The effect of cycling in the heat on gastrointestinal-induced damage and neuromuscular fatigue
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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.
KeywordsThermoregulation Endotoxemia Cycling Central fatigue Hyperthermia
Half relaxation time
Central nervous system
Coefficient of variation
Enzyme-linked immunosorbent assay
Intestinal fatty acid-binding protein
Interleukin 1 beta
Markov chain Monte Carlo
Maximum voluntary contraction
Maximal aerobic power output
Rating of perceived exertion
Rate of relaxation
Rate of torque development
Tumour necrosis factor alpha
Time to peak torque
Mean skin temperature
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.
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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