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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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Notley SR, Mitchell D, Taylor NAS. A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise. Eur J Appl Physiol 2024; 124:1-145. [PMID: 37796292 DOI: 10.1007/s00421-023-05276-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 07/04/2023] [Indexed: 10/06/2023]
Abstract
In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.
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Affiliation(s)
- Sean R Notley
- Defence Science and Technology Group, Department of Defence, Melbourne, Australia
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa
- School of Human Sciences, University of Western Australia, Crawley, Australia
| | - Nigel A S Taylor
- Research Institute of Human Ecology, College of Human Ecology, Seoul National University, Seoul, Republic of Korea.
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Notley SR, Mitchell D, Taylor NAS. A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements. Eur J Appl Physiol 2023; 123:2587-2685. [PMID: 37796291 DOI: 10.1007/s00421-023-05284-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 07/14/2023] [Indexed: 10/06/2023]
Abstract
In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.
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Affiliation(s)
- Sean R Notley
- Defence Science and Technology Group, Department of Defence, Melbourne, Australia
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa
- School of Human Sciences, University of Western Australia, Crawley, Australia
| | - Nigel A S Taylor
- College of Human Ecology, Research Institute of Human Ecology, Seoul National University, Seoul, Republic of Korea.
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Notley SR, Mitchell D, Taylor NAS. A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 1: Foundational principles and theories of regulation. Eur J Appl Physiol 2023; 123:2379-2459. [PMID: 37702789 DOI: 10.1007/s00421-023-05272-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2022] [Accepted: 06/30/2023] [Indexed: 09/14/2023]
Abstract
This contribution is the first of a four-part, historical series encompassing foundational principles, mechanistic hypotheses and supported facts concerning human thermoregulation during athletic and occupational pursuits, as understood 100 years ago and now. Herein, the emphasis is upon the physical and physiological principles underlying thermoregulation, the goal of which is thermal homeostasis (homeothermy). As one of many homeostatic processes affected by exercise, thermoregulation shares, and competes for, physiological resources. The impact of that sharing is revealed through the physiological measurements that we take (Part 2), in the physiological responses to the thermal stresses to which we are exposed (Part 3) and in the adaptations that increase our tolerance to those stresses (Part 4). Exercising muscles impose our most-powerful heat stress, and the physiological avenues for redistributing heat, and for balancing heat exchange with the environment, must adhere to the laws of physics. The first principles of internal and external heat exchange were established before 1900, yet their full significance is not always recognised. Those physiological processes are governed by a thermoregulatory centre, which employs feedback and feedforward control, and which functions as far more than a thermostat with a set-point, as once was thought. The hypothalamus, today established firmly as the neural seat of thermoregulation, does not regulate deep-body temperature alone, but an integrated temperature to which thermoreceptors from all over the body contribute, including the skin and probably the muscles. No work factor needs to be invoked to explain how body temperature is stabilised during exercise.
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Affiliation(s)
- Sean R Notley
- Defence Science and Technology Group, Department of Defence, Melbourne, Australia
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa
- School of Human Sciences, University of Western Australia, Crawley, Australia
| | - Nigel A S Taylor
- Research Institute of Human Ecology, College of Human Ecology, Seoul National University, Seoul, Republic of Korea.
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Foster J, Balmain BN, Wilhite DP, Watso JC, Babb TG, Cramer MN, BelvaL LN, Crandall CG. Inhibiting regional sweat evaporation modifies the ventilatory response to exercise: interactions between core and skin temperature. J Appl Physiol (1985) 2023; 134:1011-1021. [PMID: 36892886 PMCID: PMC10110718 DOI: 10.1152/japplphysiol.00597.2022] [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: 10/10/2022] [Revised: 02/27/2023] [Accepted: 03/03/2023] [Indexed: 03/10/2023] Open
Abstract
In humans, elevated body temperatures can markedly increase the ventilatory response to exercise. However, the impact of changing the effective body surface area (BSA) for sweat evaporation (BSAeff) on such responses is unclear. Ten healthy adults (9 males, 1 female) performed eight exercise trials cycling at 6 W/kg of metabolic heat production for 60 min. Four conditions were used where BSAeff corresponded to 100%, 80%, 60%, and 40% of BSA using vapor-impermeable material. Four trials (one at each BSAeff) were performed at 25°C air temperature, and four trials (one at each BSAeff) at 40°C air temperature, each with 20% humidity. The slope of the relation between minute ventilation and carbon dioxide elimination (V̇E/V̇co2 slope) assessed the ventilatory response. At 25°C, the V̇E/V̇co2 slope was elevated by 1.9 and 2.6 units when decreasing BSAeff from 100 to 80 and to 40% (P = 0.033 and 0.004, respectively). At 40°C, V̇E/V̇co2 slope was elevated by 3.3 and 4.7 units, when decreasing BSAeff from 100 to 60 and to 40% (P = 0.016 and P < 0.001, respectively). Linear regression analyses using group average data from each condition demonstrated that end-exercise mean body temperature (integration of core and mean skin temperature) was better associated with the end-exercise ventilatory response, compared with core temperature alone. Overall, we show that impeding regional sweat evaporation increases the ventilatory response to exercise in temperate and hot environmental conditions, and the effect is mediated primarily by increases in mean body temperature.NEW & NOTEWORTHY Exercise in the heat increases the slope of the relation between minute ventilation and carbon dioxide elimination (V̇E/V̇co2 slope) in young healthy adults. An indispensable role for skin temperature in modulating the ventilatory response to exercise is noted, contradicting common belief that internal/core temperature acts independently as a controller of ventilation during hyperthermia.
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Affiliation(s)
- Josh Foster
- Thermal and Vascular Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Bryce N Balmain
- Pulmonary Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Daniel P Wilhite
- Pulmonary Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Joseph C Watso
- Thermal and Vascular Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
- Cardiovascular and Applied Physiology Laboratory, Department of Nutrition & Integrative Physiology, Florida State University, Tallahassee, Florida, United States
| | - Tony G Babb
- Pulmonary Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Matthew N Cramer
- Thermal and Vascular Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Luke N BelvaL
- Thermal and Vascular Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Craig G Crandall
- Thermal and Vascular Physiology Laboratory, Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, United States
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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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Schmidt MD, Notley SR, Meade RD, Akerman AP, Rutherford MM, Kenny GP. Revisiting regional variation in the age-related reduction in sweat rate during passive heat stress. Physiol Rep 2022; 10:e15250. [PMID: 35411704 PMCID: PMC9001962 DOI: 10.14814/phy2.15250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Accepted: 03/17/2022] [Indexed: 06/14/2023] Open
Abstract
Aging is associated with attenuated sweat gland function, which has been suggested to occur in a peripheral-to-central manner. However, evidence supporting this hypothesis remains equivocal. We revisited this hypothesis by evaluating the sweat rate across the limbs and trunk in young and older men during whole-body, passive heating. A water-perfused suit was used to raise and clamp esophageal temperature at 0.6°C (low-heat strain) and 1.2°C (moderate-heat strain) above baseline in 14 young (24 (SD 5) years) and 15 older (69 (4) years) men. Sweat rate was measured at multiple sites on the trunk (chest, abdomen) and limbs (biceps, forearm, quadriceps, calf) using ventilated capsules (3.8 cm2 ). Sweat rates, expressed as the average of 5 min of stable sweating at low- and moderate-heat strain, were compared between groups (young, older) and regions (trunk, limbs) within each level of heat strain using a linear mixed-effects model with nested intercepts (sites nested within region nested within participant). At low-heat strain, the age-related reduction in sweat rate (older-young values) was greater at the trunk (0.65 mg/cm2 /min [95% CI 0.44, 0.86]) compared to the limbs (0.42 mg/cm2 /min [0.22, 0.62]; interaction: p = 0.010). At moderate-heat strain, sweat rate was lower in older compared to young (main effect: p = 0.025), albeit that reduction did not differ between regions (interaction: p = 0.888). We conclude that, contrary to previous suggestions, the age-related decline in sweat rate was greater at the trunk compared to the limbs at low-heat strain, with no evidence of regional variation in that age-related decline at moderate-heat strain.
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Affiliation(s)
- Madison D. Schmidt
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
| | - Sean R. Notley
- 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 UniversityBostonMassachusettsUSA
| | - Ashley P. Akerman
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
| | - Maura M. Rutherford
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
| | - Glen P. Kenny
- Human and Environmental Physiology Research UnitSchool of Human KineticsUniversity of OttawaOttawaOntarioCanada
- Clinical Epidemiology ProgramOttawa Hospital Research InstituteOttawaOntarioCanada
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8
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Pokora I, Sadowska-Krępa E, Wolowski Ł, Wyderka P, Michnik A, Drzazga Z. The Effect of Medium-Term Sauna-Based Heat Acclimation (MPHA) on Thermophysiological and Plasma Volume Responses to Exercise Performed under Temperate Conditions in Elite Cross-Country Skiers. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2021; 18:6906. [PMID: 34199101 PMCID: PMC8297353 DOI: 10.3390/ijerph18136906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 06/04/2021] [Accepted: 06/22/2021] [Indexed: 11/16/2022]
Abstract
The influence of a series of ten sauna baths (MPHA) on thermophysiological and selected hematological responses in 14 elite cross-country skiers to a submaximal endurance exercise test performed under thermoneutral environmental conditions was studied. Thermal and physiological variables were measured before and after the exercise test, whereas selected hematological indices were studied before, immediately after, and during recovery after a run, before (T1) and after sauna baths (T2). MPHA did not influence the baseline internal, body, and skin temperatures. There was a decrease in the resting heart rate (HR: p = 0.001) and physiological strain (PSI: p = 0.052) after MPHA and a significant effect of MPHA on systolic blood pressure (p = 0.03), hematological indices, and an exercise effect but no combined effect of treatments and exercise on the tested variables. A positive correlation was reported between PSI and total protein (%ΔTP) in T2 and a negative between plasma volume (%ΔPV) and mean red cellular volume (%ΔMCV) in T1 and T2 in response to exercise and a positive one during recovery. This may suggest that MPHA has a weak influence on body temperatures but causes a moderate decrease in PSI and modifications of plasma volume restoration in response to exercise under temperate conditions in elite athletes.
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Affiliation(s)
- Ilona Pokora
- Department of Physiological-Medical Sciences, Institute of Sport Sciences, The Jerzy Kukuczka Academy of Physical Education in Katowice, Mikołowska 72a, 40-065 Katowice, Poland;
| | - Ewa Sadowska-Krępa
- Department of Physiological-Medical Sciences, Institute of Sport Sciences, The Jerzy Kukuczka Academy of Physical Education in Katowice, Mikołowska 72a, 40-065 Katowice, Poland;
| | - Łukasz Wolowski
- Doctoral Studies, The Jerzy Kukuczka Academy of Physical Education in Katowice, Mikołowska 72a, 40-065 Katowice, Poland; (Ł.W.); (P.W.)
| | - Piotr Wyderka
- Doctoral Studies, The Jerzy Kukuczka Academy of Physical Education in Katowice, Mikołowska 72a, 40-065 Katowice, Poland; (Ł.W.); (P.W.)
| | - Anna Michnik
- The Silesian Centre for Education and Interdisciplinary Research, Faculty of Science and Technology, University of Silesia in Katowice, 75 Pułku Piechoty 1A, 41-500 Chorzow, Poland; (A.M.); (Z.D.)
| | - Zofia Drzazga
- The Silesian Centre for Education and Interdisciplinary Research, Faculty of Science and Technology, University of Silesia in Katowice, 75 Pułku Piechoty 1A, 41-500 Chorzow, Poland; (A.M.); (Z.D.)
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Sharma B, Sengupta T, Chandra Vishwakarma L, Akhtar N, Mallick HN. Muscle temperature is least altered during total sleep deprivation in rats. J Therm Biol 2021; 98:102910. [PMID: 34016337 DOI: 10.1016/j.jtherbio.2021.102910] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 03/11/2021] [Accepted: 03/11/2021] [Indexed: 11/27/2022]
Abstract
It has often been said that the brain is mostly benefitted from sleep. To understand the importance of sleep, extensive studies on other organs are too required. One such unexplored area is the understanding of muscle physiology during the sleep-wake cycle. Changes in muscle tone with different sleep phases are evident from the rapid eye movement sleep muscle atonia. There is variation in brain and body temperature during sleep stages, the brain temperature being higher during rapid eye movement sleep than slow-wave sleep. However, the change in muscle temperature with different sleep stages is not known. In this study, we have implanted pre-calibrated K-type thermocouples in the hypothalamus and the dorsal nuchal muscle, and a peritoneal transmitter to monitor the hypothalamic, muscle, and body temperature respectively in rats during 24 h sleep-wake cycle. The changes in muscle, body, and hypothalamic temperature during total sleep deprivation were also monitored. During normal sleep-wake stages, the temperature in the decreasing order was that of the hypothalamus, body, and muscle. Total sleep deprivation by gentle handling caused a significant increase in hypothalamic and body temperature, while there was least change in the muscle temperature. The circadian rhythm of the hypothalamic and body temperature in the sleep-deprived rats was disrupted, while the same was preserved in the muscle temperature. The results of our study show that muscle atonia during rapid eye movement sleep is a physiologically regulated thermally quiescent muscle state offering a conducive environment for muscle rest and repair.
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Affiliation(s)
- Binney Sharma
- Department of Physiology, All India Institute of Medical Sciences, New Delhi, 110029, India.
| | - Trina Sengupta
- Department of Physiology, All India Institute of Medical Sciences, New Delhi, 110029, India; Department of Physiology, All India Institute of Medical Sciences, Jodhpur, 342005, India.
| | - Lal Chandra Vishwakarma
- Department of Physiology, All India Institute of Medical Sciences, New Delhi, 110029, India.
| | - Nasreen Akhtar
- Department of Physiology, All India Institute of Medical Sciences, New Delhi, 110029, India.
| | - Hruda Nanda Mallick
- Department of Physiology, All India Institute of Medical Sciences, New Delhi, 110029, India; Department of Physiology, Faculty of Medicine & Health Sciences, SGT University, Gurgaon, Haryana, 122505, India.
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Girardi M, Gattoni C, Mauro L, Capelli C. The effects of sinusoidal linear drifts on the estimation of cardiorespiratory dynamic parameters during sinusoidal workload forcing: a simulation study. Respir Physiol Neurobiol 2021; 289:103652. [PMID: 33677090 DOI: 10.1016/j.resp.2021.103652] [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] [Received: 12/16/2020] [Revised: 02/20/2021] [Accepted: 02/26/2021] [Indexed: 11/15/2022]
Abstract
This study aimed at investigating whether: 1) different sinusoidal linear drifts would affect the estimation of the dynamic parameters amplitude (A) and phase lag (φ) of minute ventilation (V˙E), oxygen uptake, carbon dioxide production and heart rate (HR) sinusoidal responses when the frequency analysis technique (F) is performed; 2) the Marquardt-Levenberg non-linear fitting technique (ML) would provide more precise estimations of A and φ of drifted sinusoidal responses compared to F. For each cardiorespiratory variable, fifteen responses to sinusoidal forcing of different sinusoidal periods were simulated by using a first-order dynamic linear model. A wide range of linear drifts were subsequently applied. A and φ were computed for all drifted and non-drifted responses by using both F (AF and φF) and ML (AML and φML). For non-drifted responses, no differences between AF vs AML and φF vs φML were found. Whereas AF and φF were affected by the sinusoidal linear drifts, AML and φML were not. Significant interaction effects (technique x drift) were found for A (P < 0.001; ƞP2 > 0.247) and φ (P < 0.001; ƞP2 > 0.851). Higher goodness of fit values were observed when using ML for drifted V˙E and HR responses only. The present findings suggest ML as a recommended technique to use when sinusoidal linear drifts occur during sinusoidal exercise, and provide new insights on how to analyse drifted cardiorespiratory sinusoidal responses.
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Affiliation(s)
- Michele Girardi
- Centre for Brain Science, Department of Psychology, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, United Kingdom.
| | - Chiara Gattoni
- Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Chatham Maritime, ME4 4AG, United Kingdom
| | - Lorenzo Mauro
- Department of Computer, Control and Management Engineering, University of Rome "La Sapienza", via Ariosto 25, 00185, Rome, Italy
| | - Carlo Capelli
- Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, via Felice Casorati 43, 1-37131, Verona, Italy
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11
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Bowes HM, Burdon CA, Taylor NAS. The scaling of human basal and resting metabolic rates. Eur J Appl Physiol 2020; 121:193-208. [PMID: 33011890 DOI: 10.1007/s00421-020-04515-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 09/23/2020] [Indexed: 11/28/2022]
Abstract
PURPOSE In tachymetabolic species, metabolic rate increases disproportionately with body mass, and that inter-specific relationship is typically modelled allometrically. However, intra-specific analyses are less common, particularly for healthy humans, so the possibility that human metabolism would also scale allometrically was investigated. METHODS Basal metabolic rate was determined (respirometry) for 68 males (18-40 years; 56.0-117.1 kg), recruited across five body-mass classes. Data were collected during supine, normothermic rest from well-rested, well-hydrated and post-absorptive participants. Linear and allometric regressions were applied, and three scaling methods were assessed. Data from an historical database were also analysed (2.7-108.9 kg, 4811 males; 2.0-96.4 kg, 2364 females). RESULTS Both linear and allometric functions satisfied the statistical requirements, but not the biological pre-requisite of an origin intercept. Mass-independent basal metabolic data beyond the experimental mass range were not achieved using linear regression, which yielded biologically impossible predictions as body mass approached zero. Conversely, allometric regression provided a biologically valid, powerful and statistically significant model: metabolic rate = 0.739 * body mass0.547 (P < 0.05). Allometric analysis of the historical male data yielded an equivalent, and similarly powerful model: metabolic rate = 0.873 * body mass0.497 (P < 0.05). CONCLUSION It was established that basal and resting metabolic rates scale allometrically with body mass in humans from 10-117 kg, with an exponent of 0.50-0.55. It was also demonstrated that ratiometric scaling yielded invalid metabolic predictions, even within the relatively narrow experimental mass range. Those outcomes have significant physiological implications, with applications to exercising states, modelling, nutrition and metabolism-dependent pharmacological prescriptions.
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Affiliation(s)
- Heather M Bowes
- Centre for Medical and Exercise Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Catriona A Burdon
- Centre for Medical and Exercise Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Nigel A S Taylor
- Centre for Medical and Exercise Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia.
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van den Heuvel AMJ, Haberley BJ, Hoyle DJR, Taylor NAS, Croft RJ. Hyperthermia, but not dehydration, alters the electrical activity of the brain. Eur J Appl Physiol 2020; 120:2797-2811. [DOI: 10.1007/s00421-020-04492-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 09/03/2020] [Indexed: 11/28/2022]
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13
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Le Ster C, Mauconduit F, Mirkes C, Bottlaender M, Boumezbeur F, Djemai B, Vignaud A, Boulant N. RF heating measurement using MR thermometry and field monitoring: Methodological considerations and first in vivo results. Magn Reson Med 2020; 85:1282-1293. [PMID: 32936510 DOI: 10.1002/mrm.28501] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 07/10/2020] [Accepted: 08/10/2020] [Indexed: 11/11/2022]
Abstract
PURPOSE A MR thermometry (MRT) method with field monitoring is proposed to improve the measurement of small temperature variations induced in brain MRI exams. METHODS MR thermometry experiments were performed at 7 Tesla with concurrent field monitoring and RF heating. Images were reconstructed with nominal k-space trajectories and with first-order spherical harmonics correction. Experiments were performed in vitro with deliberate field disturbances and on an anesthetized macaque in 2 different specific absorption rate regimes, that is, at 50% and 100% of the maximal specific absorption rate level allowed in the International Electrotechnical Commission normal mode of operation. Repeatability was assessed by running a second separate session on the same animal. RESULTS Inclusion of magnetic field fluctuations in the reconstruction improved temperature measurement accuracy in vitro down to 0.02°C. Measurement precision in vivo was on the order of 0.15°C in areas little affected by motion. In the same region, temperature increase reached 0.5 to 0.8°C after 20 min of heating at 100% specific absorption rates and followed a rough factor of 2 with the 50% specific absorption rate scans. A horizontal temperature plateau, as predicted by Pennes bioheat model with thermal constants from the literature and constant blood temperature assumption, was not observed. CONCLUSION Inclusion of field fluctuations in image reconstruction was beneficial for the measurement of small temperature rises encountered in standard brain exams. More work is needed to correct for motion-induced field disturbances to extract reliable temperature maps.
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Affiliation(s)
- Caroline Le Ster
- Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Franck Mauconduit
- Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | | | - Michel Bottlaender
- Université Paris-Saclay, CEA, CNRS, Inserm, BioMaps, Service Hospitalier Frederic Joliot, Orsay, France.,UNIACT, Neurospin, CEA, Gif-sur-Yvette, France
| | - Fawzi Boumezbeur
- Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Boucif Djemai
- Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Alexandre Vignaud
- Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Nicolas Boulant
- Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
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14
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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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15
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Notley SR, Meade RD, D'Souza AW, Rutherford MM, Kim JH, Kenny GP. Heat Exchange in Young and Older Men during Constant- and Variable-Intensity Work. Med Sci Sports Exerc 2020; 52:2628-2636. [PMID: 32433432 DOI: 10.1249/mss.0000000000002410] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
PURPOSE Current occupational heat stress guidelines rely on time-weighted averaging to quantify the metabolic demands of variable-intensity work. However, variable-intensity work may be associated with impairments in whole-body total heat loss (dry + evaporative heat loss), especially in older workers, which exacerbate heat strain relative to constant-intensity work eliciting the same time-weighted average metabolic rate. We, therefore, used direct calorimetry to evaluate whether variable-intensity work would cause decrements in the average rate of whole-body total heat loss that augment body heat storage and core temperature compared with constant-intensity work in young and older men. METHODS Eight young (19-31 yr) and eight older (54-65 yr) men completed four trials involving 90 min of work (cycling) eliciting an average metabolic heat production of ~200 W·m in dry-heat (40°C, 20% relative humidity). One trial involved constant-intensity work (CON), whereas the others involved 10-min cycles of variable-intensity work: 5-min low-intensity and 5-min high-intensity (VAR 5:5), 6-min low-intensity and 4-min very high-intensity (VAR 6:4), and 7-min low- and 3-min very, very high-intensity (VAR 7:3). Metabolic heat production, total heat loss, body heat storage (heat production minus total heat loss), and core (rectal) temperature were measured throughout. RESULTS When averaged over each 90-min work period, metabolic heat production, total heat loss, and heat storage were similar between groups and conditions (all P ≥ 0.152). Peak core temperature (average of final 10 min) was also similar between groups and conditions (both P ≥ 0.111). CONCLUSIONS Whole-body total heat loss, heat storage, and core temperature were not significantly influenced by the partitioning of work intensity in young or older men, indicating that time-weighted averaging appears to be appropriate for quantifying the metabolic demands of variable-intensity work to assess occupational heat stress.
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Affiliation(s)
- Sean R Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA
| | - Robert D Meade
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA
| | - Andrew W D'Souza
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA
| | - Maura M Rutherford
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA
| | - Jung-Hyun Kim
- College of Physical Education, Kyung Hee University, Gyeonggi-do, SOUTH KOREA
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA
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16
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Cernych M, Satas A, Rapalis A, Marozas V, Malciene L, Lukosevicius A, Daniuseviciute L, Brazaitis M. Exposure to total 36-hr sleep deprivation reduces physiological and psychological thermal strain to whole-body uncompensable passive heat stress in young adult men. J Sleep Res 2020; 30:e13055. [PMID: 32363754 DOI: 10.1111/jsr.13055] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Revised: 03/24/2020] [Accepted: 04/07/2020] [Indexed: 12/26/2022]
Abstract
Total sleep deprivation (TSD) is associated with endothelial dysfunction and a consequent decrease in vascular reactivity and increase in peripheral vascular resistance. These effectors compromise the body's ability to thermoregulate in hot and cold stress conditions. We investigated heat-unacclimated young adult men (26 ± 2 years) to determine whether 36 hr of TSD compared to an 8 or 4-hr sleep condition, would suppress the responses of the autonomic system (body rectal temperature [Tre ], heart rate [HR], root mean square of successive interbeat intervals, physiological strain, blood pressure [BP], circulating blood catecholamines, sweating rate and subjective sensations) to whole-body uncompensable passive heat stress in traditional Finnish sauna heat (Tair = 80-90°C, rh = 30%). Sauna bathing that induced whole-body hyperthermia had a residual effect on reducing BP in the 8-hr and 4-hr sleep per night conditions according to BP measurements. By contrast, 36 hr of total wakefulness led to an increase in BP. These observed sleep deprivation-dependent differences in BP modifications were not accompanied by changes in the blood plasma epinephrine and norepinephrine concentrations. However, during sauna bathing, an increase in BP following 36 hr of TSD was accompanied by significant decreases in body Tre , HR and physiological strain, together with a diminished sweating rate, enhanced vagus-mediated autonomic control of HR variability, and improved thermal perception by the subjects. Our results suggest the impaired ability of the body to accumulate external heat in the body's core under uncompensable passive heat conditions following 36 hr of TSD, because of the TSD-attenuated autonomic system response to acute heat stress.
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Affiliation(s)
- Margarita Cernych
- Institute of Sport Science and Innovations, Lithuanian Sports University, Kaunas, Lithuania
| | - Andrius Satas
- Institute of Sport Science and Innovations, Lithuanian Sports University, Kaunas, Lithuania
| | - Andrius Rapalis
- Biomedical Engineering Institute, Kaunas University of Technology, Kaunas, Lithuania
| | - Vaidotas Marozas
- Biomedical Engineering Institute, Kaunas University of Technology, Kaunas, Lithuania
| | - Lina Malciene
- Institute of Physiology and Pharmacology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Arunas Lukosevicius
- Biomedical Engineering Institute, Kaunas University of Technology, Kaunas, Lithuania
| | - Laura Daniuseviciute
- Department of Educational Studies, Kaunas University of Technology, Kaunas, Lithuania
| | - Marius Brazaitis
- Institute of Sport Science and Innovations, Lithuanian Sports University, Kaunas, Lithuania
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17
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The origin, significance and plasticity of the thermoeffector thresholds: Extrapolation between humans and laboratory rodents. J Therm Biol 2019; 85:102397. [DOI: 10.1016/j.jtherbio.2019.08.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2019] [Revised: 08/05/2019] [Accepted: 08/05/2019] [Indexed: 01/07/2023]
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18
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Ko Y, Jung JY, Kim HT, Lee JY. Auditory canal temperature measurement using a wearable device during sleep: Comparisons with rectal temperatures at 6, 10, and 14 cm depths. J Therm Biol 2019; 85:102410. [PMID: 31657752 DOI: 10.1016/j.jtherbio.2019.102410] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 08/29/2019] [Accepted: 09/03/2019] [Indexed: 10/26/2022]
Abstract
Monthly rhythms in the body core temperature of women during sleep can provide significant information concerning hormonal fluctuations. The purpose of the present study was to examine and evaluate auditory canal temperature (Tauditory), measured with a newly-developed wearable and wireless device, as a practical index to estimate body core temperature variations during a 7-h sleep period. Comparisons with rectal temperature (Tre) at different depths were conducted. Nine young females slept in a climate chamber at an air temperature of 27 °C with 50% relative humidity. Rectal temperatures at 6, 10 and 14 cm depths, as well as partially insulated Tauditory were simultaneously measured every 5 s during sleep. The results showed that Tauditory was, on average, 0.32 °C lower than Tre at 14 cm depth (P = 0.010), while significant relationships between Tauditory and Tre at 10 cm (r2 = 0.634, P = 0.010), and at 14 cm depths were also found (r2 = 0.826, P = 0.001). Rectal temperatures at 6 cm and 10 cm depths fell between those of Tauditory and Tre at 14 cm. We concluded that Tauditory, as measured using the newly-developed wearable device, can be a reliable, practical and continuous estimate of body core temperature during sleep.
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Affiliation(s)
- Yelin Ko
- College of Human Ecology, Seoul National University, South Korea
| | - Jae Yeon Jung
- College of Human Ecology, Seoul National University, South Korea
| | - Hyun-Tae Kim
- College of Human Ecology, Seoul National University, South Korea
| | - Joo-Young Lee
- College of Human Ecology, Seoul National University, South Korea; Research Institute of Human Ecology, Seoul National University, South Korea.
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19
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Baker LB. Physiology of sweat gland function: The roles of sweating and sweat composition in human health. Temperature (Austin) 2019; 6:211-259. [PMID: 31608304 PMCID: PMC6773238 DOI: 10.1080/23328940.2019.1632145] [Citation(s) in RCA: 242] [Impact Index Per Article: 48.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 06/06/2019] [Accepted: 06/08/2019] [Indexed: 12/21/2022] Open
Abstract
The purpose of this comprehensive review is to: 1) review the physiology of sweat gland function and mechanisms determining the amount and composition of sweat excreted onto the skin surface; 2) provide an overview of the well-established thermoregulatory functions and adaptive responses of the sweat gland; and 3) discuss the state of evidence for potential non-thermoregulatory roles of sweat in the maintenance and/or perturbation of human health. The role of sweating to eliminate waste products and toxicants seems to be minor compared with other avenues of excretion via the kidneys and gastrointestinal tract; as eccrine glands do not adapt to increase excretion rates either via concentrating sweat or increasing overall sweating rate. Studies suggesting a larger role of sweat glands in clearing waste products or toxicants from the body may be an artifact of methodological issues rather than evidence for selective transport. Furthermore, unlike the renal system, it seems that sweat glands do not conserve water loss or concentrate sweat fluid through vasopressin-mediated water reabsorption. Individuals with high NaCl concentrations in sweat (e.g. cystic fibrosis) have an increased risk of NaCl imbalances during prolonged periods of heavy sweating; however, sweat-induced deficiencies appear to be of minimal risk for trace minerals and vitamins. Additional research is needed to elucidate the potential role of eccrine sweating in skin hydration and microbial defense. Finally, the utility of sweat composition as a biomarker for human physiology is currently limited; as more research is needed to determine potential relations between sweat and blood solute concentrations.
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Affiliation(s)
- Lindsay B. Baker
- Gatorade Sports Science Institute, PepsiCo R&D Physiology and Life Sciences, Barrington, IL, USA
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20
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Rocha LM, Devillers N, Maldague X, Kabemba FZ, Fleuret J, Guay F, Faucitano L. Validation of Anatomical Sites for the Measurement of Infrared Body Surface Temperature Variation in Response to Handling and Transport. Animals (Basel) 2019; 9:E425. [PMID: 31284574 PMCID: PMC6680931 DOI: 10.3390/ani9070425] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Revised: 06/26/2019] [Accepted: 07/04/2019] [Indexed: 11/17/2022] Open
Abstract
This study aimed at validating the anatomical sites for the measurement of infrared (IR) body surface temperature as a tool to monitor the pigs' response to handling and transport stress. The selected anatomical sites were the neck (infrared neck temperature-IRNT), rump (infrared rump temperature-IRRT), orbital (infrared orbital temperature-IROT) and behind ears (infrared behind ears temperature-IRBET) regions. A total of 120 pigs were handled from the finishing pen to the loading dock through a handling test course. Two handling types (gentle vs. rough) and number of laps (1 vs. 3) were applied according to a 2 × 2 factorial design. After loading, pigs were transported for 40 min and returned to their home pens. Animal behavior, heart rate, rectal temperature and salivary cortisol concentration were measured for validation. Increased IR body temperature, heart rate and salivary cortisol levels were observed in response to rough handling and longer distance walk (P < 0.05 for all). The greatest correlations were found between IROT and IRBET temperatures and salivary cortisol concentration at the end of the handling test (r = 0.49 and r = 0.50, respectively; P < 0.001 for both). Therefore, IR pig's head surface temperature may be useful for a comprehensive assessment of the physiological response to handling and transport stress.
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Affiliation(s)
- Luiene M Rocha
- Sherbrooke Research and Development Centre, Agriculture and Agri-Food Canada, 2000 College Street, Sherbrooke, QC J1M 0C8, Canada.
| | - Nicolas Devillers
- Sherbrooke Research and Development Centre, Agriculture and Agri-Food Canada, 2000 College Street, Sherbrooke, QC J1M 0C8, Canada
| | - Xavier Maldague
- Département de génie électrique, Université Laval, 2325 Rue de l'Université, Quebec, QC G1V A06, Canada
| | - Fidèle Z Kabemba
- Sherbrooke Research and Development Centre, Agriculture and Agri-Food Canada, 2000 College Street, Sherbrooke, QC J1M 0C8, Canada
- Département des sciences animales, Université Laval, 2425 Rue de l'Agriculture, Quebec, QC G1V 0A6, Canada
| | - Julien Fleuret
- Département de génie électrique, Université Laval, 2325 Rue de l'Université, Quebec, QC G1V A06, Canada
| | - Fréderic Guay
- Département des sciences animales, Université Laval, 2425 Rue de l'Agriculture, Quebec, QC G1V 0A6, Canada
| | - Luigi Faucitano
- Sherbrooke Research and Development Centre, Agriculture and Agri-Food Canada, 2000 College Street, Sherbrooke, QC J1M 0C8, Canada
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Schwarck JB, Burdon CA, Taylor EA, Peoples GE, Machado-Moreira CA, Taylor NAS. Thermogenic and psychogenic sweating in humans: Identifying eccrine glandular recruitment patterns from glabrous and non-glabrous skin surfaces. J Therm Biol 2019; 82:242-251. [PMID: 31128655 DOI: 10.1016/j.jtherbio.2019.04.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 04/03/2019] [Accepted: 04/21/2019] [Indexed: 12/21/2022]
Abstract
In this experiment, psychogenic (mental arithmetic), thermogenic (mean body temperature elevation of 0.6 °C) and combined thermo-psychogenic treatments were used to explore eccrine sweat-gland recruitment from glabrous (volar hand and forehead) and non-glabrous skin surfaces (chest). It was hypothesised that each treatment would activate the same glands, and that glandular activity would be intermittent. Nine individuals participated in a single trial with normothermic and mildly hyperthermic phases. When normothermic, a 10-min arithmetical challenge was administered, during which sudomotor activity was recorded. Following passive heating and thermal clamping, sweating responses were again evaluated (10 min). A second arithmetical challenge (10 min) was administered during clamped hyperthermia, with its sudorific impact recorded. The activity of individual sweat glands was recorded at 60-s intervals, using precisely positioned, and uniformly applied, starch-iodide papers. Those imprints were digitised and analysed. Peak activity typically occurred during the thermo-psychogenic treatment, revealing physiologically active densities of 128 (volar hand), 165 (forehead) and 77 glands.cm-2 (chest). Except for the hand (46%), glands uniquely activated by one treatment were consistently <10% of the total glands identified. Glandular activations were most commonly of an intermittent nature, particularly during the thermogenic treatment. Accordingly, we accepted the hypothesis that psychogenic, thermogenic and thermo-psychogenic stimuli activate the same sweat glands in both the glabrous and non-glabrous regions. In addition, this investigation has provided detailed descriptions of the intermittent nature of sweat-gland activity, revealing that a consistent proportion of the physiologically active glands are recruited during these thermal and non-thermal stimuli.
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Affiliation(s)
- Janne B Schwarck
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Catriona A Burdon
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Elizabeth A Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Gregory E Peoples
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Christiano A Machado-Moreira
- Departamento de Educação Física, Universidade Federal de Juiz de Fora, Campus Avançado de Governador Valadares, Brasil
| | - Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia.
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Frei R, Notley SR, Taylor EA, Burdon CA, Ohnishi N, Taylor NAS. Revisiting the dermatomal recruitment of, and pressure-dependent influences on, human eccrine sweating. J Therm Biol 2019; 82:52-62. [PMID: 31128659 DOI: 10.1016/j.jtherbio.2019.03.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 03/10/2019] [Accepted: 03/18/2019] [Indexed: 10/27/2022]
Abstract
Herein we describe two experiments in which the recruitment and pressure-induced modifications of human eccrine sweating were investigated. In one experiment, the longstanding belief that glandular recruitment follows a gradual, caudal-to-rostral (dermatomal) recruitment pattern was re-evaluated. The onset of sweating was simultaneously determined (ventilated capsules) from four spinal (dermatomal) segments (forehead, dorsal hand, lower chest and dorsal foot) during the passive heating of supine participants (N = 8). No evidence was found to support either dermatomal or simultaneous glandular recruitment patterns. Instead, the results were more consistent with individualised (random) patterns of regional activation (P > 0.05), with significant time delays among sites. Such delays in the appearance of discharged sweat may reflect differences in neurotransmitter sensitivity, precursor sweat production or ductal reabsorption. In the second experiment, the pressure-induced hemihidrotic reflex (contralateral sudomotor enhancement) was revisited, using pressures applied over 10 cm2 areas of the chest (left side: 6 N cm-2) and left heel (3 N cm-2) during both supine and seated postures (N = 12). Participants were passively heated and thermally clamped before pressure application. Hemihidrosis was not observed from the contralateral surfaces within the same (chest) or lower spinal segments (abdomen; both P > 0.05) during chest pressure, but a generalised enhancement followed heel pressure when supine. We suggest that previous observations of hemihidrosis possibly resulted from elevated heat storage, rather than a neural reflex. Chest pressure significantly inhibited ipsilateral sweating (forehead, hand, chest; all P < 0.05), and that influence is hypothesised to result from interactions between ascending mechanoreceptor afferents and the descending sudomotor pathways.
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Affiliation(s)
- Remo Frei
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Sean R Notley
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Elizabeth A Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Catriona A Burdon
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Norikazu Ohnishi
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia; Faculty of Nursing, Mie Prefectural College of Nursing, Mie, 514-0116, Japan
| | - Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia.
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Fujimoto T, Tsuji B, Sasaki Y, Dobashi K, Sengoku Y, Fujii N, Nishiyasu T. Low-intensity exercise delays the shivering response to core cooling. Am J Physiol Regul Integr Comp Physiol 2019; 316:R535-R542. [DOI: 10.1152/ajpregu.00203.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hypothermia can occur during aquatic exercise despite production of significant amounts of heat by the active muscles. Because the characteristics of human thermoregulatory responses to cold during exercise have not been fully elucidated, we investigated the effect of low-intensity exercise on the shivering response to core cooling in cool water. Eight healthy young men (24 ± 3 yr) were cooled through cool water immersion while resting (rest trial) and during loadless pedaling on a water cycle ergometer (exercise trial). Before the cooling, body temperature was elevated by hot water immersion to clearly detect a core temperature at which shivering initiates. Throughout the cooling period, mean skin temperature remained around the water temperature (25°C) in both trials, whereas esophageal temperature (Tes) did not differ between the trials ( P > 0.05). The Tes at which oxygen uptake (V̇o2) rapidly increased, an index of the core temperature threshold for shivering, was lower during exercise than rest (36.2 ± 0.4°C vs. 36.5 ± 0.4°C, P < 0.05). The sensitivity of the shivering response, as indicated by the slope of the Tes-V̇o2 relation, did not differ between the trials (−441.3 ±177.4 ml·min−1·°C−1 vs. −411.8 ± 268.1 ml·min−1·°C−1, P > 0.05). The thermal sensation response to core cooling, assessed from the slope and intercept of the regression line relating Tes and thermal sensation, did not differ between the trials ( P > 0.05). These results suggest that the core temperature threshold for shivering is delayed during low-intensity exercise in cool water compared with rest although shivering sensitivity is unaffected.
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Affiliation(s)
- Tomomi Fujimoto
- Faculty of Health and Sport Sciences, University of Tsukuba, Ibaraki, Japan
| | - Bun Tsuji
- Department of Health Sciences, Prefectural University of Hiroshima, Hiroshima, Japan
| | - Yosuke Sasaki
- Faculty of Health and Sport Sciences, University of Tsukuba, Ibaraki, Japan
- Faculty of Economics, Niigata Sangyo University, Niigata, Japan
| | - Kohei Dobashi
- Faculty of Health and Sport Sciences, University of Tsukuba, Ibaraki, Japan
| | - Yasuo Sengoku
- Faculty of Health and Sport Sciences, University of Tsukuba, Ibaraki, Japan
| | - Naoto Fujii
- Faculty of Health and Sport Sciences, University of Tsukuba, Ibaraki, Japan
| | - Takeshi Nishiyasu
- Faculty of Health and Sport Sciences, University of Tsukuba, Ibaraki, Japan
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24
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Morris NB, Chaseling GK, Bain AR, Jay O. Temperature of water ingested before exercise alters the onset of physiological heat loss responses. Am J Physiol Regul Integr Comp Physiol 2018; 316:R13-R20. [PMID: 30403496 DOI: 10.1152/ajpregu.00028.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study sought to determine whether the temperature of water ingested before exercise alters the onset threshold and subsequent thermosensitivity of local vasomotor and sudomotor responses after exercise begins. Twenty men [24 (SD 4) yr of age, 75.8 (SD 8.1) kg body mass, 52.3 (SD 7.7) ml·min-1·kg-1 peak O2 consumption (V̇o2peak)] ingested 1.5°C, 37°C, or 50°C water (3.2 ml/kg), rested for 5 min, and then cycled at 50% V̇o2peak for 15 min at 23.0 (SD 0.9) °C and 32 (SD 10) % relative humidity. Mean body temperature (Tb), local sweat rate (LSR), and skin blood flow (SBF) were measured. In a subset of eight men [25 (SD 5) yr of age, 78.6 (SD 8.3) kg body mass, 48.9 (SD 11.1) ml·min-1·kg-1 V̇o2peak], blood pressure was measured and cutaneous vascular conductance (CVC) was determined. The change in Tb was greater at the onset of LSR measurement with ingestion of 1.5°C than 50°C water [ΔTb = 0.19 (SD 0.15) vs. 0.11 (SD 0.12) °C, P = 0.04], but not 37°C water [ΔTb = 0.14 (SD 0.14) °C, P = 0.23], but did not differ between trials for SBF measurement [ΔTb = 0.18 (SD 0.15) °C, 0.11 (SD 0.13) °C, and 0.09 (SD 0.09) °C with 1.5°C, 37°C, and 50°C water, respectively, P = 0.07]. Conversely, the thermosensitivity of LSR and SBF was not different [LSR = 1.11 (SD 0.75), 1.11 (SD 0.75), and 1.34 (SD 1.11) mg·min-1·cm-2·°C-1 with 1.5°C, 37°C, and 50°C ingested water, respectively ( P = 0.46); SBF = 717 (SD 882), 517 (SD 606), and 857 (SD 904) %baseline arbitrary units (AU)/°C with 1.5°C, 37°C, and 50°C ingested water, respectively ( P = 0.95)]. After 15 min of exercise, LSR and SBF were greater with ingestion of 50°C than 1.5°C water [LSR = 0.40 (SD 0.17) vs. 0.31 (SD 0.19) mg·min-1·cm-2 ( P = 0.02); SBF = 407 (SD 149) vs. 279 (SD 117) %baseline AU ( P < 0.001)], but not 37°C water [LSR = 0.50 (SD 0.22) mg·min-1·cm-2; SBF = 324 (SD 169) %baseline AU]. CVC was statistically unaffected [275 (SD 81), 340 (SD 114), and 384 (SD 160) %baseline CVC with 1.5°C, 37°C, and 50°C ingested water, respectively, P = 0.30]. Collectively, these results support the concept that visceral thermoreceptors modify the central drive for thermoeffector responses.
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Affiliation(s)
- Nathan B Morris
- Thermal Ergonomics Laboratory, Exercise and Sport Science, Faculty of Health Sciences, University of Sydney , Sydney, New South Wales , Australia.,School of Human Kinetics, University of Ottawa , Ottawa, Ontario , Canada
| | - Georgia K Chaseling
- Thermal Ergonomics Laboratory, Exercise and Sport Science, Faculty of Health Sciences, University of Sydney , Sydney, New South Wales , Australia
| | - Anthony R Bain
- School of Human Kinetics, University of Ottawa , Ottawa, Ontario , Canada.,Integrative Vascular Biology Laboratory, Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Ollie Jay
- Thermal Ergonomics Laboratory, Exercise and Sport Science, Faculty of Health Sciences, University of Sydney , Sydney, New South Wales , Australia.,School of Human Kinetics, University of Ottawa , Ottawa, Ontario , Canada
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25
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Nicolò A, Girardi M, Bazzucchi I, Felici F, Sacchetti M. Respiratory frequency and tidal volume during exercise: differential control and unbalanced interdependence. Physiol Rep 2018; 6:e13908. [PMID: 30393984 PMCID: PMC6215760 DOI: 10.14814/phy2.13908] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Revised: 10/02/2018] [Accepted: 10/03/2018] [Indexed: 01/14/2023] Open
Abstract
Differentiating between respiratory frequency (fR ) and tidal volume (VT ) may improve our understanding of exercise hyperpnoea because fR and VT seem to be regulated by different inputs. We designed a series of exercise manipulations to improve our understanding of how fR and VT are regulated during exercise. Twelve cyclists performed an incremental test and three randomized experimental sessions in separate visits. In two of the three experimental visits, participants performed a moderate-intensity sinusoidal test followed, after recovery, by a moderate-to-severe-intensity sinusoidal test. These two visits differed in the period of the sinusoid (2 min vs. 8 min). In the third experimental visit, participants performed a trapezoidal test where the workload was self-paced in order to match a predefined trapezoidal template of rating of perceived exertion (RPE). The results collectively reveal that fR changes more with RPE than with workload, gas exchange, VT or the amount of muscle activation. However, fR dissociates from RPE during moderate exercise. Both VT and minute ventilation ( V ˙ E ) showed a similar time course and a large correlation with V ˙ CO 2 in all the tests. Nevertheless, V ˙ CO 2 was associated more with V ˙ E than with VT because VT seems to adjust continuously on the basis of fR levels to match V ˙ E with V ˙ CO 2 . The present findings provide novel insight into the differential control of fR and VT - and their unbalanced interdependence - during exercise. The emerging conceptual framework is expected to guide future research on the mechanisms underlying the long-debated issue of exercise hyperpnoea.
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Affiliation(s)
- Andrea Nicolò
- Department of Movement, Human and Health SciencesUniversity of Rome “Foro Italico”RomeItaly
| | - Michele Girardi
- Department of Movement, Human and Health SciencesUniversity of Rome “Foro Italico”RomeItaly
| | - Ilenia Bazzucchi
- Department of Movement, Human and Health SciencesUniversity of Rome “Foro Italico”RomeItaly
| | - Francesco Felici
- Department of Movement, Human and Health SciencesUniversity of Rome “Foro Italico”RomeItaly
| | - Massimo Sacchetti
- Department of Movement, Human and Health SciencesUniversity of Rome “Foro Italico”RomeItaly
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26
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Abstract
Maintenance of a homeostatic body core temperature is a critical brain function accomplished by a central neural network. This orchestrates a complex behavioral and autonomic repertoire in response to environmental temperature challenges or declining energy homeostasis and in support of immune responses and many behavioral states. This review summarizes the anatomical, neurotransmitter, and functional relationships within the central neural network that controls the principal thermoeffectors: cutaneous vasoconstriction regulating heat loss and shivering and brown adipose tissue for heat production. The core thermoregulatory network regulating these thermoeffectors consists of parallel but distinct central efferent pathways that share a common peripheral thermal sensory input. Delineating the neural circuit mechanism underlying central thermoregulation provides a useful platform for exploring its functional organization, elucidating the molecular underpinnings of its neuronal interactions, and discovering novel therapeutic approaches to modulating body temperature and energy homeostasis.
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Affiliation(s)
- S F Morrison
- Department of Neurological Surgery, Oregon Health and Science University, Portland, Oregon 97239, USA;
| | - K Nakamura
- Department of Integrative Physiology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
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Notley SR, Flouris AD, Kenny GP. On the use of wearable physiological monitors to assess heat strain during occupational heat stress. Appl Physiol Nutr Metab 2018; 43:869-881. [DOI: 10.1139/apnm-2018-0173] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Workers in many industries are required to perform arduous work in high heat-stress conditions, which can lead to rapid increases in body temperature that elevate the risk of heat-related illness and even death. Traditionally, effort to mitigate work-related heat injury has been directed toward the assessment of environmental heat stress (e.g., wet-bulb globe temperature), rather than toward the associated physiological strain responses (e.g., heart rate and skin and core temperatures). However, because a worker’s physiological response to a given heat stress is modified independently by inter-individual factors (e.g., age, sex, chronic disease, others) and intra-individual factors both within (e.g., medication use, fitness, acclimation and hydration state, others) and beyond (e.g., shift duration, illness, others) the worker’s control, it becomes challenging to protect workers on an individual basis from heat-related injury without assessing those physiological responses. Recent advancements in wearable technology have made it possible to monitor one or more physiological indices of heat strain. Nonetheless, information on the utility of the wearable systems available for assessing occupational heat strain is unavailable. This communication is therefore directed toward identifying the physiological indices of heat strain that may be quantified in the workplace and evaluating the wearable monitoring systems available for assessing those responses. Finally, emphasis is placed on the barriers associated with implementing these devices to assist in mitigating work-related heat injury. This information is fundamental for protecting worker health and could also be utilized to prevent heat illnesses in vulnerable people during leisure or athletic activities.
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Affiliation(s)
- Sean R. Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - Andreas D. Flouris
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON K1N 6N5, Canada
- Functional Architecture of Mammals in their Environment (FAME) Laboratory, Department of Exercise Science, University of Thessaly, Trikala, Greece
| | - Glen P. Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON K1N 6N5, Canada
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28
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Caldwell JN, van den Heuvel AMJ, Kerry P, Clark MJ, Peoples GE, Taylor NAS. A vascular mechanism to explain thermally mediated variations in deep-body cooling rates during the immersion of profoundly hyperthermic individuals. Exp Physiol 2018; 103:512-522. [DOI: 10.1113/ep086760] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 01/15/2018] [Indexed: 11/08/2022]
Affiliation(s)
- Joanne N. Caldwell
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Anne M. J. van den Heuvel
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Pete Kerry
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Mitchell J. Clark
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Gregory E. Peoples
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Nigel A. S. Taylor
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
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29
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Abstract
In humans, sweating is the most powerful autonomic thermoeffector. The evaporation of sweat provides by far the greatest potential for heat loss and it represents the only means of heat loss when air temperature exceeds skin temperature. Sweat production results from the integration of afferent neural information from peripheral and central thermoreceptors which leads to an increase in skin sympathetic nerve activity. At the neuroglandular junction, acetylcholine is released and binds to muscarinic receptors which stimulate the secretion of a primary fluid by the secretory coil of eccrine glands. The primary fluid subsequently travels through a duct where ions are reabsorbed. The end result is the expulsion of hypotonic sweat on to the skin surface. Sweating increases in proportion with the intensity of the thermal challenge in an attempt of the body to attain heat balance and maintain a stable internal body temperature. The control of sweating can be modified by biophysical factors, heat acclimation, dehydration, and nonthermal factors. The purpose of this article is to review the role of sweating as a heat loss thermoeffector in humans.
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30
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Notley SR, Taylor EA, Ohnishi N, Taylor NAS. Cutaneous vasomotor adaptation following repeated, isothermal heat exposures: evidence of adaptation specificity. Appl Physiol Nutr Metab 2017; 43:415-418. [PMID: 29156142 DOI: 10.1139/apnm-2017-0569] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Unequivocal enhancement of cutaneous vasomotor function has yet to be demonstrated following heat acclimation, possibly because the adaptation stimulus was not sustained, or because thermoeffector function was not assessed at equivalent deep-body temperatures. Therefore, forearm and local cutaneous vascular conductances were evaluated during exercise eliciting matched deep-body temperatures (37.5 °C, 38.5 °C), before and after isothermal heat acclimation. Both indices increased (21% and 25%), confirming cutaneous vasomotor adaptation can occur, provided those experimental design specifications are satisfied.
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Affiliation(s)
- Sean R Notley
- a Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Elizabeth A Taylor
- a Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Norikazu Ohnishi
- a Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia.,b Faculty of Nursing, Mie Prefectural College of Nursing, Mie 514-0116, Japan
| | - Nigel A S Taylor
- a Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
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31
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Ravanelli N, Jay O, Gagnon D. Sustained increases in skin blood flow are not a prerequisite to initiate sweating during passive heat exposure. Am J Physiol Regul Integr Comp Physiol 2017; 313:R140-R148. [PMID: 28566303 DOI: 10.1152/ajpregu.00033.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 05/08/2017] [Accepted: 05/23/2017] [Indexed: 11/22/2022]
Abstract
Some studies have observed a functional relationship between sweating and skin blood flow. However, the implications of this relationship during physiologically relevant conditions remain unclear. We manipulated sudomotor activity through changes in sweating efficiency to determine if parallel changes in vasomotor activity are observed. Eight young men completed two trials at 36°C and two trials at 42°C. During these trials, air temperature remained constant while ambient vapor pressure increased from 1.6 to 5.6 kPa over 2 h. Forced airflow across the skin was used to create conditions of high (HiSeff) or low (LoSeff) sweating efficiency. Local sweat rate (LSR), local skin blood flow (SkBF), as well as mean skin and esophageal temperatures were measured continuously. It took longer for LSR to increase during HiSeff at 36°C (HiSeff: 99 ± 11 vs. LoSeff: 77 ± 11 min, P < 0.01) and 42°C (HiSeff: 72 ± 16 vs. LoSeff: 51 ± 15 min, P < 0.01). In general, an increase in LSR preceded the increase in SkBF when expressed as ambient vapor pressure and time for all conditions (P < 0.05). However, both responses were activated at a similar change in mean body temperature (average across all trials, LSR: 0.26 ± 0.15 vs. SkBF: 0.30 ± 0.18°C, P = 0.26). These results demonstrate that altering the point at which LSR is initiated during heat exposure is paralleled by similar shifts for the increase in SkBF. However, local sweat production occurs before an increase in SkBF, suggesting that SkBF is not necessarily a prerequisite for sweating.
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Affiliation(s)
- Nicholas Ravanelli
- Faculty of Health Sciences, University of Ottawa, Ottawa, Ontario, Canada.,Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, Australia
| | - Ollie Jay
- Faculty of Health Sciences, University of Ottawa, Ottawa, Ontario, Canada.,Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, Australia
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montréal, Québec, Canada; and .,Département de Pharmacologie et Physiologie, Faculté de Médecine, Université de Montréal, Montréal, Québec, Canada
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32
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Nicolò A, Marcora SM, Bazzucchi I, Sacchetti M. Differential control of respiratory frequency and tidal volume during high-intensity interval training. Exp Physiol 2017; 102:934-949. [PMID: 28560751 DOI: 10.1113/ep086352] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 05/25/2017] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? By manipulating recovery intensity and exercise duration during high-intensity interval training (HIIT), we tested the hypothesis that fast inputs contribute more than metabolic stimuli to respiratory frequency (fR ) regulation. What is the main finding and its importance? Respiratory frequency, but not tidal volume, responded rapidly and in proportion to changes in workload during HIIT, and was dissociated from some markers of metabolic stimuli in response to both experimental manipulations, suggesting that fast inputs contribute more than metabolic stimuli to fR regulation. Differentiating between fR and tidal volume may help to unravel the mechanisms underlying exercise hyperpnoea. Given that respiratory frequency (fR ) has been proposed as a good marker of physical effort, furthering the understanding of how fR is regulated during exercise is of great importance. We manipulated recovery intensity and exercise duration during high-intensity interval training (HIIT) to test the hypothesis that fast inputs (including central command) contribute more than metabolic stimuli to fR regulation. Seven male cyclists performed an incremental test, a 10 and a 20 min continuous time trial (TT) as preliminary tests. Subsequently, recovery intensity and exercise duration were manipulated during HIIT (30 s work and 30 s active recovery) by performing four 10 min and one 20 min trial (recovery intensities of 85, 70, 55 and 30% of the 10 min TT mean workload; and 85% of the 20 min TT mean workload). The work intensity of the HIIT sessions was self-paced by participants to achieve the best performance possible. When manipulating recovery intensity, fR , but not tidal volume (VT ), showed a fast response to the alternation of the work and recovery phases, proportional to the extent of workload variations. No association between fR and gas exchange responses was observed. When manipulating exercise duration, fR and rating of perceived exertion were dissociated from VT , carbon dioxide output and oxygen uptake responses. Overall, the rating of perceived exertion was strongly correlated with fR (r = 0.87; P < 0.001) but not with VT . These findings may reveal a differential control of fR and VT during HIIT, with fast inputs appearing to contribute more than metabolic stimuli to fR regulation. Differentiating between fR and VT may help to unravel the mechanisms underlying exercise hyperpnoea.
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Affiliation(s)
- Andrea Nicolò
- Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
| | - Samuele M Marcora
- Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Chatham Maritime, Kent, UK
| | - Ilenia Bazzucchi
- Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
| | - Massimo Sacchetti
- Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
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33
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Indirect hand and forearm vasomotion: Regional variations in cutaneous thermosensitivity during normothermia and mild hyperthermia. J Therm Biol 2017; 65:95-104. [DOI: 10.1016/j.jtherbio.2017.02.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 02/24/2017] [Accepted: 02/24/2017] [Indexed: 11/21/2022]
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34
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Thermogenic and psychogenic recruitment of human eccrine sweat glands: Variations between glabrous and non-glabrous skin surfaces. J Therm Biol 2017; 65:145-152. [DOI: 10.1016/j.jtherbio.2017.03.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 03/07/2017] [Accepted: 03/07/2017] [Indexed: 11/23/2022]
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35
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Notley SR, Park J, Tagami K, Ohnishi N, Taylor NAS. Variations in body morphology explain sex differences in thermoeffector function during compensable heat stress. Exp Physiol 2017; 102:545-562. [PMID: 28231604 DOI: 10.1113/ep086112] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 02/08/2017] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Can sex-related differences in cutaneous vascular and sudomotor responses be explained primarily by variations in the ratio between body surface area and mass during compensable exercise that elicits equivalent heat-loss requirements and mean body temperature changes across participants? What is the main finding and its importance? Mass-specific surface area was a significant determinant of vasomotor and sudomotor responses in men and women, explaining 10-48% of the individual thermoeffector variance. Nonetheless, after accounting for changes in mean body temperature and morphological differences, sex explained only 5% of that inter-individual variability. It was concluded that sex differences in thermoeffector function are morphologically dependent, but not sex dependent. Sex is sometimes thought to be an independent modulator of cutaneous vasomotor and sudomotor function during heat exposure. Nevertheless, it was hypothesized that, when assessed during compensable exercise that evoked equal heat-loss requirements across participants, sex differences in those thermoeffectors would be explained by variations in the ratio between body surface area and mass (specific surface area). To evaluate that possibility, vasomotor and sudomotor functions were assessed in 60 individuals (36 men and 24 women) with widely varying (overlapping) specific surface areas (range, 232.3-292.7 and 241.2-303.1 cm2 kg-1 , respectively). Subjects completed two trials in compensable conditions (28°C, 36% relative humidity) involving rest (20 min) and steady-state cycling (45 min) at fixed, area-specific metabolic heat-production rates (light, ∼135 W m-2 ; moderate, ∼200 W m-2 ). Equivalent heat-loss requirements and mean body temperature changes were evoked across participants. Forearm blood flow and vascular conductance were positively related to specific surface area during light work in men (r = 0.67 and r = 0.66, respectively; both P < 0.05) and during both exercise intensities in women (light, r = 0.57 and r = 0.69; and moderate, r = 0.64 and r = 0.68; all P < 0.05). Whole-body and local sweat rates were negatively related to that ratio (correlation coefficient range, -0.33 to -0.62; all P < 0.05) during both work rates in men and women. Those relationships accounted for 10-48% of inter-individual thermoeffector variance (P < 0.05). Furthermore, after accounting for morphological differences, sex explained no more than 5% of that variability (P < 0.05). It was concluded that, when assessed during compensable exercise, sex differences in thermoeffector function were largely determined morphologically, rather than being sex dependent.
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Affiliation(s)
- Sean R Notley
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Joonhee Park
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Kyoko Tagami
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Norikazu Ohnishi
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia.,Faculty of Nursing, Mie Prefectural College of Nursing, Mie, 514-0116, Japan
| | - Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
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36
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van den Heuvel AMJ, Haberley BJ, Hoyle DJR, Taylor NAS, Croft RJ. The independent influences of heat strain and dehydration upon cognition. Eur J Appl Physiol 2017; 117:1025-1037. [DOI: 10.1007/s00421-017-3592-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 03/18/2017] [Indexed: 01/08/2023]
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37
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38
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Gordon CJ, Caldwell JN, Taylor NAS. Non-thermal modulation of sudomotor function during static exercise and the impact of intensity and muscle-mass recruitment. Temperature (Austin) 2016; 3:252-261. [PMID: 27857955 PMCID: PMC4964990 DOI: 10.1080/23328940.2016.1176102] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Revised: 04/03/2016] [Accepted: 04/05/2016] [Indexed: 11/04/2022] Open
Abstract
Aim: Static muscle activation elicits intensity-dependent, non-thermal sweating that is presumably controlled by feedforward (central command) mechanisms. However, it is currently unknown how the size of the recruited muscle mass interacts with that mechanism. To investigate the possible muscle-size dependency of that non-thermal sweating, the recruitment of two muscle groups of significantly different size was investigated in individuals within whom steady-state thermal sweating had been established and clamped. Methods: Fourteen passively heated subjects (climate chamber and water-perfusion garment) performed 60-s, static handgrip and knee-extension activations at 30% and 50% of maximal voluntary force, plus a handgrip at 40% intensity (143.4 N) and a third knee extension at the same absolute force. Local sweating from four body segments (averaged to represent whole-body sudomotor activity), three deep-body and eight skin temperatures, heart rates and perceptions of physical effort were measured continuously, and analyzed over the final 30 s of exercise. Results: In the presence of thermal clamping and low-level, steady-state sweating, static muscle activation resulted in exercise-intensity dependent changes in the whole-body sudomotor response during these handgrip and knee-extension actions (P < 0.05). However, there was no evidence of a dependency on the size of the recruited muscle mass (P > 0.05), yet both dependencies were apparent for heart rate, and partially evident for the sensations of physical effort. Conclusion: These observations represent the first evidence that exercise-related sudomotor feedforward is not influenced by the size of the activated muscle mass, but is instead primarily dictated by the intensity of the exercise itself.
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Affiliation(s)
- Christopher J Gordon
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong , Wollongong, NSW, Australia
| | - Joanne N Caldwell
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong , Wollongong, NSW, Australia
| | - Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong , Wollongong, NSW, Australia
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Notley SR, Park J, Tagami K, Ohnishi N, Taylor NAS. Morphological dependency of cutaneous blood flow and sweating during compensable heat stress when heat-loss requirements are matched across participants. J Appl Physiol (1985) 2016; 121:25-35. [PMID: 27125845 PMCID: PMC4967244 DOI: 10.1152/japplphysiol.00151.2016] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 04/26/2016] [Indexed: 11/22/2022] Open
Abstract
Human heat loss is thought, in part, to be morphologically related. It was therefore hypothesized that when heat-loss requirements and body temperatures were matched, that the mass-specific surface area alone could significantly explain both cutaneous vascular and sudomotor responses during compensable exercise. These thermoeffector responses were examined in 36 men with widely varying mass-specific surface areas (range, 232.3-292.7 cm(2)/kg), but of similar age, aerobic fitness, and adiposity. Subjects completed two trials under compensable conditions (28.1°C, 36.8% relative humidity), each involving rest (20 min) and steady-state cycling (45 min) at two matched metabolic heat-production rates (light, ∼135 W/m(2); moderate, ∼200 W/m(2)). Following equivalent mean body temperature changes, forearm blood flow and vascular conductance (r = 0.63 and r = 0.65) shared significant, positive associations with the mass-specific surface area during light work (P < 0.05), explaining ∼45% of the vasomotor variation. Conversely, during light and moderate work, whole body sweat rate, as well as local sweat rate and sudomotor sensitivity at three of four measured sites, revealed moderate, negative relationships with the mass-specific surface area (correlation coefficient range -0.37 to -0.73, P < 0.05). Moreover, those relationships could uniquely account for between 10 and 53% of those sweating responses (P < 0.05). Therefore, both thermoeffector responses displayed a significant morphological dependency in the presence of equivalent thermoafferent drive. Indeed, up to half of the interindividual variation in these effector responses could now be explained through morphological differences and the first principles governing heat transfer.
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Affiliation(s)
- Sean R Notley
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, New South Wales, Australia; and
| | - Joonhee Park
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, New South Wales, Australia; and
| | - Kyoko Tagami
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, New South Wales, Australia; and
| | - Norikazu Ohnishi
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, New South Wales, Australia; and Faculty of Nursing, Mie Prefectural College of Nursing, Mie, Japan
| | - Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, New South Wales, Australia; and
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Affiliation(s)
- R. Mrowka
- Experimentelle Nephrologie; Universitätsklinikum Jena; Jena Germany
| | - S. Reuter
- Experimentelle Nephrologie; Universitätsklinikum Jena; Jena Germany
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de Rome L, Taylor EA, Croft RJ, Brown J, Fitzharris M, Taylor NAS. Thermal and cardiovascular strain imposed by motorcycle protective clothing under Australian summer conditions. ERGONOMICS 2016; 59:504-513. [PMID: 26280297 DOI: 10.1080/00140139.2015.1082632] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Motorcycle protective clothing can be uncomfortably hot during summer, and this experiment was designed to evaluate the physiological significance of that burden. Twelve males participated in four, 90-min trials (cycling 30 W) across three environments (25, 30, 35 °C [all 40% relative humidity]). Clothing was modified between full and minimal injury protection. Both ensembles were tested at 25 °C, with only the more protective ensemble investigated at 30 and 35 °C. At 35 °C, auditory canal temperature rose at 0.02 °C min(-1) (SD 0.005), deviating from all other trials (p < 0.05). The thresholds for moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 min (SD 20.6) and 180 min (SD 33.0), respectively. Profound hyperthermia might eventuate in ~10 h at 30 °C, but should not occur at 25 °C. These outcomes demonstrate a need to enhance the heat dissipation capabilities of motorcycle clothing designed for summer use in hot climates, but without compromising impact protection. Practitioner's Summary: Motorcycle protective clothing can be uncomfortably hot during summer. This experiment was designed to evaluate the physiological significance of this burden across climatic states. In the heat, moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 and 180 min, respectively.
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Affiliation(s)
- Liz de Rome
- a Neuroscience Research Australia , Sydney , Australia
| | - Elizabeth A Taylor
- b Centre for Human and Applied Physiology, School of Medicine , University of Wollongong , Wollongong , Australia
| | - Rodney J Croft
- c School of Psychology , University of Wollongong , Wollongong , Australia
| | - Julie Brown
- a Neuroscience Research Australia , Sydney , Australia
| | - Michael Fitzharris
- d Monash Injury Research Institute and Monash University Accident Research Centre , Monash University , Melbourne , Australia
| | - Nigel A S Taylor
- b Centre for Human and Applied Physiology, School of Medicine , University of Wollongong , Wollongong , Australia
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Taylor NA, Burdon CA, van den Heuvel AM, Fogarty AL, Notley SR, Hunt AP, Billing DC, Drain JR, Silk AJ, Patterson MJ, Peoples GE. Balancing ballistic protection against physiological strain: evidence from laboratory and field trials. Appl Physiol Nutr Metab 2016; 41:117-24. [DOI: 10.1139/apnm-2015-0386] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This project was based on the premise that decisions concerning the ballistic protection provided to defence personnel should derive from an evaluation of the balance between protection level and its impact on physiological function, mobility, and operational capability. Civilians and soldiers participated in laboratory- and field-based studies in which ensembles providing five levels of ballistic protection were evaluated, each with progressive increases in protection, mass (3.4–11.0 kg), and surface-area coverage (0.25–0.52 m2). Physiological trials were conducted on volunteers (N = 8) in a laboratory, under hot-dry conditions simulating an urban patrol: walking at 4 km·h−1 (90 min) and 6 km·h−1 (30 min or to fatigue). Field-based trials were used to evaluate tactical battlefield movements (mobility) of soldiers (N = 31) under tropical conditions, and across functional tests of power, speed, agility, endurance, and balance. Finally, trials were conducted at a jungle training centre, with soldiers (N = 32) patrolling under tropical conditions (averaging 5 h). In the laboratory, work tolerance was reduced as protection increased, with deep-body temperature climbing relentlessly. However, the protective ensembles could be grouped into two equally stressful categories, each providing a different level of ballistic protection. This outcome was supported during the mobility trials, with the greatest performance decrement evident during fire and movement simulations, as the ensemble mass was increased (–2.12%·kg−1). The jungle patrol trials similarly supported this outcome. Therefore, although ballistic protection does increase physiological strain, this research has provided a basis on which to determine how that strain can be balanced against the mission-specific level of required personal protection.
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Affiliation(s)
- Nigel A.S. Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Catriona A. Burdon
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Anne M.J. van den Heuvel
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Alison L. Fogarty
- Land Division, Defence Science and Technology, Melbourne VIC 3207, Australia
| | - Sean R. Notley
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Andrew P. Hunt
- Land Division, Defence Science and Technology, Melbourne VIC 3207, Australia
| | - Daniel C. Billing
- Land Division, Defence Science and Technology, Melbourne VIC 3207, Australia
| | - Jace R. Drain
- Land Division, Defence Science and Technology, Melbourne VIC 3207, Australia
| | - Aaron J. Silk
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Mark J. Patterson
- Land Division, Defence Science and Technology, Melbourne VIC 3207, Australia
| | - Gregory E. Peoples
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
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Taylor NAS, Haberley BJ, Hoyle DJR. Thermal performance trials on the habitability of private bushfire shelters: part 1. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2015; 59:983-993. [PMID: 25336107 DOI: 10.1007/s00484-014-0911-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2014] [Revised: 10/10/2014] [Accepted: 10/12/2014] [Indexed: 06/04/2023]
Abstract
This communication is the first of two in which specifications for private bushfire shelters were evaluated during human trials. The purpose of this investigation (series 1) was to test the hypothesis that shelters capable of maintaining the internal environment at, or below, a modified discomfort index of 39 °C would prevent a deep-body temperature elevation of >2 °C. This was tested over 96 trials during which eight men and eight women were exposed at rest (60 min) to three regulated shelter conditions satisfying that standard: 40 °C and 70 % relative humidity, 45 °C and 50 % relative humidity and 50 °C and 30 % relative humidity. Subjects were tested twice in each condition following exercise- and heat-induced dehydration (2 % body mass reduction) and pre-heating to each of two deep-body thermal states (37.5 and 38.5 °C). Participants presented well rested and euhydrated, and pre-treatments successfully achieved the thermal and hydration targets prior to exposure. Auditory canal temperatures declined as exposures commenced, with subsequent rises of >0.5 °C not evident within any trial. However, each increment in air temperature elicited a significant elevation in the respective within-trial mean auditory canal temperature (37.4, 37.7 and 37.9 °C) and heart rate (103, 116 and 122 beats.min(-1)) when subjects were moderately hyperthermic (all P < 0.05). Nevertheless, on average, subjects successfully defended deep-body temperature at levels significantly below those associated with heat illness, and it was concluded that this thermal specification for bushfire shelters appeared adequate, providing the physical characteristics of the internal air remained stable.
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Affiliation(s)
- Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia,
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Considerations for the measurement of core, skin and mean body temperatures. J Therm Biol 2014; 46:72-101. [DOI: 10.1016/j.jtherbio.2014.10.006] [Citation(s) in RCA: 228] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 10/24/2014] [Accepted: 10/27/2014] [Indexed: 11/23/2022]
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Kenny GP. Muscle temperature and sweating during exercise: a new link? Acta Physiol (Oxf) 2014; 212:11-3. [PMID: 24957481 DOI: 10.1111/apha.12335] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- G. P. Kenny
- Human and Environmental Physiology Research Unit; School of Human Kinetics; University of Ottawa; Ottawa ON Canada
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