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Topham TH, Smallcombe JW, Brown HA, Clark B, Woodward AP, Telford RD, Jay O, Périard JD. Biological sex does not independently influence core temperature change and sweating of children exercising in uncompensable heat stress. J Appl Physiol (1985) 2024; 136:1440-1449. [PMID: 38660730 DOI: 10.1152/japplphysiol.00877.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 04/03/2024] [Accepted: 04/21/2024] [Indexed: 04/26/2024] Open
Abstract
The purpose of this study was to investigate the influence of biological sex, independent of differences in aerobic fitness and body fatness, on the change in gastrointestinal temperature (ΔTgi) and whole body sweat rate (WBSR) of children exercising under uncompensable heat stress. Seventeen boys (means ± SD; 13.7 ± 1.3 yr) and 18 girls (13.7 ± 1.4 yr) walked for 45 min at a fixed rate of metabolic heat production per kg body mass (8 W·kg-1) in 40°C and 30% relative humidity. Sex and peak oxygen consumption (V̇o2peak) were entered into a Bayesian hierarchical general additive model (HGAM) for Tgi. Sex, V̇o2peak, and the evaporative requirement for heat balance (Ereq) were entered into a Bayesian hierarchical linear regression for WBSR. For 26 (12 M and 14 F) of the 35 children with measured body composition, body fat percentage was entered in a separate HGAM and hierarchical linear regression for Tgi and WBSR, respectively. Conditional on sex-specific mean V̇o2peak, ΔTgi was 1.00°C [90% credible intervals (Crl): 0.84, 1.16] for boys and 1.17°C [1.01, 1.33] for girls, with a difference of 0.17°C [-0.39, 0.06]. When sex differences in V̇o2peak were accounted for, the difference in ΔTgi between boys and girls was 0.01°C [-0.25, 0.22]. The difference in WBSR between boys and girls was 0.03 L·h-1 [-0.02, 0.07], when isolated from differences in Ereq. The difference in ΔTgi between boys and girls was -0.10°C [-0.38, 0.17] when sex differences in body fat (%) were accounted for. Biological sex did not independently influence the ΔTgi and WBSR of children exercising under uncompensable heat stress.NEW & NOTEWORTHY Limited studies have investigated the thermoregulatory responses of boys and girls exercising under uncompensable heat stress. Boys and girls often differ in physiological characteristics other than biological sex, such as aerobic fitness and body fat percentage, which may confound interpretations. We investigated the influence of biological sex on exercise thermoregulation in children, independent of differences in aerobic fitness and body fatness.
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Affiliation(s)
- Thomas H Topham
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, Australian Capital Territory, Australia
| | - James W Smallcombe
- Faculty of Medicine and Health, Heat and Health Research Incubator, The University of Sydney, Sydney, New South Wales, Australia
| | - Harry A Brown
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, Australian Capital Territory, Australia
| | - Brad Clark
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, Australian Capital Territory, Australia
| | - Andrew P Woodward
- Faculty of Health, University of Canberra, Bruce, Australian Capital Territory, Australia
| | - Richard D Telford
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, Australian Capital Territory, Australia
| | - Ollie Jay
- Faculty of Medicine and Health, Heat and Health Research Incubator, The University of Sydney, Sydney, New South Wales, Australia
| | - Julien D Périard
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, Australian Capital Territory, Australia
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Topham TH, Smallcombe JW, Brown HA, Clark B, Woodward AP, Telford RD, Jay O, Périard JD. Influence of Biological Sex and Fitness on Core Temperature Change and Sweating in Children Exercising in Warm Conditions. Med Sci Sports Exerc 2024; 56:697-705. [PMID: 38051094 DOI: 10.1249/mss.0000000000003347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
PURPOSE This study aimed to investigate the associations of biological sex and aerobic fitness (i.e., V̇O 2peak ) on the change in gastrointestinal temperature (∆ Tgi ) and whole-body sweat rate (WBSR) of children exercising in warm conditions. METHODS Thirty-eight children (17 boys, mean ± SD = 13.7 ± 1.2 yr; 21 girls, 13.6 ± 1.8 yr) walked for 45 min at a fixed rate of metabolic heat production (8 W·kg -1 ) in 30°C and 40% relative humidity. Biological sex and relative V̇O 2peak were entered as predictors into a Bayesian hierarchical generalized additive model for Tgi . For a subsample of 13 girls with measured body composition, body fat percent was entered into a separate hierarchical generalized additive model for Tgi . Sex, V̇O 2peak , and the evaporative requirement for heat balance ( Ereq ) were entered into a Bayesian hierarchical linear regression for WBSR. RESULTS The mean ∆ Tgi for boys was 0.71°C (90% credible interval = 0.60-0.82) and for girls 0.78°C (0.68-0.88). A predicted 20 mL·kg -1 ·min -1 higher V̇O 2peak resulted in a 0.19°C (-0.03 to 0.43) and 0.24°C (0.07-0.40) lower ∆ Tgi in boys and girls, respectively. A predicted ~13% lower body fat in the subsample of girls resulted in a 0.15°C (-0.12 to 0.45) lower ∆ Tgi . When Ereq was standardized to the grand mean, the difference in WBSR between boys and girls was -0.00 L·h -1 (-0.06 to 0.06), and a 20-mL·kg -1 ·min -1 higher predicted V̇O 2peak resulted in a mean difference in WBSR of -0.07 L·h -1 (-0.15 to 0.00). CONCLUSIONS Biological sex did not independently influence ∆ Tgi and WBSR in children. However, a higher predicted V̇O 2peak resulted in a lower ∆ Tgi of children, which was not associated with a greater WBSR, but may be related to differences in body fat percent between high and low fitness individuals.
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Affiliation(s)
- Thomas H Topham
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, AUSTRALIA
| | - James W Smallcombe
- The University of Sydney, Heat and Health Research Incubator, Faculty of Medicine and Health, Sydney, NSW, AUSTRALIA
| | - Harry A Brown
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, AUSTRALIA
| | - Brad Clark
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, AUSTRALIA
| | | | - Richard D Telford
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, AUSTRALIA
| | - Ollie Jay
- The University of Sydney, Heat and Health Research Incubator, Faculty of Medicine and Health, Sydney, NSW, AUSTRALIA
| | - Julien D Périard
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, AUSTRALIA
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Brown HA, Topham TH, Clark B, Ioannou LG, Flouris AD, Smallcombe JW, Telford RD, Jay O, Périard JD. Quantifying Exercise Heat Acclimatisation in Athletes and Military Personnel: A Systematic Review and Meta-analysis. Sports Med 2023:10.1007/s40279-023-01972-4. [PMID: 38051495 DOI: 10.1007/s40279-023-01972-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/10/2023] [Indexed: 12/07/2023]
Abstract
BACKGROUND Athletes and military personnel are often expected to compete and work in hot and/or humid environments, where decrements in performance and an increased risk of exertional heat illness are prevalent. A physiological strategy for reducing the adverse effects of heat stress is to acclimatise to the heat. OBJECTIVE The aim of this systematic review was to quantify the effects of relocating to a hotter climate to undergo heat acclimatisation in athletes and military personnel. ELIGIBILITY CRITERIA Studies investigating the effects of heat acclimatisation in non-acclimatised athletes and military personnel via relocation to a hot climate for < 6 weeks were included. DATA SOURCES MEDLINE, SPORTDiscus, CINAHL Plus with Full Text and Scopus were searched from inception to June 2022. RISK OF BIAS A modified version of the McMaster critical review form was utilised independently by two authors to assess the risk of bias. DATA SYNTHESIS A Bayesian multi-level meta-analysis was conducted on five outcome measures, including resting core temperature and heart rate, the change in core temperature and heart rate during a heat response test and sweat rate. Wet-bulb globe temperature (WBGT), daily training duration and protocol length were used as predictor variables. Along with posterior means and 90% credible intervals (CrI), the probability of direction (Pd) was calculated. RESULTS Eighteen articles from twelve independent studies were included. Fourteen articles (nine studies) provided data for the meta-analyses. Whilst accounting for WBGT, daily training duration and protocol length, population estimates indicated a reduction in resting core temperature and heart rate of - 0.19 °C [90% CrI: - 0.41 to 0.05, Pd = 91%] and - 6 beats·min-1 [90% CrI: - 16 to 5, Pd = 83%], respectively. Furthermore, the rise in core temperature and heart rate during a heat response test were attenuated by - 0.24 °C [90% CrI: - 0.67 to 0.20, Pd = 85%] and - 7 beats·min-1 [90% CrI: - 18 to 4, Pd = 87%]. Changes in sweat rate were conflicting (0.01 L·h-1 [90% CrI: - 0.38 to 0.40, Pd = 53%]), primarily due to two studies demonstrating a reduction in sweat rate following heat acclimatisation. CONCLUSIONS Data from athletes and military personnel relocating to a hotter climate were consistent with a reduction in resting core temperature and heart rate, in addition to an attenuated rise in core temperature and heart rate during an exercise-based heat response test. An increase in sweat rate is also attainable, with the extent of these adaptations dependent on WBGT, daily training duration and protocol length. PROSPERO REGISTRATION CRD42022337761.
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Affiliation(s)
- Harry A Brown
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, Australia
| | - Thomas H Topham
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, Australia
| | - Brad Clark
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, Australia
| | - Leonidas G Ioannou
- FAME Laboratory, Department of Physical Education and Sport Science, University of Thessaly, Trikala, Greece
| | - Andreas D Flouris
- FAME Laboratory, Department of Physical Education and Sport Science, University of Thessaly, Trikala, Greece
| | - James W Smallcombe
- Faculty of Medicine and Health, Heat and Health Research Incubator, The University of Sydney, Sydney, NSW, Australia
| | - Richard D Telford
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, Australia
| | - Ollie Jay
- Faculty of Medicine and Health, Heat and Health Research Incubator, The University of Sydney, Sydney, NSW, Australia
| | - Julien D Périard
- Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, ACT, Australia.
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Ravanelli N, Newhouse D, Foster F, Caldwell AR. Agreement between the ventilated capsule and the KuduSmart® device for measuring sweating responses to passive heat stress and exercise. Appl Physiol Nutr Metab 2023; 48:946-953. [PMID: 37566898 DOI: 10.1139/apnm-2023-0149] [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] [Indexed: 08/13/2023]
Abstract
The present study assessed agreement between a wireless sweat rate monitor (KuduSmart® device) and the ventilated capsule (VC) technique for measuring: (i) minute-averaged local sweat rate (LSR), (ii) sweating onset, (iii) sudomotor thermosensitivity, and (iv) steady-state LSR, during passive heat stress and exercise. It was hypothesized that acceptable agreement with no bias would be observed between techniques for all assessed sweating characteristics. On two separate occasions for each intervention, participants were either passively heated by recirculating hot water (49 °C) through a tube-lined garment until rectal temperature increased 1 °C over baseline (n = 8), or a 60 min treadmill march at a fixed rate of heat production (∼500 W, n = 9). LSR of the forearm was concurrently measured with a VC and the KuduSmart® device secured within ∼2 cm. Using a ratio scale Bland-Altman analysis with the VC as the reference, the KuduSmart® device demonstrated systematic bias and not acceptable agreement for minute-averaged LSR (1.17 [1.09, 1.27], CV = 44.5%), systematic bias and acceptable agreement for steady-state LSR (1.16 [1.09,1.23], CV = 19.5%), no bias and acceptable agreement for thermosensitivity (1.07 [0.99, 1.16], CV = 23.2%), and no bias and good agreement for sweating onset (1.00 [1.00, 1.00], CV = 11.1%). In total, ≥73% of all minute-averaged LSR observations with the KuduSmart® device (n = 2743) were within an absolute error of <0.2 mg/cm2/min to the VC, the reference minimum detectable change in measurement error of a VC on the forearm. Collectively, the KuduSmart® device may be a satisfactory solution for assessing the sweating response to heat stress where a VC is impractical.
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Affiliation(s)
- Nicholas Ravanelli
- School of Kinesiology, Lakehead University, Thunder Bay, ON, Canada
- Centre for Research in Occupational Safety and Health, Laurentian University, Sudbury, ON, Canada
| | - Douglas Newhouse
- School of Kinesiology, Lakehead University, Thunder Bay, ON, Canada
- Centre for Research in Occupational Safety and Health, Laurentian University, Sudbury, ON, Canada
| | - Fergus Foster
- School of Kinesiology, Lakehead University, Thunder Bay, ON, Canada
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Cramer MN, Gagnon D, Laitano O, Crandall CG. Human temperature regulation under heat stress in health, disease, and injury. Physiol Rev 2022; 102:1907-1989. [PMID: 35679471 PMCID: PMC9394784 DOI: 10.1152/physrev.00047.2021] [Citation(s) in RCA: 57] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Revised: 05/10/2022] [Accepted: 05/28/2022] [Indexed: 12/30/2022] Open
Abstract
The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.
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Affiliation(s)
- Matthew N Cramer
- Defence Research and Development Canada-Toronto Research Centre, Toronto, Ontario, Canada
| | - Daniel Gagnon
- Montreal Heart Institute and School of Kinesiology and Exercise Science, Université de Montréal, Montréal, Quebec, Canada
| | - Orlando Laitano
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
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Abstract
Background Physiological heat adaptations can be induced following various protocols that use either artificially controlled (i.e. acclimation) or naturally occurring (i.e. acclimatisation) environments. During the summer months in seasonal climates, adequate exposure to outdoor environmental heat stress should lead to transient seasonal heat acclimatisation. Objectives The aim of the systematic review was to assess the available literature and characterise seasonal heat acclimatisation during the summer months and identify key factors that influence the magnitude of adaptation. Eligibility Criteria English language, full-text articles that assessed seasonal heat acclimatisation on the same sample of healthy adults a minimum of 3 months apart were included. Data Sources Studies were identified using first- and second-order search terms in the databases MEDLINE, SPORTDiscus, CINAHL Plus with Full Text, Scopus and Cochrane, with the last search taking place on 15 July 2021. Risk of Bias Studies were independently assessed by two authors for the risk of bias using a modified version of the McMaster critical review form. Data Extraction Data for the following outcome variables were extracted: participant age, sex, body mass, height, body fat percentage, maximal oxygen uptake, time spent exercising outdoors (i.e. intensity, duration, environmental conditions), heat response test (i.e. protocol, time between tests), core temperature, skin temperature, heart rate, whole-body sweat loss, whole-body and local sweat rate, sweat sodium concentration, skin blood flow and plasma volume changes. Results Twenty-nine studies were included in this systematic review, including 561 participants across eight countries with a mean summer daytime wet-bulb globe temperature (WBGT) of 24.9 °C (range: 19.5–29.8 °C). Two studies reported a reduction in resting core temperature (0.16 °C; p < 0.05), 11 reported an increased sweat rate (range: 0.03–0.53 L·h−1; p < 0.05), two observed a reduced heart rate during a heat response test (range: 3–8 beats·min−1; p < 0.05), and six noted a reduced sweat sodium concentration (range: − 22 to − 59%; p < 0.05) following summer. The adaptations were associated with a mean summer WBGT of 25.2 °C (range: 19.6–28.7 °C). Limitations The available studies primarily focussed on healthy male adults and demonstrated large differences in the reporting of factors that influence the development of seasonal heat acclimatisation, namely, exposure time and duration, exercise task and environmental conditions. Conclusions Seasonal heat acclimatisation is induced across various climates in healthy adults. The magnitude of adaptation is dependent on a combination of environmental and physical activity characteristics. Providing environmental conditions are conducive to adaptation, the duration and intensity of outdoor physical activity, along with the timing of exposures, can influence seasonal heat acclimatisation. Future research should ensure the documentation of these factors to allow for a better characterisation of seasonal heat acclimatisation. PROSPERO Registration CRD42020201883. Supplementary Information The online version contains supplementary material available at 10.1007/s40279-022-01677-0.
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Martins YAT, Passos RLF, Marques AL, Gonçalves DAP, Mendes TT, Núñez-Espinosa C, Rodrigues LOC, Wanner SP, Moraes MM, Arantes RME, Soares DD. A 32-day long fieldwork in Antarctica improves heat tolerance during physical exercise. AN ACAD BRAS CIENC 2022; 94:e20210593. [PMID: 35239799 DOI: 10.1590/0001-3765202220210593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2021] [Accepted: 08/20/2021] [Indexed: 11/22/2022] Open
Abstract
We evaluated the influence of a 32-day camping in Antarctica on physical performance and exercise-induced thermoregulatory responses. In Brazil, before and after the Antarctic camping, the volunteers performed an incremental exercise at temperate conditions and, two days later, an exercise heat stress protocol (45-min running at 60% of maximum aerobic speed, at 31°C and 60% of relative humidity). In Antarctica, core temperature was assessed on a day of fieldwork, and average values higher than 38.5°C were reported. At pre- and post-Antarctica, physiological (whole-body and local sweat rate, number of active sweat glands, sweat gland output, core and skin temperatures) and perceptual (thermal comfort and sensation) variables were measured. The Antarctic camping improved the participants' performance and induced heat-related adaptations, as evidenced by sweat redistribution (lower in the chest but higher in grouped data from the forehead, forearm, and thigh) and reduced skin temperatures in the forehead and chest during the exercise heat stress protocol. Notwithstanding the acclimatization, the participants did not report differences of the thermal sensation and comfort. In conclusion, staying in an Antarctic camp for 32 days improved physical performance and elicited physiological adaptations to heat due to the physical exertion-induced hyperthermia in the field.
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Affiliation(s)
- Ygor A T Martins
- Universidade Federal de Minas Gerais, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Laboratório de Fisiologia do Exercício, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
| | - Renata L F Passos
- Universidade Federal de Minas Gerais, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Laboratório de Fisiologia do Exercício, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
| | - Alice L Marques
- Universidade Rural do Rio de Janeiro, Programa de Pós-Graduação em Ciências Sociais em Desenvolvimento, Agricultura e Sociedade, Av. Presidente Vargas, 417, 20071-003 Rio de Janeiro, RJ, Brazil
| | - Dawit A P Gonçalves
- Universidade Federal de Minas Gerais, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Laboratório de Fisiologia do Exercício, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
| | - Thiago T Mendes
- Universidade Federal do Maranhão, Centro de Ciências Humanas, Naturais, Saúde e Tecnologia, Estrada Pinheiro/Pacas, Km 10, s/n, 65200-000 Pinheiro, MA, Brazil
| | - Cristian Núñez-Espinosa
- Universidad de Magallanes, School of Medicine, Physiology Laboratory, Pdte. Manuel Bulnes Avenue, 01855, Punta Arenas, Magallanes and Chilean Antarctica, Chile
| | - Luiz O C Rodrigues
- Universidade Federal de Minas Gerais, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Laboratório de Fisiologia do Exercício, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
| | - Samuel P Wanner
- Universidade Federal de Minas Gerais, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Laboratório de Fisiologia do Exercício, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
| | - Michele M Moraes
- Universidade Federal de Minas Gerais, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Laboratório de Fisiologia do Exercício, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil.,Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Patologia geral, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil.,Universidade Federal de Minas Gerais, Faculdade de Medicina, Núcleo de Ações e Pesquisa em Apoio Diagnóstico, (UFMG/FM-NUPAD), Av. Alfredo Balena, 189, 30130-100 Belo Horizonte, MG, Brazil
| | - Rosa M E Arantes
- Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Patologia geral, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil.,Universidade Federal de Minas Gerais, Faculdade de Medicina, Núcleo de Ações e Pesquisa em Apoio Diagnóstico, (UFMG/FM-NUPAD), Av. Alfredo Balena, 189, 30130-100 Belo Horizonte, MG, Brazil
| | - Danusa D Soares
- Universidade Federal de Minas Gerais, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Laboratório de Fisiologia do Exercício, Av. Presidente Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
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Foster J, Smallcombe JW, Hodder S, Jay O, Flouris AD, Havenith G. Quantifying the impact of heat on human physical work capacity; part II: the observed interaction of air velocity with temperature, humidity, sweat rate, and clothing is not captured by most heat stress indices. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2022; 66:507-520. [PMID: 34743228 PMCID: PMC8850241 DOI: 10.1007/s00484-021-02212-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 10/14/2021] [Accepted: 10/16/2021] [Indexed: 05/20/2023]
Abstract
Increasing air movement can alleviate or exacerbate occupational heat strain, but the impact is not well defined across a wide range of hot environments, with different clothing levels. Therefore, we combined a large empirical study with a physical model of human heat transfer to determine the climates where increased air movement (with electric fans) provides effective body cooling. The model allowed us to generate practical advice using a high-resolution matrix of temperature and humidity. The empirical study involved a total of 300 1-h work trials in a variety of environments (35, 40, 45, and 50 °C, with 20 up to 80% relative humidity) with and without simulated wind (3.5 vs 0.2 m∙s-1), and wearing either minimal clothing or a full body work coverall. Our data provides compelling evidence that the impact of fans is strongly determined by air temperature and humidity. When air temperature is ≥ 35 °C, fans are ineffective and potentially harmful when relative humidity is below 50%. Our simulated data also show the climates where high wind/fans are beneficial or harmful, considering heat acclimation, age, and wind speed. Using unified weather indices, the impact of air movement is well captured by the universal thermal climate index, but not by wet-bulb globe temperature and aspirated wet-bulb temperature. Overall, the data from this study can inform new guidance for major public and occupational health agencies, potentially maintaining health and productivity in a warming climate.
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Affiliation(s)
- Josh Foster
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, LE11 3TU, UK
| | - James W Smallcombe
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, LE11 3TU, UK
| | - Simon Hodder
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, LE11 3TU, UK
| | - Ollie Jay
- Thermal Ergonomics Laboratory, Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia
| | | | - George Havenith
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, LE11 3TU, UK.
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Zheng H, Badenhorst CE, Lei TH, Che Muhamed AM, Liao YH, Amano T, Fujii N, Nishiyasu T, Kondo N, Mündel T. Measurement error of self-paced exercise performance in athletic women is not affected by ovulatory status or ambient environment. J Appl Physiol (1985) 2021; 131:1496-1504. [PMID: 34590913 DOI: 10.1152/japplphysiol.00342.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Measurement error(s) of exercise tests for women are severely lacking in the literature. The purpose of this investigation was to 1) determine whether ovulatory status or ambient environment were moderating variables when completing a 30-min self-paced work trial and 2) provide test-retest norms specific to athletic women. A retrospective analysis of three heat stress studies was completed using 33 female participants (31 ± 9 yr, 54 ± 10 mL·min-1·kg-1) that yielded 130 separate trials. Participants were classified as ovulatory (n = 19), anovulatory (n = 4), and oral contraceptive pill users (n = 10). Participants completed trials ∼2 wk apart in their (quasi-) early follicular and midluteal phases in two of moderate (1.3 ± 0.1 kPa, 20.5 ± 0.5°C, 18 trials), warm-dry (2.2 ± 0.2 kPa, 34.1 ± 0.2°C, 46 trials), or warm-humid (3.4 ± 0.1 kPa, 30.2 ± 1.1°C, 66 trials) environments. We quantified reliability using limits of agreement, intraclass correlation coefficient (ICC), standard error of measurement (SEM), and coefficient of variation (CV). Test-retest reliability was high, clinically valid (ICC = 0.90, P < 0.01), and acceptable with a mean CV of 4.7%, SEM of 3.8 kJ (2.1 W), and reliable bias of -2.1 kJ (-1.2 W). The various ovulatory status and contrasting ambient conditions had no appreciable effect on reliability. These results indicate that athletic women can perform 30-min self-paced work trials ∼2 wk apart with an acceptable and low variability irrespective of their hormonal status or heat-stressful environments.NEW & NOTEWORTHY This study highlights that aerobically trained women perform 30-min self-paced work trials ∼2 wk apart with acceptably low variability and their hormonal/ovulatory status and the introduction of greater ambient heat and humidity do not moderate this measurement error.
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Affiliation(s)
- Huixin Zheng
- School of Sport Exercise and Nutrition, Massey University, Palmerston North, New Zealand
| | - Claire E Badenhorst
- School of Sport Exercise and Nutrition, Massey University, Auckland, New Zealand
| | - Tze-Huan Lei
- College of Physical Education, Hubei Normal University, Huangshi, China
| | - Ahmad Munir Che Muhamed
- Advanced Medical and Dental Institute, Universiti Sains Malaysia, Kepala Batas, Pulau Pinang, Malaysia
| | - Yi-Hung Liao
- Department of Exercise and Health Science, National Taipei University of Nursing and Health Sciences, Taipei, Taiwan
| | - Tatsuro Amano
- Faculty of Education, Niigata University, Niigata, Japan
| | - Naoto Fujii
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
| | - Takeshi Nishiyasu
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
| | - Narihiko Kondo
- Laboratory for Applied Human Physiology, Graduate School of Human Development and Environment, Kobe University, Kobe, Japan
| | - Toby Mündel
- School of Sport Exercise and Nutrition, Massey University, Palmerston North, New Zealand
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10
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Sekiguchi Y, Benjamin CL, Manning CN, Struder JF, Armstrong LE, Lee EC, Huggins RA, Stearns RL, Distefano LJ, Casa DJ. Effects of Heat Acclimatization, Heat Acclimation, and Intermittent Exercise Heat Training on Time-Trial Performance. Sports Health 2021; 14:694-701. [PMID: 34706597 DOI: 10.1177/19417381211050643] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND The purpose of this study was to investigate effects of heat acclimatization (HAz) followed by heat acclimation (HA), and intermittent heat training (IHT) on time-trial performance. HYPOTHESIS Time-trial performance will improve after HA and will further improve with twice a week of IHT. STUDY DESIGN Interventional study. LEVEL OF EVIDENCE Level 3. METHODS A total of 26 male athletes (mean ± SD; age, 35 ± 12 years; body mass, 72.8 ± 8.9 kg; peak oxygen consumption [VO2peak], 57.3 ± 6.7 mL·kg-1·min-1) completed five 4-km time trials (baseline, post-HAz, post-HA, post-IHT4, post-IHT8) in the heat (ambient temperature, 35.4°C ± 0.3°C; relative humidity, 46.7% ± 1.2%) on a motorized treadmill. After baseline time trial, participants performed HAz (109 ± 10 days) followed by post-HAz time trial. Then, participants completed 5 days of HA, which involved exercising to induce hyperthermia (38.50°C-39.75°C) for 60 minutes. Participants were then divided into 3 groups and completed IHT either twice per week (IHTMAX), once per week (IHTMIN), or not at all (IHTCON) over an 8-week period. The exercise used for the IHT matched the HA. Four-kilometer time trials were performed after 4 weeks (post-IHT4) and 8 weeks of IHT (post-IHT8). RESULTS Time trial was faster in post-HA (17.98 ± 2.51 minutes) compared with baseline (18.61 ± 3.06 minutes; P = 0.037) and post-HAz (18.66 ± 3.12 minutes; P = 0.023). Percentage change in time trial was faster in IHTMAX (-3.9% ± 5.2%) compared with IHTCON (11.5% ± 16.9%) (P = 0.020) and approached statistical significance with large effect (effect size = 0.96) compared with IHTMIN (1.6% ± 6.2%; P = 0.059) at post-IHT8. Additionally, IHTMAX (-2.2% ± 4.2%) was faster than IHTCON (3.6% ± 6.9%) (P = 0.05) at post-IHT4. CONCLUSION These results indicate that HA after HAz induces additional improvement in time-trial performance. IHT twice per week shows improvement after 8 weeks, while once per week maintains performance for 8 weeks. No IHT results in a loss of adaptations after 4 weeks and even greater losses after 8 weeks. CLINICAL RELEVANCE HA after HAz improves time-trial performance, twice a week of IHT improves performance further, and once a week of IHT maintains performance for at least 8 weeks.
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11
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Hunt LA, Hospers L, Smallcombe JW, Mavros Y, Jay O. Caffeine alters thermoregulatory responses to exercise in the heat only in caffeine-habituated individuals: a double-blind placebo-controlled trial. J Appl Physiol (1985) 2021; 131:1300-1310. [PMID: 34435513 DOI: 10.1152/japplphysiol.00172.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
To assess the impact of acute caffeine ingestion on thermoregulatory responses during steady-state exercise under moderate heat stress conditions in caffeine-habituated and nonhabituated individuals. Twenty-eight participants [14 habituated (HAB) (4 females) and 14 nonhabituated (NHAB) (6 females)] cycled at a fixed metabolic heat production (7 W·kg-1) for 60 min on two separate occasions 1 h after ingesting 1) 5 mg·kg-1 caffeine (CAF) or 2) 5 mg·kg-1 placebo (PLA), in a double-blinded, randomized, and counterbalanced order. Environmental conditions were 30.6 ± 0.9°C, 31 ± 1% relative humidity (RH). The end-exercise rise in esophageal temperature (ΔTes) from baseline was greater with CAF in the HAB group (CAF = 0.88 ± 0.29°C, PLA = 0.62 ± 0.34°C, P < 0.001), but not in the NHAB group (CAF = 1.00 ± 0.42°C, PLA = 1.00 ± 0.39°C, P = 0.94). For a given change in mean body temperature, rises in % of maximum skin blood flow were attenuated with CAF on the forearm (P = 0.015) and back (P = 0.021) in the HAB group, but not in the NHAB group (P ≥ 0.65). Dry heat loss was similar in the HAB (CAF = 31 ± 5 W·m-2, PLA = 33 ± 7 W·m-2) and NHAB groups (CAF = 31 ± 3 W·m-2, PLA 30 ± 4 W·m-2) (P ≥ 0.37). There were no differences in whole body sweat losses in both groups (HAB: CAF = 0.59 ± 0.15 kg, PLA = 0.56 ± 0.17 kg, NHAB:CAF = 0.53 ± 0.19 kg, PLA 0.52 ± 0.19 kg) (P ≥ 0.32). As the potential for both dry and evaporative heat loss was uninhibited by caffeine, we suggest that the observed ΔTes differences with CAF in the HAB group were due to alterations in internal heat distribution. Our findings support the common practice of participants abstaining from caffeine before participation in thermoregulatory research studies in compensable conditions.NEW & NOTEWORTHY We provide empirical evidence that acute caffeine ingestion exerts a thermoregulatory effect during exercise in the heat in caffeine-habituated individuals but not in nonhabituated individuals. Specifically, caffeine habituation was associated with a greater rise in esophageal temperature with caffeine compared with placebo, which appears to be driven by a blunted skin blood flow response. In contrast, no thermoregulatory differences were observed with caffeine in nonhabituated individuals. Caffeine did not affect sweating responses during exercise in the heat.
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Affiliation(s)
- Lindsey A Hunt
- Thermal Ergonomics Laboratory, Faculty of Medicine and Health, Sydney School of Health Sciences, The University of Sydney, Camperdown, New South Wales, Australia
| | - Lily Hospers
- Thermal Ergonomics Laboratory, Faculty of Medicine and Health, Sydney School of Health Sciences, The University of Sydney, Camperdown, New South Wales, Australia
| | - James W Smallcombe
- Thermal Ergonomics Laboratory, Faculty of Medicine and Health, Sydney School of Health Sciences, The University of Sydney, Camperdown, New South Wales, Australia
| | - Yorgi Mavros
- Thermal Ergonomics Laboratory, Faculty of Medicine and Health, Sydney School of Health Sciences, The University of Sydney, Camperdown, New South Wales, Australia.,Charles Perkins Centre, The University of Sydney, Camperdown, New South Wales, Australia
| | - Ollie Jay
- Thermal Ergonomics Laboratory, Faculty of Medicine and Health, Sydney School of Health Sciences, The University of Sydney, Camperdown, New South Wales, Australia.,Charles Perkins Centre, The University of Sydney, Camperdown, New South Wales, Australia
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12
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McCubbin AJ. Exertional heat stress and sodium balance: Leaders, followers, and adaptations. Auton Neurosci 2021; 235:102863. [PMID: 34391123 DOI: 10.1016/j.autneu.2021.102863] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 06/30/2021] [Accepted: 07/24/2021] [Indexed: 12/20/2022]
Abstract
Exertional heat stress presents a different acute challenge to salt balance compared to at rest. Sodium (Na+) and chloride (Cl-) losses during exercise are overwhelmingly driven by eccrine sweat glands (the "leader"), with minimal urinary excretion. Total salt losses are therefore largely influenced by thermoregulatory need, although adaptations from prior heat exposure or altered dietary intake influences sweat gland ion reabsorption, and therefore sweat Na+ ([Na+]sweat) and Cl- concentrations. The hypotheses that body Na+ and Cl- conservation, or their release from osmotically inactive stores, can occur during the timeframe of a single bout of exertional heat stress, has not been studied to date. The consequences of unreplaced Na+ and Cl- losses during exertional heat stress appear limited primarily to their interactions with water balance. However, the water volume ingested is substantially more influential than salt intake on total body water, plasma volume, osmolality, and thermoregulation during exercise. Acute salt and water loading 1-3 h prior to exercise can induce isosmotic hyperhydration in situations where this is deemed beneficial. During exercise, only scenarios of whole body [Na+]sweat > 75th centile, combined with fluid replacement >80% of losses, are likely to require significant replacement to prevent hyponatremia. Post-exercise, natriuresis resumes as the main regulator of salt losses, with the kidneys (the "follower") working to restore salt balance incurred from any exercise-induced deficit. If such a deficit exceeds usual dietary intake, and rapid restoration of hydration status is desirable, a deliberate increase in salt intake may assist in volume restoration.
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Affiliation(s)
- Alan J McCubbin
- Department of Nutrition, Dietetics and Food, Monash University, Notting Hill, Victoria, Australia.
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13
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Ravanelli N, Gendron P, Gagnon D. Revisiting the evaluation of central versus peripheral thermoregulatory control in humans. Am J Physiol Regul Integr Comp Physiol 2021; 321:R91-R99. [PMID: 34075801 DOI: 10.1152/ajpregu.00321.2020] [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] [Indexed: 11/22/2022]
Abstract
Human thermoregulatory control is often evaluated through the relationship between thermoeffector output and core or mean body temperature. In addition to providing a general indication of whether a variable of interest alters thermoregulatory control, this relationship is often used to determine how this alteration may occur. This latter interpretation relies upon two parameters of the thermoeffector output-body temperature relationship: the onset threshold and thermosensitivity. Traditionally, changes in the onset threshold and thermosensitivity are interpreted as "central" or "peripheral" modulation of thermoregulatory control, respectively. This mini-review revisits the origins of the thermoeffector output-body temperature relationship and its use to interpret "central" or "peripheral" modulation of thermoregulatory control. Against this background, we discuss the strengths and weaknesses of this approach and highlight that "central" thermoregulatory control reflects the neural control of body temperature whereas "peripheral" thermoregulatory control reflects properties specific to the thermoeffector organs. We highlight studies that employed more direct approaches to investigate the neural control of body temperature and peripheral properties of thermoeffector organs. We conclude by encouraging future investigations interested in studying thermoregulatory control to more directly investigate the component of the thermoeffector loop under investigation.heat; human; skin blood flow; sweat; thermoregulatory.
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Affiliation(s)
| | - Philippe Gendron
- Département des Sciences de l'Activité Physique, Université du Québec à Trois-Rivières, Trois-Rivières, Quebec, Canada.,Montreal Heart Institute, Montreal, Quebec, Canada
| | - Daniel Gagnon
- Montreal Heart Institute, Montreal, Quebec, Canada.,School of Kinesiology and Exercise Science, Faculty of Medicine, Université de Montréal, Montreal, Quebec, Canada
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14
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Ravanelli N, Jay O. The Change in Core Temperature and Sweating Response during Exercise Are Unaffected by Time of Day within the Wake Period. Med Sci Sports Exerc 2021; 53:1285-1293. [PMID: 33273272 DOI: 10.1249/mss.0000000000002575] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
INTRODUCTION Exercise thermoregulation studies typically control for time of day. The present study assessed whether circadian rhythm independently alters time-dependent changes in core temperature and sweating during exercise at a fixed rate of metabolic heat production (Hprod) during the wake period. METHODS Ten men (26 ± 2 yr, 76.6 ± 6.3 kg, 1.95 ± 0.10 m2) cycled for 60 min in three combinations of ambient temperature and Hprod (23°C-7.5 W·kg-1, 33°C-5.5 W·kg-1, and 33°C-7.5 W·kg-1) at two times of day (a.m.: 0800 h, p.m.: 1600 h). Rectal temperature (Tre), local sweat rate, and whole-body sweat losses were measured. RESULTS Absolute Tre was lower at baseline in a.m. versus p.m. for all three conditions (a.m.: 36.8°C ± 0.2°C, p.m.: 37.0°C ± 0.2°C, P < 0.01). The ΔTre was not altered by time of day (P > 0.22) and not different at 60 min between a.m. and p.m. for 23°C-7.5 W·kg-1 (a.m.: 0.83°C ± 0.14°C, p.m.: 0.75°C ± 0.20°C; P = 0.20), 33°C-5.5 W·kg-1 (a.m.: 0.51°C ± 0.14°C, p.m.: 0.47°C ± 0.14°C; P = 0.22), and 33°C-7.5 W·kg-1 (a.m.: 0.77°C ± 0.20°C, p.m.: 0.73°C ± 0.21°C; P = 0.80). The change in local sweat rate was unaffected by time of day (P > 0.16) and not different at 60 min in 23°C-7.5 W·kg-1 (a.m.: 0.67 ± 0.20 mg·cm-2·min-1, p.m.: 0.62 ± 0.21 mg·cm-2·min-1; P = 0.55), 33°C-5.5 W·kg-1 (a.m.: 0.59 ± 0.13 mg·cm-2·min-1, p.m.: 0.57 ± 0.12 mg·cm-2·min-1; P = 0.65), and 33°C-7.5 W·kg-1 (a.m.: 0.91 ± 0.19 mg·cm-2·min-1, p.m.: 0.84 ± 0.15 mg·cm-2·min-1; P = 0.33). Whole-body sweat loss was not different between a.m. and p.m. for 23°C-7.5 W·kg-1 (a.m.: 579 ± 72 g, p.m.: 579 ± 96 g; P = 0.99), 33°C-5.5 W·kg-1 (a.m.: 558 ± 48 g, p.m.: 555 ± 83 g; P = 0.89), and 33°C-7.5 W·kg-1 (a.m.: 796 ± 72 g, p.m.: 783 ± 75 g; P = 0.31). CONCLUSIONS The change in core temperature and sweating throughout a 60-min exercise bout in 23°C and 33°C were unaffected by circadian rhythm during the wake period when exercise intensity was prescribed to elicit comparable rates of Hprod, suggesting that scheduling thermoregulatory exercise trials for the same time of day is unnecessary.
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15
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Pizzey FK, Smith EC, Ruediger SL, Keating SE, Askew CD, Coombes JS, Bailey TG. The effect of heat therapy on blood pressure and peripheral vascular function: A systematic review and meta-analysis. Exp Physiol 2021; 106:1317-1334. [PMID: 33866630 DOI: 10.1113/ep089424] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Accepted: 04/08/2021] [Indexed: 01/09/2023]
Abstract
NEW FINDINGS What is the topic of this review? We have conducted a systematic review and meta-analysis on the current evidence for the effect of heat therapy on blood pressure and vascular function. What advances does it highlight? We found that heat therapy reduced mean arterial, systolic and diastolic blood pressure. We also observed that heat therapy improved vascular function, as assessed via brachial artery flow-mediated dilatation. Our results suggest that heat therapy is a promising therapeutic tool that should be optimized further, via mode and dose, for the prevention and treatment of cardiovascular disease risk factors. ABSTRACT Lifelong sauna exposure is associated with reduced cardiovascular disease risk. Recent studies have investigated the effect of heat therapy on markers of cardiovascular health. We aimed to conduct a systematic review with meta-analysis to determine the effects of heat therapy on blood pressure and indices of vascular function in healthy and clinical populations. Four databases were searched up to September 2020 for studies investigating heat therapy on outcomes including blood pressure and vascular function. Grading of Recommendations, Assessment, Development and Evaluations (GRADE) was used to assess the certainty of evidence. A total of 4522 titles were screened, and 15 studies were included. Healthy and clinical populations were included. Heat exposure was for 30-90 min, over 10-36 sessions. Compared with control conditions, heat therapy reduced mean arterial pressure [n = 4 studies; mean difference (MD): -5.86 mmHg, 95% confidence interval (CI): -8.63, -3.10; P < 0.0001], systolic blood pressure (n = 10; MD: -3.94 mmHg, 95% CI: -7.22, -0.67; P = 0.02) and diastolic blood pressure (n = 9; MD: -3.88 mmHg, 95% CI: -6.13, -1.63; P = 0.0007) and improved flow-mediated dilatation (n = 5; MD: 1.95%, 95% CI: 0.14, 3.76; P = 0.03). Resting heart rate was unchanged (n = 10; MD: -1.25 beats/min; 95% CI: -3.20, 0.70; P = 0.21). Early evidence also suggests benefits for arterial stiffness and cutaneous microvascular function. The certainty of evidence was moderate for the effect of heat therapy on systolic and diastolic blood pressure and heart rate and low for the effect of heat therapy on mean arterial pressure and flow-mediated dilatation. Heat therapy is an effective therapeutic tool to reduce blood pressure and improve macrovascular function. Future research should aim to optimize heat therapy, including the mode and dose, for the prevention and management of cardiovascular disease.
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Affiliation(s)
- Faith K Pizzey
- Physiology and Ultrasound Laboratory in Science and Exercise (PULSE), Centre for Research on Exercise, Physical Activity and Health (CRExPAH), School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - Emily C Smith
- Physiology and Ultrasound Laboratory in Science and Exercise (PULSE), Centre for Research on Exercise, Physical Activity and Health (CRExPAH), School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - Stefanie L Ruediger
- Physiology and Ultrasound Laboratory in Science and Exercise (PULSE), Centre for Research on Exercise, Physical Activity and Health (CRExPAH), School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - Shelley E Keating
- Physiology and Ultrasound Laboratory in Science and Exercise (PULSE), Centre for Research on Exercise, Physical Activity and Health (CRExPAH), School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - Christopher D Askew
- VasoActive Research Group, School of Health and Behavioural Sciences, University of the Sunshine Coast, Sippy Downs, Queensland, Australia.,Sunshine Coast Health Institute, Sunshine Coast Hospital and Health Service, Birtinya, Queensland, Australia
| | - Jeff S Coombes
- Physiology and Ultrasound Laboratory in Science and Exercise (PULSE), Centre for Research on Exercise, Physical Activity and Health (CRExPAH), School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - Tom G Bailey
- Physiology and Ultrasound Laboratory in Science and Exercise (PULSE), Centre for Research on Exercise, Physical Activity and Health (CRExPAH), School of Human Movement and Nutrition Sciences, The University of Queensland, St Lucia, Queensland, Australia.,School of Nursing Midwifery and Social Work, The University of Queensland, St Lucia, Queensland, Australia
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16
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Périard JD, Eijsvogels TMH, Daanen HAM. Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies. Physiol Rev 2021; 101:1873-1979. [PMID: 33829868 DOI: 10.1152/physrev.00038.2020] [Citation(s) in RCA: 132] [Impact Index Per Article: 44.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances, and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat by examining the benefits of heat acclimation, cooling strategies, and hyperhydration. Finally, contemporary controversies are summarized and future research directions are provided.
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Affiliation(s)
- Julien D Périard
- University of Canberra Research Institute for Sport and Exercise, Bruce, Australia
| | - Thijs M H Eijsvogels
- Department of Physiology, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Hein A M Daanen
- Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
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17
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Ashworth ET, Cotter JD, Kilding AE. Methods for improving thermal tolerance in military personnel prior to deployment. Mil Med Res 2020; 7:58. [PMID: 33248459 PMCID: PMC7700709 DOI: 10.1186/s40779-020-00287-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 11/10/2020] [Indexed: 12/16/2022] Open
Abstract
Acute exposure to heat, such as that experienced by people arriving into a hotter or more humid environment, can compromise physical and cognitive performance as well as health. In military contexts heat stress is exacerbated by the combination of protective clothing, carried loads, and unique activity profiles, making them susceptible to heat illnesses. As the operational environment is dynamic and unpredictable, strategies to minimize the effects of heat should be planned and conducted prior to deployment. This review explores how heat acclimation (HA) prior to deployment may attenuate the effects of heat by initiating physiological and behavioural adaptations to more efficiently and effectively protect thermal homeostasis, thereby improving performance and reducing heat illness risk. HA usually requires access to heat chamber facilities and takes weeks to conduct, which can often make it impractical and infeasible, especially if there are other training requirements and expectations. Recent research in athletic populations has produced protocols that are more feasible and accessible by reducing the time taken to induce adaptations, as well as exploring new methods such as passive HA. These protocols use shorter HA periods or minimise additional training requirements respectively, while still invoking key physiological adaptations, such as lowered core temperature, reduced heart rate and increased sweat rate at a given intensity. For deployments of special units at short notice (< 1 day) it might be optimal to use heat re-acclimation to maintain an elevated baseline of heat tolerance for long periods in anticipation of such an event. Methods practical for military groups are yet to be fully understood, therefore further investigation into the effectiveness of HA methods is required to establish the most effective and feasible approach to implement them within military groups.
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Affiliation(s)
- Edward Tom Ashworth
- Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, 17 Antares Place, Rosedale, Auckland, 0632 New Zealand
| | - James David Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, Otago 9016 New Zealand
| | - Andrew Edward Kilding
- Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, 17 Antares Place, Rosedale, Auckland, 0632 New Zealand
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18
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Ravanelli N, Gagnon D, Imbeault P, Jay O. A retrospective analysis to determine if exercise training-induced thermoregulatory adaptations are mediated by increased fitness or heat acclimation. Exp Physiol 2020; 106:282-289. [PMID: 32118324 DOI: 10.1113/ep088385] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 02/28/2020] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Are fitness-related improvements in thermoregulatory responses during uncompensable heat stress mediated by aerobic capacity V ̇ O 2 max or is it the partial heat acclimation associated with training? What is the main finding and its importance? During uncompensable heat stress, individuals with high and low V ̇ O 2 max displayed similar sweating and core temperature responses whereas exercise training in previously untrained individuals resulted in a greater sweat rate and a smaller rise in core temperature. These observations suggest that it is training, not V ̇ O 2 max per se, that mediates thermoregulatory improvements during uncompensable heat stress. ABSTRACT It remains unclear whether aerobic fitness, as defined by the maximum rate of oxygen consumption V ̇ O 2 max , independently improves heat dissipation in uncompensable environments, or whether the thermoregulatory adaptations associated with heat acclimation are due to repeated bouts of exercise-induced heat stress during regular aerobic training. The present analysis sought to determine if V ̇ O 2 max independently influences thermoregulatory sweating, maximum skin wettedness (ωmax ) and the change in rectal temperature (ΔTre ) during 60 min of exercise in an uncompensable environment (37.0 ± 0.8°C, 4.0 ± 0.2 kPa, 64 ± 3% relative humidity) at a fixed rate of heat production per unit mass (6 W kg-1 ). Retrospective analyses were performed on 22 participants (3 groups), aerobically unfit (UF; n = 7; V ̇ O 2 max : 41.7 ± 9.4 ml kg-1 min-1 ), aerobically fit (F; n = 7; V ̇ O 2 max : 55.6 ± 4.3 ml kg-1 min-1 ; P < 0.01) and aerobically unfit (n = 8) individuals, before (pre; V ̇ O 2 max : 45.8 ± 11.6 ml kg-1 min-1 ) and after (post; V ̇ O 2 max : 52.0 ± 11.1 ml kg-1 min-1 ; P < 0.001) an 8-week training intervention. ωmax was similar between UF (0.74 ± 0.09) and F (0.78 ± 0.08, P = 0.22). However, ωmax was greater post- (0.84 ± 0.08) compared to pre- (0.72 ± 0.06, P = 0.02) training. During exercise, mean local sweat rate (forearm and upper-back) was greater post- (1.24 ± 0.20 mg cm-2 min-1 ) compared to pre- (1.04 ± 0.25 mg cm-2 min-1 , P < 0.01) training, but similar between UF (0.94 ± 0.31 mg cm-2 min-1 , P = 0.90) and F (1.02 ± 0.30 mg cm-2 min-1 ). The ΔTre at 60 min of exercise was greater pre- (1.13 ± 0.16°C, P < 0.01) compared to post- (0.96 ± 0.14°C) training, but similar between UF (0.85 ± 0.29°C, P = 0.22) and F (0.95 ± 0.22°C). Taken together, aerobic training, not V ̇ O 2 max per se, confers an increased ωmax , greater sweat rate, and smaller rise in core temperature during uncompensable heat stress in fit individuals.
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Affiliation(s)
- Nicholas Ravanelli
- Cardiovascular Prevention and Rehabilitation Centre and Research Centre, Montreal Heart Institute, Montreal, QC, Canada.,Département de pharmacologie et physiologie, Université de Montréal, Montreal, QC, Canada
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Centre and Research Centre, Montreal Heart Institute, Montreal, QC, Canada.,Département de pharmacologie et physiologie, Université de Montréal, Montreal, QC, Canada
| | - Pascal Imbeault
- School of Human Kinetics, University of Ottawa, 200 Lees Ave, Ottawa, Canada
| | - Ollie Jay
- Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, NSW, Australia.,Charles Perkins Centre, University of Sydney, Sydney, NSW, Australia
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19
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Barry H, Chaseling GK, Moreault S, Sauvageau C, Behzadi P, Gravel H, Ravanelli N, Gagnon D. Improved neural control of body temperature following heat acclimation in humans. J Physiol 2020; 598:1223-1234. [PMID: 32011734 DOI: 10.1113/jp279266] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Accepted: 01/21/2020] [Indexed: 12/30/2022] Open
Abstract
KEY POINTS With the advent of more frequent extreme heat events, adaptability to hot environments will be crucial for the survival of many species, including humans. However, the mechanisms that mediate human heat adaptation have remained elusive. We tested the hypothesis that heat acclimation improves the neural control of body temperature. Skin sympathetic nerve activity, comprising the efferent neural signal that activates heat loss thermoeffectors, was measured in healthy adults exposed to passive heat stress before and after a 7 day heat acclimation protocol. Heat acclimation reduced the activation threshold for skin sympathetic nerve activity, leading to an earlier activation of cutaneous vasodilatation and sweat production. These findings demonstrate that heat acclimation improves the neural control of body temperature in humans. ABSTRACT Heat acclimation improves autonomic temperature regulation in humans. However, the mechanisms that mediate human heat adaptation remain poorly understood. The present study tested the hypothesis that heat acclimation improves the neural control of body temperature. Body temperatures, skin sympathetic nerve activity, cutaneous vasodilatation, and sweat production were measured in 14 healthy adults (nine men and five women, aged 27 ± 5 years) during passive heat stress performed before and after a 7 day heat acclimation protocol. Heat acclimation increased whole-body sweat rate [+0.54 L h-1 (0.32, 0.75), P < 0.01] and reduced resting core temperature [-0.29°C (-0.40, -0.18), P < 0.01]. During passive heat stress, the change in mean body temperature required to activate skin sympathetic nerve activity was reduced [-0.21°C (-0.34, -0.08), P < 0.01] following heat acclimation. The earlier activation of skin sympathetic nerve activity resulted in lower activation thresholds for cutaneous vasodilatation [-0.18°C (-0.35, -0.01), P = 0.04] and local sweat rate [-0.13°C (-0.24, -0.01), P = 0.03]. These results demonstrate that heat acclimation leads to an earlier activation of the neural efferent outflow that activates the heat loss thermoeffectors of cutaneous vasodilatation and sweating.
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Affiliation(s)
- Hadiatou Barry
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Georgia K Chaseling
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Samuel Moreault
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Claudia Sauvageau
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Parya Behzadi
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Hugo Gravel
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Nicholas Ravanelli
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Canada, Montréal, QC, Canada.,Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
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