Temperate performance and metabolic adaptations following endurance training performed under environmental heat stress

Ed Maunder*, Daniel J. Plews, Gareth A. Wallis, Matthew J. Brick, Warren B. Leigh, Wee Leong Chang, Casey M. Watkins, Andrew E. Kilding

*Corresponding author for this work

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Endurance athletes are frequently exposed to environmental heat stress during training. We investigated whether exposure to 33°C during training would improve endurance performance in temperate conditions and stimulate mitochondrial adaptations. Seventeen endurance-trained males were randomly assigned to perform a 3-week training intervention in 18°C (TEMP) or 33°C (HEAT). An incremental test and 30-min time-trial preceded by 2-h low-intensity cycling were performed in 18°C pre- and post-intervention, along with a resting vastus lateralis microbiopsy. Training was matched for relative cardiovascular demand using heart rates measured at the first and second ventilatory thresholds, along with a weekly “best-effort” interval session. Perceived training load was similar between-groups, despite lower power outputs during training in HEAT versus TEMP (p <.05). Time-trial performance improved to a greater extent in HEAT than TEMP (30 ± 13 vs. 16 ± 5 W, N = 7 vs. N = 6, p =.04), and citrate synthase activity increased in HEAT (fold-change, 1.25 ± 0.25, p =.03, N = 9) but not TEMP (1.10 ± 0.22, p =.22, N = 7). Training-induced changes in time-trial performance and citrate synthase activity were related (r =.51, p =.04). A group × time interaction for peak fat oxidation was observed (Δ 0.05 ± 0.14 vs. −0.09 ± 0.12 g·min−1 in TEMP and HEAT, N = 9 vs. N = 8, p =.05). Our data suggest exposure to moderate environmental heat stress during endurance training may be useful for inducing adaptations relevant to performance in temperate conditions.

Original languageEnglish
Article numbere14849
Number of pages14
JournalPhysiological reports
Issue number9
Publication statusPublished - 12 May 2021

Bibliographical note

Funding Information:
E.M. was supported by an Education New Zealand International Doctoral Research Scholarship. No other sources of funding were used in the preparation of this manuscript.

Publisher Copyright:
© 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society


  • adaptation
  • endurance training
  • heat stress
  • mitochondria
  • performance

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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