Study of Thermoregulatory Processes in Ultra-endurance Runners in a Hot and Humid Environment

Intensive Sport

Human beings are characterized by their extraordinary ability to thermoregulate. During a physical exercise, only 20% of the energy provided by the substrates is converted into muscular mechanical work. The remaining 80% is released as heat. In temperate environments, so-called metabolic heat is dissipated by several physical phenomena (radiation, conduction, convection and evaporation). However, if the dissipation capacity (in a hot and humid environment for example) is lower than the production of metabolic heat, the body temperature increases progressively until exercise stops or heat-related pathologies develop. This pathological entity defined by the acronym EHI for Exertional Heat Illness gather a wide spectrum of clinical forms ranging from oedema or heat rash, to muscle cramps, to syncope; up to more serious forms such as heat exhaustion or heat stroke during exercise. Heatstroke during exercise is the second most common cause of death in athletes after heart disease. However, the results of the epidemiological studies and the recommendations are limited to events with effort durations or distances not exceeding those of the marathon. They therefore do not consider ultra-endurance disciplines. These disciplines, defined by durations of effort of at least 6 hours, have specific characteristics (duration of effort, intensity, steep gradients, exotic destinations, extreme environments) which means that extrapolation of the results and knowledge of the physiology of thermoregulation from classic endurance events, such as marathons, to ultra-endurance events is hazardous. There are therefore significant areas of uncertainty in understanding the thermoregulatory function, prevalence of EHI (Exertional Heat Illness) and health implications of ultra-endurance running in a hot environment. This is the context of ERUPTION-2.

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