Once- and twice-daily heat acclimation confer similar heat adaptations, inflammatory responses and exercise tolerance improvements

Ashley Willmott, Mark Hayes, Carl James, Jeanne Dekerle, Oliver Gibson, Neil Maxwell

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This experiment aimed to investigate the efficacy of twice-daily, nonconsecutiveheat acclimation (TDHA) in comparison to once-daily heatacclimation (ODHA) and work matched once- or twice-daily temperateexercise (ODTEMP, TDTEMP) for inducing heat adaptations, improvedexercise tolerance, and cytokine (immune) responses. Forty males,matched biophysically and for aerobic capacity, were assigned to ODHA,TDHA, ODTEMP or TDTEMP. Participants completed a cycling gradedexercise test, heat acclimation state test and a time to task failure(TTTF) at 80% peak power output in temperate (TTTFTEMP: 22°C/40%RH) and hot conditions (TTTFHOT: 38°C/20% RH), before and after 10-sessions (60-min of cycling at ~2W.kg-1) in 45°C/20% RH (ODHA andTDHA) or 22°C/40% RH (ODTEMP or TDTEMP). Plasma IL-6, TNF-α andcortisol were measured pre- and post-sessions 1, 5 and 10. ODHA andTDHA induced equivalent heat adaptations (P<0.05) (resting rectaltemperature [-0.28±0.22, -0.28±0.19°C], heart rate [-10±3, -10±4b.min-1] and plasma volume expansion [+10.1±5.6, +8.5±3.1%]) andimproved heat acclimation state (sweat setpoint [-0.22±0.18, -0.22±0.14°C] and gain [+0.14±0.10, +0.15±0.07g.sec-1.°C-1]).TTTFHOT increased (P<0.001) following ODHA (+25±4%) and TDHA(+24±10%), but not ODTEMP (+5±14%) or TDTEMP (+5±17%).TTTFTEMP did not improve (P>0.05) following ODHA (+14±4%), TDHA(14±8%), ODTEMP (9±10%) or TDTEMP (8±13%). Acute (P<0.05) butno chronic (P>0.05) increases were observed in IL-6, TNF-α or cortisolduring ODHA and TDHA, or ODTEMP and TDTEMP. Once- and twice-dailyheat acclimation conferred similar magnitudes of heat adaptation andexercise tolerance improvements, without differentially altering immune function, thus non-consecutive TDHA provides an effective, logisticallyflexible method of HA, benefitting individuals preparing for exercise-heatstress.
Original languageEnglish
Article numbere13936
JournalPhysiological Reports
Issue number24
Publication statusPublished - 21 Dec 2018

Bibliographical note

© 2018 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.
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.


  • heat acclimatization
  • heat adaptation
  • immune
  • performance
  • thermoregulation
  • training


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