Heat Stroke Risk for Open-Water Swimmers During Long-Distance Events

Hyperthermia and Exertional Heatstroke During Running, Cycling, Open Water Swimming, and Triathlon Events

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.

Environmental challenges facing athletes, stakeholders and spectators at Paris 2024 Olympic and Paralympic Games: an evidence-based review of mitigation strategies and recommendations

The upcoming Paris 2024 Olympic and Paralympic Games could face environmental challenges related to heat, air quality and water quality. These challenges will pose potential threats to athletes and impact thousands of stakeholders and millions of spectators. Recognising the multifaceted nature of these challenges, a range of strategies will be essential for mitigating adverse effects on participants, stakeholders and spectators alike. From personalised interventions for athletes and attendees to comprehensive measures implemented by organisers, a holistic approach is crucial to address these challenges and the possible interplay of heat, air and water quality factors during the event. This evidence-based review highlights various environmental challenges anticipated at Paris 2024, offering strategies applicable to athletes, stakeholders and spectators. Additionally, it provides recommendations for Local Organising Committees and the International Olympic Committee that may be applicable to future Games. In summary, the review offers solutions for consideration by the stakeholders responsible for and affected by the anticipated environmental challenges at Paris 2024.

Thermal Sensation After the 10-km Open-Water Swimming in Cool Water Depends on the Skin's Thermal Sensitivity Rather Than Core Temperature

PURPOSE

To assess the core temperature fluctuations during 10-km open-water swimming (OWS) in cool water and the relationship between thermal sensation (TS) after 10-km OWS, core temperature, and local skin thermal sensitivity.

METHODS

Nine highly trained OWS swimmers (4 female; age 22 [3] y) completed a single 10-km trial in cool water (22.3 °C) wearing swimsuits for OWS. During the trial, core temperature was continuously recorded via ingestible temperature sensors, and TS after trial was also measured. Then, local skin warm/cool sensitivity was measured in the forearm.

RESULTS

All swimmers completed the 10-km OWS. Mean swimming speed for males and females were 1.39 (1.37-1.42 m/s) and 1.33 m/s (1.29-1.38 m/s), respectively. Core temperature increased in 8 out of 9 swimmers during 10-km OWS (P = .047), with an average increase of 0.8 °C. TS after 10-km OWS varied among swimmers. There were no correlations between post-OWS TS and post-OWS core temperature (P = .9333), whereas there was a negative correlation between post-OWS TS and local skin cool sensitivity (P = .0056).

CONCLUSION

These results suggest that core temperature in elite swimmers might not decrease during 10-km OWS in the cool water temperature of official OWS. In addition, individual differences in TS after 10-km OWS may be related to skin cool sensitivity rather than core temperature.

Exertional heat stroke in sport and the military: epidemiology and mitigation

NEW FINDINGS

What is the topic of this review? Exertional heat stroke epidemiology in sport and military settings, along with common risk factors and strategies and policies designed to mitigate its occurrence. What advances does it highlight? Individual susceptibility to exertional heat stroke risk is dependent on the interaction of intrinsic and extrinsic factors. Heat policies in sport should assess environmental conditions, as well as the characteristics of the athlete, clothing/equipment worn and activity level of the sport. Exertional heat stroke risk reduction in the military should account for factors specific to training and personnel.

ABSTRACT

Exertional heat illness occurs along a continuum, developing from the relatively mild condition of muscle cramps, to heat exhaustion, and in some cases to the life-threatening condition of heat stroke. The development of exertional heat stroke (EHS) is associated with an increase in core temperature stemming from inadequate heat dissipation to offset the rate of metabolically generated heat. Susceptibility to EHS is linked to the interaction of several factors including environmental conditions, individual characteristics, health conditions, medication and drug use, behavioural responses, and sport/organisational requirements. Two settings in which EHS is commonly observed are competitive sport and the military. In sport, the exact prevalence of EHS is unclear due to inconsistent exertional heat illness terminology, diagnostic criteria and data reporting. In contrast, exertional heat illness surveillance in the military is facilitated by standardised case definitions, a requirement to report all heat illness cases and a centralised medical record repository. To mitigate EHS risk, several strategies can be implemented by athletes and military personnel, including heat acclimation, ensuring adequate hydration, cold-water immersion and mandated work-to-rest ratios. Organisations may also consider developing sport or military task-specific heat stress policies that account for the evaporative heat loss requirement of participants, relative to the evaporative capacity of the environment. This review examines the epidemiology of EHS along with the strategies and policies designed to reduce its occurrence in sport and military settings. We highlight the nuances of identifying individuals at risk of EHS and summarise the benefits and shortcomings of various mitigation strategies.

Relative changes in brain and kidney biomarkers with Exertional Heat Illness during a cool weather marathon

Background

Medical personnel may find it challenging to distinguish severe Exertional Heat Illness (EHI), with attendant risks of organ-injury and longer-term sequalae, from lesser forms of incapacity associated with strenuous physical exertion. Early evidence for injury at point-of-incapacity could aid the development and application of targeted interventions to improve outcomes. We aimed to investigate whether biomarker surrogates for end-organ damage sampled at point-of-care (POC) could discriminate EHI versus successful marathon performance.

Methods

Eight runners diagnosed as EHI cases upon reception to medical treatment facilities and 30 successful finishers of the same cool weather marathon (ambient temperature 8 rising to 12 ºC) were recruited. Emerging clinical markers associated with injury affecting the brain (neuron specific enolase, NSE; S100 calcium-binding protein B, S100β) and renal system (cystatin C, cysC; kidney-injury molecule-1, KIM-1; neutrophil gelatinase-associated lipocalin, NGAL), plus copeptin as a surrogate for fluid-regulatory stress, were sampled in blood upon marathon collapse/completion, as well as beforehand at rest (successful finishers only).

Results

Versus successful finishers, EHI showed significantly higher NSE (10.33 [6.37, 20.00] vs. 3.17 [2.71, 3.92] ug.L-1, P<0.0001), cysC (1.48 [1.10, 1.67] vs. 1.10 [0.95, 1.21] mg.L-1, P = 0.0092) and copeptin (339.4 [77.0, 943] vs. 18.7 [7.1, 67.9] pmol.L-1, P = 0.0050). Discrimination of EHI by ROC (Area-Under-the-Curve) showed performance that was outstanding for NSE (0.97, P<0.0001) and excellent for copeptin (AUC = 0.83, P = 0.0066).

Conclusions

As novel biomarker candidates for EHI outcomes in cool-weather endurance exercise, early elevations in NSE and copeptin provided sufficient discrimination to suggest utility at point-of-incapacity. Further investigation is warranted in patients exposed to greater thermal insult, followed up over a more extended period.

Thermal Strain During Open-Water Swimming Competition in Warm Water Environments

Open-water swim racing in warm water is associated with significant physiological strain. However, existing international policy that governs safe participation during competition relies only on a fixed water temperature threshold for event cancellation and has an unclear biophysical rationale. The current policy does not factor other environmental factors or race distance, nor provide a stratification of risk (low, moderate, high, or extreme) prior to the threshold for cancellation. Therefore, the primary aim of this Perspectives article is to highlight considerations for the development of modernized warm-water competition policies. We highlight current accounts (or lack thereof) of thermal strain, cooling interventions, and performance in warm-water swimming and opportunities for advancement of knowledge. Further work is needed that systematically evaluate real-world thermal strain and performance during warm water competition (alongside reports of environmental conditions), novel preparatory strategies, and in-race cooling strategies. This could ultimately form a basis for future development of modernized policies for athlete cohorts that stratifies risk and mitigation strategies according to important environmental factors and race-specific factors (distance).

Heat Injury in Open-Water Swimming: A Narrative Review

ABSTRACT

Swimming is one of the most popular sports in the world with open-water swimming (OWS) gaining more and more prominence since being featured in the Federation Internationale De Natation World Aquatics Championships in 1992 and the Olympic Games in 2000. The aim of this review is to analyze the existing literature on heat injury in OWS. Relevant literature was located via computer-generated citations during November of 2020 through online computer searches of multiple major databases. Athletes participating in OWS are exposed to environmental conditions that place them at risk for unique medical conditions such as heat injury. Clinicians providing care for OWS athletes should be educated and trained to recognize these conditions and minimize risks to optimize athlete safety. This article identifies medical challenges related to heat injury in OWS while investigating water temperature recommendations, physiological effects of hyperthermia, risk mitigation strategies, and treatment measures.

Physiological Responses to Swimming Repetitive "Ice Miles"

ABSTRACT

Knechtle, B, Stjepanovic, M, Knechtle, C, Rosemann, T, Sousa, CV, and Nikolaidis, PT. Physiological responses to swimming repetitive "Ice Miles." J Strength Cond Res 35(2): 487-494, 2021-"Ice Mile" swimming (i.e., 1,608 m in water of below 5° C) is becoming increasingly popular. Since the foundation of the International Ice Swimming Association (IISA) in 2009, official races are held as World Cup Races and World Championships. Ice swimming was a demonstration sport at the 2014 Winter Olympics in Sochi, Russia. This case study aimed to identify core body temperature and selected hematological and biochemical parameters before and after repeated "Ice Miles." An experienced ice swimmer completed 6 consecutive Ice Miles within 2 days. Three Ice Miles adhered to the strict criteria for the definition of Ice Miles, whereas the other 3 were very close (i.e., 5.2, 6.1, and 6.6° C) to the temperature limit. Swimming times, changes in core body temperatures, and selected urinary and hematological parameters were recorded. The athlete showed after each Ice Mile a metabolic acidosis (i.e., an increase in lactate and TCO2; a decrease in base excess and HCO3-) and an increase in blood glucose, cortisol, and creatine kinase concentration. The decrease in pH correlated significantly and negatively with the increase in cortisol level, indicating that this intense exercise causes a metabolic stress. The change in core body temperature between start and finish was negatively associated with metabolic acidosis. The increase in creatine kinase suggests skeletal muscle damages due to shivering after an Ice Mile. For athletes and coaches, swimming in cold water during Ice Miles leads to a metabolic acidosis, which the swimmer tries to compensate with a respiratory response. Considering the increasing popularity of ice swimming, the findings have practical value for swimmers and practitioners (e.g., coaches, exercise physiologists, and physicians) working with them because our results provide a detailed description of acute physiological responses to repeated swimming in cold conditions. These findings are of importance for athletes and coaches for National Championships and World Championships in Ice Swimming following the IISA rules.

Hypothesised mechanisms of swimming-related death: a systematic review

BACKGROUND

Recent reports from triathlon and competitive open-water swimming indicate that these events have higher rates of death compared with other forms of endurance sport. The potential causal mechanism for swimming-related death is unclear.

OBJECTIVE

To examine available studies on the hypothesised mechanisms of swimming-related death to determine the most likely aetiologies.

MATERIAL AND METHODS

MEDLINE, EMBASE and the Cochrane Database of Systematic Reviews (1950 to present) were searched, yielding 1950 potential results, which after title and citation reviews were reduced to 83 possible reports. Studies included discussed mechanisms of death during swimming in humans, and were Level 4 evidence or higher.

RESULTS

A total of 17 studies (366 total swimmers) were included for further analysis: 5 investigating hyperthermia/hypothermia, 7 examining cardiac mechanisms and responses, and 5 determining the presence of pulmonary edema. The studies provide inconsistent and limited-quality or disease-oriented evidence that make definitive conclusions difficult.

CONCLUSIONS

The available evidence is limited but may suggest that cardiac arrhythmias are the most likely aetiology of swimming-related death. While symptoms of pulmonary edema may occur during swimming, current evidence does not support swimming-induced pulmonary edema as a frequent cause of swimming-related death, nor is there evidence to link hypothermia or hyperthermia as a causal mechanism. Further higher level studies are needed.

Impact of high ambient temperature on unintentional injuries in high-income countries: a narrative systematic literature review

OBJECTIVES

Given the likelihood of increased hot weather due to climate change, it is crucial to have prevention measures in place to reduce the health burden of high temperatures and heat waves. The aim of this review is to summarise and evaluate the evidence on the effects of summertime weather on unintentional injuries in high-income countries.

DESIGN

3 databases (Global Public Health, EMBASE and MEDLINE) were searched by using related keywords and their truncations in the title and abstract, and reference lists of key studies were scanned. Studies reporting heatstroke and intentional injuries were excluded.

RESULTS

13 studies met our inclusion criteria. 11 out of 13 studies showed that the risk of unintentional injuries increases with increasing ambient temperatures. On days with moderate temperatures, the increased risk varied between 0.4% and 5.3% for each 1 °C increase in ambient temperature. On extreme temperature days, the risk of injuries decreased. 2 out of 3 studies on occupational accidents found an increase in work-related accidents during high temperatures. For trauma hospital admissions, 6 studies reported an increase during hot weather, whereas 1 study found no association. The evidence for impacts on injuries by subgroups such as children, the elderly and drug users was limited and inconsistent.

CONCLUSIONS

The present review describes a broader range of types of unintentional fatal and non-fatal injuries (occupational, trauma hospital admissions, traffic, fire entrapments, poisoning and drug overdose) than has previously been reported. Our review confirms that hot weather can increase the risk of unintentional injuries and accidents in high-income countries. The results are useful for injury prevention strategies.