Article

Respiratory water losses during exercise

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Abstract

Evaporative water loss from the respiratory tract was determined over a wide range of exercise. The absolute humidity of the expired air was the same at all levels of exercise and equal to that measured at rest. The rate of respiratory water loss during exercise was found to be 0.019 of the oxygen uptake times (44 minus water vapor pressure). The rate of weight loss during exercise due to CO2-O2 exchange was calculated. For exercise at oxygen consumption rates exceeding 1.5 L/min in a dry environment with a water vapor pressure of 10 mm Hg, the total rate of weight loss via the respiratory tract is on the order of 2-5 g/min.

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... A regulação da iniciação da tradução do mRNA seria pela ativação da mammalian target of rapamycin (mTOR) e de suas proteínas sinalizadoras dowstream, proteína ribossômica-70kDa S6 quinase (p70S6k1) e proteína ligadora do fator de iniciação eucariótico 4E (4E-BP1) [7]. Ambas as proteínas (p70S6k1 e 4E-BP1) modulam a iniciação da tradução do mRNA por controlarem a ligação do mRNA à subunidade ribossomal 40S. ...
... Ambas as proteínas (p70S6k1 e 4E-BP1) modulam a iniciação da tradução do mRNA por controlarem a ligação do mRNA à subunidade ribossomal 40S. A ligação efi ciente da subunidade 40S ao mRNA necessita do fator de iniciação eucariótico 4F (eIF4F) cuja formação é reprimida pela ligação do fator eIF4E a 4E-BP1; complexo que atua como repressor da tradução [7,8] (Figura 1). ...
... A fosforilação da 4E-BP1 (via mTOR) libera-a do fator eIF4E permitindo a ativação do eIF4E facilitando a ligação do mRNA à subunidade 40S (via eIF4F) e permitindo que o processo de iniciação da tradução do mRNA se perpetue [7]. ...
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... Sweat rate (SR) SR was determined from nude pre-and post-exercise bodyweight. Fluid intake, urine excretion and respiration were used to obtain a corrected SR (Mitchell et al. 1972). Units for SR are expressed relative to exercise duration and calculated as follows (Mitchell et al. 1972): ...
... Fluid intake, urine excretion and respiration were used to obtain a corrected SR (Mitchell et al. 1972). Units for SR are expressed relative to exercise duration and calculated as follows (Mitchell et al. 1972): ...
... where BW ¼ body weight. Respiratory water loss (Mitchell et al. 1972): ...
Article
Heat accumulation from wearing personal protective equipment can result in the development of heat-related illnesses. This study aimed to investigate factors of heat stress with and without a US standard issue wildland firefighter helmet. Ten male subjects finished a 90-min exercise protocol in a heat chamber (35°C and 30% relative humidity), with standard issue meta-aramid shirt and pants and a cotton t-shirt, and either with or without a wildland firefighter helmet. A randomised crossover design was implemented, with a minimum 2-week washout period. Heart rate, physiologic strain index, perceived head heat, head heat and skin blood flow of the head and neck were measured. At the conclusion of the 90-min trial, heart rate, physiological strain index, core temperature, rating of perceived exertion and perceived head heat showed a main effect of time (P < 0.05). Perceived head heat and head heat exhibited a main effect of trial (P < 0.05). The change in physiologic strain was positively correlated with the change in skin blood flow of the head (r = 0.72, P = 0.02). These data suggest that the current wildland firefighter helmet contributes to heat accumulation. The design of the wildland firefighter helmet lacks ventilation, which, from these data, may result in metabolic alterations and perceived discomfort.
... where M is metabolic rate in W m −2 , T a is air temperature in °C and P a is the ambient water vapour pressure in kPa. The rate of respiratory heat loss is dependent on the temperature and humidity of inspired air [23,24] and minute ventilation [25,26]. As such, the amount of convective heat transfer through respiration during exercise in the heat compared to the cold is minimal due to the small temperature gradient between ambient and core temperature. ...
... As such, the amount of convective heat transfer through respiration during exercise in the heat compared to the cold is minimal due to the small temperature gradient between ambient and core temperature. Additionally, the amount of evaporative heat loss via respiration is dependent on the humidity gradient between the lungs and the air, and the rate of ventilation which is assumed to have a linear relationship with the rate of metabolic rate (up to 80% of maximum oxygen consumption [26]). ...
Chapter
This chapter describes the fundamental factors that influence heat exchange between the human body and its surrounding environment. The bulk of heat exchange takes place at the skin surface via sensible heat transfer (i.e. convection and radiation) and evaporation. With increasing ambient temperature, the gradient for sensible heat transfer declines, meaning that the human body becomes increasingly dependent on the evaporation of sweat for heat dissipation. If the combination of climate (air temperature, radiant temperature, humidity and air velocity) and clothing permit a sufficient level of heat dissipation to counterbalance the rate of internal heat production, elevations in core temperature are moderated (i.e. compensable heat stress). However, if heat production exceeds the upper capacity to lose heat from the skin surface due to high ambient temperatures, humidity, low wind speeds or high evaporative resistance of clothing, a continuous increase in core temperature occurs (i.e. uncompensable heat stress).
... Whole body sweating rate (WBSR) during steady state exercise was calculated as the difference in pre and post 60 min exercise nude body weight with correction for respiratory moisture loss (Mitchell et al., 1972) and incorporating volume of fluid consumed. Participant's perception of the difficulty of the exercise effort was recorded based on the 6-20 point RPE scale (Borg, 1982) and was recorded at 10 min intervals. ...
Article
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The understanding that fluid ingestion attenuates thermoregulatory and circulatory stress during exercise in the heat was based on studies conducted in relatively dry (∼50% RH) environments. It remains undetermined whether similar effects occur during exercise in a warm and more humid environment, where evaporative capacity is reduced. Nine well-trained, unacclimatised male runners were randomly assigned to perform four experimental trials where they ran for 60 min at an intensity of 70% VO2max followed by an incremental exercise test until volitional exhaustion. The four trials consisted of non-fluid ingestion (NF) and fluid ingestion (FI) in a warm-dry (WD) and warm-humid condition (WH). Time to exhaustion (TTE), body temperature (Tb), whole body sweat rate, partitional calorimetry measures, heart rate and plasma volume were recorded during exercise. There was no significant difference in Tb following 60 min of exercise in FI and NF trial within both WD (37.3°C ± 0.4 vs. 37.4°C ± 0.3; p > 0.05) and WH conditions (38.0°C ± 0.4 vs. 38.1°C ± 0.4; p > 0.05). The TTE was similar between FI and NF trials in both WH and WD, whereas exercise capacity was significantly shorter in WH than WD (9.1 ± 2.8 min vs. 12.7 ± 2.4 min, respectively; p = 0.01). Fluid ingestion failed to provide any ergogenic benefit in attenuating thermoregulatory and circulatory stress during exercise in the WH and WD conditions. Consequently, exercise performance was not enhanced with fluid ingestion in the warm-humid condition, although the humid environment detrimentally affected exercise endurance.
... Whole-body sweat loss was computed using the pre-to postchange in body mass, corrected for respiratory water losses and the body mass losses associated with substrate oxidation (Mitchell et al. 1972). Whole-body sweat rate was computed by further correcting for time and body surface area, which was computed using the Dubois and Dubois equation (Verbraecken et al. 2006). ...
Article
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Purposes: This study investigated the impact of permanently tattooed skin on local sweat rate, sweat sodium concentration and skin temperature and determined whether tattoos alter the relationship between local and whole-body sweat sodium concentration. Methods: Thirteen tattooed men (27 ± 6 years) completed a 1 h (66 ± 4% of VO2peak) cycling trial at 32 °C, 35% relative humidity. Sweat rate and sweat sodium concentration were measured using the whole-body washdown and local absorbent patch techniques. Patches and skin-temperature probes were applied over the right/left thighs and tattooed/non-tattooed (contralateral) regions. Results: Local sweat rates did not differ (p > 0.05) between the right (1.11 ± 0.38) and left (1.21 ± 0.37) thighs and the permanently tattooed (1.93 ± 0.82) and non-tattooed (1.72 ± 0.81 mg cm −2 min −1) regions. There were no differences in local sweat sodium concentration between the right (58.2 ± 19.4) and left (55.4 ± 20.3) thighs and the permanently tattooed (73.0 ± 22.9) and non-tattooed (70.2 ± 18.9 mmol L −1) regions. Difference in local skin temperature between the right and left thighs (− 0.043) was similar to that between the permanently tattooed and non-tattooed (− 0.023 °C) regions. Prediction of whole-body sweat sodium concentration for the permanently tattooed (41.0 ± 6.7) and the non-tattooed (40.2 ± 5.3 mmol L −1) regions did not differ. Conclusion: Permanent tattoos do not alter local sweat rate, sweat sodium concentration or local skin temperature during moderate-intensity cycling exercise in a warm environment. Results from a patch placed over a tattooed surface correctly predicts whole-body sweat sodium concentration from an equation developed from a non-tattooed region.
... For accurate measures, corrections must be made for any food or fluid intake during the period of measurement, as well as output of body wastes (Cheuvront and Kenefick, 2017). Once corrected, changes in body mass are typically considered equivalent to sweat losses, although respiratory water losses and metabolic exchanges should also be taken into account ( Mitchell et al., 1972;Cheuvront and Kenefick, 2017). Measuring changes in body mass is the only practical means of quantifying whole-body sweat production and its relative ease of use makes it an ideal tool in field settings. ...
Chapter
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.
... WB sweat loss (WBSL) was calculated from the change in pre-to post-exercise nude-body mass, corrected for fluid intake, respiratory water loss, and weight loss due to substrate oxidation. Respiratory water loss and weight loss due to substrate oxidation were estimated using equations from ACSM (2014) and Mitchell et al. (1972). Subjects did not use the bathroom between the pre-and post-exercise nude body mass measurements. ...
Article
Full-text available
Purpose To quantify total sweat electrolyte losses at two relative exercise intensities and determine the effect of workload on the relation between regional (REG) and whole body (WB) sweat electrolyte concentrations. Methods Eleven recreational athletes (7 men, 4 women; 71.5 ± 8.4 kg) completed two randomized trials cycling (30 °C, 44% rh) for 90 min at 45% (LOW) and 65% (MOD) of VO2max in a plastic isolation chamber to determine WB sweat [Na⁺] and [Cl⁻] using the washdown technique. REG sweat [Na⁺] and [Cl⁻] were measured at 11 REG sites using absorbent patches. Total sweat electrolyte losses were the product of WB sweat loss (WBSL) and WB sweat electrolyte concentrations. Results WBSL (0.86 ± 0.15 vs. 1.27 ± 0.24 L), WB sweat [Na⁺] (32.6 ± 14.3 vs. 52.7 ± 14.6 mmol/L), WB sweat [Cl⁻] (29.8 ± 13.6 vs. 52.5 ± 15.6 mmol/L), total sweat Na⁺ loss (659 ± 340 vs. 1565 ± 590 mg), and total sweat Cl⁻ loss (931 ± 494 vs. 2378 ± 853 mg) increased significantly (p < 0.05) from LOW to MOD. REG sweat [Na⁺] and [Cl⁻] increased from LOW to MOD at all sites except thigh and calf. Intensity had a significant effect on the regression model predicting WB from REG at the ventral wrist, lower back, thigh, and calf for sweat [Na⁺] and [Cl⁻]. Conclusion Total sweat Na⁺ and Cl⁻ losses increased by ~ 150% with increased exercise intensity. Regression equations can be used to predict WB sweat [Na⁺] and [Cl⁻] from some REG sites (e.g., dorsal forearm) irrespective of intensity (between 45 and 65% VO2max), but other sites (especially ventral wrist, lower back, thigh, and calf) require separate prediction equations accounting for workload.
... This level of fluid intake/ infusion was chosen to minimize the risk of hypohydration/hyperhydration developing from the extrapolation of sweat rates from the 15-min exercise in the first trial. This trial was used to determine water loss during the 2-h preload from body mass change minus mass loss through expired CO 2 (37) and was used to determine the water volume provided in experimental trials. ...
Article
Knowledge of hydration status may contribute to hypohydration-induced exercise performance decrements; therefore, this study compared blinded and unblinded hypohydration on cycling performance. Fourteen trained, nonheat-acclimated cyclists (age: 25 ± 5 yr; V̇o2peak: 63.3 ± 4.7 ml·kg-1·min-1; cycling experience: 6 ± 3 yr) were pair matched to blinded (B) or unblinded (UB) groups. After familiarization, subjects completed euhydrated (B-EUH; UB-EUH) and hypohydrated (B-HYP; UB-HYP) trials in the heat (31°C); 120-min cycling preload (50% Wpeak) and a time trial (~15 min). During the preload of all trials, 0.2 ml water·kg body mass-1 was ingested every 10 min, with additional water provided during EUH trials to match sweat losses. To blind the B group, a nasogastric tube was inserted in both trials and used to provide water in B-EUH. The preload induced similar ( P = 0.895) changes in body mass between groups (B-EUH: -0.6 ± 0.5%; B-HYP: -3.0 ± 0.5%; UB-EUH: -0.5 ± 0.3%; UB-HYP -3.0 ± 0.3%). All variables responded similarly between B and UB groups ( P ≥ 0.558), except thirst ( P = 0.004). Changes typical of hypohydration (increased heart rate, rating of perceived exertion, gastrointestinal temperature, serum osmolality and thirst, and decreased plasma volume; P ≤ 0.017) were apparent in HYP by 120 min. Time trial performance was similar between groups ( P = 0.710) and slower ( P ≤ 0.013) with HYP for B (B-EUH: 903 ± 89 s; B-HYP: 1,008 ± 121 s; -11.4%) and UB (UB-EUH: 874 ± 108 s; UB-HYP: 967 ± 170 s; -10.1%). Hypohydration of ~3% body mass impairs time trial performance in the heat, regardless of knowledge of hydration status. NEW & NOTEWORTHY This study demonstrates, for the first time, that knowledge of hydration status does not exacerbate the negative performance consequences of hypohydration when hypohydration is equivalent to ~3% body mass. This is pivotal for the interpretation of the many previous studies that have not blinded subjects to their hydration status and suggests that these previous studies are not likely to be confounded by the overtness of the methods used to induce hypohydration.
... Sweat rate was calculated using pre-and post-exercise BWs and corrected for urine excreted, fluid intake and respiratory water loss (Mitchell et al. 1972). Sweat rate is expressed relative to body surface area (BSA). ...
Article
Our aim was to examine the effect of a synthetic material undergarment on heat stress during exercise in a hot environment. Ten active males completed two trials of intermittent (50 min walking, 10 min sitting) treadmill walking over 3 h in 35°C and 30% relative humidity. Subjects wore wildland firefighter flame-resistant meta-aramid blend pants and shirt with either a 100% cotton (C) or flame-retardant modacrylic undergarment (S), while carrying a 16-kg pack, helmet and leather gloves. Exercise was followed by a 30-min rest period without pack, helmet, gloves, and outerwear shirt. Rectal temperature and physiological strain were greater in S than C (P = 0.04). No significant differences were found for heart rate, rating of perceived exertion, energy expenditure or skin temperature between C and S. Skin blood flow increased significantly in S following the second hour of exercise, resulting in a time × trial interaction (P = 0.001). No significant differences for skin blood flow were found post exercise. Sweat rate and percent dehydration were not different between C and S. These data indicate that, of the two undergarments investigated, the synthetic undergarment negatively affected physiological factors that have been shown to indicate an increased risk of heat-related injuries.
... W resp was determined after calculating the rate of evaporative water loss in expired air ( ṁ e , g/min), from V O 2 (L/min) and the ambient water vapor pressure (P a , mmHg) (Mitchell et al. 1972): ...
Article
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Purpose To examine if ad libitum drinking will adequately support hydration during exertional heat stress. Methods Ten endurance-trained runners ran for 2 h at 60% of maximum oxygen uptake under different conditions. Participants drank water ad libitum during separate trials at mean ambient temperatures of 22 °C, 30 °C and 35 °C. Participants also completed three trials at a mean ambient temperature of 35 °C while drinking water ad libitum in all trials, and with consumption of programmed glucose or whey protein hydrolysate solutions to maintain euhydration in two of these trials. Heart rate, oxygen uptake, rectal temperature, perceived effort, and thermal sensation were monitored, and nude body mass, hemoglobin, hematocrit, and plasma osmolality were measured before and after exercise. Water and mass balance equations were used to calculate hydration-related variables. Results Participants adjusted their ad libitum water intake so that the same decrease in body mass (1.1–1.2 kg) and same decrease in body water (0.8–0.9 kg) were observed across the range of ambient temperatures which yielded significant differences (p < .001) in sweat loss. Overall, water intake and total water gain replaced 57% and 66% of the water loss, respectively. The loss in body mass and body water associated with ad libitum drinking resulted in no alteration in physiological and psychophysiological variables compared with the condition when hydration was nearly fully maintained (0.3 L body water deficit) relative to pre-exercise status from programmed drinking. Conclusions Ad libitum drinking is an appropriate strategy for supporting hydration during running for 2 h duration under hot conditions.
... MML were calculated using Eq. 6 from Mitchell et al (1972). ...
Article
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This study investigated the relationship between high (85%) and low (19%) relative humidity (RH) and sweat rate during inactive recovery after high-intensity work in a hot environment (30 °C). Ten male subjects performed two 20-minute run trials at 68 ± 4 % of maximal oxygen consumption (VO2max) followed by 36 minutes of inactive recovery in standing position. Regional sweat rate (RSR) was measured on the forearm and mid-central back by technical absorbent pads, and gross sweat loss was estimated from change in body weight. Core temperature (Tc) and six skin temperatures for calculation of mean skin temperature (Ts) were measured continuously together with heart rate (HR) during running and recovery. Results show that RSR was significantly (p
... Instructions were to remove clothes, remove any access sweat with a given a towel, and step onto the scale. Total nude body mass and total body water loss were considered equivalent (1 mL = 1g) after correction for respiratory water loss [17,18]. Urine specific gravity was determined from urine samples. ...
Article
Full-text available
Dehydration in the human body arises due to inadequate replenishment of fluids. An appropriate level of hydration is essential for optimal functioning of the human body, and complications ranging from mild discomfort to, in severe cases, death, could result from a neglected imbalance in fluid levels. Regular and accurate monitoring of hydration status can provide meaningful information for people operating in stressful environmental conditions, such as athletes, military professionals and the elderly. In this study, we propose a non-invasive hydration monitoring technique employing non-ionizing electromagnetic power in the microwave band to estimate the changes in the water content of the whole body. Specifically, we investigate changes in the attenuation coefficient in the frequency range 2–3.5 GHz between a pair of planar antennas positioned across a participant’s arm during various states of hydration. Twenty healthy young adults (10M, 10F) underwent controlled hypohydration and euhydration control bouts. The attenuation coefficient was compared among trials and used to predict changes in body mass. Volunteers lost 1.50±0.44% and 0.49±0.54% body mass during hypohydration and euhydration, respectively. The microwave transmission-based attenuation coefficient (2–3.5 GHz) was accurate in predicting changes in hydration status. The corresponding regression analysis demonstrates that building separate estimation models for dehydration and rehydration phases offer better predictive performance (88%) relative to a common model for both the phases (76%).
... Very high altitude (4900-7600 m) exposure tends to increase water and electrolyte losses, decrease plasma volume and total body water content [43]. In both cold air and high altitudes, respiratory water losses may increase and require additional fluid consumption due to low air water vapor pressures [44]. Therefore, athletes should acclimate to altitude over several days and maintain euhydration prior to competition to ensure optimal athletic performance. ...
Article
Full-text available
Personalized hydration strategies play a key role in optimizing the performance and safety of athletes during sporting activities. Clinicians should be aware of the many physiological, behavioral, logistical and psychological issues that determine both the athlete’s fluid needs during sport and his/her opportunity to address them; these are often specific to the environment, the event and the individual athlete. In this paper we address the major considerations for assessing hydration status in athletes and practical solutions to overcome obstacles of a given sport. Based on these solutions, practitioners can better advise athletes to develop practices that optimize hydration for their sports.
... The total sweat loss (Dm sw,tot ) was determined from the nude body mass, which was obtained before and after the experiment using a scale with an accuracy of 10 g (FW-100K; AND) and was corrected for respiratory water loss (23). ...
Article
The purpose of this study was to determine whether the effects of thermal states in exercising muscle on repeated sprint cycling (RSC) performance differ between the first and latter half of trials. Nine male subjects performed 8 × 8 seconds of RSC with a 40-second rest period. The subjects wore water-perfused trousers with water at 6° C (COLD), 17° C (COOL), 30° C (WARM), or 44° C (HOT). During the first half of trials, the peak power output (PPO), mean power output (MPO), and sum of work output (SWO) were significantly (p < 0.05) greater under the WARM and HOT conditions than under the COLD and COOL conditions, and a difference in the PPO and MPO between WARM and HOT was noted in the second sprint bout during the first half of the exercise. However, during the latter half of trials, there was no significant difference in the PPO, MPO, and SWO among the 4 conditions. The tympanic temperature (Tty) was significantly elevated under the HOT condition but fell under the COLD and COOL conditions, whereas the Tty under the WARM condition did not change significantly (p < 0.05) during the experiment. The total sweat loss was significantly (p < 0.05) greater in the HOT condition than in the other conditions. These results suggest that the effect of thermal states in exercising muscle on the RSC performance is greater in the first half of exercise than in the latter half, possibly because of the elevation of the core temperature and sweat loss under HOT conditions.
... Mean skin temperature (T sk ) was derived from the weighted average of four skin temperature measurements (Ramanathan, 1964) (Kenefick, Cheuvront, Elliott, Ely, & Sawka, 2012;Vieth, 1989). Whole body sweat loss was calculated as the net difference in pre-and post-exercise nude body mass measurements expressed relative to body surface area (g m −2 ), and corrected for metabolic mass loss, and respiratory vapour loss (Mitchell, Nadel, & Stolwijk, 1972 ...
Article
New findings: What is the central question of this study? Are fitness-related improvements in thermoregulatory responses during uncompensable heat stress mediated by aerobic capacity (VO2max ) or is it the partial acclimation associated with training? What is the main finding and its importance? During uncompensable heat stress, individuals with high and low VO2max displayed similar sweating and core temperature responses whereas exercise training in previously untrained individuals resulted in a greater sweat rate and a smaller rise in core temperature. These observations suggest that it is training, not VO2max per se, that mediate thermoregulatory improvements during uncompensable heat stress. Abstract: It remains unclear whether aerobic fitness, as defined by the maximum rate of oxygen consumption (VO2max ), independently improves heat dissipation in uncompensable environments, or whether the thermoregulatory adaptations associated with heat acclimation are due to repeated bouts of exercise-induced heat stress during regular aerobic training. The present analysis sought to determine if VO2max independently influences thermoregulatory sweating, maximum skin wettedness (ωmax ) and the change in rectal temperature (ΔTre ) during 60 minutes of exercise in an uncompensable environment (37.0 ± 0.8°C, 4.0 ± 0.2 kPa, 64 ± 3% RH) at a fixed rate of heat production per unit mass (6 W·kg-1 ). Retrospective analyses were performed on 22 participants (3 groups): aerobically unfit (UF; n = 7; VO2max : 41.7 ± 9.4 ml·kg-1 ·min-1 ), aerobically fit (F; n = 7; VO2max : 55.6 ± 4.3 ml·kg-1 ·min-1 ; P < 0.01), and a group of aerobically unfit individuals (n = 8) before (PRE; VO2max : 45.8 ± 11.6 ml·kg-1 ·min-1 ) and after (POST; VO2max : 52.0 ± 11.1 ml·kg-1 ·min-1 ; P < 0.001) an 8-week training intervention. ωmax was similar between UF (0.74 ± 0.09) and F (0.78 ± 0.08, P = 0.22). However, ωmax was greater POST (0.84 ± 0.08) compared to PRE (0.72 ± 0.06, P = 0.02) training. During exercise, mean local sweat rate (forearm and upper-back) was greater POST (1.24 ± 0.20 mg·cm-2 ·min-1 ) compared to PRE (1.04 ± 0.25 mg·cm-2 ·min-1 , P < 0.01) training, but similar between UF (0.94 ± 0.31 mg·cm-2 ·min-1 , P = 0.90) and F (1.02 ± 0.30 mg·cm-2 ·min-1 ). The ΔTre at 60 min of exercise was greater PRE (1.13 ± 0.16°C, P < 0.01) compared to POST (0.96 ± 0.14°C) training, but similar between UF (0.85 ± 0.29°C, P = 0.22) and F (0.95 ± 0.22°C). Taken together, aerobic training, not VO2max per se, confers an increased ωmax , greater sweat rate, and smaller rise in core temperature during uncompensable heat stress in fit individuals. This article is protected by copyright. All rights reserved.
... Thermistors integrated into heat flow sensors (2252 ohms, Concept Engineering, Old Saybrook, CT, USA) measured skin temperature (T sk ) at four sites (Ramanathan, 1964). Double-sided adhesive discs and surgical tape Whole-body sweat losses (WBSL) were estimated from the difference between pre-and post-exercise body mass measurements collected with a platform scale (Combics 2, Sartorius, Mississauga, ON, Canada), and corrected for metabolic and vapour mass losses from respiration (Mitchell, Nadel, & Stolwijk, 1972). Additionally, local sweat rates (LSR) were measured from ventilated capsules placed on the skin of the upper back, forearm and forehead. ...
Article
New findings: What is the central question of this study? Hypoxia reportedly does not impair thermoregulation during exercise in compensable heat stress conditions, but whether it has an impact on maximal heat dissipation and therefore the critical environmental limit for the physiological compensability of core temperature is unknown. What is the main finding and its importance? Although skin blood flow was higher in hypoxia, no differences in sweat rates or the critical environmental limit for the physiological compensability of core temperature - an indicator of maximal heat loss - were found compared to exercise in normoxia, indicating no influence of normobaric hypoxia on thermoregulatory capacity in warm conditions. Abstract: Altered control of skin blood flow (SkBF) in hypoxia does not impair thermoregulation during exercise in compensable conditions, but its impact on maximal heat dissipation is unknown. This study therefore sought to determine whether maximum heat loss is altered by hypoxia during exercise in warm conditions. On separate days, eight males exercised for 90 min at a fixed heat production of ∼500 W in normoxia (NORM) or normobaric hypoxia (HYP, FI O2 = 13%) in a 34 °C environment. Ambient vapour pressure was maintained at 2.13 kPa for 45 min, after which it was raised 0.11 kPa every 7.5 min. The critical ambient vapour pressure at which esophageal temperature inflected upward (Pcrit ) indicated that maximum heat dissipation had been reached. Neither local sweat rates on the upper arm, back and forehead [average NORM: 1.46 (0.15) vs. HYP: 1.41 (0.16) mg cm-2 min-1 ; P = 0.59] nor whole-body sweat losses [NORM: 1029 (137) g vs. HYP: 1025 (150) g; P = 0.95] were different between trials. Laser-Doppler flux values (LDF; arbitrary units), an index of SkBF, were not different between NORM and HYP on the forearm (P = 0.23) or back (P = 0.73); however, when normalized as a percentage of maximum, LDF values tended to be higher in HYP compared to NORM at the forearm (condition effect, P = 0.05) but not back (P = 0.19). Despite potentially greater SkBF in hypoxia, there was no difference in Pcrit between conditions [NORM: 3.67 (0.35) kPa; HYP: 3.46 (0.39) kPa; P = 0.22). These findings suggest that hypoxia does not independently alter thermoregulatory capacity during exercise in warm conditions. This article is protected by copyright. All rights reserved.
... Rate of metabolic heat production (M 2 W) was calculated as the difference between M and external work rate (W) (Kenny & Jay, 2013). Whole-body sweat rate during heat acclimation assessments was calculated as the difference between preand post-exercise body mass adjusted for respiratory water loss (Mitchell, Nadel, & Stolwijk, 1972) and metabolic mass loss (Kenny & Jay, 2013). Prism 5 computer software (GraphPad Software, La Jolla, CA) with segmental regression (Cheuvront et al., 2009) analysis was used to determine slopes and " T b onset thresholds for local sweating. ...
... Body mass was measured in triplicate at 15-min intervals during the experimental protocol using a precision scale with an accuracy of T2 g (Sartorius Combics 2, Goettingen, Germany). WBSL was determined as the change in body mass from baseline minus respiratory vapor exchange and metabolic mass losses (13). Local sweat rate (LSR) was collected continuously throughout the exercise protocol at the upper back and forearm using capacitance hygrometry (Vaisala HMT333, Helsinki, Finland) via the ventilated capsule method (14). ...
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Introduction: Impairments in sudomotor function during passive whole-body heating have been reported in multiple sclerosis (MS), a demyelinating disease of the CNS that disrupts autonomic function. However, the capability of the thermoregulatory system to control body temperature during exercise has never been assessed in MS. Thus, the aim of the present study was to test the hypothesis that thermoregulatory function is impaired in MS patients compared with healthy controls (CON) exercising at similar rates of metabolic heat production. Methods: Sweating and skin blood flow responses were compared between 12 individuals diagnosed with relapsing-remitting MS (9 females, 3 males) and 12 sex-, age-, mass-, and BSA-matched CON during a single bout of cycling exercise (rate of metabolic heat production: ∼4.5 W·kg) for 60 min in a climate-controlled room (25°C, 30% RH). Results: Individuals with MS exhibited an attenuated increase in cumulative whole-body sweat loss after 30 min (MS, 72 ± 51 g; CON, 104 ± 37 g; P = 0.04) and 60 min (MS, 209 ± 94 g; CON, 285 ± 62 g; P = 0.02), as well as lower sweating thermosensitivity (MS, 0.49 ± 0.26 mg·cm·min·°C; CON, 0.86 ± 0.30 mg·cm·min·°C; P = 0.049). Despite evidence for thermoregulatory dysfunction, there were no differences between MS and CON in esophageal or rectal temperatures at 30- or 60-min time points (P > 0.05). Cutaneous vasculature responses were also not different in MS compared with CON (P > 0.05). Conclusion: Taken together, MS blunts sweating responses during exercise while cutaneous vasculature responses are preserved. Altered mechanisms of body temperature regulation in persons with MS may lead to temporary worsening of disease symptoms and limit exercise tolerance under more thermally challenging conditions.
... Percent dehydration was calculated from the change in pre-exercise, mid-exercise, and post-trial nude body weights ( Figure 1). Sweat rate (L·h -1 ) was calculated from the change in pre-trial, mid-exercise, and post-trial nude body weights and corrected for urine excretion, fluid consumed, and respiratory water loss 26 : Urine was collected pre-and post-trial to determine the amount of fluid retained throughout the exercise bout (urine volume, mL), as well as urine specific gravity. ...
Article
Introduction: This study compared 2 commercially available beverages, an oral rehydration solution (ORS; 60.9 mM Na+; 3.4% carbohydrate) and a sports drink (SDS; 18.4 mM Na+; 5.9% carbohydrate), on hydration and metabolism during submaximal exercise in the heat. Methods: Ten male subjects completed two 90-min exercise trials (39ºC, 30%) of walking at 50% VO2maxfollowed by a 30-min rest period in the heat while wearing wildland firefighter personal protective clothing. After 45 min of exercise, fluid delivery by either ORS or SDS replaced 150% of sweat loss. Subjects continued the exercise for 45 additional minutes followed by a 30-min rest period. Blood samples were collected pre-exercise (0 min), post-exercise (90 min), and post-trial (120 min) to measure plasma volume (%) and blood glucose (mg·dL-1). Expired gases were collected twice for 3 min for substrate oxidation. Results: The sweat rate and percent dehydration did not differ between the groups (P=0.86 and P=0.79, respectively). Changes in plasma volume did not differ (P=0.55). Hemoglobin levels significantly increased in both groups post-trial (P=0.009). Blood glucose was significantly greater post-trial in SDS versus ORS (116±19 vs 103±13 mg·dL-1, respectively; P=0.01). Fat oxidation was lower post-exercise in SDS vs ORS (0.38±0.1 vs 0.47±0.2 g·min-1, respectively; P=0.049). Conclusions: These data indicate no difference in fluid retention between ORS or SDS when supplemented during exercise in the heat. This implies that fluid volume, and not drink contents, may be more important when ingested during exercise in a hot environment.
... When the respiratory exchange ratio exceeded 1, it was considered that glycogen and glucose accounted for 80% and 20% of the substrate used, respectively [19]. Respiratory water losses were computed as in Mitchell et al. [20]. Sweat loss is the remaining fraction of the body mass lost after considering the water and gels consumption, urine production, metabolic mass loss, and respiratory water loss. ...
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We compared the effect of programmed (PFI) and thirst-driven (TDFI) fluid intake on prolonged cycling performance and exercise associated muscle cramps (EAMC). Eight male endurance athletes (26 ± 6 years) completed two trials consisting of 5 h of cycling at 61% VO2peak followed by a 20 km time-trial (TT) in a randomized crossover sequence at 30 °C, 35% relative humidity. EAMC was assessed after the TT with maximal voluntary isometric contractions of the shortened right plantar flexors. Water intake was either programmed to limit body mass loss to 1% (PFI) or consumed based on perceived thirst (TDFI). Body mass loss reached 1.5 ± 1.0% for PFI and 2.5 ± 0.9% for TDFI (p = 0.10). Power output during the 20 km TT was higher (p < 0.05) for PFI (278 ± 41 W) than TDFI (263 ± 39 W), but the total performance time, including the breaks to urinate, was similar (p = 0.48) between conditions. The prevalence of EAMC of the plantar flexors was similar between the drinking conditions. Cyclists competing in the heat for over 5 h may benefit from PFI aiming to limit body mass loss to <2% when a high intensity effort is required in the later phase of the race and when time lost for urination is not a consideration.
... Sweating rate was calculated from the differences in nude body weight obtained before and immediately after the experiment, corrected for fluid intake, respiratory water loss (16), and urine volume and corrected for surface area (m 2 ) and time (min). Sweat lactate and NH 3 losses were calculated by multiplying the volume of total body sweat by its respective concentration. ...
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The dependence of sweat composition and acidity on sweating rate (SR) suggests that the lower SR in children compared to adults may be accompanied by a higher level of sweat lactate (Lac-) and ammonia (NH3) and a lower sweat pH. Four groups (15 girls, 18 boys, 8 women, 8 men) cycled in the heat (42ºC, 20% relative humidity) at 50% VO2max for two 20-min bouts with a 10-min rest before bout 1 and between bouts. Sweat was collected into plastic bags attached to the subject's lower back. During bout 1, sweat from girls and boys had higher Lac- concentrations (23.6 ± 1.2 and 21.2 ± 1.7 mM; P 0.05; r = -0.27). Sweat Lac- concentration dropped during exercise bout 2, reaching similar levels among all groups (overall mean = 13.7 ± 0.4 mM). Children had a higher sweat NH3 than adults during bout 1 (girls = 4.2 ± 0.4, boys = 4.6 ± 0.6, women = 2.7 ± 0.2, and men = 3.0 ± 0.2 mM; P
... Fully instrumented body mass measurements were taken in triplicate immediately pre and post exercise using a platform scale (Mettler Toledo, Germany; ± 2 g), with participants toweled dry of sweat before the measurement after exercise. Whole body sweat loss (WBSL) was taken as the difference between the average of the three pre and three post measurements after adjusting for respiratory mass loss during exercise (27). Given the minimal, standardized clothing worn, and the practical limitations of having to remain seated in the climate chamber postexercise, to obtain maximum skin blood flow measures, any sweat trapped inside the clothing after exercise was not quantified. ...
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Purpose: To assess the impact of acute caffeine ingestion on thermoregulatory responses during steady-state exercise under moderate heat stress conditions in caffeine-habituated and non-habituated individuals. Methods: 28 participants (14 habituated (HAB) (4 females); and 14 non-habituated (NHAB) (6 females)) cycled at a fixed metabolic heat production (7 W·kg-1) for 60 minutes on two separate occasions 1 hour after ingesting i) 5 mg·kg-1 caffeine (CAF) or ii) 5 mg·kg-1 placebo (PLA), in a double-blinded, randomized and counter-balanced order. Environmental conditions were 30.6±0.9°C, 31±1% RH. Results: The end-exercise rise in esophageal temperature (ΔTes) from baseline was greater with CAF in the HAB group (CAF=0.88±0.29°C, PLA=0.62±0.34°C, P<0.001), but not the NHAB group (CAF=1.00±0.42°C, PLA=1.00±0.39°C, P=0.94). For a given change in mean body temperature, rises in % of maximum skin blood flow were attenuated with CAF on the forearm (P=0.015) and back (P=0.021) in the HAB group, but not in the NHAB group (P≥0.65). Dry heat loss similar in the HAB (CAF=31±5 W·m-2, PLA=33±7 W·m-2) and NHAB groups (CAF=31±3 W·m-2, PLA 30±4 W·m-2) (P≥0.37). There were no differences in whole-body sweat losses in both groups (HAB: CAF=0.59±0.15 kg, PLA=0.56±0.17 kg, NHAB:CAF=0.53±0.19 kg, PLA 0.52±0.19 kg) (P≥0.32). Conclusion: As the potential for both dry and evaporative heat loss was uninhibited by caffeine, we suggest the observed ΔTes differences with CAF in the HAB group were due to alterations in internal heat distribution. Our findings support the common practice of participants abstaining from caffeine prior to participation in thermoregulatory research studies in compensable conditions.
... Sweat rate SR was calculated using pre-and post-exercise body weights (BW) and corrected for urine production, fluid intake, and respiratory water loss (Mitchell et al. 1972). SR is expressed relative to body surface area: ...
Article
Uncompensable heat from wildland firefighter personal protective equipment decreases the physiological tolerance while exercising in the heat. Our previous work demonstrated that the standard wildland firefighter helmet significantly increases both perceived and actual head heat. This study compared heat accumulation under simulated working conditions while wearing a standard non-vented helmet versus a vented helmet. Ten male subjects randomly completed two trials separated by a 2-week washout. Subjects walked 180min (5.6kmh−1, 5% grade) in a heat chamber (35°C, 30% relative humidity) broken into three segments of 50min of exercise and 10min rest, followed by a work capacity test to exhaustion. Each trial measured the physiological strain index, perceived head heat, helmet temperature and relative humidity, rating of perceived exertion and heart rate. At the end of the 3-h trial heart rate, physiological strain, perceived exertion, helmet temperature and humidity showed the main effects of time (P<0.05) but were not different between trials. Work capacity was significantly greater in the vented trial (P=0.001). End-trial strain and heart rate were significantly related to work performed (r=–0.8, P<0.001). Elevated work, trends for changes in perceived exertion, helmet microenvironment and perceived head heat suggest greater heat dissipation and comfort with the vented helmet.
... In the field of sports rehabilitation and physical therapy, it is important to comprehensively evaluate the responses to exercise so as to accurately prescribe and assess the effectiveness of the exercise program. These responses to exercise have been highly documented and include the morphological 1 , neurological 1) , biochemical 2) , biomechanical 3) , metabolic 4) , cardiovascular [5][6][7] , respiratory 8,9) , cognitive 10,11) , and emotional 12,13) adaptations to exercise. ...
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Purpose] The aims of this study were 1) to examine the convergent validity between Lactate pro 2 and a standard JCA-BM 8000 automatic analyzer using salivary lactate and 2) to investigate the relationship between blood and salivary lactate levels after a vertical squat jump. [Participants and Methods] Healthy non-athletes participated in this observational study. The participants performed a vertical squat jump for 1 min 30 s. Blood and salivary lactate levels were measured before and after exercise using Lactate Pro 2. [Results] The intraclass correlation coefficient between Lactate Pro 2 and the JCA-BM 8000 automatic analyzer was 0.773, which can be considered as substantial convergent validity. However, in some samples, the salivary lactate level was out of the measurable range, and numerical values could not be obtained. The cross-correlation function between the blood and salivary lactate levels was 0.535 at lag 0 and 0.750 at lag 1, which indicated a 5-min lag between the salivary and blood lactate values. [Conclusion] Salivary lactate levels can be easily measured using Lactate Pro 2, although its sensitivity needs to be resolved. Further research is required for salivary lactate level, which can be collected non-invasively, to be used as an alternative parameter to blood lactate level.
... Urine was collected and measured for volume and urine specific gravity (USG) (URC-NE, Atago, Cohasset, MA) before, during (60 and 120 min), and 60 min after exercise. Sweat rate was calculated using nude body weight changes in kg (BW), urine output in kg (U), fluid consumption in kg (FC), respiratory water loss in kg (RWL), 34 and water vapor pressure 35 : ...
Article
Introduction Wildfire suppression is characterized by high total energy expenditure and water turnover rates. Hydration position stands outside hourly fluid intake rates. However, dose interval remains ambiguous. We aimed to determine the effects of microdosing and bolus-dosing water and microdosing and bolus-dosing carbohydrate-electrolyte solutions on fluid balance, heat stress (physiologic strain index [PSI]), and carbohydrate oxidation during extended thermal exercise. Methods In a repeated-measures cross-over design, subjects completed four 120-min treadmill trials (1.3 m·s⁻¹, 5% grade, 33°C, 30% relative humidity) wearing a US Forest Service wildland firefighter uniform and a 15-kg pack. Fluid delivery approximated losses calculated from a pre-experiment familiarization trial, providing 22 doses·h⁻¹ or 1 dose·h⁻¹ (46±11, 1005±245 mL·dose⁻¹). Body weight (pre- and postexercise) and urine volume (pre-, during, and postexercise) were recorded. Heart rate, rectal temperature, skin temperature, and steady-state expired air samples were recorded throughout exercise. Statistical significance (P<0.05) was determined via repeated-measures analysis of variance. Results Total body weight loss (n=11, –0.6±0.3 kg, P>0.05) and cumulative urine output (n=11, 677±440 mL, P>0.05) were not different across trials. The micro-dosed carbohydrate-electrolyte trial sweat rate was lower than that of the bolus-dosed carbohydrate-electrolyte, bolus-dosed water, and microdosed water trials (n=11, 0.8±0.2, 0.9±0.2, 0.9±0.2, 0.9±0.2 L·h⁻¹, respectively; P<0.05). PSI was lower at 60 than 120 min (n=12, 3.6±0.7 and 4.5±0.9, respectively; P<0.05), with no differences across trials. The carbohydrate-electrolyte trial’s carbohydrate oxidation was higher than water trial’s (n=12, 1.5±0.3 and 0.8±0.2 g·min⁻¹, respectively; P<0.05), with no dosing style differences. Conclusions Equal-volume diverse fluid delivery schedules did not affect fluid balance, PSI, or carbohydrate oxidation during extended thermal work.
... where MML was metabolic mass loss and RWL was respiratory water loss. MML and RWL were calculated using published equations (Mitchell et al. 1972), for which oxygen consumption and respiratory quotient were estimated based on corresponding heart rate measurements between the trial and the graded exercise test (preliminary visit). All calculations were performed for the laboratory-based testing. ...
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The aims of this study were to determine: (1) trapped sweat (TS) in basketball uniforms and the effect on sweat loss (SL) estimates during a laboratory-based basketball simulation protocol; (2) the impact of exercise intensity, body mass, age, and SL on TS; and (3) TS during on-court training to assess the ecological validity of the laboratory-based results. Twenty-four recreational/competitive male basketball players (23 ± 10 years, 77.0 ± 16.7 kg) completed three randomized laboratory-based trials (Low, Moderate, and High intensity) consisting of 150-min intermittent exercise. Eighteen elite male players (23 ± 4 years, 92.0 ± 20.6 kg) were observed during coach-led, on-court training. Nude and clothed body mass were measured pre and postexercise to determine TS. Data are mean ± SD. There was a significant effect of intensity on SL and TS (P < 0.001, Low<Moderate<High, ANOVA). During Low, subjects lost 1.10 ± 0.59 kg sweat and TS was 0.11 ± 0.15 kg (8.0 ± 5.1% SL). During Moderate, subjects lost 1.60 ± 0.56 kg sweat and TS was 0.21 ± 0.21 kg (11.6 ± 6.3% SL). During High, subjects lost 2.12 ± 0.66 kg sweat and TS was 0.38 ± 0.28 kg (16.0 ± 7.4% SL). Multiple regression and partial correlation analysis suggested TS was significantly related to SL (P < 0.0001; partial r = 0.81–0.89), whereas the contributions of body mass (P = 0.22–0.92) and age (P = 0.29–0.44) were not significant. TS during on-court training was 0.35 ± 0.36 kg, which was associated with a 14.1 ± 11.5% underestimation in SL, and was not statistically different than laboratory-based results (P = 0.59). Clothed body mass measurements should be used with caution, as TS is highly variable and can cause a significant underestimation in SL in athletes with high sweating rates.
... Convection forcée Mitchell et al. (1972) 9-1,9 Danielson (1993) -Pva la pression partielle de vapeur d'eau de l'air expiré (Pa). ...
Thesis
Ce travail porte sur la modélisation physique et numérique des écoulements d'air et des échanges de chaleur dans les stations de métro. L'étude se base sur une description des écoulements par les équations d'Euler tridimensionnelles instationnaires auxquelles sont ajoutés des termes source. Ces équations sont discrétisées par une formulation de volumes finis et résolues par un algorithme de type SIMPLE couplé à un schéma de Van Leer. La description de la géométrie du domaine de calcul est assurée par un maillage cartésien. Afin de prendre en compte le déplacement des rames dans la station, une technique de maillage glissant est élaborée. Le modèle est validé sur des écoulements générés par convection mixte dans un canal de section rectangulaire contenant une plaque chauffante dans sa partie centrale. L'étude se termine par quelques applications du code de calcul dans une station de métro type du métro parisien.
... Sweat measurements. Differences between nude and dressed body masses before and after each trial were corrected for respiratory (38) and metabolic weight losses (45) as well as for fluid intake. The rate of sweat produced (SR) was calculated as the sum of pretrial nude body mass and fluid given minus posttrial (corrected) nude body mass divided by exercise time. ...
Article
This study examined the independent and combined importance of aerobic fitness and body fatness on physiological tolerance and exercise time during weight-bearing exercise while wearing a semipermeable protective ensemble. Twenty-four men and women were matched for aerobic fitness and body fatness in one of four groups (4 men and 2 women in each group). Aerobic fitness was expressed per kilogram of lean body mass (LBM) to eliminate the influence of body fatness on the expression of fitness. Subjects were defined as trained (T; regularly active with a peak aerobic power of 65 ml · kg LBM ⁻¹ · min ⁻¹ ) or untrained (UT; sedentary with a peak aerobic power of 53 ml · kg LBM ⁻¹ · min ⁻¹ ) with high (High; 20%) or low (Low; 11%) body fatness. Subjects exercised until exhaustion or until rectal temperature reached 39.5°C or heart rate reached 95% of maximum. Exercise times were significantly greater in T Low (116 ± 6.5 min) compared with their matched sedentary (UT Low ; 70 ± 3.6 min) or fatness (T High ; 82 ± 3.9 min) counterparts, indicating an advantage for both a high aerobic fitness and low body fatness. However, similar effects were not evident between T High and UT High (74 ± 4.1 min) or between the UT groups (UT Low and UT High ). The major advantage attributed to a higher aerobic fitness was the ability to tolerate a higher core temperature at exhaustion (the difference being as great as 0.9°C), whereas both body fatness and rate of heat storage affected the exercise time as independent factors.
... E's during the race were calculated by difference, utilizing the energy balance equation. E,, was estimated by the equation E,, = 0.0023M (44 -P,), (where Pi = partial pressure of water vapor in inspired air) as derived by Fanger (8) and recently validated for workloads of up to 80% x70, rnax by Mitchell et al. (16). E, was then taken as the difference between E and E,,. ...
Article
Page 909: M. B. Maron, J. A. Wagner, and S. M. Horvath. “Thermoregulatory responses during competitive marathon running.” In three places TR (black globe, radiant temperature) should be substituted for Tre. Page 910: at the bottom of the left-hand column, substitute ... R was calculated from the Stefan-Boltzmann equation (See PDF) And in the fourth and fifth lines from the top of the right-hand column, substitute... and Tdb was used as an approximation of TR.... Page 911: in the seventeenth line from the top of the right-hand column, substitute.... The use of Tdb as an approximation of TR should not influence the results greatly....
... Whole body sweating rate. WB sweat loss was calculated from the change in pre-to postexercise nude body mass, corrected for fluid intake (difference in drink bottle mass from pre-to postexercise to the nearest 0.001 kg using a compact digital scale; model CS2000; Ohaus), respiratory water loss, and weight loss due to substrate oxidation (29). Subjects did not use the bathroom between the preand postexercise nude body mass measurements; thus, no correction was needed for urine or stool loss. ...
Article
This study determined the relations between regional (REG) and whole body (WB) sweating rate (RSR and WBSR, respectively) and REG and WB sweat [Na+] during exercise. Twenty-six recreational athletes (17 men, 9 women) cycled for 90 min while WB sweat [Na+] was measured using the washdown technique. RSR and REG sweat [Na+] were measured from 9 regions using absorbent patches. RSR and REG sweat [Na+] from all regions were significantly (p<0.05) correlated with WBSR (r=0.58-0.83) and WB sweat [Na+] [r=0.74-0.88), respectively. However, the slope and y-intercept of the regression lines for most models were significantly different than 1 and 0, respectively. The coefficients of determination (r2) were 0.44-0.69 for RSR predicting WBSR (best predictors: dorsal forearm (r2=0.62) and triceps (r2=0.69)) and 0.55-0.77 for REG predicting WB sweat [Na+] (best predictors: ventral forearm (r2=0.73) and thigh (r2=0.77)). There was a significant (p<0.05) effect of day-to-day variability on the regression model predicting WBSR from RSR at most regions, but no effect on predictions of WB sweat [Na+] from REG. Results suggest that REG cannot be used as a direct surrogate for WB sweating responses. Nonetheless, the use of regression equations to predict WB sweat [Na+] from REG can provide an estimation of WB sweat [Na+] with an acceptable level of accuracy, especially using the forearm or thigh. However, the best practice for measuring WBSR remains conventional WB mass balance calculations since prediction of WBSR from RSR using absorbent patches does not meet the accuracy or reliability required to inform fluid intake recommendations.
... Sweat rate was calculated from change in nude body weight (kg), adjusted for urine output, fluid intake, and respiratory water loss (Mitchell et al., 1972), and calculated relative to time spent in the heat chamber. Nude weight measurements were collected at the end of the HST (to the nearest 10 g). ...
Article
Heat acclimation lowers physiological strain when exercising in the heat, and may be enhanced by promoting dehydration during acclimation. The purpose was to compare fluid intake during heat acclimation by promoting dehydration (DEH=0.5 mL kg⁻¹ 15 min⁻¹, ~2.4% dehydration per acclimation session) compared to euhydration (EUH=2.0 mL kg⁻¹ 15 min⁻¹, ~1.4% dehydration per acclimation session) following four heat acclimation bouts on thermal strain, and exercise performance. Thirteen males completed 90 min heat stress tests (HST) at 50% VO2max (40 °C, 30%RH) before and after three 90 min heat acclimation trials, involving consecutive bouts with 4-fold less fluid (DEH) or EUH. DEH and EUH trials were separated by 48 h and assigned in a random crossover design separated by a 5 week washout. Wildland firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt baselayer were worn. Peak core temperature (Tc) from the HST significantly decreased following both DEH (39.5 ± 0.1–39.0 ± 0.1 °C: P < 0.001) and EUH acclimation (39.5 ± 0.1–38.9 ± 0.1 °C: P < 0.001). HR, RPE, physiological strain index (PSI), and total work (J) completed in a graded exercise test to exhaustion were improved (P < 0.001) in effect for acclimation, but not different when comparing DEH or EUH fluid delivery. SBF was unchanged (P = 0.313). Sweat rate increased greater following DEH (1.52 ± 0.06–1.89 ± 0.09 L h⁻¹) compared to EUH acclimation (1.57 ± 0.06–1.79 ± 0.08 L h⁻¹: P = 0.015). Resting plasma volume increased in effect for acclimation (P = 0.002). Aldosterone decreased in effect for acclimation (P < 0.001) at rest and following exercise, and total protein was unaffected (P = 0.83). In conclusion, short-term heat acclimation (~360 min) attenuates heat stress, and improves exercise capacity in the heat, and was not impaired nor improved by promoting DEH during acclimation.
Article
New findings: What is the topic of this review? There is a need to revisit the basic principles of exercise mass and water balance, the use of common equations and the practice of interpreting outcomes. What advances does it highlight? We propose use of the following equation as a way of simplifying exercise mass and water balance calculations in conditions where food is not consumed and waste is not excreted: ∆body mass - 0.20 g/kcal(-1) = ∆body water. The relative efficacy of exercise drinking behaviours can be judged using the following equation: percentage dehydration = [(∆body mass - 0.20 g kcal(-1) )/starting body mass] × 100. Changes in body mass occur because of flux in liquids, solids and gases. This knowledge is crucial for understanding metabolism, health and human water needs. In exercise science, corrections to observed changes in body mass to estimate water balance are inconsistently applied and often misinterpreted, particularly after prolonged exercise. Although acute body mass losses in response to exercise can represent a close surrogate for body water losses, the discordance between mass and water balance equivalence becomes increasingly inaccurate as more and more energy is expended. The purpose of this paper is briefly to clarify the roles that respiratory water loss, gas exchange and metabolic water production play in the correction of body mass changes for fluid balance determinations during prolonged exercise. Computations do not include waters of association with glycogen because any movement of water among body water compartments contributes nothing to water or mass flux from the body. Estimates of sweat loss from changes in body mass should adjust for non-sweat losses when possible. We propose use of the following equation as a way of simplifying the study of exercise mass and water balance: ∆body mass - 0.20 g kcal(-1) = ∆body water. This equation directly controls for the influence of energy expenditure on body mass balance and the approximate offsetting equivalence of respiratory water loss and metabolic water production on body water balance. The relative efficacy of exercise drinking behaviours can be judged using the following equation: percentage dehydration = [(∆body mass - 0.20 g kcal(-1) )/starting body mass] × 100.
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With the continued increase in international travel and immigration to Georgia, the Department of Public Health (DPH) continued its mission to prevent and respond to Zika virus (ZIKV) transmission. Methods: We analyzed surveillance data from the DPH to compare the geographical distribution of counties conducting surveillance, total number, and overall percentage of mosquito species collected in 2016 and 2017. Mosquito surveillance in 2017 was mapped by county and species using ArcMap 10.2.0. Results: From 2016 and 2017, mosquito surveillance increased from 60 to 159 counties (165% increase). A total of 145,346 mosquitoes were trapped and identified in 2016 compared to 152,593 in 2017 (5.43% increase). There was a difference in the type of mosquito species found by year. Some species collected in previous years were not collected in 2017, while other species found in 2017 were not previously collected during mosquito surveillance. Also, certain mosquito species were found outside of their expected geographical range. Conclusion: The continued collaborative response to ZIKV by the DPH allowed a continued increase in its surveillance program. Existing and new partnerships continued to develop with military and local health departments to expand and share data. This additional surveillance data allowed DPH to make sound public health decisions regarding mosquito-borne disease risks and close gaps in data related to vector distribution.
Article
The measurement of whole body sweat losses (WBSL) is important to the study of body heat balance, body water balance, establishing guidelines for water and electrolyte consumption, and the study of metabolism and health. In principal, WBSL is measured by an acute change in body mass (ΔBM) in response to a thermoregulatory sweating stimulus. In this CORP review, we re-visit several basic, but rarely discussed assumptions important to WBSL research, including the common equivalences: mass = weight = water = sweat. Sources of large potential measurement errors are also discussed, as are best practices for avoiding them. The goal of this CORP review is to ultimately improve the accuracy, reproducibility, and application of WBSL research.
Article
Stone, BL, Ashley, JD, Skinner, RM, Polanco, JP, Walters, MT, Schilling, BK, and Kellawan, JM. Effects of a short-term heat acclimation protocol in elite amateur boxers. J Strength Cond Res XX(X): 000-000, 2022-Boxing requires proficient technical and tactical skills coupled with high levels of physiological capacity. Although heat and humidity negatively affect acute exercise performance, short-term exercise training in hot and humid environments can lead to physiological adaptations that enhance exercise performance in both hot and thermoneutral conditions. In highly trained endurance athletes, exercise-induced acclimation can occur in as little as 5 days (known as short-term heat acclimation [STHA]). However, the impact of a 5-day heat acclimation (5-DayHA) in combat athletes, such as elite amateur boxers, is unknown. The aim of the present investigation was to determine whether a 5-DayHA improves aerobic performance in a thermoneutral environment and causes positive physiological adaptations in elite boxers. Seven elite amateur boxers underwent a 5-DayHA protocol, consisting of 60-minute exercise sessions in an environmental chamber at 32 °C and 70% relative humidity. Repeat sprint test (RST) evaluated aerobic performance in a thermoneutral environment 24 hours before and after the 5-DayHA. Presession and postsession hydration status (urine specific gravity) and body mass were assessed. After a 5-DayHA period, boxers significantly improved RST performance (13 ± 7 to 19 ± 7 sprints, d = 0.92, p = 0.03) but not pre-exercise hydration status (1.02 ± 0.01 to 1.01 ± 0.01, d = 0.82, p = 0.07). Therefore, these findings suggest 5-DayHA enhances aerobic performance in elite-level amateur boxers and may provide a viable training option for elite combat athletes.
Chapter
Sensible heat transfer from humans to the environment decreases as ambient temperature increases. When sensible heat transfer is insufficient to maintain acceptable bodily temperature, sweat is secreted to wet the skin and effect evaporative cooling. In this chapter, we discuss factors that affect sweating in human beings.
Chapter
Human thermal behavior is determined by the combined effect of physiological and physical phenomena. Physiological factors discussed separately in previous chapters, act in a coordinated complementary manner to regulate bodily temperature. Institution provides qualitative understanding of some interactions, but an analytical approach is required to develop a quantitative understanding of human thermal regulation.
Article
This study assessed whether, notwithstanding lower resting absolute core temperatures, alterations in time-dependent changes in thermoregulatory responses following partial and complete heat acclimation (HA) are only evident during uncompensable heat stress. Eight untrained individuals underwent 8-weeks of aerobic training (i.e. partial HA) followed by 6-days of HA in 38°C/65%RH (i.e. complete HA). On separate days, esophageal temperature (T es ), arm (LSR arm ) and back (LSR back ) sweat rate, and whole-body sweat rate (WBSR) were measured during a 45-min compensable (37°C/30%RH) and 60-min uncompensable (37°C/60%RH) heat stress trial pre-training (PRE-TRN), post-training (POST-TRN), and post-heat acclimation (POST-HA). For compensable heat stress trials, resting T es was lower POST-TRN (36.74±0.27°C, P=0.05) and POST-HA (36.60±0.27°C, P=0.001) compared to PRE-TRN (36.99±0.19°C), howeve rΔT es was similar in all trials (PRE-TRN:0.40±0.23°C; POST-TRN:0.42±0.20°C; POST-HA:0.43±0.12°C, P=0.97). While LSR back was unaltered by HA (P=0.94), end-exercise LSR arm was higher POST-TRN (0.70±0.14 mg/cm ² /min, P<0.001) and POST-HA (0.75±0.16 mg/cm ² /min, P<0.001) compared to PRE-TRN (0.61±0.15 mg/cm ² /min). Despite matched evaporative heat balance requirements, steady-state WBSR (31 st -45 th min) was greater POST-TRN (12.7±1.0 g/min, P=0.02) and POST-HA (12.9±0.8 g/min, P=0.004), compared to PRE-TRN (11.7±0.9 g/min). For uncompensable heat stress trials, resting T es was lower POST-TRN (36.77±0.22°C, P=0.05) and POST-HA (36.62±0.15°C, P=0.03) compared to PRE-TRN (36.86±0.24°C). But, ΔT es was smaller POST-TRN (0.77±0.19°C, P=0.05) and POST-HA (0.75±0.15°C, P=0.04) compared to PRE-TRN (1.10±0.32°C). LSR back and LSR arm increased with HA (P<0.007) supporting the greater WBSR with HA (POST-TRN:14.4±2.4 g/min, P<0.001; POST-HA:16.8±2.8 g/min, P<0.001) compared to PRE-TRN (12.7±3.2 g/min).In conclusion, the thermal benefits of HA are primarily evident when conditions challenge the physiological capacity to dissipate heat.
Article
The present study evaluated whether wearing a water-soaked t-shirt, with or without electric fan use, mitigates thermal and cardiovascular strain in older individuals exposed to hot and moderately humid conditions. Nine healthy older individuals (68 ± 4 years; five females) completed three 120-min heat exposures (42.4 ± 0.2°C, 34.2 ± 0.9% relative humidity) on separate days while wearing a dry t-shirt (CON), a t-shirt soaked with 500 ml of tap water (WET), or a t-shirt soaked with 500 ml of tap water while facing an electric fan (2.4 ± 0.4 m/s; WET+FAN). Measurements included core and skin temperatures, evaporative mass losses, heart rate, and blood pressure. In the WET condition, elevations in core temperature were attenuated compared to DRY from 30-120 min and compared to WET+FAN from 30-90 min (P < 0.05). Evaporative mass losses (inclusive of sweat and water losses from the shirt) were greatest in WET+FAN, followed by WET, and then DRY (P < 0.01). Sweat losses were lowest in WET, followed by DRY, and then WET+FAN (P < 0.01). Heart rate was lower only at 60 min in WET vs. DRY (P = 0.01). No differences in mean arterial pressure were observed (P = 0.51). In conclusion, wearing a water-soaked t-shirt without, but not with, electric fan use is an effective heat management strategy to mitigate thermal strain and lower sweat losses in older individuals exposed to hot and moderately-humid conditions.
Article
Introduction: Although evaporative heat loss capacity is reduced in burn-injured individuals with extensive skin grafts, the thermoregulatory strain due to a prior burn injury during exercise-heat stress may be negligible if the burn is located underneath protective clothing with low vapor permeability. Purpose: This study aimed to test the hypothesis that heat strain during exercise in a hot-dry environment while wearing protective clothing would be similar with and without a simulated torso burn injury. Methods: Ten healthy individuals (8 men/2 women) underwent three trials wearing: uniform (combat uniform, tactical vest, and replica torso armor plates), uniform with a 20% total body surface area simulated torso burn (uniform + burn), or shorts (and sports bra) only (control). Exercise consisted of treadmill walking (5.3 km·h; 3.7% ± 0.9% grade) for 60 min at a target heat production of 6.0 W·kg in 40.0°C ± 0.1°C and 20.0% ± 0.6% relative humidity conditions. Measurements included rectal temperature, heart rate, ratings of perceived exertion (RPE), and thermal sensation. Results: No differences in rectal temperature (P ≥ 0.85), heart rate (P ≥ 0.99), thermal sensation (P ≥ 0.73), or RPE (P ≥ 0.13) occurred between uniform + burn and uniform trials. In the control trial, however, core temperature, heart rate, thermal sensation, and RPE were lower compared with the uniform and uniform + burn trials (P ≤ 0.04 for all). Conclusions: A 20% total body surface area simulated torso burn injury does not further exacerbate heat strain when wearing a combat uniform. These findings suggest that the physiological strain associated with torso burn injuries is not different from noninjured individuals when wearing protective clothing during an acute exercise-heat stress.
Conference Paper
Introduction Water transport and local hydration of the airways play a critical role in the lungs, with dysfunction of airway water balance commonly associated with disease states such as cystic fibrosis and exercise-induced bronchoconstriction. The bronchial circulation, which arises from the systemic circulation, is the main supplier of water to the airways; however, limited and contradictory information is currently available on the effects of systemic dehydration on lung function. Aim To clarify the impact of systemic dehydration on lung function in healthy individuals and to determine the role of local hydration status on any observed changes. Methods Seven healthy young adults participated in a randomised crossover study that involved spirometry and body plethysmography at baseline (euhydration), after 28 hour of fluid restriction (systemic dehydration), and after 1 hour of systemic (oral fluid intake) or local (ultrasonic nebulisation of isotonic saline) rehydration (rehydrated). Hydration status was quantified via changes in body mass and plasma osmolality. Repeated-measures ANOVA were conducted. Results Fluid restriction induced mild dehydration, with an average body mass loss of 2.5%±0.6% (p=0.001) and an increase in plasma osmolality from 292±2 to 298±1 mOsm·kg⁻¹ (p<0.001). These changes were at least partly reversed by systemic, but not local rehydration (p<0.05). Lung function data are presented in table 1. Forced vital capacity (FVC) decreased by 122±64 ml following dehydration (p=0.003) and returned to baseline post-rehydration, with no difference between modes of rehydration. Neither total lung capacity (TLC) nor residual volume (RV) were affected significantly by hydration status (p>0.05); however, RV/TLC increased by 2.1%±2.5% following dehydration (p=0.010), with this change reversed by both modes of rehydration. Functional residual capacity (FRC) increased post-dehydration by 143±161 ml, but the difference reached significance only on one study day (nebuliser day: p=0.014).View this table: • View inline • View popup Abstract P225 Table 1 Mean (±SD) lung function values recorded in 7 healthy individuals in a hydrated, dehydrated and rehydrated state with two modes or rehydration (oral and nebuliser) Conclusions Subtle alterations in lung volumes occur following mild dehydration in healthy individuals. That local rehydration reversed the lung function changes as effectively as systemic rehydration confirms that airway water loss contributes to the observed impairments. Assessment of hydration status may be an important consideration in the management of patients with lung diseases.
Chapter
Identified over 80 years ago, pantothenic acid is an essential vitamin, which serves as the metabolic precursor for coenzyme A (CoA). In the form of CoA and as a component of acyl carrier protein, pantothenic acid is a participant in myriad metabolic reactions involving lipids, proteins, and carbohydrates. Though essential, pantothenic acid deficiency in humans is rare due to its ubiquitous distribution in foods of both animal and plant origin. Supplementation with pantothenic acid or its derivatives may have some health benefits, but further investigation into various health claims is necessary before any specific recommendations may be given.
Article
Background: The effects of a reduced or mildly elevated exercising muscle temperature on the graded exercise test (GXT) performance have yet to be studied. The present study clarified the effects of a range of exercising muscle temperatures on GXT performance in a temperate environment. Methods: Eight male subjects (age, 24.0±0.5 years old; height, 175±2 cm; weight, 64.8±2.0 kg; peak oxygen consumption [V̇ O2peak], 51.1±2.4 ml/kg/min) performed 4 GXTs at different exercising muscle temperatures using a cycle-ergometer in a temperate environment (24.1 ± 0.2 °C). The exercise began at 0.3 kp with 60 rpm and increased 0.3 kp every minute until volitional exhaustion. Subjects passively cooled (averaged deep thigh and calf temperature [Tmm], COLD, 31 °C or COOL, 33 °C) or warmed (Tmm; WARM, 35 °C or HOT, 37 °C) the exercising muscle using water perfusion pants throughout the test. The peak oxygen consumption (V̇ O2peak), exercise time to exhaustion (TTE), heart rate (HR), tympanic (Tty) and mean body temperature (Tb), and total sweat loss were also measured. Results: No significant differences were observed in the V̇ O2peak or TTE among the 4 conditions; however, the HR, Tb, and total sweat loss were significantly higher (p<0.05) under warming conditions than cooling conditions. Conclusions: These results suggest that although the cardiovascular and thermoregulatory strain is higher under warming conditions than cooling conditions, the exercising muscle temperature does not affect the performance of a GXT lasting approximately 15 min in a temperate environment.
Article
Full-text available
Water transport and local (airway) hydration are critical for the normal functioning of lungs and airways. Currently, there is uncertainty regarding the effects of systemic dehydration on pulmonary function. Our aims were: i) to clarify the impact of exercise- or fluid restriction-induced dehydration on pulmonary function in healthy adults; and ii) to establish whether systemic or local rehydration can reverse dehydration-induced alterations in pulmonary function. Ten healthy participants performed four experimental trials in a randomized order (2 h exercise in the heat twice, and 28 h fluid restriction twice). Pulmonary function was assessed using spirometry and whole-body plethysmography in the euhydrated, dehydrated, and rehydrated states. Oral fluid consumption was used for systemic rehydration, and nebulized isotonic saline inhalation for local rehydration. Both exercise and fluid restriction induced mild dehydration (2.7±0.7% and 2.5±0.4% body mass loss, respectively; p<0.001) and elevated plasma osmolality (p<0.001). Dehydration across all four trials was accompanied by a reduction in forced vital capacity (152±143 mL, p<0.01) and concomitant increases in residual volume (216±177 mL, p<0.01) and functional residual capacity (130±144 mL, p<0.01), with no statistical differences between modes of dehydration. These changes were normalized by fluid consumption, but not nebulization. Our results suggest that, in healthy adults: i) mild systemic dehydration induced by exercise or fluid restriction leads to pulmonary function impairment, primarily localized to small airways; and ii) systemic, but not local, rehydration reverses these potentially deleterious alterations.
Chapter
Water, Potassium, sodium, and chloride play key roles in health. Each nutrient has a physiologic role, homeostatic balance, and relationship to disease when ingested in inappropriate amounts. Water is an essential nutrient with multiple functions in the human body. Adequate intake of water helps maintain circulating volume and prevent impairments in cognition and exercise capacity due to dehydration. Water is best administered orally, and when not possible via tube feeding; alternate means include intravenous and subcutaneous approaches, the latter termed hypodermoclysis. Potassium is needed to maintain electrochemical gradients across cellular membranes; adequate intake from dietary sources can reduce blood pressure, bone demineralization, and formation of kidney stones. Potassium intake in dietary forms is often inadequate among older adults. Sodium and chloride also impact membrane potential as the principal extracellular ions. A sodium intake of 1.5 g/day is generally considered adequate to maintain balance in most healthy adults. When consumed in excess, sodium increases blood pressure and cardiovascular risk in salt-sensitive populations such as older adults and African-Americans. The ideal sodium: potassium ratios in the diet as recommended by the World Health Organization (WHO) and other groups are seldom achieved. Education and policy measures to promote appropriate intakes of water, potassium, and sodium can translate into population-wide health benefits.
Article
Passengers usually walk a long distance before arriving at the seating areas of the departure lounge in airport terminals. The current standards for airport terminals have not considered passengers' thermal comfort during the walking status and the variations in thermal comfort with the dwell time during the sedentary period after walking. Therefore, 14 male subjects dressed in 0.57 clo were recruited to simulate passengers in the summer in the climate chamber. The subjects walked for 5 min, 10 min, and 15 min, respectively, at a pace of 1.1–1.2 m/s with a 5 kg bag at 26 °C. Subsequently, they entered the sedentary phase under three conditions with different operative temperatures (Top) (23 °C, 26 °C, and 29 °C). Each subject participated in nine experiments. Variations in subjective perceptions and physiological parameters were recorded throughout the study. The summer design parameters for Chinese airport terminals (25–26 °C, 50% RH) did not satisfy the passengers’ thermal comfort when the walking time exceeded 10 min. Exponential relationships between neutral Top (Tn) and time were acquired for the sedentary phase. After walking for 5 min, 10 min, and 15 min, the Tn values were 24.0 °C, 21.0 °C, and 18.9 °C, respectively. Tn required 17.6–21.0 min to recover to the steady-state sedentary level. Thus, the comfort zones under the current standards may not meet the thermal comfort demands of passengers with short dwell times.
Article
Interested in the influences of wind on human body under exercise, the present authors had prepared a handmade wind tunnel with air conditionning and studied some physiological reactions under wind. Five healthy male subjects (aged 22-24 yrs.) were loaded with a bicycle ergometer work at the rate of 600 kpm/min for 30 minutes, under three different wind velocities (no wind: W0, 3.8m/sec: W1 and 5.7 m/sec: W2), with an air conditionning of temperature: 24°C, relative humidity: 60%. Following results were obtained: 1) Heart rate decreased by wind (at W0: 128, W1: 121 and W2: 120 beats/min) ; but oxygen intake remained constant (1.5-1.6l/min) . 2) Mean skin temperature kept a certain level rather lower under wind and the change of rectal temperature was not observed. 3) Total sweat rate and local sweat rate showed a decrease by wind, but Na and Cl concentrations in sweat did not change, though there were individual differences. 4) Heat Tolerance Index (HTI) decreased under wind. 5) Under wind, the heat loss by evaporation and convection decreased double and that by radiation decreased to about 1/3 compared with the no wind conditions.
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