Exertional-heat stress-associated gastrointestinal perturbations during Olympic sports: Management strategies for athletes preparing and competing in the 2020 Tokyo Olympic Games

Abstract

Exercise-induced gastrointestinal syndrome (EIGS) is a common characteristic of exercise. The causes appear to be multifactorial in origin, but stem primarily from splanchnic hypoperfusion and increased sympathetic drive. These primary causes can lead to secondary outcomes that include increased intestinal epithelial injury and gastrointestinal hyperpermeability, systemic endotoxemia, and responsive cytokinemia, and impaired gastrointestinal function (i.e. transit, digestion, and absorption). Impaired gastrointestinal integrity and functional responses may predispose individuals, engaged in strenuous exercise, to gastrointestinal symptoms (GIS), and health complications of clinical significance, both of which may have exercise performance implications. There is a growing body of evidence indicating heat exposure during exercise (i.e. exertional-heat stress) can substantially exacerbate these gastrointestinal perturbations, proportionally to the magnitude of exertional-heat stress, which is of major concern for athletes preparing for and competing in the upcoming 2020 Tokyo Olympic Games. To date, various hydration and nutritional strategies have been explored to prevent or ameliorate exertional-heat stress associated gastrointestinal perturbations. The aims of the current review are to comprehensively explore the impact of exertional-heat stress on markers of EIGS, examine the evidence for the prevention and (or) management of EIGS in relation to exertional-heat stress, and establish best-practice nutritional recommendations for counteracting EIGS and associated GIS in athletes preparing for and competing in Tokyo 2020.

Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments

“…The impact of exercise in hot environments on the gastrointestinal tract merits special attention, as it contributes to the pathophysiology of exertional heat illnesses (EHIs) and/or gastrointestinal complications that compromise the athlete's capacity to address their nutritional goals and optimize thermoregulation. Prolonged exercise in hot ambient conditions, resulting in a core temperature ≥39.0°C, exacerbates the perturbations to gastrointestinal integrity, function, and systemic responses compared with exercise in cooler conditions (Costa et al, 2019a). Such perturbations, known as exercise-induced gastrointestinal syndrome, have been linked to performance-debilitating gastrointestinal symptoms and clinical implications ranging from mild inconvenience to fatality (Costa et al, 2017).…”

“…Concomitantly, an increase in sympathetic activation reduces overall gastrointestinal functional capacity, possibly via suppressed myenteric and submucosal plexus activity (Costa et al, 2017;Horner et al, 2015;Strid et al, 2011). The initiation of these physiological responses is dependent on the exercise stress per se (i.e., intensity, duration, and modality) but is exacerbated with heat exposure (Costa et al, 2017(Costa et al, , 2019a. The secondary outcomes of these exercise-associated gastrointestinal abnormalities include mucosal erosion, epithelial cell injury and dysfunction, tight junction damage and dysfunction, luminal bacterial endotoxin translocation, local epithelium and systemic Figure 2 -Schematic description of exercise-induced gastrointestinal syndrome: Physiological changes in circulatory and neuroendocrine pathways at the onset of exercise resulting in perturbed gastrointestinal integrity and function, and may lead to gastrointestinal symptoms, and/or acute or chronic health complications.…”

“…c Increase in neuroendocrine activation and suppressed submucosal and myenteric plexus result in epithelial cell loss and subsequent perturbed tight junctions (Holzer et al, 2017;Barrett, 2012 innate/adaptive immune cell and inflammatory responses, suppressed gastric emptying, and suppressed nutrient digestion and absorption (Costa et al, 2017). Current and emerging evidence shows that hot and/or humid ambient conditions play a key role in determining the magnitude of exercise-induced gastrointestinal syndrome (Costa et al, 2019a;Pires et al, 2017Pires et al, , 2018.…”

“…Endurance (30 min to 4 hr) and ultra-endurance (>4 hr) exercise encompasses a range of exercise modalities, terrain and environments. Sustained elevations in thermal strain during endurance exercise present unique physiological challenges to athletes, including large accumulated fluid and electrolyte deficits (Shirreffs & Sawka, 2011), increased risk of gastrointestinal disturbance during exercise (Costa et al, 2019a), and EHI (Leon & Bouchama, 2015). The unique challenges of endurance sports include the potential for large variations in ambient conditions within an event, as well as increased emphasis on during-event nutrition and hydration strategies due to the continuous nature of most sports.…”

Heat acclimation attenuates the increased sensations of fatigue reported during acute exercise-heat stress

“…interleukin-6 [IL-6]) and/or stress responses (e.g. cortisol) during HA [10,24,26,27] have been investigated, this data in conjunction with the sensations of fatigue has not been reported and may be an important element of an athlete-focused wellbeing monitoring strategy [28,29]. This requires attention given higher concentrations of IL-6 and cortisol appear to augment perceived fatigue and subsequently impair aerobic endurance [30] and cognitive performance [8], with evidence indicating correlations between perceived fatigue and cortisol concentrations, and body mass loss (e.g.…”