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The effect of prolonged interval and continuous exercise in the heat on circulatory markers of intestinal barrier integrity

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The purpose of this study was to determine the effect of prolonged high-intensity interval (INT) and moderate-intensity continuous (CONT) treadmill exercise in the heat on markers of enterocyte injury and bacterial endotoxin translocation.


Nine males completed 2 h of work-matched exercise in the heat (40 °C and 15% RH) as either INT (2 min at 80% VO2max and 3 min at 30% VO2max) or CONT (~ 50% of VO2max). Blood samples collected pre- and post-exercise were assayed for intestinal fatty acid-binding protein (I-FABP), claudin-3 (CLDN-3), and lipopolysaccharide-binding protein (LBP).


I-FABP was significantly increased from pre- to post-exercise in CONT (913.96 ± 625.13 to 1477.26 ± 760.99 pg•mL−1; p = 0.014, d = 0.766) and INT (714.59 ± 470.27 to 1547.93 ± 760.99 pg•mL−1; p = 0.001, d = 1.160). Pre- to post-exercise changes in I-FABP were not different between CONT and INT (p = 0.088, d = 0.414). LBP was significantly increased from pre- to post-exercise in INT (15.94 ± 2.90 to 17.35 ± 3.26 μg•mL−1; p = 0.028, d = 0.459) but not CONT (18.11 ± 5.35 to 16.93 ± 5.39 μg•mL−1; p = 0.070, d = 0.226), and pre- to post-exercise changes in LBP were higher in the INT compared to CONT (p < 0.001, d = 1.160). No significant changes were detected from pre- to post-exercise for CLDN-3 in CONT (14.90 ± 2.21 to 15.30 ± 3.07 μg•mL−1) or INT (15.55 ± 1.63 to 16.41 ± 2.11 μg•mL−1) (p > 0.05).


We conclude that prolonged exercise in the heat induces enterocyte injury, but interval (or intermittent) exercise may cause greater bacterial endotoxin translocation which may increase the risk for local and systemic inflammation.

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ηp 2 :

Partial eta squared


Area under the curve




Coefficient of variation


Cohen’s d


Enzyme-linked immunosorbent assays


Heart rate


Intestinal fatty acid-binding protein


Lipopolysaccharide-binding protein




Physiological strain index


Relative humidity


Standard deviation

Trectal :

Rectal temperature


Urine specific gravity


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Partial funding for this study was provided by the Graduate and Professional Student Association at the University of New Mexico.

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Authors and Affiliations



ZM, FA, and JH conceived the research. ZM, JH, CM, MD, OL, and FA designed the experiments. ZM, JH, JD, ZL, QB, ZF, AW, and FA collected data. ZM, JH, ZL, QB, CM, MD, OL, and FA analyzed data. ZM and JH drafted the manuscript. All authors contributed to the final manuscript.

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Correspondence to Zachary McKenna.

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The authors declare that they have no conflicts of interest.

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This study was approved by the Institutional Review Board at the University of New Mexico Main Campus.

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All participants have read and signed an informed consent prior to participating in the study.

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Communicated by Narihiko kondo.

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McKenna, Z., Houck, J., Ducharme, J. et al. The effect of prolonged interval and continuous exercise in the heat on circulatory markers of intestinal barrier integrity. Eur J Appl Physiol 122, 2651–2659 (2022).

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