European Journal of Applied Physiology

, Volume 119, Issue 8, pp 1829–1840 | Cite as

The effect of cycling in the heat on gastrointestinal-induced damage and neuromuscular fatigue

  • John O. OsborneEmail author
  • Ian B. Stewart
  • Kenneth W. Beagley
  • Geoffrey M. Minett
Original Article



This study investigated the effect of exercise in the heat on neuromuscular function, gastrointestinal damage, endotoxemia and inflammatory cytokines.


Eight male cyclists completed two 60 min cycling trials in both hot (HOT 34.5 ± 0.1 °C and 53 ± 1% relative humidity) and temperate environments (CON 20.2 ± 0.3 °C and 55 ± 3% relative humidity). The cycling task comprised of alternating 3 min intervals at a moderate-vigorous intensity (50% and 70% of maximum power output; Pmax) for 30 min, followed by 30 min at moderate intensity (40–50% Pmax). Neuromuscular function was assessed at pre-, post-exercise and 60 min post-exercise. Circulating levels of endotoxins, inflammatory cytokines and markers of gut permeability and damage were also collected at these time points. Heart rate, core temperature, skin temperature, perceived exertion, thermal sensation and comfort were also measured.


Post-exercise voluntary activation of HOT (87.9% [85.2, 90.8]) was statistically lower (mean difference − 2.5% [− 4.5, − 0.5], d = 2.50) than that of CON (90.5% [87.8, 93.2]). The HOT trial resulted in statistically elevated (+ 69%) markers of gastrointestinal damage compared to CON (mean difference 0.424 ng mL−1 [0.163, 0.684, d = − 3.26]), although this was not observed for endotoxin, other inflammatory markers, or gastrointestinal permeability.


This research provides evidence that short-duration cycling in the heat results in sub-optimal neuromuscular activation and increased expression of gastrointestinal damage markers, without a simultaneous elevation in circulating endotoxins or pro-inflammatory cytokines.


Thermoregulation Endotoxemia Cycling Central fatigue Hyperthermia 



Half relaxation time


Contraction duration


Credible interval


Claudin 3


Central nervous system


Coefficient of variation


Enzyme-linked immunosorbent assay




Heart rate


Intraclass correlation


Intestinal fatty acid-binding protein


Interleukin 1 beta


Markov chain Monte Carlo


Mean difference


Maximum voluntary contraction


Maximal aerobic power output


Peak torque


Rating of perceived exertion


Rate of relaxation


Rate of torque development


Core temperature


Tumour necrosis factor alpha


Time to peak torque


Mean skin temperature


Voluntary activation


Vastus lateralis


Vastus medialis


Maximal aerobic capacity



The authors sincerely thank Mr Logan Trim (Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia) for his technical assistance with the immunoassay analysis.

Author contributions

Study conception and design: JOO, IBS, KWB and GMM. Data collection: JOO. Data analysis: JOO, IBS and GMM. Contributed materials/tools: GMM, KWB and IBS. Wrote manuscript: JOO. Drafted and approved manuscript: JOO, IBS, KWB and GMM.



Compliance with ethical standards

Conflict of interests

The authors have no conflict of interests to declare.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.School of Exercise and Nutrition SciencesQueensland University of TechnologyBrisbaneAustralia
  2. 2.Institute of Health and Biomedical InnovationQueensland University of TechnologyBrisbaneAustralia
  3. 3.School of Biomedical SciencesQueensland University of TechnologyBrisbaneAustralia

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