1
|
Su Y, Hoekstra SP, Leicht CA. Hot water immersion is associated with higher thermal comfort than dry passive heating for a similar rise in rectal temperature and plasma interleukin-6 concentration. Eur J Appl Physiol 2024; 124:1109-1119. [PMID: 37870668 PMCID: PMC10954860 DOI: 10.1007/s00421-023-05336-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 09/28/2023] [Indexed: 10/24/2023]
Abstract
PURPOSE To compare the perceptual responses and interleukin-6 (IL-6) concentration following rectal temperature-matched dry heat exposure (DH) and hot water immersion (HWI). METHODS Twelve healthy young adults (BMI 23.5 ± 3.6 kg/m2; age: 25.8 ± 5.7 years) underwent 3 trials in randomised order: DH (air temperature 68.9 °C), HWI (water temperature 37.5 °C), and thermoneutral dry exposure (CON, air temperature 27.3 °C). Blood samples to determine IL-6 plasma concentration were collected; basic affect and thermal comfort, rectal and skin temperature (Tskin) were assessed throughout the intervention. RESULTS Rectal temperature (Trec) did not differ between DH (end temperature 38.0 ± 0.4 °C) and HWI (37.9 ± 0.2 °C, P = 0.16), but was higher compared with CON (37.0 ± 0.3 °C; P ≤ 0.004). Plasma IL-6 concentration was similar after DH (pre to post: 0.8 ± 0.5 to 1.4 ± 1.5 pg·ml-1) and HWI (0.5 ± 0.2 to 0.9 ± 0.6 pg·ml-1; P = 0.46), but higher compared with CON (0.6 ± 0.5 to 0.6 ± 0.4 pg·ml-1; P = 0.01). At the end of the intervention, basic affect and thermal comfort were most unfavourable during DH (Basic affect; DH: - 0.7 ± 2.9, HWI: 0.8 ± 1.9, CON 1.9 ± 1.9, P ≤ 0.004; Thermal comfort; 2.6 ± 0.8, HWI: 1.4 ± 0.9 and CON: 0.2 ± 0.4; P ≤ 0.004). Mean Tskin was highest for DH, followed by HWI, and lowest for CON (DH: 38.5 ± 1.3 °C, HWI: 36.2 ± 0.5 °C, CON: 31.6 ± 0.7 °C, P < 0.001). CONCLUSION The IL-6 response did not differ between DH and HWI when matched for the elevation in Trec. However, thermal comfort was lower during DH compared to HWI, which may be related to the higher Tskin during DH.
Collapse
Affiliation(s)
- Yunuo Su
- Peter Harrison Centre for Disability Sport, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, LE11 3TU, UK
| | - Sven P Hoekstra
- Peter Harrison Centre for Disability Sport, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, LE11 3TU, UK
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, San Antonio, USA
| | - Christof A Leicht
- Peter Harrison Centre for Disability Sport, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, LE11 3TU, UK.
| |
Collapse
|
2
|
Willmott AGB, James CA, Hayes M, Maxwell NS, Roberts J, Gibson OR. The reliability of a portable steam sauna pod for the whole-body passive heating of humans. J Therm Biol 2023; 118:103743. [PMID: 37979477 DOI: 10.1016/j.jtherbio.2023.103743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 10/16/2023] [Accepted: 10/17/2023] [Indexed: 11/20/2023]
Abstract
INTRODUCTION Passive heating is receiving increasing attention within human performance and health contexts. A low-cost, portable steam sauna pod may offer an additional tool for those seeking to manipulate physiological (cardiovascular, thermoregulatory and sudomotor) and perceptual responses for improving sporting or health profiles. This study aimed to 1) report the different levels of heat stress and determine the pods' inter-unit reliability, and 2) quantify the reliability of physiological and perceptual responses to passive heating. METHOD In part 1, five pods were assessed for temperature and relative humidity (RH) every 5 min across 70 min of heating for each of the 9 settings. In part 2, twelve males (age: 24 ± 4 years) completed two 60 min trials of passive heating (3 × 20 min at 44 °C/99% RH, separated by 1 week). Heart rate (HR), rectal (Trectal) and tympanic temperature (Ttympanic) were recorded every 5 min, thermal comfort (Tcomfort) and sensation (Tsensation) every 10 min, mean arterial pressure (MAP) at each break period and sweat rate (SR) after exiting the pod. RESULTS In part 1, setting 9 provided the highest temperature (44.3 ± 0.2 °C) and longest time RH remained stable at 99% (51±7 min). Inter-unit reliability data demonstrated agreement between pods for settings 5-9 (intra-class correlation [ICC] >0.9), but not for settings 1-4 (ICC <0.9). In part 2, between-visits, high correlations, and low typical error of measurement (TEM) and coefficient of variation (CV) were found for Trectal, HR, MAP, SR, and Tcomfort, but not for Ttympanic or Tsensation. A peak Trectal of 38.09 ± 0.30 °C, HR of 124 ± 15 b min-1 and a sweat loss of 0.73 ± 0.33 L were reported. No between-visit differences (p > 0.05) were observed for Trectal, Ttympanic, Tsensation or Tcomfort, however HR (+3 b.min-1) and MAP (+4 mmHg) were greater in visit 1 vs. 2 (p < 0.05). CONCLUSION Portable steam sauna pods generate reliable heat stress between-units. The highest setting (44 °C/99% RH) also provides reliable but modest adjustments in physiological and perceptual responses.
Collapse
Affiliation(s)
- A G B Willmott
- Cambridge Centre for Sport and Exercise Sciences (CCSES), Anglia Ruskin University, Cambridge, UK; Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.
| | - C A James
- Hong Kong Sports Institute (HKSI), Hong Kong; Department of Sport, Physical Education and Health, Hong Kong Baptist University. Kowloon Tong, Hong Kong
| | - M Hayes
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK
| | - N S Maxwell
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK
| | - J Roberts
- Cambridge Centre for Sport and Exercise Sciences (CCSES), Anglia Ruskin University, Cambridge, UK
| | - O R Gibson
- Centre for Physical Activity in Health and Disease (CHPAD), Division of Sport, Health and Exercise Sciences, Brunel University London, Uxbridge, UK
| |
Collapse
|
3
|
Buguet A, Radomski MW, Reis J, Spencer PS. Heatwaves and human sleep: Stress response versus adaptation. J Neurol Sci 2023; 454:120862. [PMID: 37922826 DOI: 10.1016/j.jns.2023.120862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 09/21/2023] [Accepted: 10/27/2023] [Indexed: 11/07/2023]
Abstract
The World Meteorological Organization considers a heatwave as "a period of statistically unusual hot weather persisting for a number of days and nights". Accompanying the ongoing global climate change, sharp heatwave bouts occur worldwide, growing in frequency and intensity, and beginning earlier in the season. Heatwaves exacerbate the risk of heat-related illnesses, hence human morbidity and mortality, particularly in vulnerable elderly and children. Heat-related illnesses present a continuum from normothermic (prickly heat, heat edema, heat cramps, heat tetany) to hyperthermic syndromes (from heat syncope and heat exhaustion to lethal heat stroke). Heat stroke may occur through passive heating and/or exertional exercise. "Normal sleep", such as observed in temperate conditions, is altered during heatwaves. Brisk excessive heat bouts shorten and fragment human sleep. Particularly, deep N3 sleep (formerly slow-wave sleep) and REM sleep are depleted, such as in other stressful situations. The resultant sleep loss is deleterious to cognitive performance, emotional brain function, behavior, and susceptibility to chronic health conditions and infectious diseases. Our group has previously demonstrated that sleep constitutes an adaptive mechanism during climatic heat acclimatization. In parallel, artificial heat acclimation procedures have been proposed in sports and military activities, and for the elderly. Other preventive actions should be considered, such as education and urban heat island cooling (vegetation, white paint), thus avoiding energy-hungry air conditioning.
Collapse
Affiliation(s)
- Alain Buguet
- Invited Scientist, Malaria Research Unit, UMR 5246 CNRS, Claude-Bernard Lyon-1 University, 69622 Villeurbanne, France.
| | - Manny W Radomski
- Professor Emeritus at the University of Toronto, Apt n° 2501, 2010 Islington Avenue, Toronto, ON M9P3S8, Canada
| | - Jacques Reis
- University of Strasbourg, 67000 Strasbourg, France; Association RISE, 3 rue du Loir, 67205 Oberhausbergen, France
| | - Peter S Spencer
- Department of Neurology, School of Medicine, Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239, USA.
| |
Collapse
|
4
|
Kelly MK, Bowe SJ, Jardine WT, Condo D, Guy JH, Snow RJ, Carr AJ. Heat Adaptation for Females: A Systematic Review and Meta-Analysis of Physiological Adaptations and Exercise Performance in the Heat. Sports Med 2023; 53:1395-1421. [PMID: 37222863 PMCID: PMC10289939 DOI: 10.1007/s40279-023-01831-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/26/2023] [Indexed: 05/25/2023]
Abstract
BACKGROUND Heat adaptation regimes are used to prepare athletes for exercise in hot conditions to limit a decrement in exercise performance. However, the heat adaptation literature mostly focuses on males, and consequently, current heat adaptation guidelines may not be optimal for females when accounting for the biological and phenotypical differences between sexes. OBJECTIVES We aimed to examine: (1) the effects of heat adaptation on physiological adaptations in females; (2) the impact of heat adaptation on performance test outcomes in the heat; and (3) the impact of various moderators, including duration (minutes and/or days), total heat dose (°C.min), exercise intensity (kcal.min-1), total energy expended (kcal), frequency of heat exposures and training status on the physiological adaptations in the heat. METHODS SPORTDiscus, MEDLINE Complete and Embase databases were searched to December 2022. Random-effects meta-analyses for resting and exercise core temperature, skin temperature, heart rate, sweat rate, plasma volume and performance tests in the heat were completed using Stata Statistical Software: Release 17. Sub-group meta-analyses were performed to explore the effect of duration, total heat dose, exercise intensity, total energy expended, frequency of heat exposure and training status on resting and exercise core temperature, skin temperature, heart rate and sweat rate. An explorative meta-regression was conducted to determine the effects of physiological adaptations on performance test outcomes in the heat following heat adaptation. RESULTS Thirty studies were included in the systematic review; 22 studies were meta-analysed. After heat adaptation, a reduction in resting core temperature (effect size [ES] = - 0.45; 95% confidence interval [CI] - 0.69, - 0.22; p < 0.001), exercise core temperature (ES = - 0.81; 95% CI - 1.01, - 0.60; p < 0.001), skin temperature (ES = - 0.64; 95% CI - 0.79, - 0.48; p < 0.001), heart rate (ES = - 0.60; 95% CI - 0.74, - 0.45; p < 0.001) and an increase in sweat rate (ES = 0.53; 95% CI 0.21, 0.85; p = 0.001) were identified in females. There was no change in plasma volume (ES = - 0.03; 95% CI - 0.31, 0.25; p = 0.835), whilst performance test outcomes were improved following heat adaptation (ES = 1.00; 95% CI 0.56, 1.45; p < 0.001). Across all moderators, physiological adaptations were more consistently observed following durations of 451-900 min and/or 8-14 days, exercise intensity ≥ 3.5 kcal.min-1, total energy expended ≥ 3038 kcal, consecutive (daily) frequency and total heat dose ≥ 23,000 °C.min. The magnitude of change in performance test outcomes in the heat was associated with a reduction in heart rate following heat adaptation (standardised mean difference = - 10 beats.min-1; 95% CI - 19, - 1; p = 0.031). CONCLUSIONS Heat adaptation regimes induce physiological adaptations beneficial to thermoregulation and performance test outcomes in the heat in females. Sport coaches and applied sport practitioners can utilise the framework developed in this review to design and implement heat adaptation strategies for females.
Collapse
Affiliation(s)
- Monica K Kelly
- Centre for Sport Research, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.
| | - Steven J Bowe
- Deakin Biostatistics Unit, Faculty of Health, Deakin University, Burwood, VIC, Australia
- Faculty and School of Health, Victoria University of Wellington, Kelburn, Wellington, New Zealand
| | - William T Jardine
- Centre for Sport Research, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia
| | - Dominique Condo
- Centre for Sport Research, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia
| | - Joshua H Guy
- School of Health, Medical and Applied Sciences, Central Queensland University, Cairns, QLD, Australia
| | - Rodney J Snow
- Institute for Physical Activity and Nutrition, Deakin University, Burwood, VIC, Australia
| | - Amelia J Carr
- Centre for Sport Research, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia
| |
Collapse
|
5
|
Jenkins EJ, Campbell HA, Lee JKW, Mündel T, Cotter JD. Delineating the impacts of air temperature and humidity for endurance exercise. Exp Physiol 2023; 108:207-220. [PMID: 36537856 PMCID: PMC10103870 DOI: 10.1113/ep090969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Accepted: 11/30/2022] [Indexed: 12/24/2022]
Abstract
NEW FINDINGS What is the central question of this study? What are the independent effects of air temperature and humidity on performance, physiological and perceptual responses during endurance exercise? What is the main finding and its importance? When examined independently, elevated air temperature increased heat strain and impaired aerobic exercise performance, but to a lesser extent than has been reported previously. These findings highlight the importance of absolute humidity relative to temperature when exercising or working under severe heat stress. ABSTRACT Many studies have reported that ambient heat stress increases physiological and perceptual strain and impairs endurance exercise, but effects of air temperature per se remain almost unexamined. Most studies have used matched relative humidity, thereby exponentially increasing absolute humidity (water content in air) concurrently with temperature. Absolute (not relative) humidity governs evaporative rate and is more important at higher work rates and air temperatures. Therefore, we examined the independent effects of air temperature and humidity on performance, thermal, cardiovascular and perceptual measures during endurance exercise. Utilizing a crossover design, 14 trained participants (7 females) completed 45 min fixed-intensity cycling (70%V ̇ O 2 peak ${\dot V_{{{\rm{O}}_{\rm{2}}}{\rm{peak}}}}$ ) followed by a 20-km time trial in each of four environments: three air temperatures at matched absolute humidity (Cool, 18°C; Moderate, 27°C; and Hot, 36°C; at 1.96 kPa, air velocity ∼4.5 m/s), and one at elevated humidity (Hot Humid, 36°C at 3.92 kPa). Warmer air caused warmer skin (0.5°C/°C; P < 0.001), higher heart rate (1 bpm/°C; P < 0.001), sweat rate (0.04 l/h/°C; P < 0.001) and thermal perceptions during fixed-intensity exercise, but minimally affected core temperature (<0.01°C/°C; P = 0.053). Time-trial performance was comparable between Cool and Moderate (95% CI: -1.4, 5.9%; P = 0.263), but 3.6-6% slower in Hot (95% CI: ±2.4%; P ≤ 0.006). Elevated humidity increased core temperature (P < 0.001), perceived temperature and discomfort but not skin temperature or heart rate, and reduced mean blood pressure (P = 0.046) during fixed-intensity exercise. Elevated humidity impaired time-trial performance by 3.4% (95% CI: ±2.2%; P = 0.006). In conclusion, these findings quantify the importance of absolute humidity alongside air temperature when exercising under severe heat stress.
Collapse
Affiliation(s)
- Elliott J. Jenkins
- School of Physical EducationSport and Exercise SciencesUniversity of OtagoDunedinNew Zealand
- Cardiff School of Sport and Health SciencesCardiff Metropolitan UniversityCardiffUK
| | - Holly A. Campbell
- Department of Surgical SciencesDunedin School of MedicineUniversity of OtagoDunedinNew Zealand
| | - Jason K. W. Lee
- Department of PhysiologyNational University of SingaporeSingapore
- Heat Resilience and Performance CentreYong Loo Lin School of MedicineNational University of SingaporeSingapore
- Human Potential Translational Research ProgrammeYong Loo Lin School of MedicineNational University of SingaporeSingapore
- Department of PhysiologyYong Loo Lin School of MedicineNational University of SingaporeSingapore
- Campus for Research Excellence and Technological Enterprise (CREATE)Singapore
| | - Toby Mündel
- School of SportExercise and NutritionMassey UniversityPalmerston NorthNew Zealand
| | - James D. Cotter
- School of Physical EducationSport and Exercise SciencesUniversity of OtagoDunedinNew Zealand
| |
Collapse
|
6
|
Periyaswamy T, Balasubramanian M. Combining multiple human physiological signals using fuzzy logic to determine stress caused by battle dress uniforms. SN APPLIED SCIENCES 2022. [DOI: 10.1007/s42452-022-05199-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Abstract
This study presents a novel stress index for clothing using physiological signals to estimate stress induced by battle dress uniforms (BDU) during physical activity. The approach uses a fuzzy logic-based nonlinear mapping to compute the stress from physiological signals. Ten healthy men performed a battery of physical activities in a controlled environment. Heart rate (HR), respiration rate (RR), skin temperature (ST), and galvanic skin response (GSR) were measured continuously for the participants during activity wearing three kinds of clothing (two BDUs and a control garment). The individual physiological responses were combined using a fuzzy-logic system to derive a stress measure called Clothed Activity Stress Index (CASI). Repeated measures ANOVA showed that the garments significantly (α = .05) affected the HR (p < .001) and RR (p < .001). In addition, interactions between the activity and garment were significant for HR, RR, and ST (p < .001, p < .001, p < .036). The physiological measures differed significantly between rest and activity for the two uniforms. The stress indices (ranging between 0 and 1) during rest and activity were 0.24 and 0.35 for control, 0.27 and 0.43 for BDU-1, and 0.33 and 0.44 for BDU-2. It is shown here that clothing systems impact human stress levels to a measurable level. This computational approach is applicable to measure stress caused by protective wear under different operational conditions and can be suitable for sports and combat gears.
Article Highlights
A computational approach to non-linearly map human physiological signals and stress is presented.
The stress caused by functional clothing systems is estimated using a fuzzy-logic mapping system for battle dress uniforms.
Heart and respiration rates are highly sensitive to stress, while skin temperature and galvanic skin response are moderately sensitive.
Collapse
|
7
|
Abstract
In this review, we highlight recent studies from our group and others that have characterized the cardiovascular adjustments that occur after acute heat exposure. Special emphasis will be placed on underlying mechanisms and clinical implications. Finally, we postulate that these acute cardiovascular adjustments may predict the long-term adaptive response to chronic heat therapy.
Collapse
Affiliation(s)
- Steven A. Romero
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center
| | - Rauchelle E. Richey
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center
| | - Holden W. Hemingway
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center
| |
Collapse
|
8
|
Mornas A, Racinais S, Brocherie F, Alhammoud M, Hager R, Desmedt Y, Guilhem G. Faster early rate of force development in a warmer muscle: an in vivo exploration of fascicle dynamics and muscle-tendon mechanical properties. Am J Physiol Regul Integr Comp Physiol 2022; 323:R123-R132. [PMID: 35579335 DOI: 10.1152/ajpregu.00280.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
While heat exposure has been shown to increase the rate of force development (RFD), the underlying processes remain unknown. This study investigated the effect of heat on gastrocnemius medialis (GM) muscle-tendon properties and interactions. Sixteen participants performed electrically-evoked and voluntary contractions combined with ultrafast ultrasound under thermoneutral (CON: 26°C, core temperature 37.0±0.3°C, muscle temperature 34.0±1.1°C) and passive heat exposure (HOT: 47°C, core temperature 38.4±0.3°C, muscle temperature 37.0±0.8°C) conditions. Maximal voluntary force was unchanged while voluntary activation decreased (-4.6±8.7%, P=0.038) in HOT. Heat exposure increased RFD before 100 ms from contraction onset (+48.2±62.7%; P=0.013), without further changes after 100 ms. GM fascicle dynamics during electrically-evoked and voluntary contractions remained unchanged between conditions. Joint velocity at a given force was higher in HOT (+7.1±6.6%; P=0.004), while the fascicle force-velocity relationship was unchanged. Passive muscle stiffness and active tendon stiffness were lower in HOT than CON (P≤0.030). This study showed that heat-induced increases in early RFD may not be attributed to changes in contractile properties. Late RFD was unaltered, probably explained by decreased soft tissues' stiffness in heat. Investigations are required to explore the possible influence of neural drive and motor unit recruitment in the enhancement of explosive strength elicited by heat exposure.
Collapse
Affiliation(s)
- Adèle Mornas
- French Institute of Sport (INSEP), Laboratory Sport, Expertise and Performance (EA 7370), Paris, France.,University of Paris, Paris, France
| | - Sebastien Racinais
- French Institute of Sport (INSEP), Laboratory Sport, Expertise and Performance (EA 7370), Paris, France.,Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar
| | - Franck Brocherie
- French Institute of Sport (INSEP), Laboratory Sport, Expertise and Performance (EA 7370), Paris, France
| | | | - Robin Hager
- French Institute of Sport (INSEP), Laboratory Sport, Expertise and Performance (EA 7370), Paris, France
| | - Yanis Desmedt
- French Institute of Sport (INSEP), Laboratory Sport, Expertise and Performance (EA 7370), Paris, France
| | - Gaël Guilhem
- French Institute of Sport (INSEP), Laboratory Sport, Expertise and Performance (EA 7370), Paris, France
| |
Collapse
|
9
|
Kissling LS, Akerman AP, Campbell HA, Prout JR, Gibbons TD, Thomas KN, Cotter JD. A crossover control study of three methods of heat acclimation on the magnitude and kinetics of adaptation. Exp Physiol 2021; 107:337-349. [PMID: 34957632 DOI: 10.1113/ep089993] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Accepted: 12/22/2021] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS Central question to the study? Are primary indices of heat adaptation (e.g., expansion of plasma volume and reduction in resting core temperature) differentially affected by the three major modes of short-term heat acclimation, i.e., exercise in the heat, hot water immersion and sauna? Main finding and its importance? The three modes elicited typical adaptations expected with short-term heat acclimation, however these were not significantly different between modes. This comparison has not previously been done and highlights that individuals can expect similar adaptation to heat regardless of the mode used. ABSTRACT Heat acclimation (HA) can improve heat tolerance and cardiovascular health. The mode of HA potentially impacts the magnitude and time course of adaptations, but almost no comparative data exist. We therefore investigated adaptive responses to three common modes of HA, particularly with respect to plasma volume. Within a crossover repeated-measures design, 13 physically-active participants (5 female) undertook four, 5-d HA regimes (60 min/d) in randomised order, separated by ≥4 wk. Rectal temperature (Tre ) was clamped at neutrality via 36.6C (thermoneutral) water immersion (TWI; i.e., control condition), or raised by 1.5°C via heat stress in 40°C water (HWI), Sauna (55°C, 52% RH), or exercise in humid heat (40°C, 52% RH; ExH). Adaptation magnitude was assessed as the pooled response across days 4 to 6, while kinetics was assessed via the 6-d time series. Plasma volume expansion was similar in all heated conditions but only higher than TWI in ExH (by 4%, p = 0.036). Approximately two thirds of the expansion was attained within the initial 24 h and was moderately related to that present on day 6, regardless of HA mode (r = 0.560-0.887). Expansion was mediated by conservation of both sodium and albumin content, with little evidence for these having differential roles between modes (p = 0.706 and 0.320, respectively). Resting Tre decreased by 0.1-0.3°C in all heated conditions, and SBP decreased by 4 mm Hg, but not differentially between conditions (p≥0.137). In conclusion, HA mode did not substantially affect the magnitude or rate of adaptation in key resting markers of short-term HA. This article is protected by copyright. All rights reserved.
Collapse
Affiliation(s)
- Lorenz S Kissling
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand
| | - Ashley P Akerman
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand.,Department of Surgical Sciences, Department of Medicine, University of Otago, Dunedin, New Zealand
| | - Holly A Campbell
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand.,Department of Surgical Sciences, Department of Medicine, University of Otago, Dunedin, New Zealand
| | - Jamie R Prout
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand
| | - Travis D Gibbons
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand.,Department of Surgical Sciences, Department of Medicine, University of Otago, Dunedin, New Zealand
| | - Kate N Thomas
- Department of Surgical Sciences, Department of Medicine, University of Otago, Dunedin, New Zealand
| | - James D Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand
| |
Collapse
|