Skin Wettedness Research Articles

Voluntary Cooling During Exercise Is Augmented In Heat Sensitive People With Multiple Sclerosis

PURPOSE: Body cooling improves exercise tolerance in heat sensitive people with Multiple Sclerosis (MS). The effectiveness of cooling modalities in real-world settings requires appropriately engaging in cooling behavior. We tested the hypothesis that people with MS voluntarily engage in cooling behavior during exercise to a greater extent than healthy controls. METHODS: In a 27.0±0.2°C, 41±2% RH environment, 7 subjects with relapsing-remitting MS who exhibited heat sensitivity (34±7y, 167±5cm, 72±15kg, EDSS: 1.9±0.8, 1 male) and 7 healthy subjects (CON, 37±7y, 168±7cm, 71±11kg, 1 male) completed two randomized trials cycling for 40 min (EX) at a fixed rate of metabolic heat production (3.5 W/kg) followed by 30 min recovery (REC). In one trial, subjects were restricted from engaging in cooling (NONE). In the other, subjects pressed a button to receive 2 min of ~2°C water perfusing a suit top as often as desired (COOL). Mean skin (Tsk, 8 site) and core (Tcore, telemetry pill) temperatures and mean skin wettedness (Wsk, 8 site) were recorded continuously. Total voluntary time in cooling provided an index of cooling behavior. Ratings of perceived exertion (RPE), composite heat sensitivity symptom scores (HSSS, MS only) and subjective fatigue (MS only) were recorded every 10 min. RESULTS: Tcore (+0.5±0.1°C, P<0.01) and Wsk (+0.52±0.02 a.u., P<0.01) increased in EX and remained elevated in REC (P<0.01) but were not different between trials (P≥0.35) or groups (P≥0.60). Tsk decreased in MS COOL compared to MS NONE from min 20 EX to 5 REC (P≤0.02). There were no other differences in Tsk (P≥0.25). MS spent more total time in cooling in EX (MS: 13.4±3.0 min; CON: 7.4±3.6 min, P<0.01) but not REC (MS: 1.7±1.4 min; CON: 0.3±0.7 min, P=0.40). In both trials, RPE was higher in MS vs. CON (P<0.01). HSSS increased in EX (P<0.01) but was not different between trials (P=0.25). Subjective fatigue was not different between trials in EX (P≥0.97) but was lower at 10 and 20 min of REC in COOL (P<0.02). CONCLUSIONS: MS engaged in body cooling during EX to a greater extent than CON. While cooling did not affect HSSS or fatigue during EX, MS reported greater reductions in fatigue following exercise when cooling was permitted. Cooling during exercise could improve exercise participation and adherence. Supported by: ACSM Foundation Research Endowment Grant

Psychrometric limits and critical evaporative coefficients for exercising older women.

Critical environmental limits are those above which human heat balance cannot be maintained for a given metabolic heat production. These limits, and associated critical evaporative coefficients (Ke') that can be used to model responses in hot environments, have not been determined for older subjects. The present paper graphically characterizes psychrometric limits and environmental isotherms and derives Ke' values for a group of unacclimated older (n = 10; age 62 - 80 yr) women exercising at 30% V̇o2max. Uniquely, we compare and contrast these data with published data from young, unacclimated and young, heat-acclimated women tested across a four-decade span using the same protocol in the same environmental chamber. These loci are presented graphically on a psychrometric chart (with confidence intervals). Isotherms constructed from biophysical modeling and sweating capacity closely fit the data but underestimated empirically derived data points in hotter, drier environments. Compared with the young (age 19-26 yr) women previously tested, the older women had significantly constrained (lower) critical environmental limits, in part due to lower sweating rates. Age-specific values of the critical evaporative coefficient, Ke', derived by partial calorimetry in the more humid environments (in which skin wettedness approached 1), were likewise lower for the older women (overall mean = 9.1 W·m-2·mmHg-1; P < 0.05) vs. unacclimated (15.4 W·m-2·mmHg-1) and acclimated (17.0 W·m-2·mmHg-1) young women. Constrained psychrometric limits and lower critical evaporative coefficients lend biophysical clarity to decreased abilities of older women for prolonged exercise in the heat.NEW & NOTEWORTHY This study is the first to describe, graphically and quantitatively, critical environmental limits for women between the ages of 62 and 80 yr based on the biophysics of heat exchange. These psychrometric limit lines define combinations of ambient temperature and humidity above which human heat balance cannot be maintained for a given metabolic heat production. These limits, and associated critical evaporative coefficients (Ke'), can be used to model low- to moderate-intensity exercise responses in hot environments and have directly translatable data that can be used for evidence-based policy decisions, to prepare for impending heat events, and for implementation of other safety interventions.

Experimental study on the effectiveness of the PCM cooling vest in persons with paraplegia of varying levels.

Persons with paraplegia (PA) from thoracic spinal cord injury (T1-T12) are prone to thermal stress during exercise due to impaired thermoregulation. This study evaluates the effectiveness of phase change material (PCM) cooling vests on persons with PA of different levels of injury during exercise in hot exposure. Sixteen participants were recruited and divided to three groups based on injury level; high-thoracic T1-T3, mid-thoracic T4-T8, and low thoracic T9-T12 to perform a 30-min arm-crank exercise at a 30°C room condition. Two types of PCM vests at melting temperature of 20°C were tested: i) V1 with PCM covering the trunk of 3.4kg overall vest mass and ii) V2 with PCM covering chest and upper back of 2.17kg overall vest mass. High thoracic and low-thoracic groups performed NV and V1 tests; whereas, mid-thoracic group performed NV, V1, and V2 tests. Heart rate, core, and skin temperatures were monitored during 15-min preconditioning, 30-min exercise, and 15-min recovery. In addition, thermal comfort, sensation, skin wettedness, and perceived exertion were recorded during exercise only. The main findings were that the effectiveness of the cooling vest was dependent on injury level and portion of sensate skin of trunk covered by the PCM packets. Rise in core temperature (ΔTcr) was reduced significantly for the low-thoracic group during exercise and recovery (ΔTcr=0.41°C, 0.26°C for NV and V1; respectively, p<0.05). For the mid-thoracic group, both V1 (p=0.001) and V2 (p=0.008) were effective in reducing ΔTcr compared to the NV test at the end of the recovery period (0.74°C,0.42°C,0.56°C, for NV, V1 and V2; respectively). For the high-thoracic group, V1 was not effective in reducing core temperature (p>0.05). For the mid-thoracic group, V2 at 36% lower mass significantly improved thermal comfort (p=0.0004) compared to the NV test and was as effective compared to V1 in reducing core temperature.

AJP-Regulatory, Integrative and Comparative Physiology: Looking Toward the Future

<i>AJP-Regulatory, Integrative and Comparative Physiology</i>: Looking Toward the Future

A retrospective analysis to determine if exercise training-induced thermoregulatory adaptations are mediated by increased fitness or heat acclimation.

What is the central question of this study? Are fitness-related improvements in thermoregulatory responses during uncompensable heat stress mediated by aerobic capacity or is it the partial heat acclimation associated with training? What is the main finding and its importance? During uncompensable heat stress, individuals with high and low 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 per se, that mediates thermoregulatory improvements during uncompensable heat stress. It remains unclear whether aerobic fitness, as defined by the maximum rate of oxygen consumption , 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 independently influences thermoregulatory sweating, maximum skin wettedness (ωmax ) and the change in rectal temperature (ΔTre ) during 60min of exercise in an uncompensable environment (37.0±0.8°C, 4.0±0.2kPa, 64±3% relative humidity) at a fixed rate of heat production per unit mass (6Wkg-1 ). Retrospective analyses were performed on 22 participants (3 groups), aerobically unfit (UF; n=7; : 41.7±9.4mlkg-1 min-1 ), aerobically fit (F; n=7; : 55.6±4.3mlkg-1 min-1 ; P<0.01) and aerobically unfit (n=8) individuals, before (pre; : 45.8±11.6mlkg-1 min-1 ) and after (post; : 52.0±11.1mlkg-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±0.20mgcm-2 min-1 ) compared to pre- (1.04±0.25mgcm-2 min-1 , P<0.01) training, but similar between UF (0.94±0.31mgcm-2 min-1 , P=0.90) and F (1.02±0.30mgcm-2 min-1 ). The ΔTre at 60min 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 per se, confers an increased ωmax , greater sweat rate, and smaller rise in core temperature during uncompensable heat stress in fit individuals.

Differences in dry-bulb temperature do not influence moderate-duration exercise performance in warm environments when vapor pressure is equivalent.

Recent studies have determined that ambient humidity plays a more important role in aerobic performance than dry-bulb temperature does in warm environments; however, no studies have kept humidity constant and independently manipulated temperature. Therefore, the purpose of this study was to determine the contribution of dry-bulb temperature, when vapor pressure was matched, on the thermoregulatory, perceptual and performance responses to a 30-min cycling work trial. Fourteen trained male cyclists (age: 32 ± 12year; height: 178 ± 6cm; mass: 76 ± 9kg; [Formula: see text]: 59 ± 9mLkg-1min-1; body surface area: 1.93 ± 0.12m2; peak power output: 393 ± 53W) volunteered, and underwent 1 exercise bout in moderate heat (MOD: 34.9 ± 0.2°C, 50.1 ± 1.1% relative humidity) and 1 in mild heat (MILD: 29.2 ± 0.2°C, 69.4 ± 0.9% relative humidity) matched for vapor pressure (2.8 ± 0.1kPa), with trials counterbalanced. Despite a higher weighted mean skin temperature during MOD (36.3 ± 0.5 vs. 34.5 ± 0.6°C, p < 0.01), none of rectal temperature (38.0 ± 0.3 vs. 37.9 ± 0.4°C, p = 0.30), local sweat rate (1.0 ± 0.3 vs. 0.9 ± 0.4mgcm-2min-1, p = 0.28), cutaneous blood flow (283 ± 116 vs. 287 ± 105 PU, p = 0.90), mean power output (206 ± 37 vs. 205 ± 41W, p = 0.87) or total work completed (371 ± 64 vs. 369 ± 70kJ, p = 0.77) showed any difference between environments during the work trial. However, all perceptual measures (perceived exertion, thermal discomfort, thermal sensation, skin wettedness, pleasantness, all p < 0.05) were affected detrimentally during MOD compared to MILD. In a warm and compensable environment, dry-bulb temperature did not influence high-intensity cycling performance when vapor pressure was maintained, whilst the perceptual responses were affected.

Thermal Behavior Augments Heat Loss Following Low Intensity Exercise.

We tested the hypothesis that thermal behavior alleviates thermal discomfort and accelerates core temperature recovery following low intensity exercise. Methods: In a 27 ± 0 °C, 48 ± 6% relative humidity environment, 12 healthy subjects (six females) completed 60 min of exercise followed by 90 min of seated recovery on two occasions. Subjects wore a suit top perfusing 34 ± 0 °C water during exercise. In the control trial, this water continually perfused throughout recovery. In the behavior trial, the upper body was maintained thermally comfortable by pressing a button to receive cool water (3 ± 2 °C) perfusing through the top for 2 min per button press. Results: Physiological variables (core temperature, p ≥ 0.18; mean skin temperature, p = 0.99; skin wettedness, p ≥ 0.09; forearm skin blood flow, p = 0.29 and local axilla sweat rate, p = 0.99) did not differ between trials during exercise. Following exercise, mean skin temperature decreased in the behavior trial in the first 10 min (by −0.5 ± 0.7 °C, p < 0.01) and upper body skin temperature was reduced until 70 min into recovery (by 1.8 ± 1.4 °C, p < 0.05). Core temperature recovered to pre-exercise levels 17 ± 31 min faster (p = 0.02) in the behavior trial. There were no differences in skin blood flow or local sweat rate between conditions during recovery (p ≥ 0.05). Whole-body thermal discomfort was reduced (by −0.4 ± 0.5 a.u.) in the behavior trial compared to the control trial within the first 20 min of recovery (p ≤ 0.02). Thermal behavior via upper body cooling resulted in augmented cumulative heat loss within the first 30 min of recovery (Behavior: 288 ± 92 kJ; Control: 160 ± 44 kJ, p = 0.02). Conclusions: Engaging in thermal behavior that results in large reductions in mean skin temperature following exercise accelerates the recovery of core temperature and alleviates thermal discomfort by promoting heat loss.

Design with Comfort: Expanding the psychrometric chart with radiation and convection dimensions

We present an expansion of the psychrometric chart for thermal comfort analysis using a new contour shading method that demonstrates a wider range of potential comfort conditions through the incorporation of additional comfort parameters. These extra dimensions include mean radiant temperature, air movement, metabolic rate, skin wettedness and the transitional behavior of occupants. The representations allow us to think outside the thermal comfort box with the use of innovative thermal design and comfort feedback for occupants. Building on the Olgyay bioclimatic chart, allowing architects to “Design with Climate”, the new chart vizualizes a wide range of conditions that illustrate a physical basis for expanding comfort zones. It uses basic spatially invariant metrics employed in adaptive and other comfort models to allow "design with comfort" across all thermal comfort variables. The development of these methods has resulted in an open-source repository and web app available for designers and researchers to reproduce the charts and color-shading for their own projects.

Preferred temperatures with and without air movement during moderate exercise

During exercise, comfort requirements are different because of the elevated metabolic heat production. It is essential to know the preferable thermal environment to give environmental design suggestions to sports facilities. Experimental studies on preferred temperature were conducted on 20 healthy human subjects walking on a treadmill at 4, 5, and 6 km/h, with and without self-controlled air movement. Physiological responses (metabolic rate, skin temperature, skin wettedness, and heart rate) were monitored, while their subjective responses were collected by questionnaires. Metabolic rates were 3.0, 3.5, and 4.5 met for 4, 5, and 6 km/h walking. Preferred temperatures were significantly lower without fan (23.3, 22.8, and 22.1 °C without fan vs. 24.9, 24.1, and 23.6 °C with fan), and all subjects were satisfied with their preferred thermal environment. PMV model was found to overestimate the cooling requirements for exercising people. Our results indicate that human in exercise does not necessarily want neutral temperature but want somewhat warm sensations, with lower temperature, higher skin wettedness, and higher core temperature. Overall, the results suggest that design temperature shall be 22–24 °C without air movement, and 24–26 °C with personally controlled air movement.

Re-visitation of the thermal environment evaluation index standard effective temperature (SET*) based on the two-node model

The standard effective temperature (SET*) is a common and extensively used model that has long been applied in the ASHRAE standard to evaluate the thermal environment. However, analysis and practical application find that SET* is only accurate for simulations of humans at rest and is relatively inaccurate for simulations during exercise. Using theoretical analysis, we find that certain problems exist in the calculation and hypothesis of the existing SET* model: 1) It is inaccurate to assume that a human subject in the standard environment has the same heat exchange at the skin surface as in the actual environment, if the metabolic rate is different in the actual environment. 2) It is difficult to find a value for the equivalent air temperature (SET*) of the standard environment in which a subject has the same mean skin temperature and skin wettedness as in the actual environment. A modified calculation method for an improved SET* model is proposed based on the results of theoretical analysis and experiments. As a result the prediction accuracy of SET* is improved, particularly in the high metabolic rate region. The improved SET* model shows better performance for the evaluation, design, and control of the thermal environment.

Walking Behavior and Outdoor Thermal Comfort: Case Study –Abu Dhabi-

The present research will focus on the concept of walkability and it is a relationship with outdoor thermal comfort. The main objective is to evaluate how far a pedestrian might be able to walk before experiencing discomfort in an outdoor environment; the thermal comfort indices used the Physiologically Equivalent Temperature (PET), calculated using Envimet 04 Software. Walking comfort indices used skin wettedness to simulate the physiological of the body that reacts to the environment. The case study located preferably in two different areas, one is a shaded area (garden), and the second one is an urban zone. The methodology adopted is based firstly on field measurement of thermal comfort and secondly on a simulation of the walking comfort of people. The findings from this research were found that shadowing affects walking behavior in Abu Dhabi during the daytime of the hot season.

Thermal Behavior Does not Differ Between Sexes During and Following High Intensity Aerobic Exercise

Females utilize thermal behavior more than males during low intensity aerobic exercise. Core temperature is elevated during high vs. low intensity aerobic exercise because of greater heat production. Thus, thermal behavior is greater during high intensity exercise because of the heightened stimulus to behave. It is unknown if sex modulates thermal behavior during high intensity exercise. PURPOSE: Test the hypothesis that thermal behavior differs between males and females during high intensity exercise and recovery. METHODS: 10 males (M) and 10 females (F) (23±3y) underwent 30 min of cycling exercise at a power output that elicited 80±5% (F) and 78±4% (M) of VO2peak (P=0.28) followed by 120 min seated recovery in a 27±1°C, 21±2% relative humidity environment. Subjects were instructed to maintain a thermally comfortable neck temperature throughout using a custom-made neck device. Neck device temperature provided an index of thermal behavior. Mean skin (10 site) and core (intestinal) temperatures, mean skin wettedness (8 site), neck device temperature, skin blood flow (laser Doppler) and local sweat rate (ventilated capsule) were measured continually. RESULTS: There were no sex differences in heat production during exercise (F: 399±68, M: 429±62 W/m2, P=0.39). During exercise, core and mean skin temperatures, skin wettedness, skin blood flow and local sweat rate increased, while neck device temperature decreased (all P<0.01). There were no sex differences in core (F: 37.7±0.2, M: 37.9±0.3°C, P> 0.50), mean skin (F: 32.6±0.3, M: 32.6±0.3°C, P>0.99) or neck device (F: 12.1±10.6, M: 11.9±10.2°C, P>0.25) temperatures, mean skin wettedness (at 30 min: F: 0.50±0.06, M: 0.53±0.04 au, P>0.99), skin blood flow (F: 163±50, M: 172±36 PU, P>0.99) or local sweat rate (F: 0.72±0.20, M: 0.85±0.27 mg/cm2/min, P>0.33) during exercise (data reported at 30 min). During recovery, core and mean skin temperatures, mean skin wettedness, skin blood flow and local sweat rate decreased, and neck device temperature increased back towards pre-exercise levels (all P<0.01). There were no differences in the dynamics of these changes between sexes (all P>0.16). CONCLUSIONS: Thermal behavior during and following high intensity aerobic exercise does not differ between males and females. This study was funded by lululemon athletica inc.

Transient human thermophysiological and comfort responses indoors after simulated summer commutes

The current study investigates the transient human physiological and comfort responses during sedentary activity following a period of elevated activity in a hot condition. Such metabolic and thermal down-steps are common in buildings as occupants arrive after commuting in summer. It creates a serious problem for thermostatic control, since arriving occupants find their transition uncomfortably warm at temperatures that resident occupants find comfortable. Fifty-nine participants (29 men, 30 women) dressed in 0.6 clo were tested while sedentary for 60 min in 26 °C, after having been exposed to 30 °C for 15 min, during which they performed activities metabolically simulating commuting: sitting (SE - 1.2 met), or doing three levels of stair-step exercises: low (LEx- 2.2 met), medium (MEx - 3.0 met), and high (HEx - 4.4 met). Subjective comfort and physiological responses (metabolic rate, skin temperature, skin blood flow rate, heart rate, core temperature, and skin wettedness) were collected. Results show that sedentary conditions at 26 °C became comfortable and acceptable within 2 min, but thermal sensation required much longer to change from ‘warm’ or ‘hot’ to ‘neutral’: 0, 8, 17, 30 min after SE, LEx, MEx, HEx respectively. Skin wettedness and core temperature did not recover within the 60 min. The delays are mainly due to body heat stored during the exercise. A room temperature of 26 °C may not provide sufficient cooling after summer commuting. Localized convective cooling of transitional spaces and work areas by ceiling or desk fans represent a way to enhance comfort recovery.

Thermal Behavior During Exercise Alleviates Thermal Discomfort Despite Exacerbating Increases in Core Temperature

PurposeIncreases in metabolic heat production during exercise stimulate perceptions of thermal discomfort as core and skin temperatures, and skin wettedness increase. Thermal discomfort is the precursor to thermal behavior. Employing thermal behavior during exercise may reduce thermal discomfort by attenuating the rise in core temperature. However, this remains unknown. We tested the hypothesis that thermal behavior attenuates the rise in core temperature and alleviates thermal discomfort during exercise.MethodsTwelve healthy subjects (24 ± 3 y, 6 females) performed two trials in which they completed 60 min of recumbent cycling exercise at a fixed rate of metabolic heat production (217 ± 28 W/m2) in a 27 ± 0°C, 48 ± 6% relative humidity environment. In both trials subjects wore a water perfused suit top. In the control trial, 34 ± 0°C water circulated through the top during the trial (CON). The experimental trial allowed for thermal behavior (BEH) where subjects were instructed to maintain their upper body thermally comfortable throughout. In BEH, subjects thermally behaved by pressing a button to receive cool water (2 ± 1°C) through the water perfused suit top for 2 min, which was followed by a 1 min wash out period. Mean skin (10 site) and core (telemetry pill) temperatures, mean skin wettedness (8 site), skin blood flow (forearm, laser Doppler), and local sweat rate (ventilated capsule) were measured continually. Local sweat rate was measured under (on mid‐axillary line) and outside (on anterior thigh, n=7) of the water perfused suit top. Whole body thermal comfort was recorded every 10 min. Water perfused suit top temperature provided an index of thermal behavior. Data are presented as mean ± SD as the absolute change from the values acquired pre‐exercise.ResultsMetabolic heat production was not different between trials (P=0.44). The increase in core temperature was greater in BEH vs. CON at 50 and 60 min (both by +0.1 ± 0.3°C, P&lt;0.01). Mean skin temperature was reduced in BEH vs. CON from 20 min (by −0.5 ± 0.7°C, P&lt;0.01) onwards (P&lt;0.01). Mean skin wettedness was greater in BEH vs. CON from 30 min (by +0.01 ± 0.03 a.u., P&lt;0.01) onwards (P&lt;0.01). Water perfused suit top temperature was reduced in BEH vs. CON from 10 min (by −5.6 ± 7.0°C, P&lt;0.01) onwards (P&lt;0.01). Mid‐axillary sweat rate was attenuated in BEH vs. CON from 10 min (by −0.1 ± 0.12 g/cm2/min) onwards (P&lt;0.01), and thigh sweat rate was attenuated at min 20 (by: −0.1 ± 0.2 g/cm2/min) and 60 (by −0.2 ± 0.2 g/cm2/min). Forearm skin blood flow was not different between BEH and CON at any time (P=0.20). Increases in whole body thermal discomfort were attenuated in BEH vs. CON within the first 10 min (by −0.4 ± 0.4 a.u., P=0.04) onwards (P&lt;0.01).ConclusionsEmploying thermal behavior that reduces mean skin temperature during exercise alleviates thermal discomfort despite exacerbating the rise in core temperature and skin wettedness. Reductions in sweat rate may contribute to the greater rise in core temperature when employing thermal behavior. These findings may question the role of skin wettedness in stimulating thermal behavior during exercise.Support or Funding InformationSupported by lululemon athletica inc.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Regulation of Body Temperature by Autonomic and Behavioral Thermoeffectors.

Thermoregulation is accomplished via autonomic and behavioral responses. Autonomic responses may influence decisions to behaviorally thermoregulate. For instance, in addition to changes in body temperature, skin wettedness and involuntary muscle contraction, which occur subsequent to sweating and shivering, likely modulate thermal behavior. This autonomic-behavioral interaction provides the rationale for our hypothesis that thermoregulatory behavior decreases the requirement for autonomic responses.

Optimizing the Measurement of Skin Wettedness in Exercising Humans

PurposeSkin wettedness is the proportion of the skin that is wet at any given time. Skin wettedness is an important contributor to the decision to initiate thermoregulatory behavior, particularly during instances in which sweat builds up on the skin. The direct measurement of skin wettedness involves measuring the partial pressure of water (PH2O) at a distance of 1–2 mm from the skin. During situations involving movement (e.g., exercise) the close proximity of the humidity sensor to the skin risks supersaturation, which occurs when a drop of sweat enters the humidity sensor. This artificially saturates the sensor independent of an increase PH2O on the skin. Thus, raising humidity sensors off the skin as far as possible, but without compromising the measurement, is advantageous to avert the risk of supersaturation. Some evidence suggests that raising the sensors 6 mm off of the skin results in skin PH2O responses that are comparable to 2 mm. However, this has never been experimentally tested. Therefore, we tested the hypothesis that raising sensors 6 mm above a surface saturated with water resembles the PH2O responses observed at 2 mm.MethodsFollowing a 5 min baseline period on a dry surface, humidity sensors (hydrochron iButtons) were placed on a paper towel saturated with water for 60 min. The paper towel was placed on a water perfused mat set to elicit 32.1±0.4°C (T32) or 34.3±0.2°C (T34). These temperatures mimic the skin temperatures observed during exercise in a 20–28°C environment. During each testing period, five humidity sensors were placed at a distance of 2, 4, 6, 8, and 10 mm above the mat. For a given humidity sensor, the height was randomly assigned and all heights were measured during each testing period to eliminate any between trial variability. Each height was measured on five occasions. All testing was conducted in a 27±1°C, 25±6% relative humidity environment. The humidity sensors measure relative humidity and temperature, which were later converted to PH2O. Data are presented as mean±SD. All comparisons were made to 2 mm, the standard height of measurement.ResultsIn T32, PH2O increased in all heights within the first 5 min and plateaued until 25 min (P≥0.41), where after PH2O returned toward baseline levels. PH2O was lower (P&lt;0.01) than 2 mm at 30 min in 8 mm (−1.0±0.9 mmHg) and 10 mm (−1.3±0.6 mmHg). For 6mm, PH2O was lower than 2 mm at 35 (−1.4±0.8 mmHg, P&lt;0.01) and 40 min (by −0.9±0.9 mmHg, P&lt;0.01). The 4 mm height was not different from 2 mm at any time (P≥0.56). PH2O for all heights were not different to 2 mm from 45–65 min (P≥0.11). In T34, PH2O increased within 5 min and plateaued through 15 min (P≥0.90), where after PH2O returned toward baseline levels. For 10 mm, PH2O was lower than 2 mm at 20 min (by −0.4±0.5 mmHg, P&lt;0.01). For 8 mm, PH2O was lower than 2 mm at 25 min (by −1.0±0.6 mmHg, P&lt;0.01). 4 mm (by −0.7±0.8 mmHg, P&lt;0.01) and 6 mm (by −1.1±1.7 mmHg, P&lt;0.01) were lower than 2 mm at 30 min. PH2O for all heights were not different to 2 mm from 35–65 min (all P≥0.22).ConclusionCompared to 2 mm, at temperatures of 32°C and 34°C, raising a humidity sensor 6 mm off the surface underestimates PH2O during dynamic changes in PH2O. Thus, to minimize the risks of supersaturation and measurement bias, PH2O during exercise should likely be measured at a height of 4 mm above the surface of the skin.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Exercise intensity independently modulates thermal behavior during exercise recovery but not during exercise.

We tested the hypothesis that thermal behavior is greater during and after high- compared with moderate-intensity exercise. In a 27°C, 20% relative humidity environment, 20 participants (10 women, 10 men) cycled for 30 min at moderate [53% (SD 6) peak oxygen uptake (V̇o2peak) or high [78% (SD 6) V̇o2peak] intensity, followed by 120 min of recovery. Mean skin and core temperatures and mean skin wettedness were recorded continuously. Participants maintained thermally comfortable neck temperatures with a custom-made neck device. Neck device temperature provided an index of thermal behavior. The weighted average of mean skin and core temperatures and mean skin wettedness provided an indication of the afferent stimulus to thermally behave. Mean skin and core temperatures were greater at end-exercise in high intensity (P < 0.01). Core temperature remained elevated in high intensity until 70 min of recovery (P = 0.03). Mean skin wettedness and the afferent stimulus were greater at 10-20 min of exercise in high intensity (P ≤ 0.03) and remained elevated until 60 min of recovery (P < 0.01). Neck device temperature was lower during exercise in high versus moderate intensity (P ≤ 0.02). There was a strong relation between the afferent stimulus and neck device temperature during exercise (high: R2 = 0.82, P < 0.01; moderate: R2 = 0.95, P < 0.01) and recovery (high: R2 = 0.97, P < 0.01; moderate: R2 = 0.93, P < 0.01). During exercise, slope (P = 0.49) and y-intercept (P = 0.91) did not differ between intensities. In contrast, slope was steeper (P < 0.01) and y-intercept was higher (P < 0.01) during recovery from high-intensity exercise. Thermal behavior is greater during high-intensity exercise because of the greater stimulus to behave. The withdrawal of thermal behavior is augmented after high-intensity exercise. NEW & NOTEWORTHY This is the first study to determine the effects of exercise intensity on thermal behavior. We show that exercise intensity does not independently modulate thermal behavior during exercise but is dependent on the magnitude of afferent stimuli. In contrast, the withdrawal of thermal behavior after high-intensity exercise is augmented. This may be a consequence of an attenuated perceptual response to afferent stimuli, which may be due to processes underlying postexercise hypoalgesia.

Moisture in clothing and its transient influence on human thermal responses through clothing microenvironment in cold environments in winter

Air humidity produces conditions of varying moisture contents in clothing, which affects the heat and moisture transfer between human body, clothing and environment, as well as the wearers’ comfort. This study was designed to evaluate the moisture effects in clothing in cold environments. A series of wearing experiments were conducted in a climate chamber, simulating transient moisture absorption and desorption in experimental clothes. Totally 20 subjects were involved in three temperature levels (16 °C/20 °C/24 °C) and two relative humidity levels (15% RH/85% RH) during winter, with physiological measurement and subjective evaluation. The results showed that moisture in clothing under 85% RH significantly reduced subject mean skin temperatures (MST) and increased the local blood flow, due to enhanced heat loss by vapour evaporation. The initial skin wettedness was approximately 0.7 at 85% RH and stabilised at 0.33 after 90min exposure. The skin heat loss (Qskin) at 85% RH was almost twice as high as that at 15% RH under the same temperature conditions, owing to larger sensible and evaporative heat loss caused by moist clothing. The inner clothing effective temperature Teff was proposed to relate to TSV that the TSV increased by 1.12 units with an increase of 1 °C of Teff, which quantified the coupled effects of air temperature and humidity in clothing microenvironment on human thermal comfort. The findings address the negative effect of clothing absorbing a large amount of moisture, which should be considered for indoor heating temperature designs in cold-humid environments.

Prediction of physiological exertion in hot environments using the JOS-2 thermoregulation model

In recent years, the outdoor summer environment in Japan has become progressively warmer due to the severity of the heat island phenomenon. The danger of heat stroke and thermal comfort outdoors in summer are regarded as problems. In order to evaluate these problems, it is important to evaluate physiological exertion in the human body. The purpose of this research is to demonstrate the possibility of predicting physiological exertion in the human body with high accuracy in an outdoor environment during summer using the JOS-2 thermoregulation model developed by our research group. First, the Japanese metabolic rate in summer and autumn was measured for various activities, including sitting, standing, and walking. As a result, we found that the metabolic rate during sitting and standing was lower by about 10% in summer than in autumn. Next, using the obtained metabolic rate measurement as an input to the model, the experiment in an outdoor environment during summer was reproduced using JOS-2. The accuracy of the predicted mean skin temperature and local skin wettedness in an outdoor environment during summer was improved by choosing the appropriate input to the model.

Skin wettedness is an important contributor to thermal behavior during exercise and recovery.

We tested the hypothesis that mean skin wettedness contributes to thermal behavior to a greater extent than core and mean skin temperatures. In a 27.0 ± 1.0°C environment, 16 young participants (8 females) cycled for 30 min at 281 ± 51 W·m2, followed by 120 min of seated recovery. Mean skin and core temperatures and mean skin wettedness were recorded continuously. Participants maintained a thermally comfortable neck temperature throughout the protocol using a custom-made device. Neck device temperature provided an index of thermal behavior. Linear regression was performed using individual minute data with mean skin wettedness and core and mean skin temperatures as independent variables and neck device temperature as the dependent variable. Standarized β-coefficients were used to determine relative contributions to thermal behavior. Mean skin temperature differed from preexercise (32.6 ± 0.5°C) to 10 min into exercise (32.3 ± 0.6°C, P < 0.01). Core temperature increased from 37.1 ± 0.3°C preexercise to 37.7 ± 0.4°C by end exercise ( P < 0.01) and remained elevated through 30 min of recovery (37.2 ± 0.3°C, P < 0.01). Mean skin wettedness increased from preexercise [0.14 ± 0.03 arbitrary units (AU)] to 20 min into exercise (0.43 ± 0.09 AU, P < 0.01) and remained elevated through 80 min of recovery (0.18 ± 0.06 AU, P ≤ 0.05). Neck device temperature decreased from 26.4 ± 1.6°C preexercise to 18.5 ± 8.7°C 10 min into exercise ( P = 0.03) and remained depressed through 20 min of recovery (14.4 ± 11.2°C, P < 0.01). Mean skin wettedness (52 ± 24%) provided a greater contribution to thermal behavior compared with core (22 ± 22%, P = 0.06) and mean skin (26 ± 16%, P = 0.04) temperatures. Skin wettedness is an important contributing factor to thermal behavior during exercise and recovery.