Heat adaptation in humans with controlled heart rate heat acclimation

2021 ◽  
Author(s):  
Julien D. Périard ◽  
Sebastien Racinais ◽  
Michael N. Sawka
Keyword(s):  
Heart Rate ◽  
Heat Acclimation ◽  
Heat Adaptation

Matching the Heart to Heat-Induced Circulatory Load: Heat-Acclimatory Responses

Physiology ◽  
2003 ◽  
Vol 18 (6) ◽  
pp. 215-221 ◽  
Author(s):  
Michal Horowitz
Keyword(s):  
Heart Rate ◽  
Oxygen Demand ◽  
Heat Acclimation ◽  
Regulatory Proteins ◽  
Contractile Apparatus ◽  
Cardiac Efficiency ◽  
Cross Tolerance ◽  
Altered Expression ◽  
Expression Of Genes ◽  
Cardiac Adaptation

Heat acclimation enhances cardiac efficiency by increasing stroke volume and decreasing heart rate. These adaptations involve biochemical changes in the contractile apparatus, switched on by altered expression of genes coding contractile and calcium-regulatory proteins and partially mediated by persistent low thyroxine. Heat acclimation also produces cross-tolerance to oxygen deprivation, thus reinforcing cardiac adaptation to oxygen demand/supply mismatching via energy-sparing pathways.

Heat acclimation, aerobic fitness, and hydration effects on tolerance during uncompensable heat stress

1998 ◽  
Vol 84 (5) ◽  
pp. 1731-1739 ◽  
Author(s):  
Stephen S. Cheung ◽  
Tom M. McLellan
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Aerobic Fitness ◽  
Protective Clothing ◽  
Sweat Rate ◽  
Heat Acclimation ◽  
Short Term ◽  
Chemical Protective Clothing ◽  
Uncompensable Heat Stress ◽  
C 30

—The purpose of the present study was to determine the separate and combined effects of aerobic fitness, short-term heat acclimation, and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in the heat (40°C, 30% relative humidity). Men who were moderately fit [(MF); <50 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 7] and highly fit [(HF); >55 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 8] were tested while they were euhydrated or hypohydrated by ∼2.5% of body mass through exercise and fluid restriction the day preceding the trials. Tests were conducted before and after 2 wk of daily heat acclimation (1-h treadmill exercise at 40°C, 30% relative humidity, while wearing the nuclear, biological, and chemical protective clothing). Heat acclimation increased sweat rate and decreased skin temperature and rectal temperature (Tre) in HF subjects but had no effect on tolerance time (TT). MF subjects increased sweat rate but did not alter heart rate, Tre, or TT. In both MF and HF groups, hypohydration significantly increased Tre and heart rate and decreased the respiratory exchange ratio and the TT regardless of acclimation state. Overall, the rate of rise of skin temperature was less, while ΔTre, the rate of rise of Tre, and the TT were greater in HF than in MF subjects. It was concluded that exercise-heat tolerance in this uncompensable heat-stress environment is not influenced by short-term heat acclimation but is significantly improved by long-term aerobic fitness.

Seven days of hot water heat acclimation does not modulate the change in heart rate variability during passive heat exposure

2020 ◽  
Author(s):  
Philippe Gendron ◽  
Hugo Gravel ◽  
Hadiatou Barry ◽  
Daniel Gagnon
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
High Frequency ◽  
Water Immersion ◽  
Heat Exposure ◽  
Thermal Strain ◽  
Heat Acclimation ◽  
Hot Water ◽  
Frequency Range ◽  
The Mean

We examined if the change in heart rate variability (HRV) during passive heat exposure is modified by hot water heat acclimation (HA). Sixteen healthy adults (28 ± 5 years, 5 females/11 males) underwent heat exposure in a water-perfused suit, pre and post 7 days of HA (60 minutes at rectal temperature ≥38.6°C). During passive heat exposure, heart rate (HR), the standard deviation of NN intervals (SDNN), the square root of the mean squared differences of successive NN intervals (RMSSD) and the power in the high frequency range (HF) were measured. No difference in HR (P=0.22), SDNN (P=0.87), RMSSD (P=0.79) and HF (P=0.23) was observed at baseline. The increase in HR (pre-HA: 43 ± 10, post-HA: 42 ± 9 bpm, P=0.57) and the decrease of SDNN (pre-HA: -54.1 ± 41.0, post-HA: -52.2 ± 36.8 ms, P=0.85), RMSSD (pre-HA: -70.8 ± 49.5, post-HA: -72.7 ± 50.4 ms, P=0.91) and HF (pre-HA: -28.0 ± 14.5, post-HA: -23.2 ± 17.1%, P=0.27) were not different between experimental visits at fixed increases in esophageal temperature. These results suggest that 7 consecutive days of hot water HA does not modify the change in HRV indices during passive heat exposure. Novelty bullets: - It remains unclear if heat acclimation alters the change in heart rate variability that occurs during passive heat exposure. - At matched levels of thermal strain, 7 consecutive days of hot water immersion did not modulate the change in indices of heart rate variability during passive heat exposure.

scholarly journals Effect of sauna-based heat acclimation on plasma volume and heart rate variability

2014 ◽  
Vol 115 (4) ◽  
pp. 785-794 ◽  
Author(s):  
Jamie Stanley ◽  
Aaron Halliday ◽  
Shaun D’Auria ◽  
Martin Buchheit ◽  
Anthony S. Leicht
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Plasma Volume ◽  
Heat Acclimation

scholarly journals Isothermic and fixed intensity heat acclimation methods induce similar heat adaptation following short and long-term timescales

2015 ◽  
Vol 49-50 ◽  
pp. 55-65 ◽  
Author(s):  
Oliver R. Gibson ◽  
Jessica A. Mee ◽  
James A. Tuttle ◽  
Lee Taylor ◽  
Peter W. Watt ◽  
...  
Keyword(s):  
Heat Acclimation ◽  
Heat Adaptation ◽  
Short And Long Term

Effect of exercise-heat acclimation on cardiac autonomic modulation in Type 2 Diabetes: a pilot study

2020 ◽  
Author(s):  
Michael J. Macartney ◽  
Sean R. Notley ◽  
Christophe Herry ◽  
Ronald J Sigal ◽  
Pierre Boulay ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Heart Rate ◽  
Heat Acclimation ◽  
Cardiac Risk ◽  
Autonomic Modulation ◽  
Older Individuals ◽  
Cardiac Autonomic Modulation ◽  
Before And After ◽  
Bullet Point

The effects of exercise-heat acclimation (HA), in individuals with type 2 diabetes (T2D), on heart rate variability (HRV) remains unclear. We assessed electrocardiogram recordings during exercise-heat stress, in middle-aged-to-older individuals (50-70 years) with (n=6) and without (n=8; CON) T2D, before and after 7-days exercise HA. Exercising heart rate was reduced (CON, -9 ±5 bpm; T2D, -14 ±9 bpm) yet HRV was unresponsive. Given the negative correlations between diminished HRV and cardiac risk, further research is warranted. <b>Novelty bullet point:</b> Our observations indicate that exercise-heat acclimation may not effectively attenuate the deviation toward reduced overall HRV and unfavourable cardiac autonomic modulation in individuals with T2D.

Responses to Moderate and Low Sodium Diets during Exercise-Heat Acclimation

1993 ◽  
Vol 3 (2) ◽  
pp. 207-221 ◽  
Author(s):  
Lawrence E. Armstrong ◽  
Roger W. Hubbard ◽  
E. Wayne Askew ◽  
Jane P. De Luca ◽  
Catherine O'Brien ◽  
...  
Keyword(s):  
Heart Rate ◽  
Plasma Volume ◽  
Rectal Temperature ◽  
Prolonged Exercise ◽  
Heat Acclimation ◽  
Treadmill Walking ◽  
Heat Illness ◽  
Low Sodium ◽  
Physiologic Function ◽  
Physiologic Responses

This investigation examined whether low sodium (Na+) (LNA; 68 mEq Na+·d-1) or moderate Na+(MNA; 137 mEq Na+.d-1) intake allowed humans to maintain health, exercise, and physiologic function during 10 days of prolonged exercise-heat acclimation (HA). Seventeen volunteers, ages 19 to 21, consumed either LNA (n=8) or MNA (n=9) during HA (41°C, 21% RH; treadmill walking for 30 min.h-1, 8 h·d-1at 5.6 kmh-l, 5% grade), which resulted in significantly reduced heart rate, rectal temperature, and urine Na+for both groups. There were few between-diet differences in any variables measured. Mean plasma volume in LNA expanded significantly less than in MNA by Days 11 and 15, but reached the MNA level on Day 17 (+12.3 vs. +12.4%). The absence of heat illness, the presence of normal physiologic responses, and the total distance walked indicated successful and similar HA with both levels of dietary Na+.

Changes in heart rate variability during the induction and decay of heat acclimation

2014 ◽  
Vol 114 (10) ◽  
pp. 2119-2128 ◽  
Author(s):  
Andreas D. Flouris ◽  
Martin P. Poirier ◽  
Andrea Bravi ◽  
Heather E. Wright-Beatty ◽  
Christophe Herry ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Heat Acclimation

scholarly journals Post-exercise hot water immersion elicites heat acclimation responses in endurance and recreational athletes. A systematic review and meta-analysis

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Jack Paul Martin
Keyword(s):  
Heart Rate ◽  
Rectal Temperature ◽  
Meta Analysis ◽  
Water Immersion ◽  
Heat Acclimation ◽  
Hot Water ◽  
Design Studies ◽  
Post Exercise ◽  
Study Results ◽  
Hot Water Immersion

Aims  This meta-analysis aims to evaluate the effectiveness of heat acclimation (HA) via hot water immersion protocols and their effect on time trial (TT) performance, heart rate (HRE, HRM and HRTT), rectal temperature (Tre), Rate of perceived exertion (RPE), psychological stress index (PhSI), thermal comfort (Tcomf), thermal sensation (Tsen) and maximum oxygen uptake (Vo2max).  Methods  Pubmed, Scopus, Sportdiscus and Web of Science databases were used alongside the grey matter sites Google Scholar and Researchgate. The databases were then searched for randomised control trials and mixed-method design studies. Two RTCs, six repeated measure design studies and one randomised crossover design study were included after screening a total of 50 titles and 28 full-text articles. Sample sizes range from 1 - 13 with all participants having not participated in any form of heat training 6 months before their inclusion in the study.  Results  The mean difference (MD) for Heart rate (HR) was -9.1125 BPM (95% CI p = 0.026) and was considered to be statistically significant. The MD for Rectal temperature (Tre) effect size was -0.3814 Tre (°C) (95% CI; p = 0.05). The MD for sweat rate was 0.085; (96% CI; p = 0.0179) The changes in RPE, PhSI, Tcomf and Tsen were too small to be considered statistically significant. There was no significant difference between pre and post HA for Vo2max and PV.  This meta-analysis implies that HA via HWI may improve tolerance to discomfort during heat exposure and thus subsequently improve physical performance during exercise in hot conditions. Conclusion  The primary finding of this meta-analysis is that athletic performance is improved with post-exercise hot water immersion heat acclimation training.  HWI HA protocols should focus on the following guidelines:  40-50 minutes of submaximal exercise (>65% of Vo2max) should be followed directly (within 10 minutes) by 40 minutes of hot water immersion at 40°C with the individual immersed up to their neck.  The HA protocol should last between 6-9 days with a single bout of HWI every day for this period. 

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