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Meade RD, Akerman AP, Notley SR, Kirby NV, Sigal RJ, Kenny GP. Exploring the contribution of inter-individual factors to the development of physiological heat strain in older adults exposed to simulated indoor overheating. Appl Physiol Nutr Metab 2024. [PMID: 38830263 DOI: 10.1139/apnm-2024-0135] [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: 06/05/2024]
Abstract
Older adults are at elevated risk of heat-related mortality due to age-associated declines in thermoregulatory and cardiovascular function. However, the inter-individual factors that exacerbate physiological heat strain during heat exposure remain unclear, making it challenging to identify more heat-vulnerable subgroups. We therefore explored factors contributing to inter-individual variability in physiological responses of older adults exposed to simulated hot weather. Thirty-seven older adults (61-80 years, 16 females) rested for 8 h in 31 and 36 °C (45% relative humidity). Core (rectal) temperature, heart rate (HR), HR variability, mean arterial pressure (MAP), and cardiac autonomic responses to standing were measured at baseline and end-exposure. Bootstrapped least absolute shrinkage and selection operator regression was used to evaluate whether variation in these responses was related to type 2 diabetes (T2D, n = 10), hypertension (n = 18), age, sex, body morphology, habitual physical activity levels, and/or heat-acclimatization. T2D was identified as a predictor of end-exposure HR (with vs. without: 13 beats/min (bootstrap 95% confidence interval: 6, 23)), seated MAP (-7 mmHg (-18, 1)), and the systolic pressure response to standing (20 mmHg (4, 36)). HR was also influenced by sex (female vs. male: 8 beats/min (1, 16)). No other predictors were identified. The inter-individual factors explored did not meaningfully contribute to the variation in body temperature responses in older adults exposed to simulated indoor overheating. By contrast, cardiovascular responses were exacerbated in females and individuals with T2D. These findings improve understanding of how inter-individual differences contribute to heat-induced physiological strain in older persons.
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Affiliation(s)
- Robert D Meade
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada
| | - Ashley P Akerman
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada
| | - Sean R Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada
| | - Nathalie V Kirby
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada
| | - Ronald J Sigal
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada
- Departments of Medicine, Cardiac Sciences and Community Health Sciences, Faculties of Medicine and Kinesiology, University of Calgary, Calgary, AB, Canada
- Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada
- Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada
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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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Kirby NV, Meade RD, Richards BJ, Notley SR, Kenny GP. Hormonal intrauterine devices and heat exchange during exercise. J Physiol 2024; 602:875-890. [PMID: 38367251 DOI: 10.1113/jp285977] [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: 11/14/2023] [Accepted: 01/22/2024] [Indexed: 02/19/2024] Open
Abstract
Synthetic progestins in oral contraceptives are thought to blunt heat dissipation by reducing skin blood flow and sweating. However, whether progestin-releasing intrauterine devices (IUDs) modulate heat loss during exercise-heat stress is unknown. We used direct calorimetry to measure whole-body total (dry + evaporative) heat loss in young, physically active women (mean (SD); aged 24 (4) years,V ̇ O 2 peak ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{peak}}}}$ 39.3 (5.3) ml/kg/min) with (IUD; n = 19) and without (Control; n = 17) IUDs in the follicular and luteal phases of the menstrual cycle during light- and moderate-intensity exercise at fixed rates of heat production (∼175 and ∼275 W/m2 ) in 30°C, ∼21% relative humidity. Between-group and -phase differences were evaluated using traditional hypothesis testing and statistical equivalence testing within pre-determined bounds (±11 W/m2 ; difference required to elicit a ±0.3°C difference in core temperature over 1 h) in each exercise bout. Whole-body total heat loss was statistically equivalent between groups within ±11 W m-2 (IUD-Control [90% CIs]; Light: -2 [-8, 5] W/m2 , P = 0.007; Moderate: 0 [-6, 6] W/m2 , P = 0.002), as were dry and evaporative heat loss (P ≤ 0.023), except for evaporative heat loss during moderate-intensity exercise (equivalence: P = 0.063, difference: P = 0.647). Whole-body total and evaporative heat loss were not different between phases (P ≥ 0.267), but dry heat loss was 3 [95% CIs: 1, 5] W/m2 greater in the luteal phase (P ≤ 0.022). Despite this, all whole-body heat loss outcomes were equivalent between phases (P ≤ 0.003). These findings expand our understanding of the factors that modulate heat exchange in women and provide valuable mechanistic insight of the role of endogenous and exogenous female sex hormones in thermoregulation. KEY POINTS: Progestin released by hormonal intrauterine devices (IUDs) may negatively impact heat dissipation during exercise by blunting skin blood flow and sweating. However, the influence of IUDs on thermoregulation has not previously been assessed. We used direct calorimetry to show that IUD users and non-users display statistically equivalent whole-body dry and evaporative heat loss, body heat storage and oesophageal temperature during moderate- and high-intensity exercise in a warm, dry environment, indicating that IUDs do not appear to compromise exercise thermoregulation. However, within IUD users and non-users, dry heat loss was increased and body heat storage and oesophageal temperature were reduced in the luteal compared to the follicular phase of the menstrual cycle, though these effects were small and unlikely to be practically meaningful. Together, these findings expand our understanding of the factors that modulate heat exchange in women and have important practical implications for the design of future studies of exercise thermoregulation.
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Affiliation(s)
- Nathalie V Kirby
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Robert D Meade
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Brodie J Richards
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Sean R Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
- Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
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Notley SR, Akerman AP, D'Souza AW, Meade RD, McCourt ER, McCormick JJ, Kenny GP. Dose-dependent nonthermal modulation of whole body heat exchange during dynamic exercise in humans. Am J Physiol Regul Integr Comp Physiol 2024; 326:R53-R65. [PMID: 37955132 DOI: 10.1152/ajpregu.00203.2023] [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: 08/21/2023] [Revised: 10/30/2023] [Accepted: 10/30/2023] [Indexed: 11/14/2023]
Abstract
To maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate whole body dry and evaporative heat exchange. These responses are modulated by the rise in body temperature (thermal factors), as well as several nonthermal factors implicated in the cardiovascular response to exercise (i.e., central command, mechanoreceptors, and metaboreceptors). However, the way these nonthermal factors interact with thermal factors to maintain heat balance remains poorly understood. We therefore used direct calorimetry to quantify the effects of dose-dependent increases in the activation of these nonthermal stimuli on whole body dry and evaporative heat exchange during dynamic exercise. In a randomized crossover design, eight participants performed 45-min cycling at a fixed metabolic heat production (200 W/m2) in warm, dry conditions (30°C, 20% relative humidity) on four separate occasions, differing only in the level of lower-limb compression applied via bilateral thigh cuffs pressurized to 0, 30, 60, or 90 mmHg. This model provoked increments in nonthermal activation while ensuring the heat loss required to balance heat production was matched across trials. At end-exercise, dry heat loss was 2 W/m2 [1, 3] lower per 30-mmHg pressure increment (P = 0.006), whereas evaporative heat loss was elevated 5 W/m2 [3, 7] with each pressure increment (P < 0.001). Body heat storage and esophageal temperature did not differ across conditions (both P ≥ 0.600). Our findings indicate that the nonthermal factors engaged during exercise exert dose-dependent, opposing effects on whole body dry and evaporative heat exchange, which do not significantly alter heat balance.NEW & NOTEWORTHY To maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate dry and evaporative heat exchange. These responses are modulated by body temperatures (thermal factors) and several nonthermal factors (e.g., central command, metaboreceptors), although the way thermal and nonthermal factors interact to regulate body temperature is poorly understood. We demonstrate that nonthermal factors exert dose-dependent, opposing effects on dry and evaporative heat loss, without altering heat storage during dynamic exercise.
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Affiliation(s)
- Sean R Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Ashley P Akerman
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Andrew W D'Souza
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Robert D Meade
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Emma R McCourt
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - James J McCormick
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
- Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
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Rastmanesh R, Flack KD. Dietary Temperature's Influence on Energy Balance in Humans: Protocol for a Randomized Controlled Trial and Crossover Design. JMIR Res Protoc 2023; 12:e42846. [PMID: 36867437 PMCID: PMC10024216 DOI: 10.2196/42846] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 12/31/2022] [Accepted: 01/03/2023] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND According to the first law of thermodynamics, energy cannot be created or destroyed in an isolated system. Water has a characteristically high heat capacity, indicating that the temperature of ingested fluids and meals could contribute to energy homeostasis. Citing the underlying molecular mechanisms, we present a novel hypothesis that states that the temperature of one's food and drink contributes to energy balance and plays a role in the development of obesity. We provide strong associations with certain molecular mechanisms that are activated by heat and correlate them with obesity and a hypothetical trial that could test this hypothesis. We conclude that if meal or drink temperature proves to contribute to energy homeostasis, then depending on its contribution and scale, future clinical trials should attempt to adjust this effect when analyzing data. In addition, previous research and established relationships of disease states with dietary patterns, energy intake, and food component intakes should be revisited. We understand the common assumption that thermal energy in food is absorbed by the body during digestion and dissipated as heat into the environment, not contributing to the energy balance. We challenge this assumption herein, including a proposed study design that would test our hypothesis. OBJECTIVE This paper hypothesizes that the temperature of ingested foods or fluids influences energy homeostasis through the expression of heat shock proteins (HSPs), especially HSP-70 and HSP-90, which are expressed to a greater extent in obesity and are known to cause deficits in glucose metabolism. METHODS We provide preliminary evidence supporting our hypothesis that greater dietary temperatures disproportionally induce activation of both intracellular and extracellular HSPs and that these HSPs influence energy balance and contribute to obesity. RESULTS This trial protocol has not been initiated and funding has not been sought at the time of this publication. CONCLUSIONS To date, no clinical trials are available regarding the potential effects of meal and fluid temperature on weight status or its confounding effects in data analysis. A potential mechanism is proposed as a basis by which higher temperatures of foods and beverages might influence energy balance via HSP expression. On the basis of the evidence supporting our hypothesis, we propose a clinical trial that will further elucidate these mechanisms. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID) PRR1-10.2196/42846.
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Affiliation(s)
| | - Kyle D Flack
- Department of Dietetics and Human Nutrition, University of Kentucky, Lexington, KY, United States
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Heating Up to Keep Cool: Benefits and Persistence of a Practical Heat Acclimation Protocol in Elite Female Olympic Team-Sport Athletes. Int J Sports Physiol Perform 2023; 18:276-283. [PMID: 36720237 DOI: 10.1123/ijspp.2022-0071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 10/14/2022] [Accepted: 11/07/2022] [Indexed: 02/02/2023]
Abstract
PURPOSE Although recommendations for effective heat acclimation (HA) strategies for many circumstances exist, best-practice HA protocols specific to elite female team-sport athletes are yet to be established. Therefore, the authors aimed to investigate the effectiveness and retention of a passive HA protocol integrated in a female Olympic rugby sevens team training program. METHODS Twelve elite female rugby sevens athletes undertook 10 days of passive HA across 2 training weeks. Tympanic temperature (TTymp), sweat loss, heart rate, and repeated 6-second cycling sprint performance were assessed using a sport-specific heat stress test Pre-HA, after 3 days (Mid-HA), after 10 days (Post-HA), and 15 days post-HA (Decay). RESULTS Compared with Pre-HA, submaximal TTymp was lower Mid-HA and Post-HA (both by -0.2 [0.7] °C; d ≥ 0.71), while resting TTymp was lower Post-HA (by -0.3 [0.2] °C; d = 0.81). There were no differences in TTymp at Decay compared with Pre-HA, nor were there any differences in heart rate or sweat loss at any time points. Mean peak 6-second power output improved Mid-HA and Post-HA (76 [36] W; 75 [34] W, respectively; d ≥ 0.45) compared with Pre-HA. The observed performance improvement persisted at Decay by 65 (45) W (d = 0.41). CONCLUSIONS Ten days of passive HA can elicit some thermoregulatory and performance benefits when integrated into a training program in elite female team-sport athletes. However, such a protocol does not provide a sufficient thermal impulse for thermoregulatory adaptations to be retained after 15 days with no further heat stimulus.
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Kirby NV, Meade RD, Poirier MP, Sigal RJ, Boulay P, Kenny GP. Association between haemoglobin A 1c and whole-body heat loss during exercise-heat stress in physically active men with type 2 diabetes. Exp Physiol 2023; 108:338-343. [PMID: 36724895 PMCID: PMC10103889 DOI: 10.1113/ep090915] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2022] [Accepted: 11/30/2022] [Indexed: 02/03/2023]
Abstract
NEW FINDINGS What is the central question of this study? Is the impairment in heat dissipation during exercise observed in men with type 2 diabetes related to glycaemic control (indexed by glycated haemoglobin; haemoglobin A1c )? What is the main finding and its importance? No association was found between haemoglobin A1c (range: 5.1-9.1%) and whole-body heat loss in men with type 2 diabetes during exercise in the heat. However, individuals with elevated haemoglobin A1c exhibited higher body core temperature and heart rate responses. Thus, while haemoglobin A1c is not associated with heat loss per se, it may still have important implications for physiological strain during exercise. ABSTRACT Type 2 diabetes is associated with a reduced capacity to dissipate heat. It is unknown whether this impairment is related to glycaemic control (indexed by glycated haemoglobin; haemoglobin A1c ) is unknown. We evaluated the association between haemoglobin A1c and whole-body heat loss (via direct calorimetry), body core temperature, and heart rate in 26 physically active men with type 2 diabetes (43-73 years; HbA1c 5.1-9.1%) during exercise at increasing rates of metabolic heat production (∼150, 200, 250 W m-2 ) in the heat (40°C, ∼17% relative humidity). Haemoglobin A1c was not associated with whole-body heat loss (P = 0.617), nor the increase in core temperature from pre-exercise (P = 0.347). However, absolute core temperature and heart rate were elevated ∼0.2°C (P = 0.014) and ∼6 beats min-1 (P = 0.049), respectively, with every percentage point increase in haemoglobin A1c . Thus, while haemoglobin A1c does not appear to modify diabetes-related reductions in capacity for heat dissipation, it may still have important implications for physiological strain during exercise-heat stress.
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Affiliation(s)
- Nathalie V. Kirby
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
| | - Robert D. Meade
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
- Harvard T.H. Chan School of Public HealthHarvard UniversityBostonMAUSA
| | - Martin P. Poirier
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
- Human Performance Research and DevelopmentCanadian Forces Morale and Welfare ServicesOttawaOntarioCanada
| | - Ronald J. Sigal
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
- Departments of MedicineCardiac Sciences, and Community Health SciencesCumming School of MedicineFaculties of Medicine and KinesiologyUniversity of CalgaryCalgaryAlbertaCanada
- Clinical Epidemiology ProgramOttawa Hospital Research InstituteOttawaOntarioCanada
| | - Pierre Boulay
- Faculty of Physical Activity SciencesUniversity of SherbrookeSherbrookeQuebecCanada
| | - Glen P. Kenny
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
- Clinical Epidemiology ProgramOttawa Hospital Research InstituteOttawaOntarioCanada
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Haugen T, Sandbakk Ø, Seiler S, Tønnessen E. The Training Characteristics of World-Class Distance Runners: An Integration of Scientific Literature and Results-Proven Practice. SPORTS MEDICINE - OPEN 2022; 8:46. [PMID: 35362850 PMCID: PMC8975965 DOI: 10.1186/s40798-022-00438-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/18/2021] [Accepted: 03/22/2022] [Indexed: 11/23/2022]
Abstract
In this review we integrate the scientific literature and results-proven practice and outline a novel framework for understanding the training and development of elite long-distance performance. Herein, we describe how fundamental training characteristics and well-known training principles are applied. World-leading track runners (i.e., 5000 and 10,000 m) and marathon specialists participate in 9 ± 3 and 6 ± 2 (mean ± SD) annual competitions, respectively. The weekly running distance in the mid-preparation period is in the range 160–220 km for marathoners and 130–190 km for track runners. These differences are mainly explained by more running kilometers on each session for marathon runners. Both groups perform 11–14 sessions per week, and ≥ 80% of the total running volume is performed at low intensity throughout the training year. The training intensity distribution vary across mesocycles and differ between marathon and track runners, but common for both groups is that volume of race-pace running increases as the main competition approaches. The tapering process starts 7–10 days prior to the main competition. While the African runners live and train at high altitude (2000–2500 m above sea level) most of the year, most lowland athletes apply relatively long altitude camps during the preparation period. Overall, this review offers unique insights into the training characteristics of world-class distance runners by integrating scientific literature and results-proven practice, providing a point of departure for future studies related to the training and development in the Olympic long-distance events.
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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: 59] [Impact Index Per Article: 29.5] [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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Zheng H, Badenhorst CE, Lei TH, Che Muhamed AM, Liao YH, Fujii N, Kondo N, Mündel T. Do E 2 and P 4 contribute to the explained variance in core temperature response for trained women during exertional heat stress when metabolic rates are very high? Eur J Appl Physiol 2022; 122:2201-2212. [PMID: 35796828 PMCID: PMC9463225 DOI: 10.1007/s00421-022-04996-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Accepted: 06/17/2022] [Indexed: 12/02/2022]
Abstract
Purpose Women remain underrepresented in the exercise thermoregulation literature despite their participation in leisure-time and occupational physical activity in heat-stressful environments continuing to increase. Here, we determined the relative contribution of the primary ovarian hormones (estrogen [E2] and progesterone [P4]) alongside other morphological (e.g., body mass), physiological (e.g., sweat rates), functional (e.g., aerobic fitness) and environmental (e.g., vapor pressure) factors in explaining the individual variation in core temperature responses for trained women working at very high metabolic rates, specifically peak core temperature (Tpeak) and work output (mean power output). Methods Thirty-six trained women (32 ± 9 year, 53 ± 9 ml·kg−1·min−1), distinguished by intra-participant (early follicular and mid-luteal phases) or inter-participant (ovulatory vs. anovulatory vs. oral contraceptive pill user) differences in their endogenous E2 and P4 concentrations, completed a self-paced 30-min cycling work trial in warm–dry (2.2 ± 0.2 kPa, 34.1 ± 0.2 °C, 41.4 ± 3.4% RH) and/or warm–humid (3.4 ± 0.1 kPa, 30.2 ± 1.2 °C, 79.8 ± 3.7% RH) conditions that yielded 115 separate trials. Stepwise linear regression was used to explain the variance of the dependent variables. Results Models were able to account for 60% of the variance in Tpeak (\documentclass[12pt]{minimal}
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\begin{document}$$\overline{R }$$\end{document}R¯2: 9% perceived exertion). Conclusion E2 contributes a small amount toward the core temperature response in trained women, whereby starting core temperature and peak aerobic power explain the greatest variance in Tpeak and work output, respectively.
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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, Nutrition, Massey University, Auckland, New Zealand
| | - Tze-Huan Lei
- College of Physical Education, Hubei Normal University, Huangshi, China
| | | | - Yi-Hung Liao
- Department of Exercise and Health Science, National Taipei University of Nursing and Health Sciences, Taipei, Taiwan
| | - Naoto Fujii
- 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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11
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Li L, Sun B, Hu Z, Zhang J, Gao S, Bian H, Wu J. Heat Strain Evaluation of Power Grid Outdoor Workers Based on a Human Bioheat Model. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:ijerph19137843. [PMID: 35805501 PMCID: PMC9266139 DOI: 10.3390/ijerph19137843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 06/20/2022] [Accepted: 06/23/2022] [Indexed: 12/10/2022]
Abstract
Power grid outdoor workers are usually exposed to hot environments and could suffer the threats to occupational health and safety like heat strain and injury. In order to predict and assess the thermophysiological responses of grid workers in the heat, the clothing thermal insulation of grid worker ensembles was measured by a thermal manikin and a multi-segment human bioheat model was employed to evaluate the thermophysiological response parameters of grid workers such as core temperature, skin temperature and sweat loss. The results show that working in a hot environment can cause a obvious increase in core temperature and skin temperature of grid workers, and the acceptable maximum working time of grid workers varies greatly in different hot environments. A reasonable work organization strategy can effectively decrease the core temperature and sweat loss, increasing the duration of acceptable maximum working time for grid workers. This study is helpful to assess heat-related risks of grid workers and support power grid companies to rationalize work organization strategies and personal protection guidelines.
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Affiliation(s)
- Letian Li
- School of Emergency Management and Safety Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China; (L.L.); (B.S.); (Z.H.)
| | - Boyang Sun
- School of Emergency Management and Safety Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China; (L.L.); (B.S.); (Z.H.)
| | - Zhuqiang Hu
- School of Emergency Management and Safety Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China; (L.L.); (B.S.); (Z.H.)
| | - Jun Zhang
- Grid Development Integrated Research Department, State Grid Energy Research Institute Co., Ltd., Beijing 102209, China; (J.Z.); (H.B.)
| | - Song Gao
- Safety Supervision and Quality Department, State Grid Liaoning Electric Power Supply Co., Ltd., Shenyang 110006, China;
| | - Haifeng Bian
- Grid Development Integrated Research Department, State Grid Energy Research Institute Co., Ltd., Beijing 102209, China; (J.Z.); (H.B.)
| | - Jiansong Wu
- School of Emergency Management and Safety Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China; (L.L.); (B.S.); (Z.H.)
- Correspondence:
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12
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Renberg J, Lignier MJ, Wiggen ØN, Færevik H, Helgerud J, Sandsund M. Heat tolerance during uncompensable heat stress in men and women wearing firefighter personal protective equipment. APPLIED ERGONOMICS 2022; 101:103702. [PMID: 35121406 DOI: 10.1016/j.apergo.2022.103702] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 12/21/2021] [Accepted: 01/26/2022] [Indexed: 06/14/2023]
Abstract
Firefighters run a risk of heat strain during occupational tasks. The number of female firefighters has been increasing, but research relevant to this group is still scarce. We aimed to investigate whether there are any sex differences in heat tolerance or physiological responses during uncompensable heat stress while wearing firefighter personal protective equipment. Twelve female (28 ± 7 years, 66 ± 5 kg, 51.7 ± 4.7 mL kg-1 min-1) and 12 male (27 ± 7 years, 83 ± 8 kg, 58.8 ± 7.5 mL kg-1 min-1) participants performed walking (maximum of 60 min) at 6W·kg-1, 40 °C, and 14% relative humidity. No differences were observed between groups in heat tolerance, rectal temperature, heart rate, percent body mass loss, thermal sensation, and rate of perceived exertion. Thus, when personnel are selected using gender-neutral physical employment standards, sex is not an independent factor influencing heat tolerance when wearing firefighter personal protective equipment during uncompensable heat stress.
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Affiliation(s)
- Julie Renberg
- SINTEF Digital, Department of Health Research, Trondheim, Norway.
| | - Maxime Jeanovitch Lignier
- Norwegian University of Science and Technology (NTNU), Department of Neuromedicine and Movement Science, Trondheim, Norway
| | | | - Hilde Færevik
- SINTEF Digital, Department of Health Research, Trondheim, Norway
| | - Jan Helgerud
- Norwegian University of Science and Technology (NTNU), Department of Circulation and Medical Imaging, Trondheim, Norway; Myworkout, Medical Rehabilitation Centre, Trondheim, Norway
| | - Mariann Sandsund
- SINTEF Digital, Department of Health Research, Trondheim, Norway
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13
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Ioannou LG, Foster J, Morris NB, Piil JF, Havenith G, Mekjavic IB, Kenny GP, Nybo L, Flouris AD. Occupational heat strain in outdoor workers: A comprehensive review and meta-analysis. Temperature (Austin) 2022; 9:67-102. [PMID: 35655665 PMCID: PMC9154804 DOI: 10.1080/23328940.2022.2030634] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 01/11/2022] [Accepted: 01/13/2022] [Indexed: 12/29/2022] Open
Abstract
The present comprehensive review (i) summarizes the current knowledge on the impacts of occupational heat stress on outdoor workers, (ii) provides a historical background on this issue, (iii) presents a meta-analysis of published data, (iv) explores inter-individual and intra-individual factors, (v) discusses the available heat mitigation strategies, (vi) estimates physical work capacity, labour productivity, and metabolic rate for the year 2030, and (vii) provides an overview of existing policy and legal frameworks on occupational heat exposure. Meta-analytic findings from 38 field studies that involved monitoring 2,409 outdoor workers across 41 jobs in 21 countries suggest that occupational heat stress increases the core (r = 0.44) and skin (r = 0.44) temperatures, as well as the heart rate (r = 0.38) and urine specific gravity (r = 0.13) of outdoor workers (all p < 0.05). Moreover, it diminishes the capacity of outdoor workers for manual labour (r = -0.82; p < 0.001) and is responsible for more than two thirds of the reduction in their metabolic rate. Importantly, our analysis shows that physical work capacity is projected to be highly affected by the ongoing anthropogenic global warming. Nevertheless, the metabolic rate and, therefore, labour productivity are projected to remain at levels higher than the workers' physical work capacity, indicating that people will continue to work more intensely than they should to meet their financial obligations for food and shelter. In this respect, complementary measures targeting self-pacing, hydration, work-rest regimes, ventilated garments, and mechanization can be adopted to protect outdoor workers.
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Affiliation(s)
- Leonidas G. Ioannou
- FAME Laboratory, Department of Physical Education and Sport Science, University of Thessaly, Trikala, Greece
| | - Josh Foster
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Nathan B. Morris
- Department of Human Physiology & Nutrition, University of Colorado, Springs, Colorado, USA
| | - Jacob F. Piil
- Department of Nutrition, Exercise and Sports, August Krogh Building, University of Copenhagen, Copenhagen, Denmark
| | - George Havenith
- Environmental Ergonomics Research Centre, Loughborough Design School, Loughborough University, Loughborough, UK
| | - Igor B. Mekjavic
- Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia
| | - Glen P. Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Lars Nybo
- Department of Nutrition, Exercise and Sports, August Krogh Building, University of Copenhagen, Copenhagen, Denmark
| | - Andreas D. Flouris
- FAME Laboratory, Department of Physical Education and Sport Science, University of Thessaly, Trikala, Greece
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
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14
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Notley SR, Akerman AP, Friesen BJ, Poirier MP, McCourt E, Flouris A, Kenny GP. Heat tolerance and the validity of occupational heat exposure limits in women during moderate-intensity work. Appl Physiol Nutr Metab 2022; 47:711-724. [PMID: 35259026 DOI: 10.1139/apnm-2022-0003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To mitigate excessive rises in core temperature (>1°C) in non heat-acclimatized workers, the American Conference of Governmental Industrial Hygienists (ACGIH) provide heat stress limits (Action Limit Values; ALV), defined by the wet-bulb globe temperature (WBGT) and a worker's metabolic rate. However, since these limits are based on data from men, their suitability for women remains unclear. We therefore assessed core temperature and heart rate in men (n=19; body surface area-to-mass ratio: 250 (SD 17) cm2/kg) and women (n=15; body surface area-to-mass ratio: 268 (SD 24) cm2/kg) aged 18-45 years during 180-min walking at a moderate metabolic rate (200 W/m2) in WBGTs below (16 and 24°C) and above (28 and 32°C) ACGIH ALV. Sex did not significantly influence (i) rises in core temperature, irrespective of WBGT, (ii) the proportion of participants with rises in core temperature >1°C in environments below ACGIH limits, and (iii) work duration before rises in core temperature exceeded 1°C or volitional termination in environments above ACGIH limits. Although further studies are needed, these findings indicate that for the purpose of mitigating rises in core temperature exceeding recommended limits (>1°C), ACGIH guidelines have comparable effectiveness in non heat-acclimatized men and women when working at a moderate metabolic rate. Novelty points • Sex did not appreciably influence thermal strain nor the proportion of participants with core temperatures exceeding recommended limits. • Sex did not significantly influence tolerance to uncompensable heat stress • Despite originating from data obtained in only men, current occupational heat stress guidance offered comparable effectiveness in men and women.
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Affiliation(s)
| | | | - Brian J Friesen
- University of Ottawa, Human Kinetics, Ottawa, Ontario, Canada;
| | - Martin P Poirier
- University of Ottawa, School of Human Kinetics, Faculty of Health Sciences, Ottawa, Ontario, Canada;
| | | | - Andreas Flouris
- FAME Laboratory, Institute of Human Performance and Rehabilitation, Centre for Research and Technology Thessaly, Trikala, Thessaly, Greece.,Department of Research and Technology Development, Biomnic Ltd., Trikala, Thessaly, Greece;
| | - Glen P Kenny
- University of Ottawa, 6363, Ottawa, Canada, K1N 6N5.,Ottawa Hospital Research Institute, 10055, Ottawa, Canada, K1Y 4E9;
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15
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Brownlow M, Mizzi JX. Epidemiology of exertional heat illness in Thoroughbred racehorses in temperate eastern Australia: The role of extrinsic (environmental) factors in disease causation. EQUINE VET EDUC 2022. [DOI: 10.1111/eve.13627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- M. Brownlow
- Racing Australia Sydney New South Wales Australia
| | - J. X. Mizzi
- Department of Regulation, Welfare and Biosecurity Policy The Hong Kong Jockey Club, Sha Tin Racecourse Hong Kong Sha Tin China
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16
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Foster J, Smallcombe JW, Hodder SG, Jay O, Flouris AD, Morris NB, Nybo L, Havenith G. Aerobic fitness as a parameter of importance for labour loss in the heat. J Sci Med Sport 2021; 24:824-830. [DOI: 10.1016/j.jsams.2021.05.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 03/16/2021] [Accepted: 05/02/2021] [Indexed: 02/07/2023]
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17
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Foster J, Smallcombe JW, Hodder S, Jay O, Flouris AD, Nybo L, Havenith G. An advanced empirical model for quantifying the impact of heat and climate change on human physical work capacity. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2021; 65:1215-1229. [PMID: 33674931 PMCID: PMC8213606 DOI: 10.1007/s00484-021-02105-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Revised: 01/14/2021] [Accepted: 02/23/2021] [Indexed: 05/20/2023]
Abstract
Occupational heat stress directly hampers physical work capacity (PWC), with large economic consequences for industries and regions vulnerable to global warming. Accurately quantifying PWC is essential for forecasting impacts of different climate change scenarios, but the current state of knowledge is limited, leading to potential underestimations in mild heat, and overestimations in extreme heat. We therefore developed advanced empirical equations for PWC based on 338 work sessions in climatic chambers (low air movement, no solar radiation) spanning mild to extreme heat stress. Equations for PWC are available based on air temperature and humidity, for a suite of heat stress assessment metrics, and mean skin temperature. Our models are highly sensitive to mild heat and to our knowledge are the first to include empirical data across the full range of warm and hot environments possible with future climate change across the world. Using wet bulb globe temperature (WBGT) as an example, we noted 10% reductions in PWC at mild heat stress (WBGT = 18°C) and reductions of 78% in the most extreme conditions (WBGT = 40°C). Of the different heat stress indices available, the heat index was the best predictor of group level PWC (R2 = 0.96) but can only be applied in shaded conditions. The skin temperature, but not internal/core temperature, was a strong predictor of PWC (R2 = 0.88), thermal sensation (R2 = 0.84), and thermal comfort (R2 = 0.73). The models presented apply to occupational workloads and can be used in climate projection models to predict economic and social consequences of climate change.
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Affiliation(s)
- Josh Foster
- Environmental Ergonomics Research Centre, School of Design and Creative Arts Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
| | - James W Smallcombe
- Environmental Ergonomics Research Centre, School of Design and Creative Arts Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
| | - Simon Hodder
- Environmental Ergonomics Research Centre, School of Design and Creative Arts Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
| | - Ollie Jay
- Thermal Ergonomics Laboratory, Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia
| | | | - Lars Nybo
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - George Havenith
- Environmental Ergonomics Research Centre, School of Design and Creative Arts Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK.
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18
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Hutchins KP, Borg DN, Bach AJE, Bon JJ, Minett GM, Stewart IB. Female (Under) Representation in Exercise Thermoregulation Research. SPORTS MEDICINE - OPEN 2021; 7:43. [PMID: 34156570 PMCID: PMC8219822 DOI: 10.1186/s40798-021-00334-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 06/06/2021] [Indexed: 01/12/2023]
Abstract
BACKGROUND Despite an increasing rate of women participating in professional sports, emergency services, and military settings where they are exposed to exertional heat stress, our understanding of female thermoregulation and the detrimental effects of heat on women's performance, especially regarding the menstrual cycle, is limited. This review aimed to quantify the representation of women in exercise thermoregulation research between 2010 and 2019 and the frequency that these articles reported details pertaining to female participants' menstrual cycle to determine the volume of novel research that is directly relevant to this growing population. METHODS Original exercise thermoregulatory studies published in three major sports medicine databases (PubMed, MEDLINE, and SPORTDiscus) between 2010 and 2019 were surveyed. Articles were screened to determine the number of female and male participants in the study and whether studies involving women reported menstrual orientation or phase. Research involving healthy adult participants and an exercise protocol with a thermoregulatory outcome measure were included in the review. RESULTS A total of 1407 articles were included in the review, involving 28,030 participants. The annual representation of women ranged from a mean of 11.6% [95% credible interval (CI); 9.2, 14.3] to 17.8% [95% CI; 15.2, 20.6] across the 10 years, indicating studies predominantly included men. Nonetheless, there was a small statistical increase in the overall proportion of women, with a mean overall proportion change of 0.7% [95% CI; 0.2, 1.2] per year. The increase appeared to be driven by a reduction in the number of studies including only men, rather than studies including more women alongside men, or increased women-only studies. Less than one third of articles involving women reported the menstrual orientation of participants and less than one quarter reported both menstrual orientation and phase. This study shows that women were proportionally underrepresented in exercise thermoregulation research during the past decade and the majority of studies did not report menstrual cycle details of female participants. Researchers should consider including women in future work where their inclusion could contribute meaningful data that enhance the evidence-based and ultimately improves our comprehension of women's thermal physiology.
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Affiliation(s)
- Kate P Hutchins
- Institute of Health and Biomedical Innovation, School of Exercise and Nutrition Sciences, Queensland University of Technology, Brisbane, Australia.
| | - David N Borg
- The Hopkins Centre, Menzies Health Institute Queensland, Griffith University, Brisbane, Australia
| | - Aaron J E Bach
- The National Climate Change Adaption Research Facility, Griffith University, Gold Coast, Australia
| | - Joshua J Bon
- School of Mathematical Sciences, Queensland University of Technology, Brisbane, Australia
- Australian Centre of Excellence for Mathematical and Statistical Frontiers, Brisbane, Australia
| | - Geoffrey M Minett
- Institute of Health and Biomedical Innovation, School of Exercise and Nutrition Sciences, Queensland University of Technology, Brisbane, Australia
| | - Ian B Stewart
- Institute of Health and Biomedical Innovation, School of Exercise and Nutrition Sciences, Queensland University of Technology, Brisbane, Australia
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19
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Meade RD, Akerman AP, Notley SR, McGinn R, Poirier P, Gosselin P, Kenny GP. Physiological factors characterizing heat-vulnerable older adults: A narrative review. ENVIRONMENT INTERNATIONAL 2020; 144:105909. [PMID: 32919284 DOI: 10.1016/j.envint.2020.105909] [Citation(s) in RCA: 96] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 05/24/2020] [Accepted: 06/17/2020] [Indexed: 05/26/2023]
Abstract
More frequent and intense periods of extreme heat (heatwaves) represent the most direct challenge to human health posed by climate change. Older adults are particularly vulnerable, especially those with common age-associated chronic health conditions (e.g., cardiovascular disease, hypertension, obesity, type 2 diabetes, chronic kidney disease). In parallel, the global population is aging and age-associated disease rates are on the rise. Impairments in the physiological responses tasked with maintaining homeostasis during heat exposure have long been thought to contribute to increased risk of health disorders in older adults during heatwaves. As such, a comprehensive overview of the provisional links between age-related physiological dysfunction and elevated risk of heat-related injury in older adults would be of great value to healthcare officials and policy makers concerned with protecting heat-vulnerable sectors of the population from the adverse health impacts of heatwaves. In this narrative review, we therefore summarize our current understanding of the physiological mechanisms by which aging impairs the regulation of body temperature, hemodynamic stability and hydration status. We then examine how these impairments may contribute to acute pathophysiological events common during heatwaves (e.g., heatstroke, major adverse cardiovascular events, acute kidney injury) and discuss how age-associated chronic health conditions may exacerbate those impairments. Finally, we briefly consider the importance of physiological research in the development of climate-health programs aimed at protecting heat-vulnerable individuals.
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Affiliation(s)
- Robert D Meade
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Ashley P Akerman
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Sean R Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Ryan McGinn
- Department of Anesthesiology and Pain Medicine, The Ottawa Hospital, University of Ottawa, Ottawa, ON, Canada
| | - Paul Poirier
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, Québec, Canada
| | - Pierre Gosselin
- Institut National de Santé Publique du Québec and Université Laval, Québec, Québec, Canada
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada; Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.
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20
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Foster J, Hodder SG, Lloyd AB, Havenith G. Individual Responses to Heat Stress: Implications for Hyperthermia and Physical Work Capacity. Front Physiol 2020; 11:541483. [PMID: 33013476 PMCID: PMC7516259 DOI: 10.3389/fphys.2020.541483] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Accepted: 08/18/2020] [Indexed: 12/11/2022] Open
Abstract
Background Extreme heat events are increasing in frequency, severity, and duration. It is well known that heat stress can have a negative impact on occupational health and productivity, particularly during physical work. However, there are no up-to-date reviews on how vulnerability to heat changes as a function of individual characteristics in relation to the risk of hyperthermia and work capacity loss. The objective of this narrative review is to examine the role of individual characteristics on the human heat stress response, specifically in relation to hyperthermia risk and productivity loss in hot workplaces. Finally, we aim to generate practical guidance for industrial hygienists considering our findings. Factors included in the analysis were body mass, body surface area to mass ratio, body fat, aerobic fitness and training, heat adaptation, aging, sex, and chronic health conditions. Findings We found the relevance of any factor to be dynamic, based on the work-type (fixed pace or relative to fitness level), work intensity (low, moderate, or heavy work), climate type (humidity, clothing vapor resistance), and variable of interest (risk of hyperthermia or likelihood of productivity loss). Heat adaptation, high aerobic fitness, and having a large body mass are the most protective factors during heat exposure. Primary detrimental factors include low fitness, low body mass, and lack of heat adaptation. Aging beyond 50 years, being female, and diabetes are less impactful negative factors, since their independent effect is quite small in well matched participants. Skin surface area to mass ratio, body composition, hypertension, and cardiovascular disease are not strong independent predictors of the heat stress response. Conclusion Understanding how individual factors impact responses to heat stress is necessary for the prediction of heat wave impacts on occupational health and work capacity. The recommendations provided in this report could be utilized to help curtail hyperthermia risk and productivity losses induced by heat.
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Affiliation(s)
- Josh Foster
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - Simon G Hodder
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - Alex B Lloyd
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - George Havenith
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
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21
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Notley SR, D'Souza AW, Meade RD, Richards BJ, Kenny GP. Whole-body heat exchange in women during constant- and variable-intensity work in the heat. Eur J Appl Physiol 2020; 120:2665-2675. [PMID: 32902693 DOI: 10.1007/s00421-020-04486-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Accepted: 08/27/2020] [Indexed: 10/23/2022]
Abstract
PURPOSE Time-weighted averaging is used in occupational heat stress guidelines to estimate the metabolic demands of variable-intensity work. However, compared to constant-intensity work of the same time-weighted average metabolic rate, variable-intensity work may cause decrements in total heat loss (dry + evaporative heat loss) that exacerbate heat storage in women. We therefore used direct calorimetry to assess whole-body total heat loss and heat storage (metabolic heat production minus total heat loss) in women and men during constant- and variable-intensity work of equal average intensity. METHODS Ten women [mean (SD); 31 (11) years] and fourteen men [30 (8) years] completed two trials involving 90-min of constant- and variable-intensity work (cycling) eliciting an average metabolic heat production of ~ 200 W/m2 in dry-heat (40 °C, ~ 15% relative humidity). External work was fixed at ~ 40 W/m2 for constant-intensity work, and alternated between ~ 15 and ~ 60 W/m2 (5-min each) for variable-intensity work. RESULTS When expressed as a time-weighted average over each work period, total heat loss did not differ between men and women (mean difference [95% CI]; 4 W/m2 [- 11, 20]; p = 0.572) or between constant- and variable-intensity work (1 W/m2 [- 3, 5]; p = 0.642). Consequently, heat storage did not differ significantly between men and women (- 4 W/m2 [- 17, 8]; p = 0.468) or between constant- and variable-intensity work (0 W/m2 [- 3, 3]; p = 0.834). CONCLUSION Neither whole-body heat loss nor heat storage was modulated by the partitioning of work intensity, indicating that time-weighted averaging is appropriate for estimating metabolic demand to assess occupational heat stress in women.
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Affiliation(s)
- Sean R Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367 Montpetit Hall, Ottawa, ON, K1N 6N5, Canada
| | - Andrew W D'Souza
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367 Montpetit Hall, Ottawa, ON, K1N 6N5, Canada
| | - Robert D Meade
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367 Montpetit Hall, Ottawa, ON, K1N 6N5, Canada
| | - Brodie J Richards
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367 Montpetit Hall, Ottawa, ON, K1N 6N5, Canada
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367 Montpetit Hall, Ottawa, ON, K1N 6N5, Canada.
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22
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Notley SR, Meade RD, Kenny GP. Effect of aerobic fitness on the relation between age and whole‐body heat exchange during exercise‐heat stress: a retrospective analysis. Exp Physiol 2020; 105:1550-1560. [DOI: 10.1113/ep088783] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 06/30/2020] [Indexed: 01/24/2023]
Affiliation(s)
- Sean R. Notley
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of Ottawa Ottawa Canada
| | - Robert D. Meade
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of Ottawa Ottawa Canada
| | - Glen P. Kenny
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of Ottawa Ottawa Canada
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23
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Meade RD, Notley SR, Kenny GP. Aging and human heat dissipation during exercise-heat stress: an update and future directions. CURRENT OPINION IN PHYSIOLOGY 2019. [DOI: 10.1016/j.cophys.2019.07.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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