Charlotte E Stevens, Joseph T Costello, Michael J Tipton, Ella F Walker, Alex A M Gould, John S Young, Ben J Lee, Thomas B Williams, Fiona A Myers, Jo Corbett
{"title":"Effect of condensed heat acclimation on thermophysiological adaptations, hypoxic cross-tolerance, exercise performance, and deacclimation.","authors":"Charlotte E Stevens, Joseph T Costello, Michael J Tipton, Ella F Walker, Alex A M Gould, John S Young, Ben J Lee, Thomas B Williams, Fiona A Myers, Jo Corbett","doi":"10.1152/japplphysiol.00775.2024","DOIUrl":null,"url":null,"abstract":"<p><p>Short duration heat acclimation (HA) (≤5 daily heat exposures) elicits incomplete adaptation compared with longer interventions, possibly due to the lower accumulated thermal \"dose.\" It is unknown if matching thermal \"dose\" over a shorter timescale elicits comparable adaptation to a longer intervention. Using a parallel-groups design, we compared: <i>1)</i> \"condensed\" HA (CHA; <i>n</i> = 17 males) consisting of 4 × 75 min·day<sup>-1</sup> heat exposures [target rectal temperature (<i>T</i><sub>rec</sub>) <i>=</i> 38.5 °C] for two consecutive days, with <i>2)</i> \"traditional\" HA (THA; <i>n</i> = 15 males) consisting of 1 × 75 min·day<sup>-1</sup> heat exposure (target <i>T</i><sub>rec</sub> = 38.5°C) for eight consecutive days. Physiological responses to exercise heat stress, hypoxia, and normoxic exercise performance were evaluated pre- and postintervention. Thermal (<i>T</i><sub>rec</sub> over final 45 min: CHA = 38.45 ± 0.17°C, THA = 38.53 ± 0.13°C, <i>P</i> = 0.126) and cardiovascular strain were not different during interventions, indicating similar thermal \"dose,\" although CHA had lower sweating rate, higher starting <i>T</i><sub>rec</sub>, and greater inflammation, gastrointestinal permeability, and renal stress (<i>P</i> < 0.05). However, CHA elicited an array of thermophysiological adaptations that did not differ from THA [reduced indices of peak thermal (e.g., Δ peak <i>T</i><sub>rec</sub> CHA = -0.28 ± 0.26°C, THA = -0.36 ± 0.17°C, <i>P</i> = 0.303) and cardiovascular strain, inflammation, and renal stress; blood and plasma volume expansion; improved perceptual indices], although improvements in resting thermal strain (e.g., Δ resting <i>T</i><sub>rec</sub> CHA = -0.14 ± 0.21°C, THA = -0.35 ± 0.29°C, <i>P</i> = 0.027) and sweating rate were less with CHA. Both interventions improved aspects of hypoxic tolerance, but effects on temperate normoxic exercise indices were limited. The diminished thermal strain was well-maintained over a 22-day decay period. In conclusion, CHA could represent a viable acclimation option for time-restricted young healthy males preparing for a hot, and possibly high-altitude, environment.<b>NEW & NOTEWORTHY</b> This study has shown, for the first time, that a novel condensed heat acclimation program can elicit an array of thermophysiological adaptations, many of which do not differ from traditional heat acclimation. These findings suggest that accumulated thermal \"dose\" is an important factor contributing to the adaptive responses to heat stress and that condensed heat acclimation may represent a viable option for time-restricted individuals (e.g., military personnel, firefighters, and athletes) preparing to enter a hot environment.</p>","PeriodicalId":15160,"journal":{"name":"Journal of applied physiology","volume":" ","pages":"634-650"},"PeriodicalIF":3.3000,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of applied physiology","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1152/japplphysiol.00775.2024","RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"2025/1/17 0:00:00","PubModel":"Epub","JCR":"Q1","JCRName":"PHYSIOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Short duration heat acclimation (HA) (≤5 daily heat exposures) elicits incomplete adaptation compared with longer interventions, possibly due to the lower accumulated thermal "dose." It is unknown if matching thermal "dose" over a shorter timescale elicits comparable adaptation to a longer intervention. Using a parallel-groups design, we compared: 1) "condensed" HA (CHA; n = 17 males) consisting of 4 × 75 min·day-1 heat exposures [target rectal temperature (Trec) = 38.5 °C] for two consecutive days, with 2) "traditional" HA (THA; n = 15 males) consisting of 1 × 75 min·day-1 heat exposure (target Trec = 38.5°C) for eight consecutive days. Physiological responses to exercise heat stress, hypoxia, and normoxic exercise performance were evaluated pre- and postintervention. Thermal (Trec over final 45 min: CHA = 38.45 ± 0.17°C, THA = 38.53 ± 0.13°C, P = 0.126) and cardiovascular strain were not different during interventions, indicating similar thermal "dose," although CHA had lower sweating rate, higher starting Trec, and greater inflammation, gastrointestinal permeability, and renal stress (P < 0.05). However, CHA elicited an array of thermophysiological adaptations that did not differ from THA [reduced indices of peak thermal (e.g., Δ peak Trec CHA = -0.28 ± 0.26°C, THA = -0.36 ± 0.17°C, P = 0.303) and cardiovascular strain, inflammation, and renal stress; blood and plasma volume expansion; improved perceptual indices], although improvements in resting thermal strain (e.g., Δ resting Trec CHA = -0.14 ± 0.21°C, THA = -0.35 ± 0.29°C, P = 0.027) and sweating rate were less with CHA. Both interventions improved aspects of hypoxic tolerance, but effects on temperate normoxic exercise indices were limited. The diminished thermal strain was well-maintained over a 22-day decay period. In conclusion, CHA could represent a viable acclimation option for time-restricted young healthy males preparing for a hot, and possibly high-altitude, environment.NEW & NOTEWORTHY This study has shown, for the first time, that a novel condensed heat acclimation program can elicit an array of thermophysiological adaptations, many of which do not differ from traditional heat acclimation. These findings suggest that accumulated thermal "dose" is an important factor contributing to the adaptive responses to heat stress and that condensed heat acclimation may represent a viable option for time-restricted individuals (e.g., military personnel, firefighters, and athletes) preparing to enter a hot environment.
期刊介绍:
The Journal of Applied Physiology publishes the highest quality original research and reviews that examine novel adaptive and integrative physiological mechanisms in humans and animals that advance the field. The journal encourages the submission of manuscripts that examine the acute and adaptive responses of various organs, tissues, cells and/or molecular pathways to environmental, physiological and/or pathophysiological stressors. As an applied physiology journal, topics of interest are not limited to a particular organ system. The journal, therefore, considers a wide array of integrative and translational research topics examining the mechanisms involved in disease processes and mitigation strategies, as well as the promotion of health and well-being throughout the lifespan. Priority is given to manuscripts that provide mechanistic insight deemed to exert an impact on the field.