Respiratory water losses during exercise

ArticleinJournal of applied physiology 32(4):474-6 · May 1972with 210 Reads
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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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  • Article
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  • Article
    Thermoregulatory responses during one hour of pedalling on a bicycle ergometer were measured in a climatic chamber of 26°C at various humidity levels. Work intensities were 30, 40, 50, 60 and 70% of VO2max. Relative humidities were 30, 60, and 90%. Oxygen intake remained nearly constant at the same work load and was not influenced by humidity level. At work intensities of more than 60% of VO2max, the elevation of rectal temperature was augmented by increased humidity. The secretion of sweat increased, but the evaporation of sweat decreased with increased humidity, particularly at work intensities of 60% and 70% of VO2max.
  • Article
    This study sought to assess the within-subject influence of acute hypoxia on exercise-induced changes in core temperature and sweating. Eight participants [1.75 (0.06) m, 70.2 (6.8) kg, 25 (4) y, 54 (8) mL(.)kg(-1)(.)min(-1)] completed 45 min of cycling, once in normoxia (NORM; FiO2=0.21) and twice in hypoxia (HYP1/HYP2; FiO2=0.13) at 34.4(0.2)°C, 46(3)% RH. These trials were designed to elicit a) two distinctly different %VO2peak [NORM:45(8)% and HYP1:62(7)%] at the same heat production (Hprod) [NORM:6.7(0.6) W(.)kg(-1) and HYP1:7.0(0.5) W(.)kg(-1)]; and b) the same %VO2peak[NORM:45(8)% and HYP2:48(5)%] with different Hprod [NORM:6.7(0.6) W(.)kg(-1) and HYP2:5.5(0.6) W(.)kg(-1)]. At a fixed %VO2peak, changes in rectal temperature (∆Tre) and changes in esophageal temperature (∆Tes) were greater at end-exercise in NORM [∆Tre:0.76(0.19)°C; ∆Tes:0.64(0.22)°C] compared to HYP2 [∆Tre:0.56(0.22)°C, P<0.01; ∆Tes:0.50(0.30)°C, P<0.01]. As a result of a greater Hprod (P<0.01) in normoxia, and therefore evaporative heat balance requirements, in order to maintain a similar %VO2peak compared to hypoxia, mean local sweat rates (LSR) from the forearm, upper back, and forehead were greater (all P<0.01) in NORM [1.10(0.20) mg(.)cm(-2)(.)min(-1)] compared to HYP2 [0.71(0.19) mg(.)cm(-2)(.)min(-1)]. However, at a fixed Hprod, ∆Tre [0.75(0.24)°C; P=0.77] and ∆Tes [0.63(0.29)°C; P=0.69] were not different in HYP1, compared to NORM. Likewise, mean LSR [1.11(0.20) mg(.)cm(-2)(.)min(-1)] was not different (P=0.84) in HYP1 compared to NORM. These data demonstrate, using a within-subjects design, that hypoxia does not independently influence thermoregulatory responses. Additionally, further evidence is provided to support that metabolic heat production, irrespective of %VO2peak, determines changes in core temperature and sweating during exercise.
  • Chapter
    Spinal cord injury (SCI) results in thermoregulatory impairment related to the disruption in autonomic function. As a result, body core temperature generally increases at a greater rate during exercise in individuals with SCI compared to their able-bodied counterparts, placing them at elevated risk for heat-related illnesses. These effects are exacerbated during exercise in the heat. Conversely, body core temperature may decrease at a greater rate during exercise in cold environments. In this chapter, we first briefly describe the anatomy and physiology of normal (non-disrupted) thermoregulation. Next, we present evidence demonstrating that SCI results in impaired thermoregulation both at rest and during exercise. We then discuss the mechanisms behind why these impairments occur, particularly in terms of how disruptions in the sympathetic nervous system affect the various arms of the thermoregulatory negative feedback loop. Next, we discuss how the types of exercise available to individuals with SCI may present additional challenges to thermoregulation, and finally, we present strategies currently in use or under investigation for combatting these thermoregulatory challenges.
  • 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.
  • 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).
  • 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.
  • 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.
  • 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.
  • 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.
  • Article
    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.
  • 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.
  • Article
    Full-text available
    Athletes lose water and electrolytes as a consequence of thermoregulatory sweating during exercise and it is well known that the rate and composition of sweat loss can vary considerably within and among individuals. Many scientists and practitioners conduct sweat tests to determine sweat water and electrolyte losses of athletes during practice and competition. The information gleaned from sweat testing is often used to guide personalized fluid and electrolyte replacement recommendations for athletes; however, unstandardized methodological practices and challenging field conditions can produce inconsistent/inaccurate results. The primary objective of this paper is to provide a review of the literature regarding the effect of laboratory and field sweat-testing methodological variations on sweating rate (SR) and sweat composition (primarily sodium concentration [Na+]). The simplest and most accurate method to assess whole-body SR is via changes in body mass during exercise; however, potential confounding factors to consider are non-sweat sources of mass change and trapped sweat in clothing. In addition, variability in sweat [Na+] can result from differences in the type of collection system used (whole body or localized), the timing/duration of sweat collection, skin cleaning procedure, sample storage/handling, and analytical technique. Another aim of this paper is to briefly review factors that may impact intra/interindividual variability in SR and sweat [Na+] during exercise, including exercise intensity, environmental conditions, heat acclimation, aerobic capacity, body size/composition, wearing of protective equipment, sex, maturation, aging, diet, and/or hydration status. In summary, sweat testing can be a useful tool to estimate athletes’ SR and sweat Na+ loss to help guide fluid/electrolyte replacement strategies, provided that data are collected, analyzed, and interpreted appropriately.
  • 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.
  • 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
    Full-text available
    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
  • 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.
  • Article
    To study some physiological reactions and the thermal sensation during exercise under wind at various air temperatures, five healthy male subjects, dressed in shorts, were exposed to a work load of bicycle ergometer pedalling (50 rpm) at fifty percent of VO2max for thirty minutes. The room conditions were set at three different ambient temperatures: 20, 25 and 300°C, under two wind velocities: 0.1 m/s and 5.0 m/s. The results were as follows; 1) Increase of the heart rate during exercise under 5.0 m/s wind was inhibited with a fall of the air temperature. 2) With the increase of the air velocity, a rise of the rectal temperature during exercise at 20°C became smaller. 3) During exercises under 0.1 m/s and 5.0 m/s wind velocities, the relations between the rectal temperature and the thermal sensation were observed. 4) It was shown that the local and the total thermal sweating rates during exercises under 0.1 m/s wind at 20 and 25°C decreased due to 5.0 m/s wind, although they did not at 30°C. 5) Thermal sweating was caused when the degree of thermal sensation was equivalent to“Slightly warm”.
  • Article
    An experiment was carried out with the objective of clarifying the impact on heat stress when covering the extremities with clothing during exercise, at a wet bulb globe temperature (WBGT) of greater than 28°C in a radiant environment. Seven male subjects performed three 20 min sessions of cycling exercise at a load intensity of either 20% or 50% of their maximal oxygen uptake (VO2max) in a room maintained at a WBGT of 28.3±0.1°C using two spot lights, while either wearing long sleeves and long pants (“L” conditions) or short sleeves and shorts (“S” conditions). As a result, no significant difference between clothing conditions was noted at 20% or 50% exercise in esophageal temperature, mean skin temperature (Tsk), mean body temperature, temperature and moisture in clothing, total sweat loss, thermal sensation or the rating of perceived exertion during the second half of exercise. However, the level of increase in Tsk (ΔTsk) and the skin temperature of the upper arms, forearms and calfs under L condition were significantly lower than those measured under S conditions at both 20% and 50% exercise, and the heart rate was also significantly lower under L conditions than under S conditions at 20% exercise. Consequently, no significant difference was noted in the heat stress caused by middle-level of exercise at a WBGT of greater than 28°C in a radiant environment between the subjects with their four limbs exposed and those without; however, during light exercise, covering all four limbs with clothing attenuated the increase in skin temperature and heart rate, thus suggesting that this may potentially reduce the heat stress on the body.
  • Article
    Full-text available
    Individuals with systemic arterial hypertension have a higher risk of heat-related complications. Thus, the aim of this study was to examine the thermoregulatory responses of hypertensive subjects during recovery from moderate-intensity exercise performed in the heat. A total of eight essential hypertensive (H) and eight normotensive (N) male subjects (age=46.5±1.3 and 45.6±1.4 years, body mass index=25.8±0.8 and 25.6±0.6 kg/m2, mean arterial pressure=98.0±2.8 and 86.0±2.3 mmHg, respectively) rested for 30 min, performed 1 h of treadmill exercise at 50% of maximal oxygen consumption, and rested for 1 h after exercise in an environmental chamber at 38°C and 60% relative humidity. Skin and core temperatures were measured to calculate heat exchange parameters. Mean arterial pressure was higher in the hypertensive than in the normotensive subjects throughout the experiment (P<0.05, unpaired t-test). The hypertensive subjects stored less heat (H=-24.23±3.99 W·m-2vs N=-13.63±2.24 W·m-2, P=0.03, unpaired t-test), experienced greater variations in body temperature (H=-0.62±0.05°C vsN=-0.35±0.12°C, P=0.03, unpaired t-test), and had more evaporated sweat (H=-106.1±4.59 W·m-2vs N=-91.15±3.24 W·m-2, P=0.01, unpaired t-test) than the normotensive subjects during the period of recovery from exercise. In conclusion, essential hypertensive subjects showed greater sweat evaporation and increased heat dissipation and body cooling relative to normotensive subjects during recovery from moderate-intensity exercise performed in hot conditions.
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