Influence of aerobic fitness on gastrointestinal barrier integrity and microbial translocation following a fixed-intensi
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ORIGINAL ARTICLE
Influence of aerobic fitness on gastrointestinal barrier integrity and microbial translocation following a fixed‑intensity military exertional heat stress test Henry B. Ogden1 · Joanne L. Fallowfield2 · Robert B. Child3 · Glen Davison4 · Simon C. Fleming5 · Simon K. Delves2 · Alison Millyard1 · Caroline S. Westwood1 · Joseph D. Layden1 Received: 14 April 2020 / Accepted: 30 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose Exertional-heat stress adversely disrupts gastrointestinal (GI) barrier integrity, whereby subsequent microbial translocation (MT) can result in potentially serious health consequences. To date, the influence of aerobic fitness on GI barrier integrity and MT following exertional-heat stress is poorly characterised. Method Ten untrained (UT; VO2max = 45 ± 3 ml·kg−1·min−1) and ten highly trained (HT; VO2max = 64 ± 4 ml·kg−1·min−1) males completed an ecologically valid (military) 80-min fixed-intensity exertional-heat stress test (EHST). Venous blood was drawn immediately pre- and post-EHST. GI barrier integrity was assessed using the serum dual-sugar absorption test (DSAT) and plasma Intestinal Fatty-Acid Binding Protein (I-FABP). MT was assessed using plasma Bacteroides/total 16S DNA. Results UT experienced greater thermoregulatory, cardiovascular and perceptual strain (p 40 °C); central nervous system dysfunction (e.g., delirium, coma); and multiple organ failure (Bouchama and Knochel 2002). In military settings, EHS poses a significant threat to operational performance and can have long-term career/health implications for incapacitated personnel (Epstein et al. 2012). The incidence of EHS in armed forces is estimated to be circa 0.5/1000 cases per person-year in both the United Kingdom (Stacey et al. 2016) and the United States (Army Forces Health Surveillance Centre 2020). This prevalence is primarily attributable to
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European Journal of Applied Physiology
the widespread exposure of highly-motivated individuals to strenuous physical activity, often whilst wearing encapsulating clothing and/or when deployed to hot ambient environments (Epstein et al. 2012). Given these issues, various policies have been published that provide guidance on EHS management (Belval et al. 2018; Military Headquarters of the Surgeon General 2019). However, until recently, little consideration had been given to the relevance of GI-MT within the pathophysiology of EHS (Lim 2018; Ogden et al. 2020a). Various intrinsic (e.g., age) and extrinsic (e.g., clothing) risk factors have been consistently advocated to predispose military personnel to EHS (Westwood et al. 2020). Aerobic fitness is one well-characterised intrinsic risk factor, whereby failure of a recent mandatory fitness test, has been associated with a 2–8-fold increased odds-ratio of EHS in comparison to a successful test (Wallace et al. 2006; Moore et al. 2016; Nelson et al. 2018). Improved cardiovascular stability (e.g., plasma volume) and cellular thermotolerance (e.g., intracellular heat shock
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