Menu
Back to Journals » Open Access Journal of Sports Medicine » Volume 15
Hyperthermia and Exertional Heatstroke During Running, Cycling, Open Water Swimming, and Triathlon Events
Authors Armstrong LE , Johnson EC, Adams WM, Jardine JF
Received 16 June 2024
Accepted for publication 6 September 2024
Published 24 September 2024 Volume 2024:15 Pages 111—127
DOI https://doi.org/10.2147/OAJSM.S482959
Checked for plagiarism Yes
Review by Single anonymous peer review
Peer reviewer comments 2
Editor who approved publication: Prof. Dr. Andreas Imhoff
Lawrence E Armstrong,1,2 Evan C Johnson,3 William M Adams,4– 7 John F Jardine2
1Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT, USA; 2Korey Stringer Institute, Department of Kinesiology, University of Connecticut, Storrs, CT, USA; 3Division of Kinesiology & Health, University of Wyoming, Laramie, WY, USA; 4Department of Sports Medicine, United States Olympic & Paralympic Committee, Colorado Springs, CO, USA; 5United States Coalition for the Prevention of Illness and Injury in Sport, Colorado Springs, CO, USA; 6Department of Kinesiology, University of North Carolina at Greensboro, Greensboro, NC, USA; 7School of Sport, Exercise and Health Sciences, Loughborough University, National Centre for Sport and Exercise Medicine (NCSEM), Loughborough, UK
Correspondence: Lawrence E Armstrong, University of Connecticut, Department of Kinesiology, Human Performance Laboratory, 2095 Hillside Road, Unit 1110, Storrs, CT, 06269, USA, Email [email protected]
Abstract: Few previous epidemiological studies, sports medicine position statements, and expert panel consensus reports have evaluated the similarities and differences of hyperthermia and exertional heatstroke (EHS) during endurance running, cycling, open water swimming, and triathlon competitions. Accordingly, we conducted manual online searches of the PubMed and Google Scholar databases using pre-defined inclusion criteria. The initial manual screenings of 1192 article titles and abstracts, and subsequent reviews of full-length pdf versions identified 80 articles that were acceptable for inclusion. These articles indicated that event medical teams recognized hyperthermia and EHS in the majority of running and triathlon field studies (range, 58.8 to 85.7%), whereas few reports of hyperthermia and EHS appeared in cycling and open water swimming field studies (range, 0 to 20%). Sports medicine position statements and consensus reports also exhibited these event-specific differences. Thus, we proposed mechanisms that involved physiological effector responses (sweating, increased skin blood flow) and biophysical heat transfer to the environment (evaporation, convection, radiation, and conduction). We anticipate that the above information will help race directors to distribute pre-race safety advice to athletes and will assist medical directors to better allocate medical resources (eg, staff number and skill sets, medical equipment) and optimize the management of hyperthermia and EHS.
Keywords: heat illness, epidemiology, pathophysiology, thermoregulation, athlete
Introduction
During the transition from rest to exercise, skeletal muscle metabolic rate increases. Depending on the mode (eg, running, cycling, swimming) and intensity of this exercise, human mechanical efficiency (ie, the ratio of external work to the amount that energy production increases) is 25% or less. Consequently, at least 75% of the energy generated during carbohydrate and fat metabolism in active tissue is eventually converted to heat.1,2 Highly trained endurance runners can produce heat at a rate of 1000–1300 kcal · h−1 (1162–1511 W) for 1–3 h.3,4 This means that the internal body temperature of a hypothetical marathon runner (70 kg body mass) could rise at the rate of 0.3°C·min−1. At this rate of heat storage, he/she could be at risk for thermal injury within 15 minutes, if heat were not dissipated from internal organs to the environment.4 The clinical relevance of these observations becomes evident when considering the nature of exertional heatstroke (EHS).
EHS is a medical emergency characterized by hyperthermia (usually > 40°C rectal temperature) with central nervous system disturbances which range from mild personality changes to confusion, delirium, stupor, or unconsciousness.5–8 The clinical outcomes of EHS are directly attributed to the duration of hyperthermia above the body’s critical threshold for cellular damage.9–12 Thus, the best practice for pre-hospital management of EHS13,14 includes rapid recognition (ie, nausea, aggressiveness, dizziness, combativeness, staggering while walking/running, or collapse), rapid assessment (ie, measuring the athlete’s core body temperature with a rectal thermometer and evaluating mental status for disorientation, confusion, altered consciousness, or irrational behavior), and rapid cooling by submerging the athlete in an ice-water bath that is maintained at ≤ 15°C.6,8,11,15 A “cool first, transport second”9,11,13 management plan is important because EHS is 100% survivable when core temperature is cooled below 40°C within 30 minutes.16,17 If whole-body cooling is not applied rapidly, the untoward sequelae of EHS may ensue,17 and patient management may require critical care interventions for organ and tissue damage, including systemic inflammatory response syndrome and disseminated intravascular coagulopathy.18–20
It is perplexing that EHS frequently strikes young, highly motivated individuals (ie, athletes, recreational enthusiasts, soldiers) during activities that they have performed previously, in similar environmental conditions, at the same exercise intensity-duration, and while wearing similar clothing or gear.21–23 It is tragic that EHS strikes some individuals more than once.24 For example, Stearns et al25 reported that 11% of EHS cases spanning 17 years of the Falmouth Road Race sustained a second EHS episode within the next 2 years. Similarly, Abriat et al26 reported that 15% of EHS patients in the French military experienced EHS recurrence at a later date. Although a few clinicians and physiologists have suggested that EHS is preventable,27–30 effective prevention has been sought for decades without eradicating this life-threatening illness.31–33 Today, no method exists to validly predict who will experience EHS during a sport or mass participation event.34 We propose that this state of affairs exists primarily because the interactive effects of recognized risk factors are unknown and understudied. Further, it is unlikely that the risk of EHS will be eliminated completely35 because (a) heat storage in deep internal organs is common when prolonged, strenuous exercise is performed in a hot environment,3,4,36–39 and (b) an athlete’s motivation and competitive drive are self-controlled.30 However, while total primary prevention is not likely, 100% survival from EHS is possible when whole-body cooling reduces internal temperature below 40°C within 30 minutes.11,16,17 This fact underscores the importance of treatment by the on-site medical team and pre-event planning.40–43 It also indicates that additional research is warranted.
Individual endurance sports and mass participation events have grown during the past 25 years globally. This includes distance running and sanctioned cycling competitions,44,45 open water swimming,46–48 triathlons,45,49 and the ultra-distance events organized for all of these.47 Endurance sport participants seek great challenges44 that often are associated with an increased incidence of serious and life-threatening medical conditions.50 As a result, meeting the clinical demands of various stressors and venues has become a priority in the realms of sports medicine and mass medical management.44,51 Relevant to the present review, EHS is included among the possible serious and life-threatening problems that participants report to the event medical team42,50,52,53 during foot races,54–57 endurance cycling events,52,58 triathlons,43,59,60 and ultra-distance events.40,52,58 It is especially relevant to triathletes that no previous review article has assessed hyperthermia and EHS across all of these endurance sports. Therefore, the dual purposes of the present review are to clarify the available evidence regarding the recognition of hyperthermia and EHS (a) by medical teams at outdoor running, cycling, open water swimming, and triathlon events; and (b) by professional organizations and writing groups in position statements and consensus documents regarding outdoor endurance activities. Prior to conducting an extensive search of the literature, we hypothesized that this effort would identify gaps in the knowledge base plus event-specific differences which are not widely recognized. We propose that this review will inform and enhance the medical care of those who participate in future endurance sports and mass participation events.
Materials and Methods
Manual searches for relevant articles were performed in the PubMed and Google Scholar databases using advanced search operators (eg, quotation marks, pertinent phrases, “and”, “or”). Inclusion criteria included English language, full-text, peer-reviewed articles, without publication year limits and available through March 5, 2024. Combinations of the following key words during literature searches emphasized the associations of hyperthermia and EHS with running, cycling, swimming, and triathlon events: “hyperthermia”, “heatstroke”, “heat stroke”, “cyclist”, “cycling”, “runner”, “running”, “triathlon”, “triathlete”, “swimmer”, “swimming”, and “open water swimming”. All manual searches included “hyperthermia”, “heatstroke” and “heat stroke” as keywords; each search excluded articles which contained the keywords “military”, “soldier”, “industry”, “industrial”, and “labor” which were beyond the scope of the present review. After removing duplicate records, the abstracts and titles of the remaining records were evaluated to determine which studies should be further assessed for eligibility. We subsequently performed manual searches of each eligible article’s reference list, as well as the bibliographies found in germane systematic reviews and meta-analyses. Finally, we investigated full text (.pdf) versions of all remaining articles to ascertain if they fit the purposes of this review.
We sought and organized relevant articles using the following approaches to the existing literature. First, research in the area of exertional heat illnesses is complicated by difficulties with definitions,61 which vary considerably and are based on non-specific terminology.62 Thus, we sought publications which described the medical encounters that specifically involved hyperthermia and EHS at outdoor mass participation/large group events, athletic competitions, or training and competition spanning a single season or multiple years. Second, we segregated running, triathlon, cycling, and open water swimming studies. Third, because previous publications have suggested that ambient conditions (ie, hot environments) influence the types and prevalence of illnesses observed at athletic competitions and recreational endurance events,56,63–67 we sought articles that reported environmental conditions (eg, dry bulb temperature, wet bulb globe temperature, relative humidity) on the day(s) that clinical observations were made. Fourth, because few publications have evaluated hyperthermia and EHS during open water swimming or cycling (eg, as an individual sport or as part of a triathlon event), we sought to identify randomized, controlled investigations regarding the effect of water temperature (swimming) and wind speed (cycling) on body heat balance and core temperature. Fifth, we evaluated the recognition of hyperthermia and EHS by professional organizations and expert panels in published position statements and consensus reports.
Definitions
To clearly describe the medical conditions presented in this review, we have employed definitions published by the International Olympic Committee68 and other respected sources. The term “medical encounter” is defined as an interaction between the medical team and a race participant that requires medical assistance or evaluation and which occurred between the start of the event and 24 hours after the event.42 The term “medical team” refers to the officially designated team of medical staff (ie, physicians, first aid providers, registered nurses, physiotherapists, athletic trainers) responsible for the medical care during the event, typically led by a medical director.42 The “recognition” of hyperthermia and EHS by the medical team refers to an a priori medical staff plan, reports from previous years, or on-site diagnosis. Hyperthermia is defined in the present review as a mild-to-moderate elevation of internal body temperature (eg, 37.7 to 39.4°C [100 to 103°F]) resulting from exercise;69,70 in trained and heat acclimatized athletes, this mild-to-moderate temperature increase is not dangerous, but it indicates that metabolic heat has been stored in bodily organs and fluids.71 EHS involves severe whole-body hyperthermia that exceeds 40°C6,8,14,29,41,72,73 and occurs when a healthy thermoregulatory system is either overloaded by exercise-induced metabolic heat production74 or when thermoregulation “fails” due to physiological dysfunction of central or peripheral effector responses.75
The following four definitions76 are relevant to hyperthermia and EHS because they refer to heat transfer within the body and at the skin surface. First, heat exchange by convection occurs via the circulation (ie, heat moves from deep organs to the periphery in blood), as well as between the skin and surrounding cool air or water.77 The temperature gradient between skin and its environment plus the speed of fluid movement determines the amount of heat absorbed or donated by a given mass of air or water. Second, conduction refers to heat transmission from the skin to a solid object (eg, clothing, shoes) or a fluid (eg, water). During running and cycling, conduction accounts for only about 2% of energy transfer. During open water swimming, however, conduction and convection are the primary avenues of heat transfer, and may involve heat gain or loss depending on the temperature gradient between the skin and water.76,78 The thermal conductivity of water is 24 times that of air; thus, water has a much greater potential for heat transfer, into or out of the body, than air.11,79 Third, radiation is defined as the transmission of energy in the form of waves. Solar energy from direct sunlight and radiant heat from the ground are relevant examples for outdoor sports. Fourth, evaporation occurs when sweat or water changes its physical state, from a liquid to a gas; this change of state removes energy from the skin and it cools. In a hot-dry environment, evaporation accounts for 85–90% of all heat dissipation during exercise.80
Results
Using the keywords and inclusion criteria described above, the manual screenings of 1192 article titles and abstracts and subsequent reviews of full-length pdf versions identified the 80 articles that were acceptable for inclusion in tables and figures. The initial 4 tables indicate if hyperthermia or EHS was recognized by medical personnel who provided care at sport and mass participation events. If “yes” a + symbol appears in that cell, and if “no” the cell is open (blank). This recognition by medical staff was due either to an a priori medical staff plan, reports from previous years, or on-site diagnosis. Column 1 of these tables also includes the number of athlete hyperthermia and EHS medical encounters, if reported by the authors. In some field studies, the potential harm to athletes of a high core body temperature was described, but the term “hyperthermia” was not used; these cases are annotated by footnotes.
Across the 18 featured studies in Table 1, hyperthermia was recognized by medical personnel in 76.5% of endurance running studies, whereas EHS was recognized in 58.8% of these articles; 3 studies (17.6%) recognized neither hyperthermia nor EHS.
 |
Table 1 Medical Team Recognition of Hyperthermia and Exertional Heatstroke in Field Studies That Were Conducted at Outdoor Endurance Running Events |
Table 2 presents the results of 7 field studies that were conducted at triathlon competitions. Hyperthermia was recognized by medical personnel in 85.7% of studies, whereas EHS was recognized in 71.4% of these articles; only 1 study (14.3%) recognized neither hyperthermia nor EHS.
 |
Table 2 Medical Team Recognition of Hyperthermia and Exertional Heatstroke in Field Studies That Were Conducted at Outdoor Triathlon Events |
Table 3 summarizes information from outdoor cycling studies which allow comparisons to the articles presented in Tables 1 and 2. Only 3 of 20 cycling studies (15.0%) recognized both hyperthermia and EHS, confirming that cycling epidemiology is different from running and triathlon events. Few of the studies in Table 3 reported ambient conditions during the event (column 2, n = 4).
 |
Table 3 Few Medical Teams Reported Hyperthermia and Heatstroke in 20 Road and off-Road Cycling Studies |
Figure 1 is reproduced from the laboratory research of Saunders et al114 with the permission of the publisher. This graph is included to illustrate the relationship between increasing air velocity and internal heat storage, during controlled cycle ergometer exercise in a hot environment. Specifically, heat dissipation from the skin surface increased at higher air velocities (ie, primarily via increased evaporation) and heat storage decreased.
 |
Figure 1 The effect of 4 air velocities on the internal heat storage of 9 men who exercised for 2 h on a stationary cycle ergometer in a controlled hot environment (33.0°C, 59%rh), as reported by Saunders et al.114 During these 4 repeated experiments, subjects consumed fluids which replaced 58–61% of sweat losses. Redrawn with the permission of the publisher John Wiley and Sons, © 2005 Scandinavian Physiological Society from Saunders AG, Dugas JP, Tucker R, Lambert MI, Noakes TD. The effects of different air velocities on heat storage and body temperature in humans cycling in a hot, humid environment. Acta Physiol Scand. 2005;183(3):241–255.114 aSignificantly different from all other data points (P < 0.05 to 0.005); bSignificantly different from 50 km·h−1 (P < 0.05). |
Table 4 presents the 5 open water swimming field studies we identified during extensive manual searches of the literature. Only one of these publications (20.0%) recognized hyperthermia and none (0%) mentioned EHS. We identified so few field studies in Tables 4 that 5 was created to summarize the information from relevant review articles and sport governing body manuals. Contrary to the findings of the studies in Table 4, the potential for hyperthermia during open water swimming was discussed in 92.3% of these articles and manuals in Table 5, whereas EHS was acknowledged in 53.8%.
 |
Table 4 Hyperthermia and Exertional Heatstroke, as Reported in 5 Open Water Swimming Field Studies |
 |
Table 5 The Risk of Hyperthermia and Exertional Heatstroke for Open Water Swimmers, as Discussed in Review Articles and Sport Governing Body Manuals |
Figure 2 provides information that clarifies the effect of water temperature on deep body temperature (eg, hypothermia or hyperthermia) in controlled swimming experiments, at different exercise intensities. The vertical dashed line depicts the maximum water temperature (31°C, 87.8°F measured at a depth of 40 cm) for open water swimming competitions that is allowed by World Aquatics, the international sport governing body.125,129 This figure is original and unique to the present review.
 |
Figure 2 The effect of water temperature on internal body temperature during 20–80 min of swimming performed during 6 controlled research studies.131–136 Each study is identified in this graph by its reference citation number. These experiments involved a range of exercise intensities (see inset box) and various exercise modes (ie, swimming flume, swimming pool, or tethered to a swim ergometer). The horizontal dashed line represents the border between net heat loss and net heat gain during exercise. The vertical dashed line depicts the maximum water temperature (31°C, 87.8°F) for open water swimming competitions that is allowed by the international governing body World Aquatics.125,129 |
Table 6 shows that hyperthermia was recognized in 63.6%, whereas EHS was recognized in 81.8%, of the position statements and reports published by professional sports medicine organizations and consensus writing groups between 2012 and 2023. Only two of these publications (18.2%) did not recognize hyperthermia or EHS.
 |
Table 6 Recognition of Hyperthermia and Exertional Heatstroke in Position Statements and Reports of Professional Sports Medicine Organizations and Consensus Writing Groups |
Discussion
The present review focuses on the available evidence regarding the recognition of hyperthermia and EHS by medical teams at outdoor running, cycling, open water swimming, and triathlon events. Prior to an exhaustive literature search, we hypothesized that this effort would identify event-specific differences which are not widely recognized. Indeed, Tables 1–4 demonstrate that event-specific differences exist in the available literature. For example, Tables 1 and 2 establish that hyperthermia and EHS are recognized by the majority of medical teams at endurance running and triathlon events (range, 58.8 to 85.7%), whereas little recognition is given to hyperthermia and EHS by medical teams at cycling and open water swimming events (Tables 3 and 4; range, 0 to 20%). Thus, the following paragraphs consider the unique features of body heat balance and temperature regulation during these endurance events.
The factors that influence metabolic heat production within contracting muscles, heat transport via blood to internal organs or to the skin, heat transfer to or from the skin, and evaporation of sweat from the skin surface (ie, to dissipate heat to the environment) are described by the following heat balance equation:92,141
In this equation, S refers to the rate of heat storage within the body, M is the rate of heat production via muscle metabolism, and W is the work rate (ie, which considers whether energy is released as heat within the body, the mode of exercise, and whether mechanical energy is applied to an external object such as a bicycle or stairs). The following terms refer to heat transfer at the skin surface: C is convection, R is radiation, K is conduction, E is evaporation of sweat or water from the skin (ie, a change of state from liquid to gas), and Resp refers to heat transmission via C and E from the respiratory tract. Energy exchange is typically expressed in terms of Watts but may be conveyed as kilocalories per hour or kilojoules per minute.141
During exercise, the brain employs two primary physiological effector responses to maintain a stable internal body temperature (ie, the state in which the rate of metabolic heat production equals the rate of heat loss to the environment; S = 0). The first involves evaporation of sweat and the second involves dilation of superficial cutaneous veins which results in increased skin blood flow; this latter response transports heat from the body core to skin via convection.141 When the skin is moist, the primary role of increased skin blood flow is to deliver the heat necessary to evaporate sweat. In the absence of sweating (ie, dry skin) or when air water vapor is high (ie, reducing evaporation), the main effect of increased skin blood flow is to increase skin temperature and promote heat loss via convection and radiation. An important detrimental outcome of increased skin blood flow is that central blood volume is diminished. This redistribution of blood limits cardiac filling, stroke volume, and cardiac output,4 thereby reducing endurance performance in hot environments;142,143 it also increases the risk of hyperthermia and exertional heat illness.8,144–147
Event & Environment Specificity
Our extensive literature search revealed no previous review article that compared either hyperthermia or EHS at endurance running, triathlon, cycling, and open water field studies. The following paragraphs delineate our findings, and provide an analysis of body heat balance and thermoregulation during each of these sports.
As shown in column 1 of Table 1, hyperthermia or EHS cases were recognized in the majority of outdoor endurance running events (52.9 and 58.8%, respectively), across a range of ambient conditions. This indicates that metabolic heat production in these cases exceeded heat transfer from the body surface to the environment. A systematic review of 33 studies by Gamage et al62 supports this observation, in that distance running was identified as the organized sport with the highest rate (per 100 participants) of exertional heat illnesses.
A majority of triathlon medical teams (71.4%) recognized both hyperthermia and EHS (Table 2, column 1). This finding in triathlon events may be somewhat greater than in running events (Table 1) because of differences in running economy, expressed as the energy cost of running a distance of 1 km (mL O2·kg−1·km−1).148 This quantity has been measured in triathletes during both isolated running and “triathlon running” (ie, after swimming and cycling segments). In highly trained triathletes, it is generally reported that the energy cost measured at the end of an Olympic distance triathlon is higher by approximately 10% when compared with an isolated run covering the same distance.149,150 The theoretical mechanisms that have been proposed to explain this deterioration of running economy in triathlon events include higher oxygen consumption of the respiratory muscles, shifts of circulating fluids (eg, to the extremities), and altered running biomechanics.149–152
With regard to outdoor cycling, Table 3 prompts a considerably different conclusion regarding internal heat storage (S). Only 3 of the 20 field studies (15.0%) recognized hyperthermia and EHS during road and off-road events; these involved a spectrum of participant capabilities that ranged from recreational to elite. We propose that this small percentage of hyperthermia and EHS is an indication of the great amount of heat that is dissipated during cycling because the airflow across the skin surface is considerably greater than during running.153,154 Especially on flat terrains, this rapid air movement facilitates cooling via evaporation and convection, reducing the risk of hyperthermia.155 This phenomenon is illustrated in Figure 1, which presents data from controlled laboratory experiments involving habitually active, moderately fit men who exercised on a stationary cycle ergometer in a controlled 33°C, 59%rh environment. In combination with additional physiological and perceptual measurements, the authors of this study114 concluded that airflow greater than 10 km·h−1 contributed to reduced physiological and perceptual strain; their calculations indicated that the reduced heat storage was primarily due to enhanced evaporation in this hot environment. Employing a similar repeated measures experimental design (30°C, 50%rh ambient conditions; cycle ergometer exercise), Otani et al156 reported that test subject thermoregulatory (ie, rectal temperature, heat storage), cardiovascular (ie, heart rate, cutaneous vascular conductance), and perceptual (ie, rating of perceived exertion, thermal sensation) strain decreased, whereas the time to exhaustion increased, as air velocity intensified from 0 to 30 km·h−1. The convective heat loss described in these two studies, however, would diminish during outdoor up-hill cycling (ie, as ground speed decreases) or when the air temperature exceeds skin temperature.7
Thermal conductivity influences heat storage (Eq. 1 above) in swimmers as they move through water, but affects runners and cyclists minimally as they move through air. The thermal conductivity of water is 24 times that of air.11 This translates into a great potential for heat transfer (ie, relative to air) into or out of the body, depending on the water-to-skin thermal gradient and the body surface area that is exposed.76,79 Although none of the field studies in Table 4 described air or water temperatures, we propose that the thermal conductivity of cool water resulted in the scarcity of hyperthermia and EHS among open water swimmers. Figure 2 supports this proposition by depicting the relationship between water temperature and internal body temperature, as reported in 6 controlled research studies. Considering the horizontal dashed line in Figure 2, no cases of net heat gain (and all cases of net heat loss) occurred when the water temperature was ≤26°C (78.8°F), across a range of exercise durations and intensities. The vertical dashed line in Figure 2 is relevant because it depicts the maximum water temperature (31°C, 87.8°F) allowed by World Aquatics125,129 during open water swimming events in 2024. The purpose of this regulation is to minimize the risk of hyperthermia when open water swimming competitions are conducted in warm water;122 it requires event organizers to either shorten or reschedule a race at a time that is likely to present a more favorable environment.126,129 Despite the fact that the field studies in Table 4 provide little evidence of hyperthermia and EHS at outdoor swimming competitions, multiple journal review articles, manuals published by sport governing bodies (Table 5), and online web sites have described the risk of hyperthermia and/or EHS during open water swimming events in warm water.119,121,122,126,127 We interpret these differences between Tables 4 and 5 to mean that the World Aquatics maximum water temperature (31°C) regulation129 is valid and that it was employed during the 5 events summarized in Table 4.
Data from multiple endurance sport studies143,157 indicate that a body water deficit impairs temperature regulation by reducing sweat rate and skin blood flow.158–161 This detrimental role of dehydration in body temperature regulation has been consistently demonstrated. For each 1% deficit of body weight, rectal temperature increases 0.2–0.4°C (0.36–0.72°F) during controlled laboratory trials.158,161–165 Thus, a body water deficit increases the risk of hyperthermia and EHS163,165,166 and this risk is influenced by the unique exercise mode and rehydration regulations of each sport. For example, the transmission of stored body heat to cool air (eg, ambient <20°C) is largely accomplished during high-speed cycling (ie, generating rapid air movement across the skin surface) via convection and radiation – forms of dry heat loss4,155 that do not result in a body water deficit. We propose that this explains, in part, the scarcity of hyperthermia and EHS in Table 3. However, during high-speed cycling in warm and hot environments (eg, ambient >20°C), evaporation of sweat becomes the predominant avenue of heat loss114,156 and dehydration progressively influences the rate of heat storage within internal organs. Furthermore, we propose that fluid availability influences the risk of hyperthermia and EHS. During endurance running, fluid intake is limited by the number of aid stations along the race course or by the size of a water bottle in hand. Open water swimmers can expect to be in the water for 2–4 hours during short course events (eg, up to 10 km) and 6–8 hours at distances >25 km; this means that they must rely on their support team to provide fluids from a watercraft.125 In contrast, cyclists can rehydrate whenever desired, because water bottles are carried in jersey pockets or are attached to the bicycle frame.142 These event-specific differences influence the hyperthermia and EHS which occur during outdoor endurance events (Tables 1–3).
Previous publications56,63–67 have suggested that hot environments influence the types and prevalence of illnesses observed at outdoor athletic competitions and recreational endurance events. Prior to our extensive literature search, we anticipated that this concept would be supported by the present data base. However, we were unable to draw conclusions regarding a systematic effect of increasing environmental heat stress on hyperthermia and EHS. This was due to the wide variety of meteorological indices (eg, dry bulb temperature, dew point, WBGT) in Tables 1 and 2 and few reports of ambient conditions in Tables 3 and 4.
Position Statements and Consensus Reports
The second purpose of this review is to clarify the available evidence regarding the recognition of hyperthermia and EHS by professional sports medicine organizations and writing groups in their position statements and consensus documents. Table 6 summarizes 11 such publications and shows that 63.6% of these articles recognized both hyperthermia and EHS. However, the articles, which focused solely on aquatic sports and competitive cycling,137,138 were the only two that recognized neither hyperthermia nor EHS. This finding agrees with field studies of cycling and open water swimming which involved considerably fewer cases of hyperthermia and EHS (column 1, Tables 3 and 4) than studies that involved endurance running and triathlons (column 1, Tables 1 and 2). In fact, any prolonged activity that involves a large metabolic heat production concurrent with diminished heat transfer to the environment (eg, insulative gear or uniform, air > skin temperature, low air velocity, relative humidity >75%, high solar radiation) may result in hyperthermia or EHS.7,29,167 Therefore, we recommend that future position statements, consensus reports, and field studies recognize both hyperthermia and EHS, including their inclusion in a priori medical planning and pre-event medical staff briefings. This recommendation supports medical diagnosis, which begins with an onsite evaluation and history, and then rules out life-threatening disorders such as EHS.6,139,146,168
Conclusion
The first purpose of the present review was to clarify the available evidence regarding the recognition of hyperthermia and EHS by medical teams at outdoor endurance races and mass participation events. At endurance running events, the majority of medical teams recognized hyperthermia and EHS (76.5 and 58.8%, respectively). Similarly, the majority of medical teams at triathlon events recognized hyperthermia and EHS (85.7 and 71.4%, respectively). In contrast, little recognition was given to these medical conditions (both hyperthermia and EHS, 15.0%) by the medical teams covering cycling events and open water swimming events (hyperthermia, 20.0, and EHS, 0%). Also, few authors of cycling field studies and no authors of open water field studies described the ambient conditions (eg, air and water temperature) during those competitions. These event-specific differences arise from complex, dynamic interactions of multiple factors. The second purpose of this review was to clarify the recognition of hyperthermia and EHS by professional organizations and writing groups in their position statements and consensus documents. Based on our findings, we recommend that sport governing bodies and on-site medical teams consider the sport-specific incidence of hyperthermia and EHS, to optimize pre-race safety advice provided to athletes, the planning and allocating of medical resources (eg, staff number and skill sets, whole-body cooling supplies), and managing patient care.
Acknowledgments
This work is the authors’ own and not that of the United States Olympic & Paralympic Committee, or any of its members or affiliates.
Disclosure
ECJ previously received conference travel financial support from Unilever and Danone Research, as well as research funding from Danone Research; he currently serves on the Scientific Advisory Committee of Danone Research. WMA receives royalties from Springer Nature on an edited textbook on Exertional Heat Illness. WMA is also the owner of Adams Sports Medicine Consulting LLC which provides solutions to clients within the realm of exertional heat stroke, personal fees from Emerja Corporation, personal fees from Wu Tsai Human Performance Alliance, personal fees from Korey Stringer Institute, and Stock Options from My Normative. The authors report no other conflicts of interest in this work.
References
1. Astrand PO, Rodahl K. Textbook of Work Physiology. New York: McGraw-Hill; 1977.
2. Castellani J. Physiology of heat stress. In: Armstrong LE, editor. Exertional Heat Illnesses. Champaign, IL: Human Kinetics; 2003:1–15.
3. Armstrong LE, Hubbard RW, Jones BH, Daniels JT. Preparing Alberto Salazar for the heat of the 1984 Olympic Marathon. Phys Sportsmed. 1986;14(3):73–81. doi:10.1080/00913847.1986.11709011
4. Gisolfi CV, Wenger CB. Temperature regulation during exercise: old concepts, new ideas. Exerc Sport Sci Rev. 1984;12:339–372. doi:10.1249/00003677-198401000-00013
5. Belval LN, Casa DJ, Adams WM, et al. Consensus statement-prehospital care of exertional heat stroke. Prehosp Emerg Care. 2018;22(3):392–397. doi:10.1080/10903127.2017.1392666
6. Casa DJ, DeMartini JK, Bergeron MF, et al. National Athletic Trainers’ Association position statement: exertional heat illnesses. J Athl Train. 2015;50(9):986–1000. doi:10.4085/1062-6050-50.9.07
7. Racinais S, Hosokawa Y, Akama T, et al. IOC consensus statement on recommendations and regulations for sport events in the heat. Br J Sports Med. 2023;57(1):8–25. doi:10.1136/bjsports-2022-105942
8. Roberts WO, Armstrong LE, Sawka MN, Yeargin SW, Heled Y, O’Connor FG. ACSM expert consensus statement on exertional heat illness: recognition, management, and return to activity. Curr Sports Med Rep. 2023;22(4):134–149. doi:10.1249/JSR.0000000000001058
9. Adams WM, Hosokawa Y, Casa DJ. The timing of exertional heat stroke survival starts prior to collapse. Curr Sports Med Rep. 2015;14(4):273–274. doi:10.1249/JSR.0000000000000166
10. Armstrong LE, Casa DJ, Millard-Stafford M, Moran DS, Pyne SW, Roberts WO. American College of Sports Medicine position stand. Exertional heat illness during training and competition. Med Sci Sports Exerc. 2007;39(3):556–572. doi:10.1249/MSS.0b013e31802fa199
11. Casa DJ, McDermott BP, Lee EC, Yeargin SW, Armstrong LE, Maresh CM. Cold water immersion: the gold standard for exertional heatstroke treatment. Exerc Sport Sci Rev. 2007;35(3):141–149. doi:10.1097/jes.0b013e3180a02bec
12. Lipman GS, Gaudio FG, Eifling KP, Ellis MA, Otten EM, Grissom CK. Wilderness medical society clinical practice guidelines for the prevention and treatment of heat illness: 2019 update. Wilderness Environ Med. 2019;30(4):S33–S46. doi:10.1016/j.wem.2018.10.004
13. Hosokawa Y. Management of Exertional Heat Stroke in Athletics: interdisciplinary Medical Care. In: Adams WM, Jardine JF, editors. Exertional Heat Illness: A Clinical and Evidence-Based Guide. Switzerland: Springer Nature; 2020:169–180.
14. Hosokawa Y, Racinais S, Akama T, et al. Prehospital management of exertional heat stroke at sports Competitions: international Olympic Committee adverse weather impact expert Working group for the Olympic Games Tokyo 2020. Br J Sports Med. 2021;55(24):1405–1410. doi:10.1136/bjsports-2020-103854
15. Huggins RA, Scarneo SE, Casa DJ, et al. The inter-association task force document on emergency health and safety: best-practice recommendations for youth sports leagues. J Athl Train. 2017;52(4):384–400. doi:10.4085/1062-6050-52.2.02
16. Costrini A. Emergency treatment of exertional heatstroke and comparison of whole body cooling techniques. Med Sci Sports Exerc. 1990;22(1):15–18. doi:10.1249/00005768-199002000-00004
17. Demartini JK, Casa DJ, Stearns RL, et al. Effectiveness of cold water immersion in the treatment of exertional heat stroke at the Falmouth Road Race. Med Sci Sports Exerc. 2015;47(2):240–245. doi:10.1249/MSS.0000000000000409
18. Epstein Y, Roberts WO, Golan R, Heled Y, Sorkine P, Halpern P. Sepsis, septic shock, and fatal exertional heat stroke. Curr Sports Med Rep. 2015;14(1):64–69. doi:10.1249/JSR.0000000000000112
19. Leon LR, Bouchama A. Heat stroke. Compr Physiol. 2015;5(2):611–647.
20. Leon LR, Kenefick RW. Pathophysiology of heat related illnesses. In: Auerbach PS, Cushing TA, Harris NS, editors. Auerbach’s Wilderness Medicine.
21. Armstrong LE, Lee EC, Armstrong EM. Interactions of gut microbiota, endotoxemia, immune function, and diet in exertional heatstroke. J Sports Med. 2018;2018:1–33. doi:10.1155/2018/5724575
22. Epstein Y, Druyan A, Heled Y. Heat injury prevention—a military perspective. J Strength Cond Res. 2012;26:S82–S86. doi:10.1519/JSC.0b013e31825cec4a
23. Shibolet S, Lancaster MC, Danon Y. Heat stroke: a review. Aviat Space Environ Med. 1976;47(3):280–301.
24. Keren G, Epstein Y, Magazanik A. Temporary heat intolerance in a heatstroke patient. Aviat Space Environ Med. 1981;52(2):116–117.
25. Stearns RL, Hosokawa Y, Adams WM, et al. Incidence of recurrent exertional heat stroke in a warm-weather road race. Medicina. 2020;56(12):1–13.720. doi:10.3390/medicina56120720
26. Abriat A, Brosset C, Bregigeon M, Sagui E. Report of 182 cases of exertional heatstroke in the French Armed Forces. Mil Med. 2014;179(3):309–314. doi:10.7205/MILMED-D-13-00315
27. Department of the Army. Heat Stress Control and Heat Casualty Management. Technical Bulletin MED 507. Washington, D.C: Headquarters, Department of the Army; 2022.
28. Epstein Y, Moran DS, Shapiro Y. Exertional heatstroke in the Israeli Defense Forces. In: Pandolf KB, Burr RE, editors. Medical Aspects of Harsh Environments. Fort Sam Houston, TX: Borden Institute; 2001:281–292.
29. Nye NS, O’Connor FG. Exertional heat illness considerations in the military. In: Adams WM, Jardine JF, editors. Exertional Heat Illness: A Clinical and Evidence-Based Guide. Switzerland: Springer Nature; 2020:181–209.
30. Périard JD, DeGroot D, Jay O. Exertional heat stroke in sport and the military: epidemiology and mitigation. Exp Physiol. 2022;107(10):1111–1121. doi:10.1113/EP090686
31. Bartley JD. Heat stroke: is total prevention possible? Mil Med. 1977;142(7):528–535. doi:10.1093/milmed/142.7.528
32. Casa DJ, Armstrong LE, Carter IIIR, Lopez R, McDermott B, Scriber K. Historical perspectives on medical care for heat stroke, part 2: 1850 through the present: a review of the literature. Athl Train Sports Health Care. 2010;2(4):178–190. doi:10.3928/19425864-20100514-01
33. Wijerathne BT, Pilapitiya SD, Vijitharan V, Farah MM, Wimalasooriya YV, Siribaddana SH. Exertional heat stroke in a young military trainee: is it preventable? Mil Med Res. 2016;3:1–4.
34. Armstrong LE. Classification, nomenclature, and incidence of the exertional heat illnesses. In: Armstrong LE, editor. Exertional Heat Illnesses. Champaign, IL: Human Kinetics; 2003:17–28.
35. Casa DJ, Armstrong LE, Ganio MS, Yeargin SW. Exertional heat stroke in competitive athletes. Curr Sports Med Rep. 2005;4(6):309–317. doi:10.1097/01.CSMR.0000306292.64954.da
36. Armstrong LE, Casa DJ, Emmanuel H, et al. Nutritional, physiological, and perceptual responses during a summer ultraendurance cycling event. J Strength Cond Res. 2012;26(2):307–318. doi:10.1519/JSC.0b013e318240f677
37. Byrne C, Lee JK, Chew SA, Lim CL, Tan EY. Continuous thermoregulatory responses to mass-participation distance running in heat. Med Sci Sports Exerc. 2006;38(5):803–810. doi:10.1249/01.mss.0000218134.74238.6a
38. Costill DL. Inside Running: Basics of Sports Physiology. Indianapolis, IN: Benchmark Press; 1986.
39. Racinais S, Moussay S, Nichols D, et al. Core temperature up to 41.5C during the UCI road cycling world championships in the heat. Br J Sports Med. 2019;53(7):426–429. doi:10.1136/bjsports-2018-099881
40. Friedman LJ, Rodi SW, Krueger MA, Votey SR. Medical care at the California AIDS Ride 3: experiences in event medicine. Ann Emerg Med. 1998;31(2):219–223. doi:10.1016/S0196-0644(98)70310-5
41. Jardine JF, Roberts WO. Considerations for Road Race Medical Staff. In: Adams WM, Jardine JF, editors. Exertional Heat Illness: A Clinical and Evidence-Based Guide. Switzerland: Springer Nature; 2020:211–224.
42. Schwellnus M, Kipps C, Roberts WO, et al. Medical encounters (including injury and illness) at mass community-based endurance sports events: an international consensus statement on definitions and methods of data recording and reporting. Br J Sports Med. 2019;53(17):1048–1055. doi:10.1136/bjsports-2018-100092
43. Yang H-R, Jeong J, Kim I, Kim JE. Medical support during an Ironman 70.3 triathlon race. F1000Res. 2017;6:1516. doi:10.12688/f1000research.12388.1
44. Chiampas GT, Goyal AV. Innovative operations measures and nutritional support for mass endurance events. Sports Med. 2015;45(Suppl 1):61–69. doi:10.1007/s40279-015-0396-6
45. Newland BL, Aicher TJ. Exploring sport participants’ event and destination choices. J Sport Tour. 2018;22(2):131–149. doi:10.1080/14775085.2018.1436464
46. World aquatics technical open water swimming committee. Lausanne, Switzerland: Open Water Swimming Manual; 2024. Available from: https://www.worldaquatics.com/rules/competition-regulations.
47. Scheer V. Participation Trends of Ultra Endurance Events. Sports Med Arthrosc. 2019;27(1):3–7. doi:10.1097/JSA.0000000000000198
48. Tipton M, Bradford C. Moving in extreme environments: open water swimming in cold and warm water. Extrem Physiol Med. 2014;3:1–11. doi:10.1186/2046-7648-3-12
49. USA Triathlon. Colorado Springs, CO: USA triathlon state of the sport, industry trends to be shared at 2023 Endurance exchange presented by BOA; 2023. Available from: https://www.usatriathlon.org/articles/news/usa-triathlon-state-of-The-sport-industry-trends-shared-at-2023-endurance-exchange-presented-by-boa.
50. Sewry N, Wiggers T, Schwellnus M. Medical encounters among 94,033 race starters during a 16.1-km running event over 3 years in the Netherlands: SAFER XXVI. Sports Health. 2023;15(2):210–217. doi:10.1177/19417381221083594
51. Adams WM, Hosokawa Y, Troyanos C, Jardine JF. Organization and execution of on-site health care during a mass participation event. Athl Train Sports Health Care. 2018;10(3):101–104. doi:10.3928/19425864-20180329-02
52. Killops J, Schwellnus M, van Rensburg DCJ, Swanevelder S, Jordaan E. Medical encounters, cardiac arrests and deaths during a 109 km community-based mass-participation cycling event: a 3-year study in 102 251 race starters—SAFER IX. Br J Sports Med. 2020;54(10):605–611. doi:10.1136/bjsports-2018-100417
53. Sewry N, Schwellnus M, Boulter J, Seocharan I, Jordaan E. Medical encounters in a 90-km ultramarathon running event: a 6-year study in 103 131 race starters—SAFER XVII. Clin J Sport Med. 2022;32(1):e61–e67. doi:10.1097/JSM.0000000000000939
54. Breslow RG, Collins JE, Troyanos C, et al. Exertional heat stroke at the Boston marathon: demographics and the environment. Med Sci Sports Exerc. 2021;53(9):1818–1825. doi:10.1249/MSS.0000000000002652
55. Breslow RG, Shrestha S, Feroe AG, Katz JN, Troyanos C, Collins JE. Medical tent utilization at 10-km road races: injury, illness and influencing factors. Med Sci Sports Exerc. 2019;51(12):2451–2457. doi:10.1249/MSS.0000000000002068
56. DeMartini JK, Casa DJ, Belval LN, et al. Environmental conditions and the occurrence of exertional heat illnesses and exertional heat stroke at the Falmouth Road Race. J Athl Train. 2014;49(4):478–485. doi:10.4085/1062-6050-49.3.26
57. Pasquina PF, Griffin SC, Anderson-Barnes VC, Tsao JW, O’Connor FG. Analysis of injuries from the Army Ten Miler: a 6-year retrospective review. Mil Med. 2013;178(1):55–60. doi:10.7205/MILMED-D-11-00447
58. Racinais S, Nichols D, Travers G, et al. Health status, heat preparation strategies and medical events among elite cyclists who competed in the heat at the 2016 UCI road world cycling Championships in Qatar. Br J Sports Med. 2020;54(16):1003–1007. doi:10.1136/bjsports-2019-100781
59. Gosling CM, Gabbe BJ, McGivern J, Forbes AB. The incidence of heat casualties in sprint triathlon: the tale of two Melbourne race events. J Sci Med Sport. 2008;11(1):52–57. doi:10.1016/j.jsams.2007.08.010
60. Singh G, Bennett KJM, Taylor L, Stevens CJ. Core body temperature responses during competitive sporting events: a narrative review. Biol Sport. 2023;40(4):1003–1017. doi:10.5114/biolsport.2023.124842
61. Driscoll TR, Cripps R, Brotherhood JR. Heat-related injuries resulting in hospitalisation in Australian sport. J Sci Med Sport. 2008;11(1):40–47. doi:10.1016/j.jsams.2007.04.003
62. Gamage PJ, Fortington LV, Finch CF. Epidemiology of exertional heat illnesses in organised sports: a systematic review. J Sci Med Sport. 2020;23(8):701–709. doi:10.1016/j.jsams.2020.02.008
63. Casa DJ, Guskiewicz KM, Anderson SA, et al. National Athletic Trainers’ Association position statement: preventing sudden death in sports. J Athl Train. 2012;47(1):96–118. doi:10.4085/1062-6050-47.1.96
64. Grundstein AJ, Hosokawa Y, Casa DJ, Stearns RL, Jardine JF. Influence of race performance and environmental conditions on exertional heat stroke prevalence among runners participating in a warm weather road race. Front Sports Act Living. 2019;1:42. doi:10.3389/fspor.2019.00042
65. Holtzhausen LM, Noakes TD. Collapsed ultraendurance athlete: proposed mechanisms and an approach to management. Clin J Sport Med. 1997;7(4):292–301. doi:10.1097/00042752-199710000-00006
66. Roberts WO. Exercise-associated collapse care matrix in the marathon. Sports Med. 2007;37(4–5):431–433. doi:10.2165/00007256-200737040-00041
67. Schwabe K, Schwellnus M, Derman W, Swanevelder S, Jordaan E. Medical complications and deaths in 21 and 56 km road race runners: a 4-year prospective study in 65 865 runners--SAFER study I. Br J Sports Med. 2014;48(11):912–918. doi:10.1136/bjsports-2014-093470
68. Bahr R, Clarsen B, Derman W; International Olympic Committee Injury and Illness Epidemiology Consensus Group. International Olympic Committee consensus statement: methods for recording and reporting of epidemiological data on injury and illness in sports 2020 (including the STROBE extension for sports injury and illness surveillance (STROBE-SIIS)). Orthop J Sports Med. 2020;8(2):2325967120902908. doi:10.1177/2325967120902908
69. Casa DJ, Almquist J, Anderson S. Inter-association task force on exertional heat illnesses consensus statement. NATA News. 2003;6:24–29.
70. Gagnon D, Lemire BB, Casa DJ, Kenny GP. Cold-water immersion and the treatment of hyperthermia: using 38.6 degrees C as a safe rectal temperature cooling limit. J Athl Train. 2010;45(5):439–444. doi:10.4085/1062-6050-45.5.439
71. McDermott BP, Casa DJ, Ganio MS, et al. Acute whole-body cooling for exercise-induced hyperthermia: a systematic review. J Athl Train. 2009;44(1):84–93. doi:10.4085/1062-6050-44.1.84
72. Epstein Y, Hadad E, Shapiro Y. Pathological factors underlying hyperthermia. J Therm Biol. 2004;29(7–8):487–494. doi:10.1016/j.jtherbio.2004.08.018
73. Gardner JW, Kark JA. Clinical diagnosis, management, and surveillance of exertional heat illness. In: Pandolf KB, Burr RE, editors. Medical Aspects of Harsh Environments. Fort Sam Houston, TX: Borden Institute; 2001:231–279.
74. Hubbard RW. The role of exercise in the etiology of exertional heatstroke. Med Sci Sports Exerc. 1990;22(1):2–5.
75. Epstein Y. Heat intolerance: predisposing factor or residual injury? Med Sci Sports Exerc. 1990;22(1):29–35. doi:10.1249/00005768-199002000-00006
76. Golden F, Tipton MJ. Essentials of Sea Survival. Champaign, IL: Human Kinetics; 2002.
77. IuI L, Nozdrachev AD. Mechanism of heat transfer in various regions of human body. Izv Akad Nauk Ser Biol. 2009;2009(1):64–69.
78. Bradford CD, Gerrard DF, Cotter JD. Open-Water Swimming. In: Périard JD, Racinais S, editors. Heat Stress in Sport and Exercise: Thermophysiology of Health and Performance. New York: Springer Nature; 2019:263–281.
79. Toner MM, McArdle WD. Human thermoregulatory responses to acute cold stress with special reference to water immersion. Compr Physiol. 2011;14:379–397.
80. Adams WC, Fox RH, Fry AJ, MacDonald IC. Thermoregulation during marathon running in cool, moderate, and hot environments. J Appl Physiol. 1975;38(6):1030–1037. doi:10.1152/jappl.1975.38.6.1030
81. Roberts WO. A 12-yr profile of medical injury and illness for the Twin Cities Marathon. Med Sci Sports Exerc. 2000;32(9):1549–1555. doi:10.1097/00005768-200009000-00004
82. Sloan BK, Kraft EM, Clark D, Schmeissing SW, Byrne BC, Rusyniak DE. On-site treatment of exertional heat stroke. Am J Sports Med. 2015;43(4):823–829. doi:10.1177/0363546514566194
83. Rygiel V, Labrador H, Jaworski CA, Chiampas G. Review of injury patterns of the 2018 Bank of America Chicago Marathon to optimize medical planning. Curr Sports Med Rep. 2022;21(5):149–154. doi:10.1249/JSR.0000000000000955
84. Divine JG, Daggy MW, Dixon EE, LeBlanc DP, Okragly RA, Hasselfeld KA. Case series of exertional heat stroke in runners during early spring: 2014 to 2016 Cincinnati Flying Pig Marathon. Curr Sports Med Rep. 2018;17(5):151–158. doi:10.1249/JSR.0000000000000485
85. Holtzhausen LM, Noakes TD. The prevalence and significance of post-exercise (postural) hypotension in ultramarathon runners. Med Sci Sports Exerc. 1995;27(12):1595–1601. doi:10.1249/00005768-199512000-00003
86. Naidoo D, Sewry N, Schwellnus M, van Rensburg DC J, Jordaan E. Longer distance races and slower running pace are associated with exercise associated collapse. SAFER XXV study in 153208 distance runners. J Sports Med Phys Fitness. 2022;62(11):1519–1525. doi:10.23736/S0022-4707.22.13107-5
87. Stearns RL, Jardine J, Yeargin SW, Szymanski MR, Casa DJ. Cooling modality effectiveness and mortality associated with prehospital care of exertional heat stroke casualties. J Emerg Med. 2024;66(3):e397–e399. doi:10.1016/j.jemermed.2023.10.034
88. Racinais S, Havenith G, Aylwin P, et al. Association between thermal responses, medical events, performance, heat acclimation and health status in male and female elite athletes during the 2019 Doha World Athletics Championships. Br J Sports Med. 2022;56(8):439–445. doi:10.1136/bjsports-2021-104569
89. Scheer BV, Murray A. Al andalus ultra trail: an observation of medical interventions during a 219-km, 5-day ultramarathon stage race. Clin J Sport Med. 2011;21(5):444–446. doi:10.1097/JSM.0b013e318225b0df
90. Krabak BJ, Waite B, Schiff MA. Study of injury and illness rates in multiday ultra-marathon runners. Med Sci Sports Exerc. 2011;43(12):2314–2320. doi:10.1249/MSS.0b013e318221bfe3
91. Graham SM, McKinley M, Chris CC, et al. Injury occurrence and mood states during a desert ultramarathon. Clin J Sport Med. 2012;22(6):462–466. doi:10.1097/JSM.0b013e3182694734
92. Havenith G, Fiala D. Thermal indices and thermophysiological modeling for heat stress. Compr Physiol. 2011;6(1):255–302.
93. Feletti F, Saini G, Naldi S, et al. Injuries in medium to long-distance triathlon: a retrospective analysis of medical conditions treated in three editions of the ironman competition. J Sports Sci Med. 2022;21(1):58–67. doi:10.52082/jssm.2022.58
94. Holtzhausen LJ, Smit CR, Joubert G, Von Hagen K. Injury and illness profiles during the 2014 South African Ironman triathlon. S Afr J Sports Med. 2018;30(1):1–6. doi:10.17159/2078-516X/2018/v30i1a1509
95. Harris KM, Creswell LL, Haas TS, et al. Death and Cardiac Arrest in U.S. Triathlon Participants, 1985 to 2016: a Case Series. Ann Intern Med. 2017;167(8):529–535. doi:10.7326/M17-0847
96. Knight N, Parkin J, Smith R, Kipps C. The incidence of exertional heat stroke during mass-participation triathlon races: optimising athlete safety. Br J Sports Med. 2017;51(4):344–345. doi:10.1136/bjsports-2016-097372.155
97. Chow TK, Bracker MD, Patrick K. Acute injuries from mountain biking. West J Med. 1993;159(2):145–148.
98. Pfeiffer RP. Off-road bicycle racing injuries--The NORBA Pro/Elite category. Care and prevention. Clin Sports Med. 1994;13(1):207–218. doi:10.1016/S0278-5919(20)30364-1
99. Kronisch RL, Chow TK, Simon LM, Wong PF. Acute injuries in off-road bicycle racing. Am J Sports Med. 1996;24(1):88–93. doi:10.1177/036354659602400116
100. Dannenberg AL, Needle S, Mullady D, Kolodner KB. Predictors of injury among 1638 riders in a recreational long-distance bicycle tour: cycle Across Maryland. Am J Sports Med. 1996;24(6):747–753. doi:10.1177/036354659602400608
101. Chow TK, Kronisch RL. Mechanisms of injury in competitive off-road bicycling. Wilderness Environ Med. 2002;13(1):27–30. doi:10.1580/1080-6032(2002)013[0027:MOIICO]2.0.CO;2
102. Kronisch RL, Pfeiffer RP, Chow TK. Acute injuries in cross-country and downhill off-road bicycle racing. Med Sci Sports Exerc. 1996;28(11):1351–1355. doi:10.1097/00005768-199611000-00002
103. Emond SD, Tayoun P, Bedolla JP, Camargo CA. Injuries in a 1-day recreational cycling tour: bike New York. Ann Emerg Med. 1999;33(1):56–61. doi:10.1016/S0196-0644(99)70417-8
104. Gaulrapp H, Weber A, Rosemeyer B. Injuries in mountain biking. Knee Surg Sports Traumatol Arthrosc. 2001;9(1):48–53. doi:10.1007/s001670000145
105. De Bernardo N, Barrios C, Vera P, Laíz C, Hadala M. Incidence and risk for traumatic and overuse injuries in top-level road cyclists. J Sports Sci. 2012;30(10):1047–1053. doi:10.1080/02640414.2012.687112
106. Decock M, De Wilde L, Bossche LV, Steyaert A, Van Tongel A. Incidence and aetiology of acute injuries during competitive road cycling. Br J Sports Med. 2016;50(11):669–672. doi:10.1136/bjsports-2015-095612
107. Roi GS, Tinti R. Requests for medical assistance during an amateur road cycling race. Accid Anal Prev. 2014;73:170–173. doi:10.1016/j.aap.2014.08.010
108. McGrath TM, Yehl MA. Injury and illness in mountain bicycle stage racing: experience from the trans-sylvania mountain bike epic race. Wilderness Environ Med. 2012;23(4):356–359. doi:10.1016/j.wem.2012.05.003
109. Haeberle HS, Navarro SM, Power EJ, Schickendantz MS, Farrow LD, Ramkumar PN. Prevalence and epidemiology of injuries among elite cyclists in the Tour de France. Orthop J Sports Med. 2018;6(9):2325967118793392. doi:10.1177/2325967118793392
110. Pommering TL, Manos DC, Singichetti B, Brown CR, Yang J. Injuries and illnesses occurring on a recreational bicycle tour: the great Ohio bicycle adventure. Wilderness Environ Med. 2017;28(4):299–306. doi:10.1016/j.wem.2017.06.002
111. Yanturali S, Canacik O, Karsli E, Suner S. Injury and illness among athletes during a multi-day elite cycling road race. Phys Sportsmed. 2015;43(4):348–354. doi:10.1080/00913847.2015.1096182
112. Jancaitis G, Snyder Valier AR, Bay C. A descriptive and comparative analysis of injuries reported in USA Cycling-sanctioned competitive road cycling events. Inj epidemiol. 2022;9(1):1–8. doi:10.1186/s40621-022-00385-7
113. Edler C, Droste J-N, Anemüller R, Pietsch A, Gebhardt M, Riepenhof H. Injuries in elite road cyclists during competition in one UCI WorldTour season: a prospective epidemiological study of incidence and injury burden. Phys Sportsmed. 2023;51(2):129–138. doi:10.1080/00913847.2021.2009744
114. Saunders AG, Dugas JP, Tucker R, Lambert MI, Noakes TD. The effects of different air velocities on heat storage and body temperature in humans cycling in a hot, humid environment. Acta Physiol Scand. 2005;183(3):241–255. doi:10.1111/j.1365-201X.2004.01400.x
115. Mountjoy M, Junge A, Alonso JM, et al. Sports injuries and illnesses in the 2009 FINA World Championships (Aquatics). Br J Sports Med. 2010;44(7):522–527. doi:10.1136/bjsm.2010.071720
116. Prien A, Mountjoy M, Miller J, et al. Injury and illness in aquatic sport: how high is the risk? A comparison of results from three FINA World Championships. Br J Sports Med. 2017;51(4):277–282. doi:10.1136/bjsports-2016-096075
117. Di Masi F, Silva GCE, De Mello DB, Szpilman D, Tipton M. Deaths in open water swimming races in Brazil from 2009 to 2019. Int J Exerc Sci. 2022;15(4):1295–1305.
118. Mountjoy M, Junge A, Benjamen S, et al. Competing with injuries: injuries prior to and during the 15th FINA World Championships 2013 (aquatics). Br J Sports Med. 2015;49(1):37–43. doi:10.1136/bjsports-2014-093991
119. Bom H-SH, Jeong YH, Cho S. Injuries and Illness during the 2019 Gwangju FINA and masters world championships in elite and amateur athletes. Chonnam Med J. 2023;59(1):83. doi:10.4068/cmj.2023.59.1.83
120. Mountjoy M, Alonso J-M, Bergeron MF, Dvorak J, Miller S, Migliorini S. Hyperthermic-related challenges in aquatics, athletics, football, tennis and triathlon. Br J Sports Med. 2012;46(11):800–804. doi:10.1136/bjsports-2012-091272
121. Macaluso F, Barone R, Isaacs AW, Farina F, Morici G, Di Felice V. Heat stroke risk for open-water swimmers during long-distance events. Wilderness Environ Med. 2013;24(4):362–365. doi:10.1016/j.wem.2013.04.008
122. Macaluso F, Barone R, Isaacs AW, Farina F, Morici G, Di Felice V. Maximum water temperature limit in open-water swimming events. Letter to the Editor. Wilderness Environ Med. 2014;25(2):245–246. doi:10.1016/j.wem.2013.12.002
123. Asplund CA, Creswell LL. Hypothesised mechanisms of swimming-related death: a systematic review. Br J Sports Med. 2016;50(22):1360–1366. doi:10.1136/bjsports-2015-094722
124. Chamberlain M, Marshall AN, Keeler S. Open water swimming: medical and water quality considerations. Curr Sports Med Rep. 2019;18(4):121–128. doi:10.1249/JSR.0000000000000582
125. Fédération Internationale de Natation Technical. Open Water Swimming Committee. Lausanne, Switzerland: FINA Open Water Swimming Manual; 2020.
126. Murphy M, Polston K, Carroll M, Alm J. Heat injury in open-water swimming: a narrative review. Curr Sports Med Rep. 2021;20(4):193–198. doi:10.1249/JSR.0000000000000829
127. Chalmers S, Shaw G, Mujika I, Jay O. Thermal strain during open-water swimming competition in warm water environments. Front Physiol. 2021;12:785399. doi:10.3389/fphys.2021.785399
128. Martínez IC, Garcia JC. Swimming, Open-Water Swimming, and Diving. In: Rocha Piedade S, Neyret P, Espregueira-Mendes J, Cohen M, Hutchinson MR, editors. Specific Sports-Related Injuries. New York: Springer International Publishing; 2021:415–429.
129. World Aquatics. Lausanne, Switzerland: Competition Regulations; 2024. Available from: https://www.worldaquatics.com/rules/competition-regulations.
130. Yao Y, DiNenna MA, Chen L, Jin S, He S, He J. Hypothesized mechanisms of death in swimming: a systematic review. BMC Sports Sci Med Rehabil. 2024;16(6):1–13. doi:10.1186/s13102-023-00799-w
131. Costill DL, Cahill PJ, Eddy D. Metabolic responses to submaximal exercise in three water temperatures. J Appl Physiol. 1967;22(4):628–632. doi:10.1152/jappl.1967.22.4.628
132. Fujishima K, Shimizu T, Ogaki T, et al. Thermoregulatory responses to low-intensity prolonged swimming in water at various temperatures and treadmill walking on land. J Physiol Anthropol Appl Hum Sci. 2001;20(3):199–206. doi:10.2114/jpa.20.199
133. Galbo H, Houston ME, Christensen NJ, et al. The effect of water temperature on the hormonal response to prolonged swimming. Acta Physiol Scand. 1979;105(3):326–337. doi:10.1111/j.1748-1716.1979.tb06348.x
134. Holmer I, Bergh U. Metabolic and thermal response to swimming in water at varying temperatures. J Appl Physiol. 1974;37(5):702–705. doi:10.1152/jappl.1974.37.5.702
135. Macaluso F, Di Felice V, Boscainoc G, et al. Effects of three different water temperatures on dehydration in competitive swimmers. Sci Sports. 2011;26:265–271. doi:10.1016/j.scispo.2010.10.004
136. Nadel ER, Holmer I, Bergh U, Astrand PO, Stolwijk JA. Energy exchanges of swimming man. J Appl Physiol. 1974;36(4):465–471. doi:10.1152/jappl.1974.36.4.465
137. Mountjoy M, Junge A, Alonso JM, et al. Consensus statement on the methodology of injury and illness surveillance in FINA (aquatic sports). Br J Sports Med. 2015;50(10):590–596. doi:10.1136/bjsports-2015-095686
138. Clarsen B, Pluim BM, Moreno-Pérez V, et al. Methods for epidemiological studies in competitive cycling: an extension of the IOC consensus statement on methods for recording and reporting of epidemiological data on injury and illness in sport 2020. Br J Sports Med. 2021;55(22):1262–1269. doi:10.1136/bjsports-2020-103906
139. O’Connor FG, Adams WB, Madsen CM, et al. Bethesda, MD: managing the collapsed runner: marine corps marathon medical triage and algorithms; 2021. Available from: https://champ.usuhs.edu/sites/default/files/2021-06/MCM%202020%20ALGORITHM%20HANDBOOK%20Final.pdf.
140. World Triathlon Medical Committee. Lausanne, Switzerland: Guidelines for exertional heat illness prevention; 2021. Available from: https://triathlon.org/about/downloads/category/medical.
141. Cramer MN, Gagnon D, Laitano O, Crandall CG. Human temperature regulation under heat stress in health, disease, and injury. Physiol Rev. 2022;102(4):1907–1989. doi:10.1152/physrev.00047.2021
142. Armstrong LE. Rehydration during endurance exercise: challenges, research, options, methods. Nutrients. 2021;13(3):887. doi:10.3390/nu13030887
143. Kenefick RW. Drinking strategies: planned drinking versus drinking to thirst. Sports Med. 2018;48(Suppl 1):31–37. doi:10.1007/s40279-017-0844-6
144. Armstrong LE. Heat exhaustion. In: Adams WM, Jardine JF, editors. Exertional Heat Illness: A Clinical and Evidence-Based Guide. Switzerland: Springer Nature; 2020:81–115.
145. Gaffin SL, Hubbard RW. Pathophysiology of heatstroke. In: Pandolf KB, Burr RE, editors. Medical Aspects of Harsh Environments. Falls Church, VA: U.S. Army Office of the Surgeon General; 2001:161–208.
146. Giersch GEW, Belval LN, Lopez RM. Minor heat illnesses. In: Adams WM, Jardine JF, editors. Exertional Heat Illness: A Clinical and Evidence-Based Guide. Switzerland: Springer Nature; 2020:137–147.
147. Gonzalez-Alonso J, Crandall CG, Johnson JM. The cardiovascular challenge of exercising in the heat. J Physiol. 2008;586(1):45–53. doi:10.1113/jphysiol.2007.142158
148. Millet GP, Vleck VE, Bentley DJ. Physiological differences between cycling and running: lessons from triathletes. Sports Med. 2009;39(3):179–206. doi:10.2165/00007256-200939030-00002
149. Guezennec CY, Vallier JM, Bigard AX, Durey A. Increase in energy cost of running at the end of a triathlon. Eur J Appl Physiol. 1996;73(5):440–445. doi:10.1007/BF00334421
150. Hausswirth C, Bigard AX, Berthelot M, Thomaidis M, Guezennec CY. Variability in energy cost of running at the end of a triathlon and a marathon. Int J Sports Med. 1996;17(8):572–579. doi:10.1055/s-2007-972897
151. Hausswirth C, Lehenaff D. Physiological demands of running during long distance runs and triathlons. Sports Med. 2001;31(9):679–689. doi:10.2165/00007256-200131090-00004
152. Millet GP, Millet GY, Hofmann MD, Candau RB. Alterations in running economy and mechanics after maximal cycling in triathletes: influence of performance level. Int J Sports Med. 2000;21(2):127–132.
153. Adams WC, Mack GW, Langhans GW, Nadel ER. Effects of varied air velocity on sweating and evaporative rates during exercise. J Appl Physiol. 1992;73(6):2668–2674. doi:10.1152/jappl.1992.73.6.2668
154. Gagge AP, Gonzalez RR. Mechanisms of heat exchange: biophysics and physiology. In: Fregly MJ, Blatteis CM, editors. Handbook of Physiology. Oxford, England: Oxford University Press; 1996:45–84.
155. Nybo L. Cycling in the heat: performance perspectives and cerebral challenges. Scand J Med Sci Sports. 2010;20(3):71–79. doi:10.1111/j.1600-0838.2010.01211.x
156. Otani H, Kaya M, Tamaki A, Watson P, Maughan RJ. Air velocity influences thermoregulation and endurance exercise capacity in the heat. Appl Physiol Nutr Metab. 2018;43(2):131–138. doi:10.1139/apnm-2017-0448
157. Cheuvront SN, Kenefick RW. Dehydration: physiology, assessment, and performance effects. Compr Physiol. 2014;4(1):257–285.
158. Armstrong LE, Maresh CM, Gabaree CV, et al. Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake. J Appl Physiol. 1997;82(6):2028–2035. doi:10.1152/jappl.1997.82.6.2028
159. Deschamps A, Levy RD, Cosio MG, Marliss EB, Magder S. Effect of saline infusion on body temperature and endurance during heavy exercise. J Appl Physiol. 1989;66(6):2799–2804. doi:10.1152/jappl.1989.66.6.2799
160. Fortney SM, Nadel ER, Wenger CB, Bove JR. Effect of acute alterations of blood volume on circulatory performance in humans. J Appl Physiol. 1981;50(2):292–298. doi:10.1152/jappl.1981.50.2.292
161. Sawka MN, Young AJ, Francesconi RP, Muza SR, Pandolf KB. Thermoregulatory and blood responses during exercise at graded hypohydration levels. J Appl Physiol. 1985;59(5):1394–1401. doi:10.1152/jappl.1985.59.5.1394
162. Buono MJ, Wall AJ. Effect of hypohydration on core temperature during exercise in temperate and hot environments. Pflugers Arch. 2000;440(3):476–480. doi:10.1007/s004240000298
163. Casa DJ, Armstrong LE, Kenny GP, O’Connor FG, Huggins RA. Exertional heat stroke: new concepts regarding cause and care. Curr Sports Med Rep. 2012;11(3):115–123. doi:10.1249/JSR.0b013e31825615cc
164. Montain SJ, Coyle EF. Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. J Appl Physiol. 1992;73(4):1340–1350. doi:10.1152/jappl.1992.73.4.1340
165. Pryor JL, Périard JD, Pryor RR. Predisposing factors for exertional heat illness. In: Adams WM, Jardine JF, editors. Exertional Heat Illness: A Clinical and Evidence-Based Guide. Switzerland: Springer Nature; 2020:29–57.
166. Costrini AM, Pitt HA, Gustafson AB, Uddin DE. Cardiovascular and metabolic manifestations of heat stroke and severe heat exhaustion. Am J Med. 1979;66(2):296–302. doi:10.1016/0002-9343(79)90548-5
167. Périard JD, Eijsvogels TMH, Daanen HAM. Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies. Physiol Rev. 2021;101(4):1873–1979. doi:10.1152/physrev.00038.2020
168. Adams WM, Stearns RL, Casa DJ. Exertional heat stroke. In: Adams WM, Jardine JF, editors. Exertional Heat Illness: A Clinical and Evidence-Based Guide. Switzerland: Springer Nature; 2020:59–79.
© 2024 The Author(s). This work is published and licensed by Dove Medical Press Limited. The
full terms of this license are available at https://www.dovepress.com/terms.php
and incorporate the Creative Commons Attribution
- Non Commercial (unported, 3.0) License.
By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted
without any further permission from Dove Medical Press Limited, provided the work is properly
attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms.