Exercise hyperthermia induces greater changes in gastrointestinal permeability than equivalent passive hyperthermia

Edward Walter, Peter Watt, Oliver Gibson, Ashley Willmott, Dominic Mitchell, Robert Moreton, Neil Maxwell

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    Hyperthermia and exertional heat illness increase gastrointestinal (GI) permeability, although whether the latter is only via hyperthermia is unclear. The aim of this pilot study was to determine whether different changes in GI permeability, characterized by an increased plasma lactulose:rhamnose concentration ratio ([L:R]), occurred in exercise hyperthermia in comparison to equivalent passive hyperthermia. Six healthy adult male participants (age 25 ± 5 years, mass 77.0 ± 6.7 kg, height 181 ± 6 cm, peak oxygen uptake [(Formula presented.)] 48 ± 8 ml.kg −1.min −1) underwent exercise under hot conditions (Ex-Heat) and passive heating during hot water immersion (HWI). Heart rate (HR), rectal temperature (T CORE), rating of perceived exertion (RPE), and whole-body sweat loss (WBSL) were recorded throughout the trials. The L:R ratio, peak HR, change in HR, and change in RPE were higher in Ex-Heat than HWI, despite no differences in trial duration, peak core temperature or WBSL. L:R was strongly correlated (p < 0.05) with HR peak (r = 0.626) and change in HR (r = 0.615) but no other variable. The greater L:R in Ex-Heat, despite equal T CORE responses to HWI, indicates that increased cardiovascular strain occurred during exercise, and exacerbates hyperthermia-induced GI permeability at the same absolute temperature.

    Original languageEnglish
    Article numbere14945
    JournalPhysiological Reports
    Issue number16
    Publication statusPublished - 19 Aug 2021

    Bibliographical note

    This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited


    • cardiovascular
    • exercise
    • gastrointestinal
    • heat illness
    • hyperthermia
    • permeability


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