Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies

Abstract

A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat, by examining the benefits of heat acclimation, cooling strategies and hyperhydration. Finally, contemporary controversies are summarized and future research directions provided.

Core Temperature Measurement—Principles of Correct Measurement, Problems, and Complications

“…Sweating starts immediately after the onset of exercise, which is most likely due to various central mechanisms, including the baroreceptor reflex [8]. With heat acclimatization, sweat volume can be as high as 2-3 l/h, mainly due to lowering the temperature threshold for sweating and the redistribution of sweat secretion more peripherally [9].…”

Beat the heat: How to become a gold medalist at the Tokyo Olympics

“…This combination will presumably result in the most challenging environmental conditions ever observed during the Olympic Games [1], leading to significant heat stress for athletes competing in outdoor disciplines. Hence, significant performance decrements can be expected and athletes are at increased risk for the development of heat-related illnesses [2]. That these heat stress induced consequences are not purely theoretical became clear during the 2019 IAAF World Championships in Doha, Qatar.…”

“…Pre-cooling and per-cooling interventions attenuate core temperature during exercise and are known to improve exercise performance in the heat [4]. And a planned hydration strategy can prevent the occurrence of dehydration and associated performance loss [2]. Outcomes of these scientific studies are translated to various practical advices for athletes and coaches.…”

Performance and thermoregulation of Dutch Olympic and Paralympic athletes exercising in the heat: Rationale and design of the Thermo Tokyo study: The journalTemperaturetoolbox

“…A recent study of athletes competing at the 2016 UCI Road World Championships in Qatar revealed that 57% of participating athletes had a history of heat-related symptoms and 17% a history of exertional heat illness [ 14 ]. It has been demonstrated that performance levels are markedly impaired during exercise in the heat [ 15 ]. For example, the maximal aerobic capacity (i.e.…”