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Respiratory water losses during exercise
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.
... 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): ...
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.
... 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]. ...
O músculo esquelético é o maior tecido do corpo e guarda relação com a autonomia somatocinética e homeostase metabólica. A miogênese é decorrente da predominância de fatores protéicos miogênicos sobre miostáticos. O crescimento ocorre predominantemente de forma hipertrófica, após o nascimento, pelo predomínio da síntese sobre o catabolismo protéico. A síntese protéica é finamente mantida por cascata de quinases controladas ou controladoras da mTOR. A mTOR controla o complexo iniciador da síntese protéica, sendo influenciada pela contração muscular, fatores de crescimento e a leucina. O estado de privação energética (↑ AMP/ATP) inibe a mTOR pelo aumento da AMPK. A síntese protéica miofibrilar é estimulada por fatores hidratantes celulares (glicose, insulina, creatina, BCAA, glutamina). Seguindo-se a lesão e necrose miofibrilar, há resposta inflamatória e ação dos fagócitos, promovendo a fagocitose tecidual. Posteriormente, os macrófagos alteram seu fenótipo para resolver a inflamação e promover a miogênese e crescimento miofibrilar.Palavras-chave: músculo esquelético, hipertrofia muscular, anabolismo protéico, mTOR, regeneração muscular.
... Lors d'exercices d'endurance prolongés il est recommandé de prendre en compte les pertes de masse liées à l'oxydation des substrats et aux échanges respiratoires (Mitchell et al., 1972) dans l'équation [2]. (Armstrong, 2007). ...
... Outre par la sudation, de l'eau est également perdue par la respiration, et de manière plus importante lors de l'exercice du fait de l'augmentation du débit ventilatoire. Les pertes d'eau respiratoires (généralement 1 à 2 g · min -1 ) peuvent varier dépendamment de l'intensité de l'exercice et de l'environnement (Mitchell et al., 1972), mais sont généralement compensées par la production d'eau métabolique (Cheuvront & Montain, 2017). ...
(Thesis written in French)
Dehydration, especially when ≥ 2% body mass, is usually associated with an alteration of physiological functions, subjective perceptions as well as endurance performance and cognitive functions. More specifically, it is frequently mentioned that together, the cardiovascular, thermal, metabolic impacts as well as subjective effects induced by dehydration could contribute to increase the perception of effort, which in turn would act as a mediator of endurance performance. While several studies have observed an exacerbation of the perception of effort with dehydration, evidence is contradictory, and some studies do not observe such an effect. In addition, evidence suggests that some individuals may better tolerate dehydration, while others are more widely affected. In this regard, a hypothesis has recently been put forward, according to which repeated exposure to dehydration could somewhat attenuate certain effects, in particular on subjective perceptions, including the perception of effort, and therefore reduce its subsequent impact on performance. In addition to being a possible key mediator in the relationship between exercise-induced dehydration and endurance performance, perception of effort could also play a central role in the process of habituation to the dehydration. However, the idea that humans can become habituated to dehydration has been discussed superficially and anecdotally. Several questions remain unanswered and must therefore be studied.
... 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]). ...
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).
... This timing is crucial to avoid artifact data and ensure an accurate assessment of hydration status [48]. Summarizing numerous physiological aspects related to the subject's condition [49][50][51][52][53], biological sex [54][55][56], and the type of activity performed [57,58] can make interpreting data from a salivary osmolarity analysis challenging [59]. ...
This case report examines the correlation between hydration, weight variation, and perceived effort in a 43-year-old amateur athlete during a self-supported 81.5 km crossing of Death Valley, completed over 3 days with significant elevation changes. Studies have shown that a body mass loss greater than 2-3% can lead to an increased perception of effort and a decline in performance. Specifically, during passive and active heat exposures, the average body mass loss was found to be 1.4 ± 0.3% and 4.1 ± 0.7%, respectively. Salivary osmolarity has demonstrated a sensitivity of 86% and specificity of 91% in diagnosing dehydration of ≥ 2%, suggesting its potential as a non-invasive indicator of hydration status. The subject monitored their own body weight, hydration (via salivary osmolarity), and perceived effort using a rate of perceived exertion (RPE) scale. Nutritional intake included isocaloric meals and nutritional bars, and hydration was managed using water and a hydroelectrolytic solution. Key bioimpedance parameters were measured to assess body composition and hydration status. A progressive decrease in body weight correlated with an increase in perceived effort (RPE score) and salivary osmolarity. Resistance (Rx) remained stable, while reactance (Xc) showed a biphasic trend and was inversely correlated with the sodium/potassium ratio (NAK). There were significant linear correlations between perceived effort and both weight loss and salivary osmolarity, indicating that salivary osmolarity is a potential early predictor of these changes. The findings highlight a linear correlation between weight loss, perceived effort, and salivary osmolarity, suggesting that monitoring salivary osmolarity would be useful for the field assessment of hydration and exertion. Further research with larger populations is necessary to validate these observations.
... Elde edilen dağılıma göre birinci alt boyut "spora özgü beslenme" (23,24,25,26,27), ikinci alt boyut "ergojenik yardımcılar" (12,13,14,15,16,17,18), üçüncü alt boyut "vitamin ve mineraller" (7,8,9,10,11), dördüncü alt boyut "enerji kaynakları" (1, 2, 3, 4, 5, 6), beşinci alt boyut "beslenmeyi etkileyen faktörler" (19,20,21,22) 42 Doğrulayıcı faktör analizinden elde edilen bulgular, ölçeğin faktör yapısının toplanan verilerle kabul edilebilir uyum gösterdiğine işaret etmektedir. ...
The purpose of this research is to develop a highly reliable and valid measurement tool to determine athletes' nutrition awareness levels in sports. For this purpose, validity and reliability studies were carried out in a rational and statistical context. Within the scope of validity; content and structure validity based on expert evaluations, statistically; exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) studies were conducted. Cronbach's alpha and equivalent halves techniques were used in reliability analyses. In the study conducted with a total of 415 athletes, a 27-item scale was obtained that explained 60.5% of the total variance, apart from the analyzes regarding the explanation of the structure. In the model tested on two completely independent groups, where CFA and EFA were applied, it was concluded that the path coefficient values of the items varied between 0.51 and 1.05, the t values were statistically significant, and the fit indices of the tested measurement model were within the acceptable range. While the Cronbach's alpha reliability coefficient was 0.93 in the five-factor structure, the entire scale and its sub-dimensions were above 0.70 in the results obtained with the equivalent halves method. In line with these findings; It can be said that the sports nutrition awareness scale, which consists of five subscales as energy sources, vitamins and minerals, ergogenic aids, factors affecting nutrition and sports-specific nutrition, is a valid and reliable measurement tool.
... Heat balance was estimated using partitional calorimetry (see Appendix A) and weighted mean T sk was calculated from four sites; chest (30 %), lateral mid-bicep (30 %), anterior mid-thigh (20 %) and the anterior calf (20 %). 18 LSR was recorded via ventilated capsules (4.0 cm 2 ) placed on the upper back~5 cm above the scapular spine and on the forearm~5 cm distal to the antecubital fossa. The flow of anhydrous air through each of the capsules was regulated at 500 mL·min −1 . ...
... Postexercise clothing mass was measured separately, following doffing and bagging of clothes. WBSL was corrected for respiratory and metabolic mass loss (31). Whole body sweat rate (WBSR; L·h À1 ) was calculated by dividing WBSL by exercise time. ...
... Glycogen-bound water was accepted to be associated with 3.5 g of water, as estimated across studies [18][19][20]. Respiratory water loss was quantified using equations used in [39] adapted from [40]. Gross ∆BM was determined from the net ∆BM corrected for fluid and food intake [41]. ...
The physiological, perceptual, and functional effects of dehydration may depend on how it is incurred (e.g., intense exercise releases endogenous water via glycogenolysis) but this basic notion has rarely been examined. We investigated the effects of active (exercise) heat- vs. passive heat-induced dehydration, and the kinetics of ad libitum rehydration following each method. Twelve fit participants (five females and seven males) completed four trials in randomised order: DEHydration to −3% change in body mass (∆BM) under passive or active heat stress, and EUHydration to prevent ∆BM under passive or active heat stress. In all trials, participants then sat in a temperate-controlled environment, ate a standard snack and had free access to water and sports drink during their two-hour recovery. During mild dehydration (≤2% ∆BM), active and passive heating caused comparable increases in plasma osmolality (Posm: ~4 mOsmol/kg, interaction: p = 0.138) and reductions in plasma volume (PV: ~10%, interaction: p = 0.718), but heat stress per se was the main driver of hypovolaemia. Thirst in DEHydration was comparably stimulated by active than passive heat stress (p < 0.161) and shared the same relation to Posm (r ≥ 0.744) and ∆BM (r ≥ 0.882). Following heat exposures, at 3% gross ∆BM, PV reduction was approximately twice as large from passive versus active heating (p = 0.003), whereas Posm perturbations were approximately twice as large from EUHydration versus DEHydration (p < 0.001). Rehydrating ad libitum resulted in a similar net fluid balance between passive versus active heat stress and restored PV despite the incomplete replacement of ∆BM. In conclusion, dehydrating by 2% ∆BM via passive heat stress generally did not cause larger changes to PV or Posm than via active heat stress. The heat stressors themselves caused a greater reduction in PV than dehydration did, whereas ingesting water to maintain euhydration produced large reductions in Posm in recovery and therefore appears to be of more physiological significance.
... Mechanisms responsible for the potential performance enhancement in response to HA include a faster onset of sweating and an increased sweat rate (2,11). This enables the body to better regulate temperature during exercise through enhanced heat dissipation and widening the core to skin temperature gradient even in an elevated heat environment (26). For example, increases in sweat rate can improve maximal oxygen uptake, time trial, and intermittent sprint test performance (6,11,15,16,23,24,34). ...
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.
... 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. ...
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%).
... 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. ...
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.
... 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. ...
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: ...
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 180 min (5.6 km h⁻¹, 5% grade) in a heat chamber (35°C, 30% relative humidity) broken into three segments of 50 min of exercise and 10 min 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. ...
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 : ...
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.
... Convection forcée Mitchell et al. (1972) 9-1,9 Danielson (1993) -Pva la pression partielle de vapeur d'eau de l'air expiré (Pa). ...
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.
... postexercise body mass from the pre-exercise body mass and was corrected for respiratory water loss. 27 This document is protected by international copyright laws. No additional reproduction is authorized. ...
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.
... 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). ...
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.
... 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. ...
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.
... 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 ...
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.
... 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. ...
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.
... 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. ...
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.
... MML were calculated using Eq. 6 from Mitchell et al (1972). ...
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
... 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). ...
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.
... 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. ...
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.
... 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. ...
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.
... 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. ...
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.
Women may be challenged to maintain thermoregulation due to hormonal changes associated with the menstrual cycle. The purpose of this study was to assess the effect of the menstrual cycle phase on core temperature, hydration status, and perceived exertion while exercising under uncompensable heat gain. Eleven eumenorrheic women (24.4±1.1 yrs, 65.7±2.4 kg, 22.7±1.5% body fat) walked for two 180-minute trials in a heat chamber (35ºC and 30% relative humidity) during early-follicular (EF) and mid-luteal (ML) phases. Subjects completed three intervals of 50 minutes of exercise at 50% VO2max. Physiological strain index (PSI), core temperature (TC), perceived heat (PH), and rating of perceived exertion (RPE) were measured throughout both trials. Nude body weight (NBW) and blood samples were collected pre- and post-trial. Blood samples were analyzed for hematocrit (Hct), hemoglobin (Hb), serum estrogen, progesterone, and aldosterone. NBW showed a main effect of time (p=0.002, ηp2=0.62). Aldosterone showed main effect of time (p=0.004, ηp2=0.59) and phase (p=0.014, ηp2=0.47), peaking post exercise in both EF and ML (527.6.1±89.0 pg·mL-1 vs 827.4±129.5 pg·mL-1 respectively, p=0.014). Estradiol and progesterone showed main effects of phase (p=0.007, ηp2=0.53; p=0.045, ηp2=0.30) but not time (p=0.68, p=0.32). TC showed main effect of time (p<0.001, ηp2=0.89) and phase, peaking at 170 min (EF: 37.8±0.1ºC vs. ML: 38.0±0.1 ºC, p=0.032, ηp2=0.38). Main effect of time was seen for PSI (p=0.002, ηp2=0.88), PH (p=0.004, ηp2=0.66), and RPE (p=0.026, ηp2=0.80). Sweat rate, Hct, Hb, and percent dehydration were not different between the phases. In conclusion, subjects demonstrated elevated Tc and basal aldosterone in ML corresponding with elevations in estrogen and progesterone. Aldosterone significantly increased following exercise in the heat but remained elevated in ML. These results indicate that elevated Tc during ML is maintained during exercise in the heat despite similar perceived heat and effort between phases.
To determine if using nicotine exacerbates exertional heat strain through an increased metabolic heat production (H prod ) or decreased skin blood flow (SkBF), ten nicotine-naïve trained males (37±12 y; VO 2 peak: 66±10 ml·min ⁻¹ ·kg ⁻¹ ) completed four trials at 20°C and 30°C following overnight transdermal nicotine (7mg·24h ⁻¹ ) and placebo use in a crossover, double-blind design. They cycled for 60 min (55% VO 2 peak) followed by a time-trial (~75% VO 2 peak) during which measures of gastro-intestinal (T gi ) and mean weighted skin ( sk ) temperatures, SkBF, H prod , and mean arterial pressure (MAP) were made. The difference in ∆T gi between nicotine and placebo trials was greater during 30°C (0.4±0.5°C) than 20°C (0.1±0.7°C), with sk higher during nicotine than placebo trials (0.5±0.5°C, p=0.02). SkBF became progressively lower during nicotine than placebo trials ( p=0.01) and progressively higher during 30°C than 20°C trials ( p<0.01); MAP increased from baseline ( p<0.01) and remained elevated in all trials. The difference in H prod between 30°C and 20°C trials was lower during nicotine than placebo ( p=0.01) and became progressively higher during 30°C than 20°C trials with exercise duration ( p=0.03). Mean power output during the time-trial was lower during 30°C than 20°C trials (24±25 W, p=0.02), and although no effect of nicotine was observed ( p>0.59) two participants (20%) were unable to complete their 30°C nicotine trials as one reached the ethical limit for T gi (40.0°C) whilst the other withdrew due to "nausea and chills" (T gi =39.7°C). These results demonstrate that nicotine use increases thermal strain and risk of exertional heat exhaustion by reducing SkBF.
Purpose: To investigate the influence of biological sex, independent of differences in aerobic fitness and body fatness, on the change in gastro-intestinal temperature (∆T gi ) and whole-body sweat rate (WBSR) of children exercising under uncompensable heat stress. Methods: Seventeen boys (mean±SD; 13.7±1.3 years) and 18 girls (13.7±1.4) years) walked for 45 min at a fixed rate of metabolic heat production per kg body mass (8 W·kg ⁻¹ ) in 40°C and 30% relative humidity. Sex and V̇O 2peak were entered into a Bayesian hierarchical general additive model (HGAM) for T gi . Sex, V̇O 2peak and the evaporative requirement for heat balance (E req ) were entered into a Bayesian hierarchical linear regression for WBSR. For 26 (12 M, 14 F) of the 35 children with measured body composition, body fat percentage was entered in a separate HGAM and hierarchical linear regression for T gi and WBSR respectively. Results: Conditional on sex-specific mean V̇O 2peak , ∆T gi was 1.00°C [90% credible intervals: 0.84, 1.16] for boys and 1.17°C [1.01, 1.33] for girls, with a difference of 0.17°C [-0.39, 0.06]. When sex differences in V̇O 2peak were accounted for, the difference in ∆T gi between boys and girls was 0.01°C [-0.25, 0.22]. The difference in WBSR between boys and girls was 0.03 L·h ⁻¹ [-0.02, 0.07], when isolated from differences in E req . The difference in ∆T gi between boys and girls was -0.10°C [-0.38, 0.17] when sex differences in body fat (%) were accounted for. Conclusion: Biological sex did not independently influence the ∆T gi and WBSR of children exercising under uncompensable heat stress.
Description
80 peer-reviewed papers address these issues:
• Hazards and Methods (including aerosols, physical resistance, biological, chemical, pesticides, and thermal and heat)
• Field tests, New tests, Evaluations, Design, Physiological, Performance (including field tests, new and improved tests, evaluations, physiological, ergonomical, design, evaluation, and performance, decontamination)
• Programsand Assessments (including program, selection, assessments, business)
• International standards
In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.
INTRODUCTION: Aerobic exercise within the habitable volume of small spacecraft needed for space exploration beyond low Earth orbit is expected to challenge the capacity of environmental control systems. Moisture control is a primary concern. Crewmembers will contribute moisture to the cabin environment in the form of sweat while exercising. The effects of continuous aerobic exercise for improving and maintaining aerobic capacity is well characterized. Likewise, evidence suggests that high intensity interval exercise for shorter durations is also effective in building and maintaining aerobic capacity.
METHODS: On separate days, measures of sweat and respiratory responses were made for continuous (30 min of steady state exercise at ∼75% of aerobic capacity) and two interval (4 × 4 min, 8 × 30 s) exercise protocols.
RESULTS: We observed that the 4-min and 30-s interval protocols produce 16% and 66% less metabolic water loss vs. the continuous exercise protocol, respectively. These responses were highly correlated with the amount of work performed (R ² = 0.81) and the amount of energy expenditure (R ² = 0.83) during exercise.
DISCUSSION: These results suggest that interval exercise may be a useful alternative to continuous aerobic exercise when metabolic water production is an environmental concern. The results may inform the choices of aerobic exercise countermeasure protocols for use in deep space exploration.
Ryder JW, Crowell JB, Song HJ, Ewert M. Sweat production during continuous and interval aerobic exercise . Aerosp Med Hum Perform. 2023; 94(8):623–628.
Sportswear worn next to the skin is easily soaked by sweat and may become a breeding ground for the microbiome, thus a source of malodor. Malodor can cause social embarrassment and discomfort to both wearer and others. Given the risks current deodorant products pose to nature and human life, the development of sustainable textiles for odor control comes to the forefront. This review introduces the odor-generating mechanism in clothing from the perspectives of perspiration composition and cutaneous microbiome. With the knowledge of the significant role of sweat in odor formation, the sweat distribution of the human body, measurement techniques, and advanced technologies developed for quick-dry function are presented in the second part. Lastly, odor management in sportswear is evaluated, covering the odor-assessing techniques, the effects of various textile materials, and emerging solutions in terms of antibacterial treatment, adsorbent materials, and photocatalytic degradations of odorous compounds. Overall, it is of both personal and social value to develop novel textile materials with odor-control functions by making use of natural materials and fabric designs.
Rodriguez, C, Florez, CM, Prather, J, Zaragoza, J, Tinnin, M, Brennan, KL, Taylor, L, and Tinsley, GM. Influence of upper-extremity and lower-extremity resistance exercise on segmental body composition and body fluid estimates. J Strength Cond Res XX(X): 000-000, 2022-The purpose of this analysis was to determine if acute, localized resistance exercise (RE) artificially influences total and regional estimates of body composition from dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA). Recreationally active male (n = 14) and female (n = 18) subjects completed 3 testing visits: rest (R), upper-extremity RE (U), and lower-extremity RE (L). Dual-energy X-ray absorptiometry scans were completed before exercise and 60 minutes after exercise. Bioelectrical impedance analysis was completed immediately before and after exercise and at 15, 30, and 60 minutes after exercise. Subjects were not allowed to intake fluid during the exercise session or during the postexercise assessment period. The effects of the acute RE session on DXA and BIA estimates were analyzed using linear mixed-effects models with a random intercept for subject. Condition by time interactions were observed for most BIA outcomes. Relative to the reference model (i.e., R condition at baseline), total body water and fat-free mass estimates were, on average, approximately 1 and approximately 1.2 kg higher, in the U condition. In contrast, lower-extremity RE exerted little or no impact on most BIA variables. Some DXA estimates exhibited time main effects, but the magnitude of changes was negligible. An acute bout of localized RE, particularly upper-extremity RE, can artificially influence BIA body fluid and composition estimates, whereas DXA may be robust to the acute biological error introduced by RE. Although body composition assessments should ideally be conducted under standardized conditions, DXA may be suitable in less standardized situations. In addition, BIA is differentially influenced by upper-extremity and lower-extremity resistance exercise.
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.
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.
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.
Water is critical to human health, serving multiple roles as a biochemical solvent and reactant for cellular metabolism, medium for substance exchange between tissues, and support for the circulatory system. Survival mechanisms for acquiring and conserving water to maintain cellular homeostasis and circulatory integrity have evolved in many mammals. Humans regulate body water balance remarkably well as a result of these survival mechanisms and also because food and fluid are commonly abundant. An adequate fluid intake is sufficient to replace body water losses and provide for dietary and metabolic solute excretion. Adequacy therefore depends on wide variations in physical activity and diet. Acute or chronic body water deficits do sometimes occur, most often with eccrine sweating from exercise and heat stress or gastrointestinal losses from illness. Negative effects of acute dehydration on body systems that support physical and mental performance and health are well recognized; effects of chronic dehydration on health are less clear.
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.
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:
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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.
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.
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.
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.
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