The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
K. Parsons - One of the best experts on this subject based on the ideXlab platform.
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personal factors in thermal comfort assessment clothing properties and Metabolic Heat Production
Energy and Buildings, 2002Co-Authors: George Havenith, Ingvar Holmer, K. ParsonsAbstract:In the assessment of thermal comfort in buildings, the use of the Predicted Mean Vote (PMV) model is very popular. For this model, data on the climate, on clothing and on Metabolic Heat Production are required. This paper discusses the representation and measurement of clothing parameters and Metabolic rate in the PMV context. Several problems are identified and for some of these solutions are provided. For clothing insulation it was shown that effects of body motion and air movement are so big that they must be accounted for in comfort prediction models to be physically accurate. However, effects on dry Heat exchange are small for stationary, light work at low air movement. Also algorithms for convective Heat exchange in prediction models should be reconsidered. For evaporative Heat resistance of the clothing worn, which is currently not an input factor in the PMV model, it was shown that in cases where special clothing with high vapour resistance is worn (e.g. clean-room clothing), comfort may be limited by the clothing as it will induce a high skin wettedness. Thus, for such cases clothing vapour resistance should not be neglected in the calculation of comfort using the PMV model, or the induced skin wettedness should be calculated separately. The effects on thermal comfort of reductions in vapour resistance due to air and body movements are also shown to have a substantial impact on the comfort limits in terms of skin wettedness and cannot be neglected either. For Metabolic Heat Production it was concluded that for precise comfort assessment a precise measure of Metabolic rate is needed. In order to improve Metabolic rate estimation based on ISO 8996, more data and detail is needed for activities with a Metabolic rate below 2 MET. Finally, it was shown that the methods for determining Metabolic rate provided in ISO 8996 (typically used in comfort assessment and evaluations) do not provide sufficient accuracy to allow determination of comfort (expressed as PMV) in sufficient precision to classify buildings to within 0.3 PMV units as proposed in the upcoming revision of ISO 7730.
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Personal factors in thermal comfort assessment: Clothing properties and Metabolic Heat Production
Energy and Buildings, 2002Co-Authors: George Havenith, Ingvar Holmér, K. ParsonsAbstract:In the assessment of thermal comfort in buildings, the use of the Predicted Mean Vote (PMV) model is very popular. For this model, data on the climate, on clothing and on Metabolic Heat Production are required. This paper discusses the representation and measurement of clothing parameters and Metabolic rate in the PMV context. Several problems are identified and for some of these solutions are provided. For clothing insulation it was shown that effects of body motion and air movement are so big that they must be accounted for in comfort prediction models to be physically accurate. However, effects on dry Heat exchange are small for stationary, light work at low air movement. Also algorithms for convective Heat exchange in prediction models should be reconsidered. For evaporative Heat resistance of the clothing worn, which is currently not an input factor in the PMV model, it was shown that in cases where special clothing with high vapour resistance is worn (e.g. clean-room clothing), comfort may be limited by the clothing as it will induce a high skin wettedness. Thus, for such cases clothing vapour resistance should not be neglected in the calculation of comfort using the PMV model, or the induced skin wettedness should be calculated separately. The effects on thermal comfort of reductions in vapour resistance due to air and body movements are also shown to have a substantial impact on the comfort limits in terms of skin wettedness and cannot be neglected either. For Metabolic Heat Production it was concluded that for precise comfort assessment a precise measure of Metabolic rate is needed. In order to improve Metabolic rate estimation based on ISO 8996, more data and detail is needed for activities with a Metabolic rate below 2 MET. Finally, it was shown that the methods for determining Metabolic rate provided in ISO 8996 (typically used in comfort assessment and evaluations) do not provide sufficient accuracy to allow determination of comfort (expressed as PMV) in sufficient precision to classify buildings to within 0.3 PMV units as proposed in the upcoming revision of ISO 7730. © 2002 Elsevier Science B.V. All rights reserved.
Glen P Kenny - One of the best experts on this subject based on the ideXlab platform.
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Local infusion of ascorbate augments NO‐dependent cutaneous vasodilatation during intense exercise in the Heat
The Journal of Physiology, 2015Co-Authors: Robert D. Meade, Naoto Fujii, Lacy M. Alexander, Gabrielle Paull, Jeffrey C. Louie, Andreas D. Flouris, Glen P KennyAbstract:Key points Recent work demonstrates that nitric oxide (NO) contributes to cutaneous vasodilatation during moderate (400 W of Metabolic Heat Production) but not high (700 W of Metabolic Heat Production) intensity exercise bouts performed in the Heat (35°C). The present study evaluated whether the impairment in NO-dependent cutaneous vasodilatation was the result of a greater accumulation of reactive oxygen species during high (700 W of Metabolic Heat Production) relative to moderate (500 W of Metabolic Heat Production) intensity exercise. It was shown that local infusion of ascorbate (an anti-oxidant) improves NO-dependent forearm cutaneous vasodilatation during high intensity exercise in the Heat. These findings provide novel insight into the physiological mechanisms governing cutaneous blood flow during exercise-induced Heat stress and provide direction for future research exploring whether oxidative stress underlies the impairments in Heat dissipation that may occur in older adults, as well as in individuals with pathophysiological conditions such as type 2 diabetes. Abstract Nitric oxide (NO)-dependent cutaneous vasodilatation is reportedly diminished during exercise performed at a high (700 W) relative to moderate (400 W) rate of Metabolic Heat Production. The present study evaluated whether this impairment results from increased oxidative stress associated with an accumuluation of reactive oxygen species (ROS) during high intensity exercise. On two separate days, 11 young (mean ± SD, 24 ± 4 years) males cycled in the Heat (35°C) at a moderate (500 W) or high (700 W) rate of Metabolic Heat Production. Each session included two 30 min exercise bouts followed by 20 and 40 min of recovery, respectively. Cutaneous vascular conductance (CVC) was monitored at four forearm skin sites continuously perfused via intradermal microdialysis with: (1) lactated Ringer solution (Control); (2) 10 mm ascorbate (Ascorbate); (3) 10 mm l-NAME; or (4) 10 mm ascorbate + 10 mm l-NAME (Ascorbate + l-NAME). At the end of each 500 W exercise bout, CVC was attenuated with l-NAME (∼35% CVCmax) and Ascorbate + l-NAME (∼43% CVCmax) compared to Control (∼60% CVCmax; all P 0.87). Conversely, CVC was elevated with Ascorbate (∼72% CVCmax; both P 0.05) at the end of both 700 W exercise bouts. We conclude that oxidative stress associated with an accumulation of ascorbate-sensitive ROS impairs NO-dependent cutaneous vasodilatation during intense exercise.
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Sex modulates whole‐body sudomotor thermosensitivity during exercise
The Journal of Physiology, 2011Co-Authors: Daniel Gagnon, Glen P KennyAbstract:Non-technical summary The human body controls its temperature through coordinated physiological processes. Prior to the current study, it remained unknown if differences between males and females existed in these processes. The results from the current study show that females have a lower whole-body sweat response during exercise in the Heat compared to males, which results in a greater increase in body temperature. The physiological process responsible for the lower whole-body sweat rate was a lower thermosensitivity of the response, meaning a lower increase in sweat Production for a given increase in body temperature. Knowledge of sex-related differences in the physiology of temperature regulation may lead to better improvements in Heat exposure guidelines for industrial, military and athletic settings. Abstract It is unclear whether true physiological differences exist in temperature regulation between males and females during exercise, independently of differences in physical characteristics and Metabolic Heat Production. Therefore, we examined differences in the onset threshold and thermosensitivity of whole-body sudomotor activity and cutaneous vascular conductance between males and females matched for body mass and surface area. Nine males and nine females performed 90 min of exercise at each of the following intensities in a warm/dry environment: 50% of maximum oxygen consumption () and at a fixed rate of Metabolic Heat Production equal to 500 W. Evaporative Heat loss (EHL, direct calorimetry) and cutaneous vascular conductance (CVC, laser-Doppler) were measured continuously. Mean body temperature was calculated from the measurements of oesophageal and mean skin temperatures. During exercise at 50%, a lower rate of sudomotor activity was observed in females (385 ± 12 vs. 512 ± 24 W, P < 0.001). However, irrespective of sex, individual EHL values were strongly associated with Metabolic Heat Production (R2= 0.82, P < 0.001). Nonetheless, a lower rate of EHL was observed in females when exercise was performed at 500 W of Metabolic Heat Production (419 ± 7 vs. 454 ± 11 W, P= 0.032). Furthermore, a lower increase in EHL per increase in mean body temperature was observed in females (553 ± 77 vs. 795 ± 85 W °C−1, P= 0.051), with no differences in the onset threshold (36.77 ± 0.06 vs. 36.61 ± 0.11°C, P= 0.242). In contrast, no differences were observed in CVC. Collectively, these findings demonstrate that females have a lower thermosensitivity of the whole-body sudomotor response compared to males during exercise in the Heat performed at a fixed rate of Metabolic Heat Production.
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Sex modulates whole-body sudomotor thermosensitivity during exercise.
The Journal of physiology, 2011Co-Authors: Daniel Gagnon, Glen P KennyAbstract:It is unclear whether true physiological differences exist in temperature regulation between males and females during exercise, independently of differences in physical characteristics and Metabolic Heat Production. Therefore, we examined differences in the onset threshold and thermosensitivity of whole-body sudomotor activity and cutaneous vascular conductance between males and females matched for body mass and surface area. Nine males and nine females performed 90 min of exercise at each of the following intensities in a warm/dry environment: 50% of maximum oxygen consumption (V(O(2)max)) and at a fixed rate of Metabolic Heat Production equal to 500 W. Evaporative Heat loss (EHL, direct calorimetry) and cutaneous vascular conductance (CVC, laser-Doppler) were measured continuously. Mean body temperature was calculated from the measurements of oesophageal and mean skin temperatures. During exercise at 50% V(O(2)max), a lower rate of sudomotor activity was observed in females (385 ± 12 vs. 512 ± 24 W, P < 0.001). However, irrespective of sex, individual EHL values were strongly associated with Metabolic Heat Production (R(2) = 0.82, P < 0.001). Nonetheless, a lower rate of EHL was observed in females when exercise was performed at 500 W of Metabolic Heat Production (419 ± 7 vs. 454 ± 11 W, P = 0.032). Furthermore, a lower increase in EHL per increase in mean body temperature was observed in females (553 ± 77 vs. 795 ± 85 W °C(-1), P = 0.051), with no differences in the onset threshold (36.77 ± 0.06 vs. 36.61 ± 0.11°C, P = 0.242). In contrast, no differences were observed in CVC. Collectively, these findings demonstrate that females have a lower thermosensitivity of the whole-body sudomotor response compared to males during exercise in the Heat performed at a fixed rate of Metabolic Heat Production.
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Short-term exercise training does not improve whole-body Heat loss when rate of Metabolic Heat Production is considered
European Journal of Applied Physiology, 2010Co-Authors: Jill M. Stapleton, Daniel Gagnon, Glen P KennyAbstract:We evaluated the effects of an 8-week exercise training program in previously sedentary individuals on whole-body Heat balance during exercise at a constant rate of Metabolic Heat Production. Prior to and after 8 weeks of training, ten participants performed 60-min of cycling exercise at a constant rate of Heat Production (~450 W) followed by 60-min of recovery, at 30°C and 15% relative humidity. Rate of total Heat loss was measured directly by whole-body calorimetry, while rate of Metabolic Heat Production was measured simultaneously by indirect calorimetry. Esophageal (T es), skin blood flow (SkBF) and local sweat rate (LSR) were also measured continuously. The 8-week exercise training program elicited a 10% increase in maximal aerobic capacity (P
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short term exercise training does not improve whole body Heat loss when rate of Metabolic Heat Production is considered
European Journal of Applied Physiology, 2010Co-Authors: Jill M. Stapleton, Daniel Gagnon, Glen P KennyAbstract:We evaluated the effects of an 8-week exercise training program in previously sedentary individuals on whole-body Heat balance during exercise at a constant rate of Metabolic Heat Production. Prior to and after 8 weeks of training, ten participants performed 60-min of cycling exercise at a constant rate of Heat Production (~450 W) followed by 60-min of recovery, at 30°C and 15% relative humidity. Rate of total Heat loss was measured directly by whole-body calorimetry, while rate of Metabolic Heat Production was measured simultaneously by indirect calorimetry. Esophageal (T es), skin blood flow (SkBF) and local sweat rate (LSR) were also measured continuously. The 8-week exercise training program elicited a 10% increase in maximal aerobic capacity (P < 0.001). Furthermore, exercise training reduced (P ≤ 0.05) baseline (37.10 ± 0.28 vs. 36.95 ± 0.24°C) and end-exercise (37.85 ± 0.30 vs. 37.55 ± 0.20°C) values for T es as well as onset thresholds for LSR (37.23 ± 0.26 vs. 36.96 ± 0.22°C, P < 0.001) and SkBF (37.16 ± 0.38 vs. 36.83 ± 0.26°C, P < 0.001). However, these improvements in thermoregulatory function did not translate into a greater rate of total Heat loss between the pre- and post-training exercise trials (P = 0.762). Furthermore, there were no differences in SkBF (P = 0.546) and LSR (P = 0.475) from pre- to post-training. Although physical training resulted in significant improvements of cardiorespiratory and thermoregulatory functions, these adaptations did not improve whole-body and local Heat loss responses during exercise performed at a given rate of Metabolic Heat Production.
George Havenith - One of the best experts on this subject based on the ideXlab platform.
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personal factors in thermal comfort assessment clothing properties and Metabolic Heat Production
Energy and Buildings, 2002Co-Authors: George Havenith, Ingvar Holmer, K. ParsonsAbstract:In the assessment of thermal comfort in buildings, the use of the Predicted Mean Vote (PMV) model is very popular. For this model, data on the climate, on clothing and on Metabolic Heat Production are required. This paper discusses the representation and measurement of clothing parameters and Metabolic rate in the PMV context. Several problems are identified and for some of these solutions are provided. For clothing insulation it was shown that effects of body motion and air movement are so big that they must be accounted for in comfort prediction models to be physically accurate. However, effects on dry Heat exchange are small for stationary, light work at low air movement. Also algorithms for convective Heat exchange in prediction models should be reconsidered. For evaporative Heat resistance of the clothing worn, which is currently not an input factor in the PMV model, it was shown that in cases where special clothing with high vapour resistance is worn (e.g. clean-room clothing), comfort may be limited by the clothing as it will induce a high skin wettedness. Thus, for such cases clothing vapour resistance should not be neglected in the calculation of comfort using the PMV model, or the induced skin wettedness should be calculated separately. The effects on thermal comfort of reductions in vapour resistance due to air and body movements are also shown to have a substantial impact on the comfort limits in terms of skin wettedness and cannot be neglected either. For Metabolic Heat Production it was concluded that for precise comfort assessment a precise measure of Metabolic rate is needed. In order to improve Metabolic rate estimation based on ISO 8996, more data and detail is needed for activities with a Metabolic rate below 2 MET. Finally, it was shown that the methods for determining Metabolic rate provided in ISO 8996 (typically used in comfort assessment and evaluations) do not provide sufficient accuracy to allow determination of comfort (expressed as PMV) in sufficient precision to classify buildings to within 0.3 PMV units as proposed in the upcoming revision of ISO 7730.
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Personal factors in thermal comfort assessment: Clothing properties and Metabolic Heat Production
Energy and Buildings, 2002Co-Authors: George Havenith, Ingvar Holmér, K. ParsonsAbstract:In the assessment of thermal comfort in buildings, the use of the Predicted Mean Vote (PMV) model is very popular. For this model, data on the climate, on clothing and on Metabolic Heat Production are required. This paper discusses the representation and measurement of clothing parameters and Metabolic rate in the PMV context. Several problems are identified and for some of these solutions are provided. For clothing insulation it was shown that effects of body motion and air movement are so big that they must be accounted for in comfort prediction models to be physically accurate. However, effects on dry Heat exchange are small for stationary, light work at low air movement. Also algorithms for convective Heat exchange in prediction models should be reconsidered. For evaporative Heat resistance of the clothing worn, which is currently not an input factor in the PMV model, it was shown that in cases where special clothing with high vapour resistance is worn (e.g. clean-room clothing), comfort may be limited by the clothing as it will induce a high skin wettedness. Thus, for such cases clothing vapour resistance should not be neglected in the calculation of comfort using the PMV model, or the induced skin wettedness should be calculated separately. The effects on thermal comfort of reductions in vapour resistance due to air and body movements are also shown to have a substantial impact on the comfort limits in terms of skin wettedness and cannot be neglected either. For Metabolic Heat Production it was concluded that for precise comfort assessment a precise measure of Metabolic rate is needed. In order to improve Metabolic rate estimation based on ISO 8996, more data and detail is needed for activities with a Metabolic rate below 2 MET. Finally, it was shown that the methods for determining Metabolic rate provided in ISO 8996 (typically used in comfort assessment and evaluations) do not provide sufficient accuracy to allow determination of comfort (expressed as PMV) in sufficient precision to classify buildings to within 0.3 PMV units as proposed in the upcoming revision of ISO 7730. © 2002 Elsevier Science B.V. All rights reserved.
Glenn E Walsberg - One of the best experts on this subject based on the ideXlab platform.
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effect of wind and solar radiation on Metabolic Heat Production in a small desert rodent spermophilus tereticaudus
The Journal of Experimental Biology, 2000Co-Authors: K M Wooden, Glenn E WalsbergAbstract:To understand better how complex interactions between environmental variables affect the energy balance of small diurnal animals, we studied the effects of the absence and presence of 950 W m(−)(2) simulated solar radiation combined with wind speeds ranging from 0. 25 to 1.00 m s(−)(1) on the Metabolic rate and body temperature of the round-tailed ground squirrel Spermophilus tereticaudus. As wind speed increased from 0.25 to 1.00 m s(−)(1), Metabolic Heat Production increased by 0.94 W in the absence of solar radiation and by 0.98 W in the presence of 950 W m(−)(2) simulated solar radiation. Exposure to simulated solar radiation reduced Metabolic Heat Production by 0.68 W at a wind speed of 0.25 m s(−)(1), by 0.64 W at 0.50 m s(−)(1) and by 0.64 W at 1.00 m s(−)(1). Body temperature was significantly affected by environmental conditions, ranging from 32. 5 degrees C at a wind speed of 1.0 m s(−)(1) and no irradiance to 35. 6 degrees C at a wind speed of 0.50 m s(−)(1) with 950 W m(−)(2)short-wave irradiance. In addition, several unusual findings resulted from this study. The coat of S. tereticaudus is very sparse, and the observed Heat transfer of 5.68+/−0.37 W m(−)(2) degrees C(−)(1) (mean +/− s.e.m., N=11) is much higher than expected from either allometric equations or comparative studies with other rodents of similar mass. Solar Heat gain was remarkably low, equalling only 10 % of intercepted radiation and suggesting a remarkably high regional thermal resistance at the tissue level. Animals remained normally active and alert at body temperatures as low as 32.5 degrees C. These findings suggest a unique combination of adaptations that allow S. tereticaudus to exploit a harsh desert environment.
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Seasonal adjustment of solar Heat gain independent of coat coloration in a desert mammal.
Physiological and Biochemical Zoology, 1997Co-Authors: Glenn E Walsberg, Todd Weaver, Blair O WolfAbstract:Despite the apparent importance of solar radiation as a source of Heat for free-living animals, there exists no substantial body of empirical data describing physiological responses to solar radiation under the range of convective conditions likely to occur in nature. We therefore quantified effects of simulated solar radiation and wind on Metabolic Heat Production in the rock squirrel, Spermophilus variegatus. This diurnal mammal inhabits the Sonoran Desert and seasonally replaces its pelage in a fashion in which it retains constant external appearance but incorporates optical and structural changes that are thought to significantly alter Heat-transfer properties of the coat. At a given wind speed, the presence of 950 W m⁻² of simulated solar radiation reduces Metabolic Heat Production by 15% (at a wind speed of 4 m s⁻¹) to 37% (at a wind speed of 0.25 m s⁻¹). Independent of effects of irradiance, Metabolic Heat Production significantly increases with wind speed such that as wind speed is increased from ...
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effects of solar radiation and wind speed on Metabolic Heat Production by two mammals with contrasting coat colours
The Journal of Experimental Biology, 1995Co-Authors: Glenn E Walsberg, Blair O WolfAbstract:We report the first empirical data describing the interactive effects of simultaneous changes in irradiance and convection on energy expenditure by live mammals. Whole-animal rates of solar Heat gain and convective Heat loss were measured for representatives of two ground squirrel species, Spermophilus lateralis and Spermophilus saturatus, that contrast in coloration. Radiative Heat gain was quantified as the decrease in Metabolic Heat Production caused by the animal’s exposure to simulated solar radiation. Changes in convective Heat loss were quantified as the variation in Metabolic Heat Production caused by changes in wind speed. For both species, exposure to 780 Wm 2 2 of simulated solar radiation significantly
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Effects of solar radiation and wind speed on Metabolic Heat Production by two mammals with contrasting coat colours.
The Journal of experimental biology, 1995Co-Authors: Glenn E Walsberg, Blair O WolfAbstract:We report the first empirical data describing the interactive effects of simultaneous changes in irradiance and convection on energy expenditure by live mammals. Whole-animal rates of solar Heat gain and convective Heat loss were measured for representatives of two ground squirrel species, Spermophilus lateralis and Spermophilus saturatus, that contrast in coloration. Radiative Heat gain was quantified as the decrease in Metabolic Heat Production caused by the animal's exposure to simulated solar radiation. Changes in convective Heat loss were quantified as the variation in Metabolic Heat Production caused by changes in wind speed. For both species, exposure to 780 W m-2 of simulated solar radiation significantly reduced Metabolic Heat Production at all wind speeds measured. Reductions were greatest at lower wind speeds, reaching 42% in S. lateralis and 29% in S. saturatus. Solar Heat gain, expressed per unit body surface area, did not differ significantly between the two species. This Heat gain equalled 14-21% of the radiant energy intercepted by S. lateralis and 18-22% of that intercepted by S. saturatus. Body resistance, an index of animal insulation, declined by only 10% in S. saturatus and 13% in S. lateralis as wind speed increased from 0.5 to 4.0 ms-1. These data demonstrate that solar Heat gain can be essentially constant, despite marked differences in animal coloration, and that variable exposure to wind and sunlight can have important consequences for both thermoregulatory stress experienced by animals and their patterns of energy allocation.
Daniel Gagnon - One of the best experts on this subject based on the ideXlab platform.
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Sex modulates whole‐body sudomotor thermosensitivity during exercise
The Journal of Physiology, 2011Co-Authors: Daniel Gagnon, Glen P KennyAbstract:Non-technical summary The human body controls its temperature through coordinated physiological processes. Prior to the current study, it remained unknown if differences between males and females existed in these processes. The results from the current study show that females have a lower whole-body sweat response during exercise in the Heat compared to males, which results in a greater increase in body temperature. The physiological process responsible for the lower whole-body sweat rate was a lower thermosensitivity of the response, meaning a lower increase in sweat Production for a given increase in body temperature. Knowledge of sex-related differences in the physiology of temperature regulation may lead to better improvements in Heat exposure guidelines for industrial, military and athletic settings. Abstract It is unclear whether true physiological differences exist in temperature regulation between males and females during exercise, independently of differences in physical characteristics and Metabolic Heat Production. Therefore, we examined differences in the onset threshold and thermosensitivity of whole-body sudomotor activity and cutaneous vascular conductance between males and females matched for body mass and surface area. Nine males and nine females performed 90 min of exercise at each of the following intensities in a warm/dry environment: 50% of maximum oxygen consumption () and at a fixed rate of Metabolic Heat Production equal to 500 W. Evaporative Heat loss (EHL, direct calorimetry) and cutaneous vascular conductance (CVC, laser-Doppler) were measured continuously. Mean body temperature was calculated from the measurements of oesophageal and mean skin temperatures. During exercise at 50%, a lower rate of sudomotor activity was observed in females (385 ± 12 vs. 512 ± 24 W, P < 0.001). However, irrespective of sex, individual EHL values were strongly associated with Metabolic Heat Production (R2= 0.82, P < 0.001). Nonetheless, a lower rate of EHL was observed in females when exercise was performed at 500 W of Metabolic Heat Production (419 ± 7 vs. 454 ± 11 W, P= 0.032). Furthermore, a lower increase in EHL per increase in mean body temperature was observed in females (553 ± 77 vs. 795 ± 85 W °C−1, P= 0.051), with no differences in the onset threshold (36.77 ± 0.06 vs. 36.61 ± 0.11°C, P= 0.242). In contrast, no differences were observed in CVC. Collectively, these findings demonstrate that females have a lower thermosensitivity of the whole-body sudomotor response compared to males during exercise in the Heat performed at a fixed rate of Metabolic Heat Production.
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Sex modulates whole-body sudomotor thermosensitivity during exercise.
The Journal of physiology, 2011Co-Authors: Daniel Gagnon, Glen P KennyAbstract:It is unclear whether true physiological differences exist in temperature regulation between males and females during exercise, independently of differences in physical characteristics and Metabolic Heat Production. Therefore, we examined differences in the onset threshold and thermosensitivity of whole-body sudomotor activity and cutaneous vascular conductance between males and females matched for body mass and surface area. Nine males and nine females performed 90 min of exercise at each of the following intensities in a warm/dry environment: 50% of maximum oxygen consumption (V(O(2)max)) and at a fixed rate of Metabolic Heat Production equal to 500 W. Evaporative Heat loss (EHL, direct calorimetry) and cutaneous vascular conductance (CVC, laser-Doppler) were measured continuously. Mean body temperature was calculated from the measurements of oesophageal and mean skin temperatures. During exercise at 50% V(O(2)max), a lower rate of sudomotor activity was observed in females (385 ± 12 vs. 512 ± 24 W, P < 0.001). However, irrespective of sex, individual EHL values were strongly associated with Metabolic Heat Production (R(2) = 0.82, P < 0.001). Nonetheless, a lower rate of EHL was observed in females when exercise was performed at 500 W of Metabolic Heat Production (419 ± 7 vs. 454 ± 11 W, P = 0.032). Furthermore, a lower increase in EHL per increase in mean body temperature was observed in females (553 ± 77 vs. 795 ± 85 W °C(-1), P = 0.051), with no differences in the onset threshold (36.77 ± 0.06 vs. 36.61 ± 0.11°C, P = 0.242). In contrast, no differences were observed in CVC. Collectively, these findings demonstrate that females have a lower thermosensitivity of the whole-body sudomotor response compared to males during exercise in the Heat performed at a fixed rate of Metabolic Heat Production.
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short term exercise training does not improve whole body Heat loss when rate of Metabolic Heat Production is considered
European Journal of Applied Physiology, 2010Co-Authors: Jill M. Stapleton, Daniel Gagnon, Glen P KennyAbstract:We evaluated the effects of an 8-week exercise training program in previously sedentary individuals on whole-body Heat balance during exercise at a constant rate of Metabolic Heat Production. Prior to and after 8 weeks of training, ten participants performed 60-min of cycling exercise at a constant rate of Heat Production (~450 W) followed by 60-min of recovery, at 30°C and 15% relative humidity. Rate of total Heat loss was measured directly by whole-body calorimetry, while rate of Metabolic Heat Production was measured simultaneously by indirect calorimetry. Esophageal (T es), skin blood flow (SkBF) and local sweat rate (LSR) were also measured continuously. The 8-week exercise training program elicited a 10% increase in maximal aerobic capacity (P < 0.001). Furthermore, exercise training reduced (P ≤ 0.05) baseline (37.10 ± 0.28 vs. 36.95 ± 0.24°C) and end-exercise (37.85 ± 0.30 vs. 37.55 ± 0.20°C) values for T es as well as onset thresholds for LSR (37.23 ± 0.26 vs. 36.96 ± 0.22°C, P < 0.001) and SkBF (37.16 ± 0.38 vs. 36.83 ± 0.26°C, P < 0.001). However, these improvements in thermoregulatory function did not translate into a greater rate of total Heat loss between the pre- and post-training exercise trials (P = 0.762). Furthermore, there were no differences in SkBF (P = 0.546) and LSR (P = 0.475) from pre- to post-training. Although physical training resulted in significant improvements of cardiorespiratory and thermoregulatory functions, these adaptations did not improve whole-body and local Heat loss responses during exercise performed at a given rate of Metabolic Heat Production.
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Short-term exercise training does not improve whole-body Heat loss when rate of Metabolic Heat Production is considered
European Journal of Applied Physiology, 2010Co-Authors: Jill M. Stapleton, Daniel Gagnon, Glen P KennyAbstract:We evaluated the effects of an 8-week exercise training program in previously sedentary individuals on whole-body Heat balance during exercise at a constant rate of Metabolic Heat Production. Prior to and after 8 weeks of training, ten participants performed 60-min of cycling exercise at a constant rate of Heat Production (~450 W) followed by 60-min of recovery, at 30°C and 15% relative humidity. Rate of total Heat loss was measured directly by whole-body calorimetry, while rate of Metabolic Heat Production was measured simultaneously by indirect calorimetry. Esophageal (T es), skin blood flow (SkBF) and local sweat rate (LSR) were also measured continuously. The 8-week exercise training program elicited a 10% increase in maximal aerobic capacity (P
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sex related differences in evaporative Heat loss the importance of Metabolic Heat Production
European Journal of Applied Physiology, 2008Co-Authors: Daniel Gagnon, Bruno Lemire, Glen P KennyAbstract:We evaluated the hypothesis that different rates of Metabolic Heat Production between sexes, during exercise at the same percentage of maximum oxygen consumption \( \left( {\dot{V}{\text{O}}_{2\max } } \right), \) give proportional differences in evaporative Heat loss. Seven males and seven females, exercised at 41.3 ± 2.7% \( \dot{V}{\text{O}}_{2\max } \) for 60-min at 40°C and 30% relative humidity. Whole-body direct air calorimetry measured rate of whole-body evaporative Heat loss \( \left( {\dot{H}_{\text{E}} } \right), \) while Metabolic Heat Production \( \left( {\dot{M} - \dot{W}} \right) \) was measured by indirect calorimetry. \( \dot{M} - \dot{W} \) was greater in males (243 ± 18 W m−2) relative to females (201 ± 4 W m−2) (P ≤ 0.05) throughout exercise. This was paralleled by a greater \( \dot{H}_{\text{E}} \) at end-exercise in males (207 ± 51 W m−2) relative to females (180 ± 3 W m−2) (P ≤ 0.05). Differences in Metabolic Heat Production between sexes during exercise at a fixed percentage of \( \dot{V}{\text{O}}_{2\max } \) give differences in evaporative Heat loss. To compare thermoregulatory function between sexes, differences in Metabolic Heat Production must therefore be accounted for.