Metabolism- and sex-dependent critical WBGT limits at rest and during exercise in the heat

2021 ◽  
Author(s):  
S. Tony Wolf ◽  
Mireille A. Folkerts ◽  
Rachel M. Cottle ◽  
Hein A.M. Daanen ◽  
W. Larry Kenney
Keyword(s):  
Sex Differences ◽  
Thermal Environment ◽  
Water Vapor Pressure ◽  
Absolute Intensity ◽  
Body Core Temperature ◽  
Moderate Intensity ◽  
Moderate Intensity Exercise ◽  
Wet Bulb Globe Temperature ◽  
Globe Temperature ◽  
Environmental Limits

Critical environmental limits are environmental thresholds above which heat gain exceeds heat loss and body core temperature (Tc) cannot be maintained at equilibrium. Those limits can be represented as critical wet-bulb globe temperature (WBGTcrit), a validated index that represents the overall thermal environment. Little is known about WBGTcrit at rest and during low-to-moderate intensity exercise, or sex differences in WBGTcrit, in unacclimated young adults. The following hypotheses were tested: (1) WBGTcrit progressively decreases as metabolic heat production (Mnet) increases, (2) no sex differences in WBGTcrit occur at rest, and (3) WBGTcrit is lower during absolute-intensity exercise but higher at relative intensities in women compared to men. Thirty-six participants (19M/17W; 23±4 yr) were tested at rest, during light, absolute-intensity exercise (10 W), or during moderate, relative-intensity exercise (30% V̇O2max) in an environmental chamber. Dry-bulb temperature was clamped as relative humidity or ambient water vapor pressure was increased until an upward inflection was observed in Tc (rectal or esophageal temperature). Sex-aggregated WBGTcrit was lower during 10 W (32.9±1.7°C, P<0.0001) and 30% V̇O2max (31.6±1.1°C, P<0.0001) exercise vs. rest (35.3±0.8°C), and lower at 30% V̇O2max vs. 10 W (P=0.01). WBGTcrit was similar between sexes at rest (35.6±0.8°C vs. 35.0±0.8°C, P=0.83), but lower during 10 W (31.9±1.7°C vs. 34.1±0.3°C, P<0 .01) and higher during 30% V̇O2max (32.4±0.8°C vs. 30.8±0.9°C, P=0.03) exercise in women vs. men. These findings suggest that WBGTcrit decreases as Mnet increases, no sex differences occur in WBGTcrit at rest, and sex differences in WBGTcrit during exercise depend upon absolute vs. relative intensities.

Body Fatness, Body Core Temperature, and Heat Loss During Moderate-Intensity Exercise

2013 ◽  
Vol 84 (11) ◽  
pp. 1153-1158 ◽  
Author(s):  
Jayme D. Limbaugh ◽  
Gregory S. Wimer ◽  
Lynn H. Long ◽  
William H. Baird
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Body Core Temperature ◽  
Moderate Intensity ◽  
Moderate Intensity Exercise ◽  
Body Fatness ◽  
Body Core

Fat and carbohydrate metabolism during exercise in elderly and young subjects

1996 ◽  
Vol 271 (6) ◽  
pp. E983-E989 ◽  
Author(s):  
S. Sial ◽  
A. R. Coggan ◽  
R. Carroll ◽  
J. Goodwin ◽  
S. Klein
Keyword(s):  
Young Adults ◽  
Carbohydrate Metabolism ◽  
Relative Intensity ◽  
The Elderly ◽  
Absolute Intensity ◽  
Substrate Oxidation ◽  
Carbohydrate Oxidation ◽  
Moderate Intensity ◽  
Elderly Subjects ◽  
Moderate Intensity Exercise

We evaluated the effect of aging on fat and carbohydrate metabolism during moderate intensity exercise. Glycerol, free fatty acid (FFA), and glucose rate of appearance (Ra) in plasma and substrate oxidation were determined during 60 min of cycle ergometer exercise in six elderly (73 +/- 2 yr) and six young adults (26 +/- 2 yr) matched by gender and lean body mass. The elderly group was studied during exercise performed at 56 +/- 3% of maximum oxygen uptake, whereas the young adults were studied during exercise performed at the same absolute and at a similar relative intensity as the elderly subjects. Mean fat oxidation during exercise was 25-35% lower in the elderly subjects than in the young adults exercising at either the same absolute or similar relative intensities (P < 0.05). Mean carbohydrate oxidation in the elderly group was 35% higher than the young adults exercising at the same absolute intensity (P < 0.001) but 40% lower than the young adults exercising at the same relative intensity (P < 0.001). Average FFA Ra in the elderly subjects was 85% higher than in the young adults exercising at the same absolute intensity (P < 0.05) but 35% lower than the young adults exercising at a similar relative intensity (P < 0.05). We conclude that fat oxidation is decreased while carbohydrate oxidation is increased during moderate intensity exercise in elderly men and women. The shift in substrate oxidation was caused by age-related changes in skeletal muscle respiratory capacity because lipolytic rates and FFA availability were not rate limiting in the older subjects.

scholarly journals Psychrometric limits and critical evaporative coefficients for exercising older women

2020 ◽  
Vol 129 (2) ◽  
pp. 263-271 ◽  
Author(s):  
W. Larry Kenney
Keyword(s):  
Older Women ◽  
Heat Balance ◽  
Moderate Intensity ◽  
Evidence Based ◽  
Moderate Intensity Exercise ◽  
Metabolic Heat ◽  
Safety Interventions ◽  
Environmental Limits ◽  
Hot Environments ◽  
Heat Events

This study is the first to describe, graphically and quantitatively, critical environmental limits for women between the ages of 62 and 80 yr based on the biophysics of heat exchange. These psychrometric limit lines define combinations of ambient temperature and humidity above which human heat balance cannot be maintained for a given metabolic heat production. These limits, and associated critical evaporative coefficients ( Ke′), can be used to model low- to moderate-intensity exercise responses in hot environments and have directly translatable data that can be used for evidence-based policy decisions, to prepare for impending heat events, and for implementation of other safety interventions.

scholarly journals Summer sleep quality and change of bedroom thermal environment – from the beginning to the end of sleep

2019 ◽  
Vol 111 ◽  
pp. 06054
Author(s):  
Noriko Umemiya ◽  
Kurumi Yamagata ◽  
Tomohiro Kobayashi
Keyword(s):  
Sleep Quality ◽  
Thermal Comfort ◽  
Thermal Environment ◽  
Subjective Sleep Quality ◽  
Wet Bulb Globe Temperature ◽  
Subjective Sleep ◽  
Environment Changes ◽  
Globe Temperature

Relations between bedroom thermal environment changes and subjective sleep quality and thermal comfort were surveyed for 63 apartment occupants during midsummer in Osaka. Changes of Wet Bulb Globe Temperature (WBGT) of 123 air-conditioned and 41 naturally ventilated nights were compared. 1) For air-conditioned bedrooms, sleep quality was better for smaller changes of WBGT from the beginning of sleep and for faster changes of WBGT to constant from the beginning of sleep. 2) For naturally ventilated bedrooms, a) WBGT increased from the beginning of sleep and decreased toward the end of sleep for higher sleep quality nights. However, WBGT decreased from the beginning of sleep and increased toward the end of sleep for lower sleep quality nights. b) The WBGT change was smaller for thermally comfortable nights.

Heat storage in horses during submaximal exercise before and after humid heat acclimation

2000 ◽  
Vol 89 (6) ◽  
pp. 2283-2293 ◽  
Author(s):  
Raymond J. Geor ◽  
Laura Jill McCutcheon ◽  
Gayle L. Ecker ◽  
Michael I. Lindinger
Keyword(s):  
Heat Stress ◽  
Heat Storage ◽  
Heat Acclimation ◽  
Exercise Duration ◽  
Moderate Intensity ◽  
Moderate Intensity Exercise ◽  
Exercise Tests ◽  
Before And After ◽  
Uncompensable Heat Stress ◽  
Globe Temperature

The effect of humid heat acclimation on thermoregulatory responses to humid and dry exercise-heat stress was studied in six exercise-trained Thoroughbred horses. Horses were heat acclimated by performing moderate-intensity exercise for 21 days in heat and humidity (HH) [34.2–35.7°C; 84–86% relative humidity (RH); wet bulb globe temperature (WBGT) index ∼32°C]. Horses completed exercise tests at 50% of peak O2 uptake until a pulmonary arterial temperature (Tpa) of 41.5°C was attained in cool dry (CD) (20–21.5°C; 45–50% RH; WBGT ∼16°C), hot dry (HD 0) [32–34°C room temperature (RT); 45–55% RH; WBGT ∼25°C], and HH conditions (HH 0), and during the second hour of HH on days 3, 7, 14, and 21, and in HD on the 18th day (HD 18) of heat acclimation. The ratios of required evaporative capacity to maximal evaporative capacity of the environment (Ereq/Emax) for CD, HD, and HH were ∼1.2, 1.6, and 2.5, respectively. Preexercise Tpa and rectal temperature were ∼0.5°C lower ( P < 0.05) on days 7, 14, and 21 compared with day 0. With exercise in HH, there was no effect of heat acclimation on the rate of rise in Tpa (and therefore exercise duration) nor the rate of heat storage. In contrast, exercise duration was longer, rate of rise in Tpa was significantly slower, and rate of heat storage was decreased on HD 18 compared with HD 0. It was concluded that, during uncompensable heat stress in horses, heat acclimation provided modest heat strain advantages when Ereq/Emax was ∼1.6, but at higher Ereq/Emax no advantages were observed.

Cardiac Autonomic and Physiological Responses to Moderate- intensity Exercise in Hypoxia

2019 ◽  
Vol 40 (14) ◽  
pp. 886-896 ◽  
Author(s):  
Alessandro Fornasiero ◽  
Spyros Skafidas ◽  
Federico Stella ◽  
Andrea Zignoli ◽  
Aldo Savoldelli ◽  
...  
Keyword(s):  
Ventilatory Threshold ◽  
Mechanical Load ◽  
Acute Hypoxia ◽  
Physiological Responses ◽  
Metabolic Stress ◽  
Absolute Intensity ◽  
Moderate Intensity ◽  
Moderate Intensity Exercise ◽  
Parasympathetic Reactivation ◽  
Hypoxic Exercise

AbstractExercise physiological responses can be markedly affected by acute hypoxia. We investigated cardiac autonomic and physiological responses to different hypoxic training protocols. Thirteen men performed three exercise sessions (5×5-min; 1-min passive recovery): normoxic exercise at 80% of the power output (PO) at the first ventilatory threshold (N), hypoxic exercise (FiO2=14.2%) with the same PO as N (HPO) and hypoxic exercise at the same heart rate (HR) as N (HHR). PO was lower in HHR (21.1±9.3%) compared to N and HPO. Mean HR was higher in HPO (154±11 bpm, p<0.01) than N and HHR (139±10 vs. 138±9 bpm; p=0.80). SpO2 was reduced (p<0.01) to a similar extent (p>0.05) in HPO and HHR compared to N. HR recovery (HRR) and HR variability indices were similar in N and HHR (p>0.05) but reduced in HPO (p<0.05), mirroring a delayed parasympathetic reactivation. Blood lactate and ventilation were similar in N and HHR (p>0.05) and increased in HPO (p<0.001). During recovery oxygen consumption and ventilation were similar in N and HHR (p>0.05) and increased in HPO (p<0.01). Moderate HR-matched hypoxic exercise triggers similar cardiac autonomic and physiological responses to normoxic exercise with a reduced mechanical load. On the contrary, the same absolute intensity exercise in hypoxia is associated with increased exercise-induced metabolic stress and delayed cardiac autonomic recovery.

scholarly journals Thermal comfort findings: Scenario at Malaysian automotive industry

2013 ◽  
Vol 17 (2) ◽  
pp. 387-396 ◽  
Author(s):  
Ahmad Ismail ◽  
Kumar Karagaratnan ◽  
Kumaran Kadirgama
Keyword(s):  
Thermal Comfort ◽  
Automotive Industry ◽  
Thermal Environment ◽  
Thermal Sensation ◽  
Human Subjects ◽  
Demographic Data ◽  
Working Environment ◽  
Paint Shop ◽  
Wet Bulb Globe Temperature ◽  
Globe Temperature

This paper discusses the findings of thermal comfort assessment at Malaysian automotive industry. Nine critical workstations were chosen as subjects for the study in order to determine the thermal comfort among workers at Malaysian automotive industry. The human subjects for the study comprises of the operators from tire receiving, dashboard assembly, drum tester, body assembly, seat assembly, door check assembly, stamping workstation, engine sub assembly and paint shop of the factory. The environmental factors such as Wet Bulb Globe Temperature (WBGT), relative humidity, air velocity, illuminance were measured using BABUC A apparatus and Thermal Comfort Measurement equipment. Through questionnaire survey, the demographic data of subjects and their perceptions on thermal comfort at each workstation were assessed based on ISO Standard 7730 and thermal sensation scale using Predicted Mean Vote (PMV). Then, Predicted Percentage of Dissatisfied (PPD) is used to estimate the thermal satisfaction of occupants. The results indicated that most of the workstations of the automotive industry are considered as uncomfortable. Tire receiving station is considered having better working environment compared to other stations with lowest PMV index of 1.09 to 1.41 and PPD of 46%. Meanwhile, the engine sub assembly station and paint shop of assembly are considered the worst thermal environment with the PMV index values ranging between 2.1 to 2.9 and PPD values of 81% to 99%. Therefore, these two workstations are considered not comfortable because the thermal sensation scale is warm and almost hot.

scholarly journals Carotid chemoreceptors have a limited role in mediating the hyperthermia-induced hyperventilation in exercising humans

2019 ◽  
Vol 126 (2) ◽  
pp. 305-313
Author(s):  
Naoto Fujii ◽  
Miki Kashihara ◽  
Glen P. Kenny ◽  
Yasushi Honda ◽  
Tomomi Fujimoto ◽  
...  
Keyword(s):  
Young Men ◽  
Progressive Increase ◽  
Peak Oxygen Uptake ◽  
Body Core Temperature ◽  
Moderate Intensity ◽  
Esophageal Temperature ◽  
Moderate Intensity Exercise ◽  
Carotid Chemoreceptors ◽  
Exercise Induced ◽  
Induced Changes

Hyperthermia causes hyperventilation at rest and during exercise. We previously reported that carotid chemoreceptors partly contribute to the hyperthermia-induced hyperventilation at rest. However, given that a hyperthermia-induced hyperventilation markedly differs between rest and exercise, the results obtained at rest may not be representative of the response in exercise. Therefore, we evaluated whether carotid chemoreceptors contribute to hyperthermia-induced hyperventilation in exercising humans. Eleven healthy young men (23 ± 2 yr) cycled in the heat (37°C) at a fixed submaximal workload equal to ~55% of the individual’s predetermined peak oxygen uptake (moderate intensity). To suppress carotid chemoreceptor activity, 30-s hyperoxia breathing (100% O2) was performed at rest (before exercise) and during exercise at increasing levels of hyperthermia as defined by an increase in esophageal temperature of 0.5°C (low), 1.0°C (moderate), 1.5°C (high), and 2.0°C (severe) above resting levels. Ventilation during exercise gradually increased as esophageal temperature increased (all P ≤ 0.05), indicating that hyperthermia-induced hyperventilation occurred. Hyperoxia breathing suppressed ventilation in a greater manner during exercise (−9 to −13 l/min) than at rest (−2 ± 1 l/min); however, the magnitude of reduction during exercise did not differ at low (0.5°C) to severe (2.0°C) increases in esophageal temperature (all P > 0.05). Similarly, hyperoxia-induced changes in ventilation during exercise as assessed by percent change from prehyperoxic levels were not different at all levels of hyperthermia (~15–20%, all P > 0.05). We show that in young men carotid chemoreceptor contribution to hyperthermia-induced hyperventilation is relatively small at low-to-severe increases in body core temperature induced by moderate-intensity exercise in the heat. NEW & NOTEWORTHY Exercise-induced increases in hyperthermia cause a progressive increase in ventilation in humans. However, the mechanisms underpinning this response remain unresolved. We showed that in young men hyperventilation associated with exercise-induced hyperthermia is not predominantly mediated by carotid chemoreceptors. This study provides important new insights into the mechanism(s) underpinning the regulation of hyperthermia-induced hyperventilation in humans and suggests that factor(s) other than carotid chemoreceptors play a more important role in mediating this response.

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