Skip to content
Heat Illness in Sport and Exercise

Signs and symptoms of heat illness

Know the signs and symptoms

What to do?

Return to play

Heat acclimatisation

Many people today spend the majority of their time in climate controlled environments (i.e. air-conditioned homes, cars, schools, workplaces, etc.). This can lead to difficulties when starting an exercise program/training/competing in the heat and requires a process of acclimatisation.

Exercise in the heat induces physiological adaptations that improve thermoregulation, attenuate physiological strain, and can reduce the risk of serious heat illness. Heat acclimatisation can improve aerobic performance in warm/hot environments and potentially in temperate environments. Given adequate water and protection from the sun, a healthy individual can adapt (within individual limits) to extended exposure to natural weather-related heat stress.

The adaptations include increased sweat rate, decreased sweat sodium and chloride concentrations, improved skin blood flow, lowered body temperatures, reduced cardiovascular strain, improved fluid balance, altered metabolism, and enhanced cellular protection. The magnitudes of these adaptations are determined by the intensity, duration, frequency, and number of heat exposures. Environmental conditions (i.e. dry or humid heat) influence adaptation, as well as individual variability of one’s genetics.

The effect of heat acclimation on submaximal exercise performance can be quite dramatic and occur within a matter of days, such that acclimated individuals can easily complete tasks in the heat that would otherwise be difficult. Full adaptation to high intensity exercise, as experienced in competition in the heat, may take weeks. The greatest adaptations occur within the first week and the thermoregulatory benefits of heat acclimation are generally thought to be complete after 10 days to 2 weeks exposure; however, additional small improvements in physiological tolerance may take longer.

It is important to be aware that variations in an individual's typical daily routine, such as sleep loss, poor nutrition, glycogen depletion, bacterial and viral infections, and certain medications can delay heat acclimatisation. When additional stressors such as these are present, it is prudent to reduce the duration of exercise and heat exposures accordingly, and temporarily reduce performance expectations.

Heat acclimation is temporary and gradually disappears if the athlete does not maintain continued and repeated heat exposure. There is no consistent agreement concerning the rate of decay for heat acclimation. It appears that adaptations that occur quickly, such as heart rate improvement, also decay more rapidly than thermoregulatory adaptations that take longer to respond. Many studies report the beneficial effects of 2 weeks heat acclimatisation can be maintained for approximately one month.

Evidence is also emerging that inducing heat acclimation outdoors in a natural field setting may provide more specific adaptations based on direct exposure to the exact environmental and exercise conditions to be encountered during competition; rather than acclimation protocols conducted in a laboratory setting.

What makes someone more susceptible?

Significant situational risk factors can contribute to an athlete, official, or spectator being at risk of hyperthermia. It should be noted that individual responses to heat illness vary.

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, (2020). 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.
  • New Law Requiring Training in Heat Illness for all California Coaches Takes Effect January 1, 2019, California Interscholastic Federation, (accessed 19 May 2021). On June 1, 2018 AB 2800, California High School Coaching Education and Training Program: heat illness, was signed into law by Governor Brown that now will require coaches when renewing their CPR/FIRST AID, Concussion and Sudden Cardiac Arrest (SCA) certification that they also complete training in the signs and symptoms of heat illness. The law takes effect on January 1, 2019.
  • How the World’s Best Athletes Handle Brutal Heat, Alex Hutchinson, Outside, (March 2021). At the 2019 World Championships, researchers gave marathoners and racewalkers swallowable thermometer pills and used thermal cameras to assess the effectiveness of hydration and cooling techniques in the heat of competition.
  • 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). A GP may have contact with athletes in one of three ways: a patient seeking advice before participation in a race; the GP providing medical cover on race day; or afterwards if a patient has suffered from EHS. This article aims to highlight current advice and research areas in the treatment of a patient.
  • Extreme heat in sport: why using a fixed temperature cut-off isn’t as simple as it seems, Ollie Jay, Associate Professor, Exercise and Sport Science; Director, Thermal Ergonomics Laboratory, University of Sydney and Samuel Chalmers, Postdoctoral Fellow in Sport Physiology and Performance, Western Sydney University, The Conversation, (12 January 2018). There are several factors that must be collectively considered when predicting heat stress risk of an athlete.
  • It’s time for Australia to change its attitude to extreme heat, Liz Hanna, Australian National University, The Conversation, (21 January 2014). Complacency can kill. You would have to be living under a rock to be unaware that heat exposure can be deadly. Yet every year Australia – supposedly the “clever country” – endangers the lives of everyone from elite athletes to construction workers by making them work in the summer heat.
  • Prolonged exercise in the heat, Periard J, ASPETAR Sports Medicine Journal, Volume 2(1), pp.8-15, (2013). An article outlining the impact of prolonged exercise performance in hot conditions which details strategies to optimise performance and improve heat tolerance.
  • Heat Acclimation Improves Heat Tolerance Test Specificity in a Criteria-dependent Manner, Mitchell KM, Salgado RM, Bradbury KE, et al., Medicine and Science in Sports and Exercise. (2021) May;53(5):1050-1055. A major ongoing challenge in sports medicine and the military is the determination of when an athlete or a military service member is ready to return to activity (RTA) after suffering an exertional heat stroke. A heat tolerance test (HTT) is one method used for RTA assessment, but its test specificity is unknown and may be affected by heat acclimation (HA) status.
  • Additional clothing increases heat load in elite female rugby sevens players, Henderson, Mitchell et. al., International Journal of Sports Physiology and Performance, (2021). The purpose of this study was to determine whether elite female rugby sevens players are exposed to core temperatures (Tc) during training in the heat that replicate the temperate match demands previously reported and to investigate whether additional clothing worn during a hot training session meaningfully increases the heat load experienced.
  • Hydration and cooling in elite athletes: relationship with performance, body mass loss and body temperatures during the Doha 2019 IAAF World Athletics Championships, Sebastien Racinais,, British Journal of Sports Medicine, (February 2021)
  • Perceptions of Secondary School Athletic Trainers in the Diagnosis of Exertional Heat Stroke, Danyale R. McLean et. al., Journal of Athletic Training, 1 October 2020; 55 (10): 1070–1080. Given that exertional heat stroke is one of the leading causes of death in athletes, clinicians in all settings must follow best practice for recognizing and treating this potentially fatal condition.
  • Spectator medicine at an international mega sports event: Rugby World Cup 2019 in Japan. Tajima T, Takazawa Y, Yamada M, et al. Environmental Health & Preventive Medicine. (2020) 25(1):N.PAG. The Rugby World Cup (RWC) is one of the biggest international mega sports events in the world. This study was conducted to identify and evaluate the volume, nature, and severity of spectator medical care in the stadiums of 12 venues across Japan during RWC 2019.
  • Do Alternative Cooling Methods Have Effective Cooling Rates for Hyperthermia Compared With Previously Established CWI Cooling Rates? Kailin C. Parker, Rachel R. Shelton, and Rebecca M. Lopez, Journal of Sport Rehabilitation, (2020) 29, 367-372. The authors searched for studies using alternative cooling methods to cool hyperthermic individuals. To be included, the studies needed a PEDro score ≥6 and a level of evidence ≥2. They found 9 studies related to our focused clinical question; of these, 5 studies met the inclusion criteria. The cooling rates for hand cooling, cold-water shower, and ice-sheet cooling were 0.03°C/min, 0.08°C/min, and 0.06°C/min, respectively, whereas the tarp-assisted cooling with oscillation (TACO) method was the only method that had an acceptable cooling rate (range 0.14-0.17°C/min).
  • Exertional heat stroke in an amateur runner – Challenges in diagnostics and the role of unhealthy competition, Joanna Marlega, Agnieszka Mickiewicz, Jadwiga Fijalkowska, Marcin Gruchala & Marcin Fijalkowski, Journal of Sports Sciences, (2020), 38:22, 2597-2602. Exertional heat stroke (EHS) is a potentially life-threatening condition with a variety of symptoms and abnormal laboratory findings. Nevertheless, data evaluating the course of making an EHS diagnosis in real-life practice, as well as the role of predisposing psychological components are limited. Thus, the aim of our study was to present a multi-faceted differentiation process and show the role of unhealthy competition in the development of EHS.
  • Translating evidence-based practice to clinical practice in Tokyo 2020: how to diagnose and manage exertional heat stroke, Hosokawa Y, Casa DJ, Racinais S, British Journal of Sports Medicine (2020) 54:883-884. Elite athletes competing at high-intensity in the hot and humid ambient conditions of the upcoming Games of the XXXII Olympiad (Tokyo 2020) are likely to reach elevated core temperature ( ≈ 41.5°C) as previously reported in elite competitions in the heat, and the risk of exertional heat stroke (EHS) is heightened. EHS is a medical condition defined as an internal body temperature exceeding 40.5°C with central nervous system dysfunction (e.g., disorientation, aggressiveness, hysteria, delirium, altered consciousness, irrational behaviour). Survival and sequela from EHS depend on the duration of hyperthermia. In 2020, evidence-based consensus suggests whole-body cooling until 39°C within the first 30 min of collapse as the critical requirement to maximise patient outcome.
  • Do sex differences in thermoregulation pose a concern for female athletes preparing for the Tokyo Olympics? Notley SR, Racinais S, Kenny GP, British Journal of Sports Medicine Published Online First (1 October 2020). The hot-humid environmental conditions (27°C–31°C, 60%–80% relative humidity) expected for the 2021 Tokyo Olympics will pose a considerable thermoregulatory challenge for athletes, which will impair performance and potentially compromise safety. Perhaps due to the conventional belief that women are at a thermoregulatory disadvantage compared with men, many coaches have questioned whether training and competing in such conditions will be particularly challenging for female athletes. As an extension of this editorial series, we therefore provide a physiologist’s perspective on three of the common questions raised.
  • Impact of Ice Slurry Ingestion during Break-Times on Repeated-Sprint Exercise in the Heat, Takashi Naito, Miki Haramura, Koji Muraishi, Misa Yamazaki, and Hideyuki Takahashi, Sports Medicine International Open, (July 2020). The study aimed to investigate the effects of ice slurry ingestion during break times and half-time (HT) on repeated-sprint performance and core temperature in the heat.
  • Effect of heat acclimation among international women rugby sevens players, Couderc A and Piscione J, Sport Performance and Science Reports, (15 April 2020). The purpose of this study was to introduce a heat acclimation protocol with the French elite femail Rugby Sevens players and to asses its effectiveness on reducing thermal sensation and discomfort before the Dubai Sevens tournament.
  • 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, Thorsson S, Rayner D, British Journal of Sports Medicine, (2019). 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. The aim of this study was to identify the thermal index that best predicts ambulance-required assistances and collapses during a city half marathon.
  • 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.
  • Predisposing Factors for Exertional Heat Illness, J. Luke Pryor, Julien D. Périard, Riana R. Pryor, in 'Exertional Heat Illness: A Clinical and Evidence-Based Guide', William M. Adams and John F. Jardine (eds.), Springer, pp.29-57, (21 November 2019). Exertional heat illnesses constitute an array of medical conditions comprising mild (heat syncope, heat rashes, exercise-associated muscle cramping, and heat exhaustion) to life-threatening disorders (exertional heat stroke). It is imperative that individuals, practitioners, and policymakers are well informed about the risk of and predisposing factors to exertional heat illnesses. Primary among these risk factors is heat stress which is the result of the combined effects of protective equipment or clothing, metabolic rate, and environmental conditions. Heat stress is a known hazard to both physical performance and health (e.g., exertional heat illness risk). Modifiable and non-modifiable risk factors are discussed as well as preventative strategies to mitigate the influence of heat stress and exertional heat illness risk.
  • The Association between Mandated Preseason Heat Acclimatization Guidelines and Exertional Heat Illness during Preseason High School American Football Practices, Zachary Y. Kerr,, Environmental Health Perspectives, (10 April 2019). The risk of heat-related illness and death may continue to increase in many locations as a consequence of climate change, but information on the effectiveness of policies to protect populations from the adverse effects of excessive heat is limited. In 2009, the National Athletic Trainers’ Association Inter-Association Task Force (NATA-IATF) released guidelines to reduce exertional heat illness (EHI) among U.S. high school athletes participating in preseason sports activities, including preseason practice sessions for American football. A subset of state high school athletic associations have implemented state-mandated guidelines consistent with the 2009 NATA-IATF recommendations, but their effectiveness for reducing preseason EHI is unknown. Our findings suggest that high school athletes would benefit from enactment of the 2009 NATA-IATF guidelines. Similar analyses of the effectiveness of other public health policies to reduce adverse health effects from ambient heat are warranted.
  • Exertional heat illness risk factors and physiological responses of youth football players, Susan W. Yeargin,, Journal of Sport and Health Science, (7 March 2019). Research aimed to determine which intrinsic and extrinsic exertional heat illness (EHI) risk factors exist in youth American football players and observe perceptual and physiological responses of players during events (games and practices). Extrinsic (disproportionate work ratios, environmental conditions) and intrinsic (higher body mass index) EHI risk factors exist in youth football. Certain risk factors may be influenced by event and league type. National youth football organizations need to create thorough guidelines that address EHI risk factors for local leagues to adopt.
  • Application of evidence-based recommendations for heat acclimation: Individual and team sport perspectives, J. Luke Pryor, et,al., Temperature, Volume 6(1), pp.37-49. (13 October 2018). Heat acclimation or acclimatization (HA) occurs with repeated exposure to heat inducing adaptations that enhance thermoregulatory mechanisms and heat tolerance leading to improved exercise performance in warm-to-hot conditions. HA is an essential heat safety and performance enhancement strategy in preparation for competitions in warm-to-hot conditions for both individual and team sports. Yet, some data indicate HA is an underutilized pre-competition intervention in athletes despite the well-known benefits; possibly due to a lack of practical information provided to athletes and coaches. Therefore, the aim of this review is to provide actionable evidence-based implementation strategies and protocols to induce and sustain HA.
  • Exertional Heat Stroke, the Return to Play Decision, and the Role of Heat Tolerance Testing: A Clinician's Dilemma, O'Connor, Francis G. Current Sports Medicine Reports , Volume 17(7), pp.244-248, (July 2018). Although clear guidelines have been established for successful treatment of EHS, the process of safely returning individuals to play/duty is not well established (3–5). This gap in clinical knowledge is due largely to the practical and ethical challenges of systematically researching potential assessment and treatment approaches in a human population. This special communication reviews current guidance on RTP/D decisions after an EHS event, discusses the current literature and evidence base for addressing heat tolerance, and examines the risks of further EHS events. In particular, we address the potential role of heat tolerance testing in the decision process.
  • The validity of the heat tolerance test in prediction of recurrent exertional heat illness events, Haggai Schermann,, Journal of Science & Medicine in Sport, Volume 21(6), pp.549-552, (June 2018). Heat-tolerance-testing (HTT) protocol is used as a screening test for secondary prevention of exertional heat illness (EHI) in the military. Subjects whose test results are positive (heat-intolerant, HI) are presumed to be at higher risk of repeated EHI events than heat-tolerant subjects (HT) and are therefore prevented from return to combat duty, but may return to unsupervised recreational activity. Our aim was to determine, whether HTT results predict the risk of repeated episodes of exertional heat illness (EHI).
  • Analysis of heat illness policies and guidelines published by sports organisations in Victoria, Australia [PowerPoint presentation], Prasanna Gamage, Australian Centre for Research into Injury in Sport and its Prevention (ACRISP) , (2017). Provides an overview of the research which analysed 25 documents from Victorian sports organisations. The research highlighted the gaps and limitations of existing documents, with considerable variation in quality and contents, and a clear suggestion for them to be revised and updated with more current and comprehensive information. A conference abstract on this topic is also available.
  • 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.
  • Heat Acclimatization and Exertional Heat Illness Prevention in Youth Football Programs, Poole, Jordan A, Stearns, Rebecca L., and Lopez, Rebecca M., Strength and Conditioning Journal, Volume 39(2), (April 2017). The purpose of this article is to review the existing literature regarding thermoregulation of younger athletes and to provide guidelines for coaches and clinicians on how to prevent ehi for safer participation in youth football.
  • 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.
  • An Exertional Heat Stroke Survivor's Return to Running: An Integrated Approach on the Treatment, Recovery, and Return to Activity, Adams WM, Hosokawa Y, Huggins RA, Mazerolle SM, Casa DJ., Journal of Sport Rehabilitation , Volume 25(3), (August 2016). This case supports prior literature examining the factors that predispose individuals to EHS. Although evidence-based best practices regarding prompt recognition and treatment of EHS ensure survival, this case highlights the lack of medical follow-up and physician-guided return to activity after EHS.
  • Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports, Periard J, Racinais S and Sawka M, Scandinavian Journal of Medicine and Science in Sports, Volume 25 (Supplement 1), (2015). This review examines the physiological adaptations associated with heat acclimation induction regimens, and emphasises their application to competitive athletes and sports.
  • Heat acclimatization to improve athletic performance in warm-hot environments, Sawka M, Periard J and Racinais S, Gatorade Sport Science Exchange # 153, (2015) . Generally about 1-2-weeks of daily exposures of 90 minutes are required; but highly aerobic fit athletes can heat acclimatise in half that time. Heat acclimatisation is specific to the climatic heat stress (desert or tropic) and physical exercise intensities the athletes are exposed to, which should simulate the expected competitive environment.
  • Implementing exertional heat illness prevention strategies in US High School Football, Kerr Z, Marshall S, Comstock R and Casa D, Medicine and Science in Sports and Exercise, Volume 46(1), pp.124-130, (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, 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 post event 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.
  • National Collegiate Athletics Association strength and conditioning coaches’ knowledge and practices regarding prevention and recognition of exertional heat stroke, Valdes A, Hoffman J, Clark M and Stout J, Journal of Strength and Conditioning Research, Volume 28(11), pp.3013-3023 (2014). The purpose of this study was to assess and determine content knowledge of National Collegiate Athletic Association Strength and Conditioning Coaches (SCCs) regarding prevention and recognition of exertional heat stroke (EHS) and to determine whether the type of professional certification is an indicator of enhanced content knowledge. In conclusion, SCCs seemed to lack essential knowledge to prevent or recognize EHS in each of the factors assessed. It is recommended that consideration be given to include EHS prevention and recognition competencies as part of the professional preparation and certification requirements for SCCs.
  • Short-term heat acclimation training improves physical performance: a systematic review, and exploration of physiological adaptations and application for team sports, Chalmers S, Esterman A, Eston R, Bowering K, and Norton K, Sports Medicine, Volume 44(7), (2014). Many studies have demonstrated that longer-term heat acclimation training (≥8 heat exposures) improves physical performance. The aim of this systematic review was to determine if seven or fewer heat exposures can improve physical performance in healthy adults. The review identified that aerobic-based performance benefit from short-term heat acclimation (STHA) training. This is possibly through a number of cardiovascular, thermoregulatory, and metabolic adaptations improving the perception of effort and fatigue through a reduction in anaerobic energy release and elevation of the anaerobic threshold. These results should be viewed with caution due to the level of available evidence, and the limited number of papers that met the inclusion criteria of the review. STHA training can be applied in a team-sport environment during a range of instances within the competitive season. A mixed high-intensity protocol may only require five sessions of60 minutes duration to potentially improve aerobic-based performance in trained athletes.
  • Age-related decrements in heat dissipation during physical activity occur as early as the age of 40, Larose J, Boulay P, Sigal R, Wright H and Kenny G, PLOS one, Volume 8(12), e83148 (2013). Older adults typically experience greater levels of thermal strain during physical efforts in the heat compared to young individuals. While this may be related to an age-dependent reduction in whole-body sweating, no study has clearly delineated at what age this occurs. In the present study, we report direct measurements of human heat dissipation during physical activity in the heat in males ranging in age from 20–70 years. Over the sum of two hours, the change in body heat content was greater in males 40–70 years compared to young males (all P<0.05). Our findings suggest that middle-aged and older adults have impairments in heat dissipation when doing physical activity in the heat, thus possibly increasing their risk of heat-related illness under such conditions.
  • Exertional heat illness: the role of heat tolerance testing, Kazman J, Heled Y, Lisman P, Druyan A, Deuster P and O’Connor F, Current Sports Medical Reports, Volume 12(2), pp.101-105, (2013). Exertional heat stroke (EHS) is a common clinical problem for both athletes and warriors; however, evidence-based guidance for return-to-play/duty (RTP/RTD) decisions is limited. Heat tolerance testing (HTT) has been proposed as a potential tool that, when combined with appropriate clinical information, may assist in RTP/RTD decisions. However, currently, no standard of care is available for performing HTT. The Israeli Defense Forces (IDF) HTT protocol, which was developed over decades of careful research, has proven useful for IDF warriors and is utilized by other militaries to assist in RTD decisions. The present case studies are used to discuss the efficacy of the IDF HTT in determining RTD for two warriors who experienced EHS. Strengths and limitations of the IDF HTT, along with current and potential roles in clinical decision-making and in future thermoregulation research, are discussed.
  • Specific exercise heat stress protocol for a triathlete's return from exertional heat stroke, Johnson E, Kolkhorst F, Richburg A, Schmitz A, Martinez J and Armstrong L, Current Sports Medical Reports, Volume 12(2), pp.106-109, (2013). A triathlete collapsed with exertional heatstroke (EHS) during 2 races over 3 months. The American College of Sports Medicine recommends a heat tolerance test (HTT) following EHS if there is a concern with return to play. The classical walking HTT may not be the best test to evaluate elite triathletes' heat tolerance due to race intensity, nor is it suited to evaluate acclimation ability, which may play a role in risk of heat illness. Is the athlete capable of returning to racing or should he retire from sport due to heat intolerance? Up to 90 min of cycling (70% of V˙O2max; 36°C, 50% relative humidity) was followed by 9 d of exercise heat acclimation and a final identical exercise heat stress test. After acclimation, exercise duration before reaching a gastrointestinal temperature (Tgi) of 39.5°C increased 25 min, sweat rate increased 0.5 L·h, initial Tgi decreased 0.85°C, and rate of Tgi rise decreased 0.6°C·h. Adaptations were deemed acceptable, and the athlete was allowed to return to competition. The athlete has since raced in hot environments without incident.
  • Effect of short-term heat acclimation on endurance time and skin blood flow in trained athletes, Chen T, Tsai P, Lin J, Lee N and Liang M, Journal of Sports Medicine, (18 June 2013). This study examined whether short-term (i.e. five days) vigorous cycling exercise and heat exposure could achieve heat acclimatisation in trained athletes and the effect of heat acclimatisation on cutaneous blood flow. This research concluded that heat acclimatisation can be achieved with five sessions of high-intensity cycling exercise in the heat in trained athletes. It found that redistribution of cutaneous blood flow in the skin and exercising muscle, and enhanced cardiovascular adaptations, provide the heat-acclimated athletes with the capability to increase their endurance time in a hot environment.
  • Reducing sports heat illness risk, Bergeron M, Pediatrics, Volume 34(6), (June 2013).
  • 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.
  • Neuromuscular function following prolonged intense self-paced exercise in hot climatic conditions, Périard J, Cramer M, Chapman P, Caillaud C and Thompson M, European Journal of Applied Physiology, Volume 111(8), pp.1561-1569, (2011). Muscle weakness following constant load exercise under heat stress has been associated with hyperthermia-induced central fatigue. However, evidence of central fatigue influencing intense self-paced exercise in the heat is lacking. The purpose of this investigation was to evaluate force production capacity and central nervous system drive in skeletal muscle pre- and post-cycle ergometer exercise in hot and cool conditions. Voluntary activation during the post-exercise MVC declined to 93.7% (hot) and 93.9% (cool) (P < 0.05 vs. control). The post-exercise decline in voluntary activation represented ~20% of the decrease in mean force production in both conditions. Therefore, the additional increase in rectal temperature did not exacerbate the loss of force production following self-paced exercise in the heat. The impairment in force production indicates that the fatigue exhibited by the quadriceps is mainly of peripheral origin and a consequence of the prolonged contractile activity associated with exercise.
  • American College of Sports Medicine Roundtable on Exertional Heat Stroke—return to duty/return to play: Conference Proceedings, O’Connor F, Casa D, Bergeron M, Carter R, Deuster P, Heled Y. Kark J, Leon L, McDermott B, O’Brien K, Roberts W and Sawka M, Current Sports Medicine Reports , Volume 9(5), pp.314-321, (2010). On 22-23 October 2008, an ACSM Roundtable was convened to discuss return-to-play or return-to-duty for people who have experienced exertional heat illness (EHI) and to develop consensus-based recommendations. Although the group was unable to move forward with new consensus recommendations, they clearly documented critical clinical concerns and scientific questions, including the following: 1) no uniform core definitions of EHI; 2) limited validated criteria to assess recovery from exertional heat stroke (EHcasaS); and 3) inadequate ability to predict who may be predisposed to a subsequent heat injury after EHS. Areas of potential future research are identified.
  • Aural canal, esophageal, and rectal temperatures during exertional heat stress and the subsequent recovery period, Gagnon D, Lemire B, Jay O and Kenny G, Journal of Athletic Training, Volume 45(2), pp.157-163, (2010). The measurement of body temperature is crucial for the initial diagnosis of exertional heat injury and for monitoring purposes during a subsequent treatment strategy. However, little information is available about how different measurements of body temperature respond during and after exertional heat stress. We found that Tac, Tes, and Tre presented different temporal responses during and after both scenarios of exertional heat stress and a subsequent recovery period. Although these results may not have direct practical implications in the field monitoring and treatment of individuals with exertional heat injury, they do quantify the extent to which these body temperature measurements differ in such scenarios.
  • Effects of active warm up on thermoregulation and intermittent-sprint performance in hot conditions, Bishop D and Maxwell N, SmartPlay research details (2009). The aim of the research was to determine the effect of active warm-up on team-sport performance in a hot environment (35 degrees Celsius) by simulating the metabolic and thermoregulatory responses of trained team-sport athletes.
  • Validity and reliability of devices that assess body temperature during indoor exercise in the heat, Ganio M, Brown C, Casa D, Becker S, Yeargin S, McDermott B, Boots L, Boyd P, Armstrong L and Maresh C, Journal of Athletic Training, Volume 44(2), pp.124-135, (2009). To assess the validity and reliability of commonly used temperature devices compared with rectal temperature in individuals exercising in a controlled, high environmental temperature indoor setting and then resting in a cool environment. Even during laboratory exercise in a controlled environment, devices used to measure forehead, temporal, oral, aural, and axillary body sites did not provide valid estimates of rectal temperature. Only intestinal temperature measurement met the criterion. Therefore, we recommend that rectal or intestinal temperature be used to assess hyperthermia in individuals exercising indoors in the heat.
  • Acute whole-body cooling for exercise-induced hyperthermia: a systematic review, McDermott B, Casa D, Ganio M, Lopez R, Yeargin S, Armstrong L and Maresh C, Journal of Athletic Training, Volume 44(1), pp.84-93, (2009). This article discusses the literature supporting a range of cooling methodologies for the treatment of exercise-induced hyperthermia. This article suggests that iced-water immersion should be included if possible, but continual dousing of the patient combined with fanning and continually rotating cold wet towels represents a viable alternative until advanced cooling is possible. Cooling before transfer to hospital cannot be overemphasised.
  • A heat acclimation protocol for team sports, Sunderland C, Morris J and Nevill M, British Journal of Sports Medicine, volume 42(5), (2008). This study assesses the impact of an acclimation protocol base upon intermittent high-intensity exercise, as found in many team sports. The impact of four short heat acclimation sessions (30-45 minutes duration, each session) of high-intensity intermittent running the heat (30 degrees C) and 27% relative humidity was examined on female athletes. Subjects were divided into three groups: (1) an intermittent high-intensity exercise group; (2) a moderate training group, and; (3) a control group that did not train, but was exposed to the same heat conditions. In a post-acclimation trial distance run, the capacity of the intermittent exercise group (i.e. acclimation group) was increased by 33%, but was unchanged in the moderate and control groups. The acclimation group had a lower rectal temperature and slower rate of rise in rectal temperature, and an increase in self-reported thermal comfort after acclimation.
  • Validity of devices that assess body temperature during outdoor exercise in the heat, Casa D, Becker S, Ganio M, Brown C, Yeargin S, Roti M, Siegler J, Blowers J, Glaviano N, Huggins R, Armstrong L and Maresh C, Journal of Athletic Training, Volume 42(3), pp.333-342, (2007). Rectal temperature is recommended by the National Athletic Trainers' Association as the criterion standard for recognizing exertional heat stroke, but other body sites commonly are used to measure temperature. Few authors have assessed the validity of the thermometers that measure body temperature at these sites in athletic settings. Compared with rectal temperature (the criterion standard), gastrointestinal temperature was the only measurement that accurately assessed core body temperature. Oral, axillary, aural, temporal, and field forehead temperatures were significantly different from rectal temperature and, therefore, are considered invalid for assessing hyperthermia in individuals exercising outdoors in the heat.
  • Core temperature measurement: methods and current insights, Moran D, Mendal L, Sports Medicine, Volume 32(14), pp.879-885 (2002). The purpose of this paper is to review the various existing methods of T(c) measurements in order to focus on the breakthrough needed for a simple, noninvasive, universally used device for T(c) measurement which is essential for preventing climatic injuries during sports events.
  • Exertional heat stroke emergency kit, Korey Stringer Institute, Neag School of Education, University of Connecticut, (accessed 19 May 2021). A list of equipment (including information on price in $USD, lifespan, practicality and purchasing information) to ensure you are fully equipped to deal with a case of heat-illness.
  • Heat Acclimatization, Korey Stringer Institute, University of Connecticut (accessed 19 May 2021). Heat acclimation (i.e. acclimatization) plays a large part in the body’s physical responses and overall ability to cope with heat exposure. The Korey Stringer Institute provides useful information about the heat acclimation process.
  • Heat Illness Prevention [online course], National Federation of State High School Associations [USA], (accessed 19 May 2021). Exertional Heat Stroke is the leading cause of preventable death in high school athletics. To help you minimize the risk of heat illness at your school, this course has designed to provide the fundamentals of a strong heat acclimatization plan and guidelines for limiting activities to account for changing environmental conditions and other contributing risk factors. It highlights the importance of an appropriate hydration plan and establishing an Emergency Action Plan in case of a suspected exertional heat stroke.
  • How to respond to an exertional heat stroke emergency, Korey Stringer Institute, Neag School of Education, University of Connecticut, (accessed 19 May 2021). A step-by step first-aid guide.
  • Best practice guideline: Smoke Pollution and Exercise, Australian Institute of Sport, (December 2019). Often co-occurring with heat 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. Increases in exercise intensity and duration result in increased airway exposure to polluted air, the AIS recommends modifying training, or training locations.
  • Taking a rectal temperature,, (last updated 24 September 2019).

Licencing restrictions apply to some resources listed below.

Public All Clearinghouse members 'Australian' members only
'High Performance' members only Restricted access Various restrictions
Please see Clearinghouse membership categories for further information.

  • Heat management and Hydration, Cricket Australia, (accessed 6 January 2020). Heat management and hydration are important, as they directly impact on players’ performance and health. There are key ways to help players manage their body temperature. These videos provide tips on how to help players stay cool and hydrated while training or competing in cricket.
  • Training and Competition in the Heat Conference, ASPETAR Conference, Doha, Qatar, (23-24/03/2014)

Is this information complete?

The Clearinghouse for Sport is a sector-wide knowledge sharing initiative, and as such your contributions are encouraged and appreciated. If you would like to suggest a resource, submit a publication, or provide feedback on this topic, please contact us.

Alternatively, if you would like to be kept up to date with research and information published about this topic, please request a research profile setup.

Return to top