Sweat Onset Time Research Articles

Coffee intake may promote sudomotor function activation via the contribution of caffeine.

To determine whether drinking coffee with caffeine accelerates the sympathetic response to acetylcholine (ACh). Tests were performed twice at 1-week intervals following the intake of coffee. Subjects were randomly divided into two groups: Group A was administered 16 fluid oz of water (CON), while Group B was given 16 fluid oz of coffee (Coffee). After 1 week, Group A was administered 16 fluid oz of coffee (Coffee), while Group B was given 16 fluid oz of water (CON). The quantitative sudomotor axon reflex test (QSART) was performed after intake of coffee and water and a 40 min break. QSART with iontophoresis and 10% ACh was performed to determine axon reflex (AXR) mediated with and without iontophoresis [AXR (1) and AXR (2), respectively], and directly activated sweating (DIR). The sweat onset time of the AXR was shorter in the Coffee compared with the CON (p < 0.05). The sweat rates in AXR (1) AXR (2) and DIR were significantly higher in the Coffee than in the CON (p < 0.05, p < 0.05, p < 0.01, respectively). In addition, the Coffee showed significantly higher density of activated sweat glands and activated sweat gland output than the CON (p < 0.05, p < 0.01, respectively). The overall results of this study showed that coffee intake could stimulate higher activation in both AXR and DIR sweat responses. Coffee intake can improve sweating sensitivity in both the AXR and DIR by the contribution of caffeine contained in coffee. This suggests that other compounds in coffee may not inhibit the sympathetic response to ACh. Therefore, coffee may be clinically worth considering as a supplement for the activation of the cholinergic and sudomotor function.

Predicting The Onset Of Sweat During Cycling In Simulated Environments

E-bikes have become a growing alternative to traditional bikes. E- bikes are often used for transportation to and from the workplace, thus, in the initiative to promote adoption, advanced features such as appropriate assistance to eliminate the onset of sweat would be appealing to most users. PURPOSE: To provide a starting point for the development of a regression equation that can predict sweat onset. METHODS: Ten participants volunteered for this study. Participants committed to 5 experimental cycling sessions that varied by workload and climate. Participants cycled on an indoor bike trainer at 2 power outputs (25W and 75W) and 2 climatic conditions (25°C @ 60% RH and 30°C @ 60% RH) until sweating commenced. Physiological measures included: electromyography, heart rate, skin temperature, core temperature, galvanic skin response, and VO2. RESULTS: The average subjective sweat onset time for the 75W condition was less effected by the climatic condition than the 25W condition. The subjective sweat onset times for the 75W condition was 8.53 ± 2.19 minutes and 5.83 ± 1.44 minutes for the low and high temperatures, respectively. The subjective sweat onset times for the 25W condition was 23.52 ± 7.40 minutes and 12.49 ± 7.08 minutes for the low and high temperatures, respectively. A regression equation was developed and is able to predict subjective sweat onset with 61.5% of the variance explained with two measured variables. Workload alone explained 41.5% of the variance for sweat onset determination. When the regression was designed with workload as the outcome instead of sweat onset time, subjective sweat onset time was able to predict wattage with 40.1% of the variance explained. CONCLUSION: For the conditions simulated in this study, external temperature had less of an influence on sweat onset times than cycling workload. Sweat onset can be predicted with 61.5% of the variance explained using only two input variables. Heart rate was a poor indicator of sweat onset and simply using power output would be a better starting point. Overall, workload proved to be the most influential variable for predicting sweat onset. This project was funded by the Natural Sciences and Engineering Research Council Engage Grant

Decreased thermal sweating of central sudomotor mechanism in African and Korean men.

Tropical natives sweat less and preserve more body fluid than temperate natives, tolerating heat stress. However, the mechanisms involved in such sweating reduction have not been fully elucidated. We examined the sudomotor responses of men of African (n = 36) and Korean (n = 41) ancestry during hot water (43 °C) leg immersion (central sudomotor response). Correlations between mean body temperature, basal metabolic rate (BMR), and sweat rate were also examined. All procedures were done in an automated climate chamber. Local skin temperatures and BMR were measured and mean body temperature was calculated. Sweating activities which include evaporative loss rate, sweat onset time, sweat rate, sweat volume, and whole-body sweat loss volume were examined. In the heat load test, Africans showed lower mean body and local skin temperatures than Koreans before and after heating. Before and after heating, BMR declined significantly in Africans, while that of Koreans declined less. Local sweat onset time increased more in Africans than in Koreans. Local evaporative loss rate, local sweat volume, local sweat rate, and whole body sweat loss volume were reduced in Africans compared with Koreans. There were positive associations of mean body temperature and resting BMR with mean sweat rate. In conclusion, we observed a larger reduction of sudomotor activity in tropical Africans than in temperate Koreans, which was associated with their lower mean body temperature and lower resting BMR.

Effect of Intensive and Repetitive Heat Exposure on the Sudomotor Activity

The sweating response is modulated in two different ways depending on adaptation conditions. In this work, we examined sudomotor activities before and after intensive and repetitive heat exposure. Nine male volunteers were exposed to 30-min half-body immersion in hot water (42 ± 0.5°C) at the same time of day on alternate days for 3 weeks. All experiments were performed in an automated climate chamber. Tympanic (Tty) and skin (Ts) temperatures were measured. Mean body temperature (mTb) was calculated. Sudomotor activities, including sweat onset time, sweat rate and volume, activated sweat gland density (ASGD) and output (ASGO), were tested in four regions of the skin: chest, abdomen, upper back and thigh. Basal Tty and mTb were found to decrease by 0.15°C (P < 0.05) and 0.16°C (P < 0.05), respectively. As a typical data (upper back), sweat onset time increased by 33.6% (P < 0.05) after heat acclimation. After heat acclimation, sweat rate decreased by 14.7% (P < 0.05), sweat volume decreased by 15.5% (P < 0.05) and ASGO also decreased by 11.1% (P < 0.05). ASGD decreased by 4.1% after heat acclimation without statistical significance. The data suggest that intensive and repetitive heat exposure induces suppression of sudomotor activities within 3 weeks.

Seasonal acclimation in sudomotor function evaluated by QSART in healthy humans.

The quantitative sudomotor axon reflex testing (QSART) is a classic test of routine postganglionic sudomotor function. We investigated sudomotor function by QSART after summer (July 2012) and winter (January 2013) seasonal acclimation (SA) in the Republic of Korea. QSART with acetylcholine (ACh) iontophoresis were performed to determine directly activated (DIR) and axon reflex-mediated (AXR1, 2) sweating rate. Onset time of axon reflex, activated sweat gland density (ASGD), activated sweat gland output (ASGO), tympanic and skin temperatures (Tty, Tsk), basal metabolic rate (BMR), and evaporative loss volume changes were measured. Tympanic and mean body temperature (Tb; calculated from Tty, Tsk) were significantly lower after summer-SA than that of winter-SA. Sweat onset time was delayed during winter-SA compared to that after summer-SA. BMR, AXR(1), AXR(2), and DIR sweat rates, ASGD and ASGO, and evaporative loss volume were significantly diminished after winter-SA relative to after summer-SA. In conclusion, changes in sweating activity measured by QSART confirmed the involvement of the peripheral nervous system in variation of sudomotor activity in seasonal acclimation.

Improved sweat gland function during active heating in tennis athletes

BackgroundRelatively few studies on the peripheral sweating mechanisms of trained tennis athletes have been conducted. The purpose of this study was to compare the sweating capacities of tennis athletes against untrained subjects (controls). MethodsThirty-five healthy male volunteers participated including 15 untrained subjects and 20 trained tennis athletes (nationally ranked). Active heat generation was performed for 30 min (running at 60%VO2max) in a climate chamber (temperature, 25.0°C ± 0.5°C; relative humidity, 60% ± 3%, termed active heating). Sweating data (local sweat onset time, local sweat volume, activated sweat glands, sweat output per gland, whole body sweat loss volume) were measured by the capacitance hygrometer-ventilated capsule method and starch-iodide paper. Mean body temperature was calculated from tympanic and skin temperatures. ResultsLocal sweat onset time was shorter for tennis athletes (p < 0.001). Local sweat volume, activated sweat glands of the torso and limbs, sweat output per gland, and whole body sweat loss volume were significantly higher for tennis athletes than control subjects after active heating (p < 0.001). Tympanic and mean body temperatures were lower among tennis athletes than controls (p < 0.05). ConclusionThese results indicate that tennis athletes had increased regulatory capacity of their sweat gland function.

Seasonal Acclimatization in Summer versus Winter to Changes in the Sweating Response during Passive Heating in Korean Young Adult Men.

We investigated the sweating response during passive heating (partial submersion up to the umbilical line in 42±0.5℃ water, 30 min) after summer and winter seasonal acclimatization (SA). Testing was performed in July during the summer, 2011 [summer-SA; temp, 25.6±1.8℃; relative humidity (RH), 82.1±8.2%] and in January during the winter, 2012 (winter-SA; temp, -2.7±2.9℃; RH, 65.0±13.1%) in Cheonan (126°52'N, 33.38'E), Republic of Korea. All experiments were carried out in an automated climatic chamber (temp, 25.0±0.5℃: RH, 60.0±3.0%). Fifteen healthy men (age, 23.4±2.5 years; height, 175.0±5.9 cm; weight, 65.3±6.1 kg) participated in the study. Local sweat onset time was delayed during winter-SA compared to that after summer-SA (p< 0.001). Local sweat volume, whole body sweat volume, and evaporative loss volume decreased significantly after winter-SA compared to those after summer-SA (p<0.001). Changes in basal metabolic rate increased significantly after winter-SA (p< 0.001), and tympanic temperature and mean body temperature were significantly lower after summer-SA (p<0.05). In conclusion, central sudomotor acitivity becomes sensitive to summer-SA and blunt to winter-SA in Rebubic of Korea. These results suggest that the body adjusts its temperature by economically controlling the sweating rate but does not lower the thermal dissipation rate through a more effective evaporation scheme after summer-SA than that after winter-SA.

Beneficial effect of Oligonol supplementation on sweating response under heat stress in humans.

Oligonol is a low-molecular weight polyphenol that possesses antioxidant and anti-inflammatory properties. However, nothing is known regarding the impact of Oligonol on sudomotor activity. This study investigated the effects of Oligonol supplementation on sudomotor activity during heat load in humans. Initially, we conducted a placebo-controlled, cross-over trial where participants took a daily dose of Oligonol 200 mg or placebo for one week. After a 2 week washout period, the subjects were switched to the other study arm. As a heat load, half-body immersion into hot water (42 ± 0.5 °C for 30 min) was performed in an automated climate chamber. Tympanic and skin temperatures were measured. Sudomotor activity, including onset time, sweat rate (SR) and volume (SV), active sweat gland density (ASGD), and sweat gland output (SGO), was tested in four or eight areas of skin. When compared with placebo, Oligonol attenuated increases in tympanic and skin temperatures after the heat load. There was an increasing trend in local sweat onset time, but there was a decrease in local SR, SV, ASGD, and SGO for Oligonol compared to placebo. The mean ASGD was significantly higher in the Oligonol group than in the placebo group for 10, 20, and 30 min. This study demonstrates that Oligonol appears to be worthy of consideration as a natural supplement to support more economical use of body fluids against heat stress.

Long Distance Runners Present Upregulated Sweating Responses than Sedentary Counterparts

Relatively few studies have investigated peripheral sweating mechanisms of long-distance runners. The aim of this study was to compare peripheral sweating mechanisms in male long-distance runners, and sedentary counterparts. Thirty six subjects, including 20 sedentary controls and 16 long-distance runners (with 7–12 years of athletic training, average 9.2±2.1 years) were observed. Quantitative sudomotor axon reflex testing (QSART) with iontophoresis (2 mA for 5 min) and 10% acetylcholine (ACh) were performed to determine axon reflex-mediated and directly activated (DIR, muscarinic receptor) sweating. Sweat onset time, sweat rate, number of activated sweat glands, sweat output per gland and skin temperature were measured at rest while maximum oxygen uptake (VO2max) were measured during maximal cycling. Sweat rate, activated sweat glands, sweat output per gland, skin temperature and VO2max were significantly higher in the trained runners than in the sedentary controls. Sweat onset time was significantly shorter for the runners. In the group of long-distance runners, significant correlations were found between VO2max and sweat onset time (r2 = 0.543, P<0.01, n = 16), DIR sweat rate (r2 = 0.584, P<0.001, n = 16), sweat output per gland (r2 = 0.539, P<0.01, n = 16). There was no correlation between VO2max and activated sweat glands. These findings suggest that habitual long-distance running results in upregulation of the peripheral sweating mechanisms in humans. Additional research is needed to determine the molecular mechanism underlying these changes. These findings complement the existing sweating data in long-distance runners.

Seasonal acclimatization to the hot summer over 60 days in the Republic of Korea suppresses sweating sensitivity during passive heating

The main objective of this study was to determine the central mechanisms involved in suppression of thermal sweating after seasonal acclimatization (SA) during passive heating (immersing the legs in 43°C hot water for 30min). Testing was performed in July (before-SA) and August (after-SA) [25.2±2.2°C, 73.9±10.3% relative humidity (RH), Cheonan (Chungnam,126° 52′N, 33.38′E), in the Republic of Korea. All experiments were carried out in an automated climatic chamber (25.0±0.5°C and RH 60.0±3.00%). Twelve healthy men (height, 174.6±5.40cm; weight, 65.4±5.71kg; age, 22.7±2.90yr) participated. The local sweat onset time was delayed in the after-SA compared to that in the before-SA (p<0.001). The local sweat rate and whole body sweat loss volume decreased in the after-SA compared to those in the before-SA (p<0.001). In addition, evaporative loss volume decreased significantly in the after-SA compared to that in the before-SA [chest, upper-back, thigh and forearm (p<0.001)]. Changes in tympanic temperature and mean body temperature were significantly lower (p<0.05) and the basal metabolic rate decreased significantly in the after-SA compared to those in the before-SA (p<0.001). These results suggest that maintenance of a lower body temperature and basal metabolic rate can occur and blunt the central sudomotor mechanisms following seasonal acclimatization, which suppresses sweating sensitivity.

Biological variation of local sweating measures during exercise‐heat stress in heat acclimated humans

Local sweat rate (SR) and sweat onset time (SO) can be altered by numerous factors, but the importance of the effect magnitude is uncertain due to poorly characterized components of biological variation in thermoregulatory sweating. Purpose to determine the analytical variation (CVa), individual variation (CVi), group variation (CVg) and bilateral differences of local SR and SO. After completing a heat acclimation program, 2 women and 8 men (26 ± 9 yrs; 79 ± 12 kg) walked (645 watts) on 3 separate occasions, for 30 min in 40°C, 20% rh, while local SR and SO were measured via dew point hygrometry. Hydration and diurnal effects were carefully controlled. SR (2.14 ± 0.72 vs. 2.02 ± 0.79 vs. 2.31 ± 0.72 mg/cm2/min, p=0.19) and SO (10.04 ± 2.97 vs. 9.87 ± 3.44 vs. 10.47 ± 2.54 min, p=0.82) were not different among days. SR (2.14 ± 0.72 vs. 2.16 ± 0.71 mg/cm2/min, p=0.56) and SO (10. 47 ± 2.54 vs.10.83 ± 2.48 min, p=0.09) were not different between arms. CVa of ≤5% is considered optimum for laboratory analytics. CVa, CVi and CVg were 2.4%, 18.8% and 56.4% for SR and 0%, 9.6% and 41% for SO, respectively. Data suggests that ventilated capsules have low imprecision. In heat acclimated humans, both SR and SO measures appear interchangeable between arms. Lower variation within SO suggests greater sensitivity vs. SR when studying factors that potentially affect sweating. Opinions should not to be construed as official views of the Army or DoD.

Tropical Malaysians and temperate Koreans exhibit significant differences in sweating sensitivity in response to iontophoretically administered acetylcholine

Natives of the tropics are able to tolerate high ambient temperatures. This results from their long-term residence in hot and often humid tropical climates. This study was designed to compare the peripheral mechanisms of thermal sweating in tropical natives with that of their temperate counterparts. Fifty-five healthy male subjects including 20 native Koreans who live in the temperate Korean climate (Temperate-N) and 35 native tropical Malaysian men that have lived all of their lives in Malaysia (Tropical-N) were enrolled in this study after providing written informed consent to participate. Quantitative sudomotor axon reflex testing after iontophoresis (2 mA for 5 min) with 10% acetylcholine (ACh) was used to determine directly activated (DIR) and axon reflex-mediated (AXR) sweating during ACh iontophoresis. The sweat rate, activated sweat gland density, sweat gland output per single gland activated, and oral and skin temperature changes were measured. The sweat onset time of AXR (nicotinic-receptor-mediated) was 56 s shorter in the Temperate-N than in the Tropical-N subjects (P < 0.0001). The nicotinic-receptor-mediated sweating activity AXR (1), and the muscarinic-receptor-mediated sweating activity DIR, in terms of sweat volume, were 103% and 59% higher in the Temperate-N compared to the Tropical-N subjects (P < 0.0001). The Temperate-N group also had a 17.8% (P < 0.0001) higher active sweat gland density, 35.4% higher sweat output per gland, 0.24 degrees C higher resting oral temperature, and 0.62 degrees C higher resting forearm skin temperature compared to the Tropical-N subjects (P < 0.01). ACh iontophoresis did not influence oral temperature, but increased skin temperature near where the ACh was administered, in both groups. These results suggest that suppressed thermal sweating in the Tropical-N subjects was, at least in part, due to suppressed sweat gland sensitivity to ACh through both recruitment of active sweat glands and the sweat gland output per each gland. This physiological trait guarantees a more economical use of body fluids, thus ensuring more efficient protection against heat stress.

Heat Adaptation of Tropic-Dwelling People

Adaptation to heat can be acquired through natural or artificial climatic stimuli. As compared to temperate natives, tropical natives have delayed onset of sweating. The sweat onset time tends to decrease with longer duration of stay in temperate zone and lower sodium concentration in sweat. The local amount of evaporation is significantly lower at the lower part of the sub scapular region associated with of higher mean skin temperature (Tsk) and rectal temperature (Tre) during rest, exercise and recovery period in the heat. The set-point of the core temperature is at a higher level in tropical natives. The heat-activated sweat gland density (HASG) is significantly lower at resting levels, and sweat gland density is lower associated with smaller output per single gland. The reduced amount of evaporation rate and delayed onset of sweating in the tropical natives is due to their higher Tsk, which accelerated dry heat loss with a reduction of the rate of sweating as a result significantly lower in dehydration. Tropic-dwelling subjects, although exposed to prolonged passive heat exposure, are not fully heat acclimatized. To achieve further heat acclimation, they need to gradually expose themselves to exercise-heat stress in a hot environment. This may be important for athletes either from tropical or temperate areas who will participate in events all over the world, in different climatic conditions. Environmental adaptation may be relevant in every event. Athletes should undergo re-acclimatization before competition to reduce the adverse effects of environmental temperature change.

Prolonged residence of temperate natives in the tropics produces a suppression of sweating

Tropical natives possess heat tolerance due to the ability to off-load endogenous and exogenous heat efficiently using a minimum amount of sweat. On the other hand, exposure of temperate natives to heat results in exaggerated production of sweat, of which part is lost by dripping and, thus, not available for evaporation. How sweating is modified in natives of temperate climate zones by prolonged residence in the tropics is not well-understood. The aim of this study was to investigate possible changes in the peripheral sweating mechanisms. Sweating responses to iontophoretically applied acetylcholine (ACh) were compared between Japanese subjects having either permanently resided in Japan (Japan resident Japanese, JRJ) or having stayed in the tropics for 2 years or longer (Tropics resident Japanese, TRJ). Quantitative sudomotor axon reflex tests by iontophoresis of ACh (10%, 2 mA for 5 min) were applied to determine directly activated (DIR) and axon reflex-mediated sweating during [AXR(1)] and after [AXR(2)] ACh iontophoresis. The sweat onset time of AXR(1) was 0.6 min shorter in JRJ than in TRJ (P<0.0001), and AXR(1) (P<0.0004), AXR(2) (P<0.0001), and DIR (P<0.0001) sweating responses were larger in JRJ than in TRJ. AXR and DIR sweating volumes (P<0.0001) were negatively correlated, and sweat onset times (P<0.0001) were positively correlated with the duration of residence in the tropics (2 to 13 years). The observed attenuation of sweating in TRJ suggests that temperate natives may acquire heat tolerance with improved sweating economy similar to tropical natives after prolonged residence in the tropics.

The change in peripheral sweating mechanisms of the tropical Malaysian who stays in Japan

Tropical subjects regulate core temperature with less amount of sweat against heat compared to temperate subjects through long-term heat-acclimatization. The purpose of the study is to determine whether acclimatization in tropical subjects decay during a stay in temperate area. The aim of this study, therefore, was to investigate the possible changes in the peripheral sweating mechanisms. Local sweating response activated by acetylcholine (ACh) applied iontophoretically among Malaysians with varying duration of stay in Japan and Japanese resident subjects. Directly activated (DIR) and axon reflex (AXR)-mediated sweating during ACh iontophoresis were measured by capacitance hygrometer (quantitative sudomotor axon reflex test, QSART) QSART was performed in a thermoneutral condition (24±0.5 °C, 40±3% rh). The sweat onset-time after the current loading was 1.05 min shorter in Malaysian with long-term stay in Japan (MLJ) than in Malaysian, and the AXR(1), AXR(2) and DIR sweating in MLJ were larger than Malaysian. From these results, suppressed neuroglandular response to ACh was confirmed in Malaysians. It is suggested that long-term heat-acclimatization acquired in tropical subjects may decay after immigration to temperate area.

Sweat distribution before and after repeated heat exposure.

We investigated the impact of short-term, moderate humidity heat acclimation upon sweat distribution. Eight males completed six daily heat exposures [cycling: ambient temperature 39.5 (0.2) degrees C, relative humidity 59.2 (0.8)%], during which auditory canal temperature (T(ac)) was maintained 1.4 degrees C above pre-exposure levels for 70 min by manipulating the work rate. On days 1 and 6, T(ac) and local sweat rates (m(sw): eight sites) were monitored. The pre-exposure, resting T(ac) and the T(ac) sweat threshold decreased from day 1 to day 6 [36.83 (0.05) degrees C vs 36.62 (0.05) degrees C, and 36.90 (0.05) degrees C vs 36.75 (0.05) degrees C, respectively; both P < 0.05]. However, the sweat-onset time, sweat sensitivity (delta m(sw)/deltaT(ac)) and established m(sw) were unaltered (P > 0.05). There was also no evidence of a post-acclimation redistribution in established m(sw) between the eight skin regions, though both the sweat sensitivity and established m(sw) for the forehead and hand were significantly greater than at the remaining sites (P < 0.05). It is concluded that the 5-day heat acclimation regimen provided only a minimal stimulus for sudomotor adaptation.