face of catastrophic failure.
  • Dehydration is how you define it: comparison of 318 blood and urine athlete spot checks, Hew-Butler TD, Eskin C, Bickham J, et al., BMJ Open Sport & Exercise Medicine, Volume 4(1), (2018). This article sort to compare blood versus urine indices of dehydration in 318 collegiate athletes undergoing routine screenings. Findings indicate that urine concentration thresholds classified 27%–55% of collegiate athletes as dehydrated, while no athlete was dehydrated according to blood [Na+] measurement. Practitioners should caution against using urine indices to diagnose or monitor dehydration, because urinary output is a response rather than a reflection of (tightly regulated) blood tonicity.
  • Exercise-associated collapse: an evidence based review and primer for clinicians, Asplund C, O’Connor F and Noakes T, British Journal of Sports Medicine, Volume 45(14), pp.1157-1162, (2011). This article looks at exercise-associated collapse (EAC), which commonly occurs after the completion of endurance running events in the absence of neurological, biochemical or thermal abnormalities. EAC is now believed to be principally the result of transient postural hypotension caused by lower extremity pooling of blood once the athlete stops running and the resultant impairment of cardiac baroreflexes. Treatment options are discussed.
  • Exertional Heat Stroke, Navarro, Chelsea S., Casa, Douglas J., Belval, Luke N., & Nye, Nathaniel S., Current Sports Medicine Reports, Volume 16(5), pp.304-305, (2017). EHS is one of the top three causes of sudden death in athletes. Provides an overview of the pathophysiology, risk factors, recognition, and treatment of the condition.
  • Exertional heat stroke, Adams T, Stacey E, Stacey S, Martin D, British Journal of Hospital Medicine, Volume 73(2), pp.72-78, (2012). A very comprehensive review outlining the potentially lethal condition of exertional heat stroke, providing guidance for recognition and treatment in field conditions.  States that exertional heat stroke is the third highest cause of death for athletes.
  • Exertional heat stroke: Strategies for prevention and treatment from the sports field to the emergency department, Pryor R, Casa D, Holschen, J, O'Connor F and Vandermark L, Clinical Pediatric Emergency Medicine, Volume 14(4), pp.267-278, (2013). Exertional heat illness is a category of conditions commonly seen during sports participation in the hot summer months. Exertional heat stroke, in particular, is a dangerous condition involving hyperthermia and central nervous system dysfunction, which, if not properly treated, is potentially deadly. All on-site medical personnel, emergency physicians, and coaches involved in sports participation need to be aware of the recognition and treatment of heat illnesses. Emergency physicians must be equally aware of recognition, treatment, and return-to-play decisions to ensure athletes are quickly and effectively treated and return to sport participation safely.
  • Exertional heatstroke: clinical characteristics, diagnostic and therapeutic considerations, Zeller L, Novack V, Barski L, Jotkowitz A and Almog Y, European Journal of Internal Medicine, Volume 22(3), pp.296-299, (2011). A retrospective study which suggests that a delayed diagnosis and management of exertional heat stroke may adversely affect outcome. Protracted systemic inflammatory response syndrome (SIRS) may complicate the course of exertional heat stroke.
  • Exertional heat stroke during a cool weather marathon: a case study, Roberts W, Medicine and Science in Sports and Exercise, Volume 38(7), pp.1197-1203, (2006). This article documents a case study of a well-trained male runner aged in his late 30’s who collapsed before the finish line of a 42.1-km marathon event contested in cool conditions (6-9.5°C and 62-99% r.h.). Despite the cool conditions the runner presented with hyperthermia (40.7°C), respiratory failure leading to intubation, and neurological, renal and cardiology function impairment. He reported having a viral syndrome a week prior to the race and was paced by a ‘fresh’ runner in the last 16 km of the race. Discharge occurred 5 days following the incident and after months of recovery, returned to running problem-free.
  • Exertional heat stroke: new concepts regarding cause and care, Casa D, Armstrong L, Kenny G, O’Connor F and Huggins R, Current Sports Medicine Reports, Volume 11(3), pp.115-123, (2012). When athletes, warfighters, and laborers perform intense exercise in the heat, the risk of exertional heat stroke (EHS) is ever present. The recent data regarding the fatalities due to EHS within the confines of organized American sport are not promising: during the past 35 years, the highest number of deaths in a 5-year period occurred from 2005 to 2009. This reminds us that, regardless of the advancements of knowledge in the area of EHS prevention, recognition, and treatment, knowledge has not been translated into practice. This article addresses important issues related to EHS cause and care. We focus on the predisposing factors, errors in care, physiology of cold water immersion, and return-to-play or duty considerations.
  • Heat Stress and Thermal Strain Challenges in Running, Michael Bergeron, Journal of Orthopaedic & Sports Physical Therapy, Volume:44(10), pp.831–838, (2014). Running well and safely in the heat is challenging for all runners, from recreational to elite. As environmental heat stress (heat stress modulated or augmented by air temperature, humidity, wind speed, and solar radiation) and the intensity and duration of a training run or race increase, so are metabolic heat production, the parallel need for heat transfer from the body to maintain thermal equilibrium, the consequent increase in blood flow to the skin, and the concomitant sweating response progressively and proportionally amplified. An accumulating total body-water deficit from extensive sweating and escalating level of cardiovascular and thermal strain will, in due course, considerably challenge a runner's physiology, perception of effort, and on-course well-being and performance. However, with the appropriate preparation and modifications to planned running intensity and distance, runners can safely tolerate and effectively train and compete in a wide range of challenging environmental conditions. Clinicians play a key role in this regard as an effective resource for providing the most effective guidelines and making the best overall individual recommendations regarding training and competing in the heat.
  • Heat Stress, Hydration, and Heat Illness in Elite Tennis Players, Julien D. Périard and Olivier Girard, in 'Tennis Medicine', Giovanni Di Giacomo, Todd S. Ellenbecker, W. Ben Kibler (eds.), Springer, pp.573-587, (9 January 2019). Tennis is a popular sport predominately played in the summer months on outdoor courts. Compared to cool conditions, playing tennis under heat stress leads to exacerbated thermal (i.e., core and skin temperatures), physiological (e.g., heart rate) and perceptual (e.g., perceived exertion and thermal comfort/sensation) strain, which in turn may influence physical performance and match tactics.
  • Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress, Sawka M, Leon L, Montain S and Sonna L, Comprehensive Physiology, Volume 1(4), pp.1883-1928 (2011). This article emphasizes significant recent advances regarding heat stress and its impact on exercise performance, adaptations, fluid electrolyte imbalances, and pathophysiology.
  • Implementing exertional heat illness prevention strategies in US High School Football, Kerr Z, Marshall S, Comstock R and Casa D, Medicine & Science in Sports & Exercise, Volume 46(1), pp.124 (2014). Approximately 6500 high school football athletes are treated annually for exertional heat illness (EHI). In 2009, the National Athletic Trainers Association (NATA)-led Inter-Association Task Force (NATA-IATF) released preseason heat acclimatization guidelines to help athletes become accustomed to environmental factors contributing to EHI. This study examines compliance with NATA-IATF guidelines and related EHI prevention strategies.A low proportion of surveyed high school football programs fully complied with all 17 NATA-IATF guidelines. However, many EHI prevention strategies were voluntarily implemented. State-level mandated EHI prevention guidelines may increase compliance with recognized best practices recommendations. Ongoing longitudinal monitoring of compliance is also recommended.
  • Managing heat and immune stress in athletes with evidence-based strategies, Pyne D, Guy J and Edwards A, International Journal of Sports Physiology and Performance, Volume 9(5), pp.744-750 (2014). Heat and immune stress can affect athletes in a wide range of sports and environmental conditions. The classical thermoregulatory model of heat stress has been well characterized, as has a wide range of practical strategies largely centered on cooling and heat-acclimation training. In the last decade evidence has emerged of an inflammatory pathway that can also contribute to heat stress. Studies are now addressing the complex and dynamic interplay between hyperthermia, the coagulation cascade, and a systemic inflammatory response occurring after transient damage to the gastrointestinal tract. Damage to the intestinal mucosal membrane increases permeability, resulting in leakage of endotoxins into the circulation. Practical strategies that target both thermoregulatory and inflammatory causes of heat stress include precooling; short-term heat-acclimation training; nutritional countermeasures including hydration, energy replacement, and probiotic supplementation; pacing strategies during events; and postevent cooling measures. Cooperation between international, national, and local sporting organizations is required to ensure that heat-management policies and strategies are implemented effectively to promote athletes' well-being and performance.
  • Misdiagnosis of exertional heat stroke and improper medical treatment, Druyan A, Janovich R and Heled Y, Military Medicine, Volume 176(11), pp.1278-1280, (2011). The following case report depicts a soldier who presented primarily with confusion and behavioural changes during physical exercise and later lost consciousness. He was misdiagnosed by the field physician as suffering from supraventricular tachycardia, was treated as such and only diagnosed as suffering from EHS later in the emergency room. Our main aims are: to highlight the possibility of misdiagnosis of EHS even among trained physicians, to describe the main symptoms of EHS, and to emphasize the importance of early diagnosis and proper treatment.
  • On-site treatment of exertional heat stroke, Sloan, B. K., Kraft, E. M., Clark, D., Schmeissing, S. W., Byrne, B. C., & Rusyniak, D. E., The American Journal of Sports Medicine, Volume 43(4), pp.823–829, (2015).  The purpose of this article was to describe an on-site exertional heat stroke treatment protocol and to compare the outcomes of patients treated on site to those transferred to hospitals. On-site treatment of athletes who develop exertional heat stroke appears to be both safe and effective. On-site treatment may decrease the local burden of critically ill patients to emergency departments during large athletic events.
  • Overview of Exertional Heat Illness, William M. Adams and John F. Jardine, in  Adams W., Jardine J. (eds) 'Exertional Heat Illness', Springer, (2019). Exertional heat illness (EHI) is a cause for concern in athletic, military, occupational, and recreational settings where individuals are participating in physical activity, especially in hot environmental conditions.
  • The pathopysiology of heat stroke: an integrative view of the final common pathway, Epstein Y, Roberts W, The Scandinavian Journal of Medicine and Science in Sports, Volume 21, pp.742–748, (2011). This review integrates the current theoretical and accepted knowledge of physiological alterations into one model that depicts a common pathway from heat stress to heat stroke.
  • Practical recommendations for endurance cycling in hot/humid environments, Nichols D, Aspetar Sports Medical Journal, Volume 5, (2016). It is well documented that exercise in a warm environment poses a significant thermal challenge to the body and has the potential to reduce exercise performance. The combination of heat production from working muscles and reduction in the rate of heat loss due to high ambient temperatures and/or humidity results in an exacerbated rise in core temperature (hyperthermia) for any given exercise intensity. Hyperthermia per se impairs aerobic performance and consequently decreases power output compared with temperate environments. In addition, dehydration during exercise in the heat further exacerbates the thermal and cardiovascular strain and further impairs aerobic performance. This article provides practical recommendations for athletes and race organisers.
  • Practice beliefs of team physicians regarding the recognition and treatment of exertional heat stroke, Mazerolle S, Pagnotta K, Casa D, McDowell L and Armstrong L, Athletic Training & Sports Health Care: The Journal for the Practicing Clinician, Volume 10(10), (2012). The National Athletic Trainers’ Association and the American College of Sports Medicine each have a position statement for exertional heat illnesses that outlines proper assessment of core body temperature via rectal thermometry (Tre) and treatment via rapid cooling by cold water immersion (CWI). The purpose of this basic inductive research study was to investigate team physicians’ practice beliefs regarding the recognition and immediate treatment of EHS and the ways to increase and promote the use of best practices within the athletic training profession. Many of the participants recognized that in their role as a team physician, they were responsible for promoting best practices, which they believed were Tre and CWI. However, they did not believe it was their professional responsibility to provide educational training for either skill to athletic trainers, but rather that the 2 parties must work together to develop appropriate patient care policies.
  • Preventing heat illness in the anticipated hot climate of the Tokyo 2020 Summer Olympic Game. Takeyasu Kakamu, Koji Wada, Derek R. Smith, Shota Endo and Tetsuhito Fukushima, Environmental Health and Preventive Medicine/BioMed Central, (19 September 2017). Overall, our study suggests that the Tokyo 2020 Summer Olympics will be held amid extremely high WBGT conditions, including at levels deemed poorly suited for conducting sporting events. Combined efforts by all stakeholders during these events will therefore be necessary to deal with these challenging conditions so that athletes can perform their best and so heat illness can be minimized among individuals taking part in these activities. Sporting committees and the Olympic organizing committee should also consider WBGT in selecting venues and the timing of events to help minimize heat illness and enable maximum performance by athletes. Similarly, the organization of the 2020 Tokyo Olympics will need to manage heat as an occupational safety issue for staff and also provide multiple solutions to help heat illness among spectators and tourists.
  • Preventing Death from Exertional Heat Stroke - The Long Road from Evidence to Policy, Casa D, Hosokawa Y, Belval L, Adams W, Stearns R., Kinesiology Review, Volume 6(1), p.99-109, (February 2017). Exertional heat stroke (EHS) is among the leading causes of sudden death during sport and physical activity. However, previous research has shown that EHS is 100% survivable when rapidly recognized and appropriate treatment is provided. Establishing policies to address issues related to the prevention and treatment of EHS, including heat acclimatization, environment-based activity modification, body temperature assessment using rectal thermometry, and immediate, onsite treatment using cold-water immersion attenuates the risk of EHS mortality and morbidity. This article provides an overview of the current evidence regarding EHS prevention and management. The transfer of scientific knowledge to clinical practice has shown great success for saving EHS patients. Further efforts are needed to implement evidence-based policies to not only mitigate EHS fatality but also to reduce the overall incidence of EHS.
  • The second Summer Youth Olympic Games in Nanjing, People's Republic of China: preparing youth athletes to compete in the heat, Brito J, Racinais S and Nassis G, Open Access Journal of Sports Medicine, (1 September 2014). The second Summer Youth Olympic Games took place in Nanjing, People’s Republic of China during the peak of the summer (August). Nanjing has been reported as one of the hottest cities in China, with temperatures reaching as high as 40°C. The estimated average wet bulb globe temperature for Nanjing in August is 32°C, which has been classified as a very high risk/stop play condition for heat illness and injury. Current guidelines for exercise in the heat appear to be inadequate or too conservative, and mostly focus on adult elite athletes. Therefore, proper preventive measures are warranted to reduce the risks of heat illness and injury. With proper heat acclimatisation and monitoring, youth athletes can exercise reasonably well and safely in the heat. Special attention should be devoted to athletes exposed to long and extensive sunny and hot conditions. If proper preventive measures are taken, the risk of heat illness and injury can be greatly reduced.
  • The Use of Technology to Protect the Health of Athletes During Sporting Competitions in the Heat, Borja Muniz-Pardos, et.al., Frontiers in Sports and Active Living, (3 October 2019). Due to the metabolic demands of the sporting events and the high environmental temperatures, the risk of exertional heat stroke (EHS) is high. Careful planning by event organizers are needed to ensure that athletes are protected from irreversible long-term health damage, or even death during sporting competitions in the heat.
  • What Is the Best Practice for the Treatment of Exertional Heat Illnesses (Heat Cramps, Heat Syncope, Heat Exhaustion, and Exertional Heat Stroke)? Nicholas D. Peterkin, MD; Joseph S. Atkin, MD; Eric E. Coris, MD, Athletic Training and Sports Health Care, Volume 8(3), pp. 97-99, (May 2016). During sports events, monitoring exercising athletes for signs of disease and having a good emergency plan in place for possible EHS is critical for protecting athletes. Heat illness may present as mild heat edema or heat cramps to more severe heat syncope, heat exhaustion, or heat stroke. Early recognition based on signs and symptoms should prompt immediate action to limit progression of injury.

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