Local Sweat Research Articles

Whole-Body Heat Loss during Exercise in the Heat Is Not Impaired in Type 1 Diabetes

The objective of this study is to determine whether individuals with type 1 diabetes exhibit impairments in local and whole-body heat loss responses that could affect core temperature regulation during exercise in the heat compared with matched, nondiabetic individuals. Twelve otherwise healthy individuals with type 1 diabetes (HbA1c = 7.7% ± 0.3%) and 12 controls matched for age, sex, body surface area, and physical fitness cycled continuously for 60 min at a set rate of metabolic heat production (approximately 400 W) in a whole-body direct calorimeter (35°C and 20% relative humidity). Local sweat rate (ventilated capsule) was measured on the back and skin blood flow (laser Doppler velocimetry) on the forearm. Core (rectal and esophageal) and mean skin temperatures and heart rate were measured continuously. Whole-body heat exchange and change in body heat content were measured using simultaneous direct whole-body and indirect calorimetry. The change (mean ± SE) in body heat content was similar between groups during exercise (diabetes, 409 ± 27 kJ; control, 386 ± 33 kJ; P = 0.584) and recovery (diabetes, -115 ± 16 kJ; control, -93 ± 24 kJ; P = 0.457). Local heat loss responses of sweating (P = 0.783) and skin blood flow (P = 0.078) as well as rectal temperature (diabetes, 37.87°C ± 0.10°C; control, 37.85°C; ± 0.13°C; P = 0.977) and heart rate (diabetes, 130 ± 9 beats·min, vs control, 126 ± 8 beats·min, P = 0.326) were comparable at the end of the exercise period. During light-to-moderate-intensity exercise performed under conditions permitting full sweat evaporation, otherwise healthy type 1 diabetic individuals did not show impaired heat loss responses during heat exposure when compared with matched individuals without diabetes.

Sweating the details: what really drives eccrine output during exercise‐heat stress

Copious sweating observed during passive or exercise-induced heat stress (exercise-heat stress) is the primary outcome of the sophisticated eccrine-dependent cooling system that has evolved in humans. One can speculate as to why sweating, with its large ability to liberate heat (580 kcal l-1), would be advantageous for a ‘naked ape’ ambulating in a warm savanna environment. Despite this grand role of sweating in human thermoregulation and evolution, it is humbling how little we know of its control and regulation. Recent work is beginning to detect the precise brain areas involved (Shafton & McAllen, 2013), but imprecise systemic factors are reported in the literature to be the primary drivers of eccrine sweating. In this issue of The Journal of Physiology, Gagnon and colleagues (Gagnon et al. 2013) challenge the notion that relative workload (current workload compared to maximum work capacity) is the primary determinant of sweat output during exercise-heat stress. In their experiment, human subjects performed exercise-heat stresses in a direct calorimeter at a fixed workload (290 W) in variable thermal environments (30, 35, 40 and 45°C) or at a variable workload (200, 350, or 500 W) in a fixed 30°C thermal environment. Using this direct method of measuring heat emitted, the evaporative requirement for heat balance was superior to relative workload in predicting whole-body sweat rate, and when relative workload was combined with the evaporative requirement for heat balance, predictions did not improve. Authors interpret these data as definitive evidence against the use of relative workload in experiments when the primary determinant is sweat rate. Rather, authors indicate that matching evaporative requirements to what is needed to maintain heat balance in both steady-state and non-steady-state exercise-heat stress is a superior experimental approach. Do these interpretations make sense? Using Occam's razor (the most direct hypothesis being most likely correct), it is logical that the evaporative requirement to maintain a regulated internal temperature would be the driving force for eccrine sweat output rather than a less direct measure such as relative workload. As one can see from a traditional heat balance equation (eqn (1)), relative workload is located within the M–Wk component vs. the more direct E: (1) where S is heat storage (balance); M is metabolism and Wk is external work; R+C+K is dry heat exchange via radiation, convection, and conduction; and E is evaporative heat loss. Relative workload has an inherent fitness bias. This can be observed with similar whole-body and local sweat rates when comparing high fitness (∼60 ml kg−1 min−1) and average fitness (∼40 ml kg−1 min−1) groups at fixed workload (100–110 W). In contrast, at a relative workload (60% of maximal), the same high fitness group had greater whole-body and local sweat rates compared to the average fitness group (Jay et al. 2011). What are the potential mechanisms of the fitness-induced increase in sweat output? Whole-body sweating mechanisms are difficult to determine and remain elusive. However, locally perfusing the sudorific agonist acetylcholine (ACh) via intradermal microdialysis stimulates muscarinic type-3 receptors on eccrine sweat glands, and if water vapour is collected via capacitance hygrometry just above the skin containing the microdialysis membrane, agonist to sweating dose–response relations can be determined in small areas of skin. Using this limited but better controlled approach, increasing maximal work capacity via 8 weeks of aerobic exercise training causes an increase in the in vivo maximal sweating responses (Wilson et al. 2010). Inactivity, such as 14 days of bedrest, decreases maximal work and sweating capacity and importantly, aerobic exercise training during bedrest rescues this response (Crandall et al. 2003). However, neither of these changes in work capacity changes the in vivo eccrine sweat gland cholinergic sensitivity. This indicates that for a given amount of ACh release from cholinergic sudomotor nerves there is not more sweating, but if the amount of ACh released increases, more eccrine sweating results. These data combined with this new study (Gagnon et al. 2013) suggest that trained individuals may release more ACh at a given relative workload, which may be responsible for their higher sweat rate. Gagnon et al. (2013) provide a long list of previous studies that compared independent groups at a relative workload rather than the more predictive evaporative requirement for heat balance. Are all these previous studies flawed? Not necessarily. Many, but not all, of these studies were fitness-matched to maximal work capacity and thus relative workloads would be similar. That said, the authors of this new study (Gagnon et al. 2013) give the field pause to consider what actually drives the sweating response during exercise-heat stress. Although more work needs to be completed to determine these precise driving forces and what can be used to compare experimental groups, future studies should be cautioned against using relative workload as a between-groups standardization when eccrine sweating is the main variable of interest.

Thermoreceptors in the upper gastrointestinal tract independently influence sudomotor activity

Warm and cool fluid ingestion during exercise has been previously shown to alter local sweat rate independently of core and skin temperatures. This study strove to identify the location of the thermoreceptors responsible. Six males cycled at 50% VO2max for 75 min in a 24.8 ± 0.7°C and 33.4 ± 3.5% RH environment, while either mouth‐swilling (SW) 1.5°C or 50°C water; or ingesting 1.5°C or 50°C water through a nasogastric (NG) tube in three 3.2 mL·kg−1 boluses after 15, 30, and 45 min of exercise. Mean skin temperature (Tsk), mean local sweat rate (MLSR) and rectal temperature (Tre) were measured continuously. For all trials, Tre and Tskwere similar throughout. In the NG trials, MLSR with 1.5°C water was lower than with 50°C water, after 30, 45, and 60 min (P<0.05), but not after 15 or 75 min (P>;0.05) of exercise. In contrast, during the SW trials, MLSR with 1.5°C and 50°C water was almost identical throughout exercise (P>;0.05). In conclusion, thermoreceptors in the stomach region, rather than thermoreceptors in the mouth, are responsible for the transient alterations of sudomotor activity previously observed following the ingestion of warm and cool water. Supported by NSERC Discovery Grant #386143–2010.

Quantitative assessment of cutaneous C‐fiber function in human skin via direct sudomotor activation

Small sympathetic cholinergic C‐fiber function was examined using intradermal electrical stimulation to activate sudomotor nerves in the forearm skin of healthy humans. We measured local sweat rate (SR) with a 0.7 cm2 capsule containing a humidity sensor and a thermocouple and flushed with dry gas. Two small stainless steel needles were place into the skin (7 mm apart, 2 mm deep) and stimulated at a constant current intensity of 2.5 mA for 30 s and 120 s at frequencies of 0.2, 1, 2, 4, 8, 16, 32, and 64 Hz. The stimulus‐response characteristics were evaluated using a non‐linear four‐parameter logistic curve fitting equation. Peak local SR occurred between 32 and 64 Hz and was similar for 30 and 120 s stimulus duration averaging 0.46 ± 0.2 and 0.49 ± 0.2 mg • min−1 • cm−2, respectively. The EC50 averaged 8.3 ± 0.3 Hz during the 30 sec stimulus but decreased to 3.6 ± 0.05 Hz (p<0.05) during the 120 s stimulus. The area under the SR‐time curve following atropine sulfate (2 μg/ml) was lower than control (p<0.05) and not different from zero. These data support the hypothesis that the SR response to intradermal electrical stimulation reflects, exclusively, the effect of direct depolarization of sympathetic cholinergic C‐fibers and release of acetylcholine. As such, this model can be used to provide a quantifiable assessment of small C‐fiber function in human skin.

Role of nitric oxide synthase on local sweat rate in older adults during intermittent exercise in the heat

Studies suggest that nitric oxide (NO) has a role in sweating. Older adults have a lower production of and sensitivity to NO which may explain why older adults have lower local sweat rates (LSR) compared with their younger counterparts during exercise. We examined the role of NO synthase (NOS) on LSR during intermittent exercise in the heat. Ten young (Y) and ten older (O) participants completed 3 × 15 min of cycling (rate of metabolic heat production of 600 W) separated by 15 min recovery in the heat (35ºC, 30% RH). Intradermal microdialysis probes were inserted in the forearm and perfused with either 0.9% saline (CON) or 10 mM L‐NAME (a NOS inhibitor). LSR was measured directly over each membrane. LSR was similar between Y and O during the exercise bouts at the CON (average of the 3 exercise bouts: Y; 0.96 ± 0.20 vs. O; 0.87 ± 0.25 mg·min−1·cm−2 p=0.327) and the LNAME (Y: 0.74 ± 0.18 vs. O: 0.83 ± 0.27 mg·min−1·cm−2 p=0.327) sites. However, the relative contribution of NO to the sweating response was reduced in Y (CON: 0.96 ± 0.20 vs. L‐NAME: 0.74 ± 0.18 mg·min−1·cm−2, p=0.017), but not O (CON: 0.87 ± 0.25 vs. L‐NAME: 0.83 ± 0.27 mg·min−1·cm−2, p=0.965). We conclude that the exercise‐induced increase in sweating is influenced by NO in younger adults. However, it appears that the level of influence is blunted in older individuals during high intensity exercise in the heat.This research was funded by Natural Sciences and Engineering Research Council (RGPIN‐298159–2009, held by Dr. Kenny).

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.

A comparison between the technical absorbent and ventilated capsule methods for measuring local sweat rate

This study assessed the accuracy of the technical absorbent (TA) method for measuring local sweat rate (LSR) relative to the well-established ventilated capsule (VC) method during steady-state and nonsteady-state sweating using large and small sample surface areas on the forearm and midback. Forty participants (38 males and two females) cycled at 60% peak oxygen consumption for 75 min in either a temperate [22.3 ± 0.9°C, 32 ± 17% relative humidity (RH)] or warm (32.5 ± 0.8°C, 29 ± 7% RH) environment. Simultaneous bilateral comparisons of 5-min LSR measurements using the TA and VC methods were performed for the back and forearm after 10, 30, 50, and 70 min. LSR values, measured using the TA method, were highly correlated with the VC method at all time points, irrespective of sample surface area and body region (all P < 0.001). On average, ≈ 79% of the variability observed in LSR measured with the VC method was described by the TA method. The mean difference in absolute LSR using the TA method (TA-VC with 95% confidence intervals) was -0.23 [-0.30,-0.16], -0.11 [-0.21,0.00], -0.03 [-0.14,+0.08], and +0.02 [-0.07,+0.11] mg · cm(-2) · min(-1) after 10, 30, 50, and 70 min of exercise, respectively. Duplicate LSR measurements within each method during steady-state sweating were highly correlated (TA: r = 0.96, P < 0.001, n = 20; VC: r = 0.97, P < 0.001, n = 20) with a mean bias of +0.07 ± 0.14 and +0.01 ± 0.10 mg · cm(-2) · min(-1) for TA and VC methods, respectively. The mean smallest detectable difference in LSR was 0.12 and 0.05 mg · min(-1) · cm(-2) for TA and VC methods, respectively. These data support the TA method as a reliable alternative for measuring the rate of sweat appearance on the skin surface.

Design data for footwear: sweating distribution on the human foot

PurposeThe purpose of this paper is to provide footwear designers, manikin builders and thermo‐physiological modellers with sweat distribution information for the human foot.Design/methodology/approachIndependent research from two laboratories, using different techniques, is brought together to describe sweat production of the foot. In total, 32 individuals were studied. One laboratory used running at two intensities in males and females, and measured sweat with absorbents placed inside the shoe. The other used ventilated sweat capsules on a passive, nude foot, with sweating evaluated during passive heating and incremental exercise to fatigue.FindingsResults from both laboratories are in agreement. Males secreted more than twice the volume of sweat produced by the females (p&lt;0.01) at the same relative work rate. Both genders demonstrated a non‐uniform sweat distribution, though this was less variable in females. Highest local sweat rates were observed from the medial ankles (p&lt;0.01). The dorsal foot sweated substantially more than the plantar (sole) areas (p&lt;0.01). Sweating on the plantar side of the foot was uniform. Wearing shoes limited the increase in sweat production with increasing load, while the sweat rate of uncovered feet kept increasing with work and thermal load.Practical implicationsThe observed variation in sweat rate across the foot shows that footwear design should follow the body mapping principle. Fabrics and materials with different properties can be used to improve comfort if applied to different foot surfaces. The data also demonstrate that foot models, whether physical (manikins) or mathematical, need to incorporate the observed variation across the foot to provide realistic simulation/testing of footwear.Originality/value

Regional variations in transepidermal water loss, eccrine sweat gland density, sweat secretion rates and electrolyte composition in resting and exercising humans

Literature from the past 168 years has been filtered to provide a unified summary of the regional distribution of cutaneous water and electrolyte losses. The former occurs via transepidermal water vapour diffusion and secretion from the eccrine sweat glands. Daily insensible water losses for a standardised individual (surface area 1.8 m2) will be 0.6–2.3 L, with the hands (80–160 g.h−1) and feet (50–150 g.h−1) losing the most, the head and neck losing intermediate amounts (40–75 g.h−1) and all remaining sites losing 15–60 g.h−1. Whilst sweat gland densities vary widely across the skin surface, this same individual would possess some 2.03 million functional glands, with the highest density on the volar surfaces of the fingers (530 glands.cm−2) and the lowest on the upper lip (16 glands.cm−2). During passive heating that results in a resting whole-body sweat rate of approximately 0.4 L.min−1, the forehead (0.99 mg.cm−2.min−1), dorsal fingers (0.62 mg.cm−2.min−1) and upper back (0.59 mg.cm−2.min−1) would display the highest sweat flows, whilst the medial thighs and anterior legs will secrete the least (both 0.12 mg.cm−2.min−1). Since sweat glands selectively reabsorb electrolytes, the sodium and chloride composition of discharged sweat varies with secretion rate. Across whole-body sweat rates from 0.72 to 3.65 mg.cm−2.min−1, sodium losses of 26.5–49.7 mmol.L−1 could be expected, with the corresponding chloride loss being 26.8–36.7 mmol.L−1. Nevertheless, there can be threefold differences in electrolyte losses across skin regions. When exercising in the heat, local sweat rates increase dramatically, with regional glandular flows becoming more homogeneous. However, intra-regional evaporative potential remains proportional to each local surface area. Thus, there is little evidence that regional sudomotor variations reflect an hierarchical distribution of sweating either at rest or during exercise.

Improved Procedure for Estimating Time-dependent Changes in Local Sweat Rates by Measuring Local Sweat Volumes

Sweat distribution over 21 body sites in 8 young males was described by determining the local sweat volume (LSRap), measured using absorbent pads throughout 3 different bicycle exercises performed at 35, 50, and 60% VO2max for 40 min, at 30°C and 50% relative humidity. The local upper back sweat rate was concurrently measured by the ventilated capsule method (LSRvc) in parallel with the absorbent method. The LSRap at the upper back correlated strongly with mean LSRvc at the position immediately above the absorbent pad (p<0.05). There were significant differences in LSRap among the 21 body sites within each exercise intensity (p<0.05). Regional comparisons showed a greater LSRap at the chest and back and lower LSRap at the flank, thighs, and legs. Moreover, LSRap was distributed symmetrically and was greater in the middle compared to the adjoining lateral sites. LSRvc data reanalysis of our previous studies on prepubertal boys, men, and women across a range of ages revealed that during passive and/or active heating, the LSRvc were arranged in order of lower limbs.

Effects of duration of stay in temperate area on thermoregulatory responses to passive heat exposure in tropical south-east Asian males residing in Japan

BackgroundIn this study, we investigated the effects of duration of stay in a temperate area on the thermoregulatory responses to passive heat exposure of residents from tropical areas, particularly to clarify whether they would lose their heat tolerance during passive heat exposure through residence in a temperate country, Japan.MethodsWe enrolled 12 males (mean ± SE age 25.7 ± 1.3 years) from south-east Asian countries who had resided in Japan for a mean of 24.5 ± 5.04 months, and 12 Japanese males (age 24.1 ± 0.9 years). Passive heat exposure was induced through leg immersion in hot water (42°C) for 60 minutes under conditions of 28°C air temperature and 50% relative humidity.ResultsCompared with the Japanese group, the tropical group displayed a higher pre-exposure rectal temperature (P < 0.01) and a smaller increase in rectal temperature during 60 minutes of leg immersion (P = 0.03). Additionally, the tropical group showed a tendency towards a lower total sweat rate (P = 0.06) and lower local sweat rate on the forehead (P = 0.07). The tropical group also had a significantly longer sweating onset time on the upper back (P = 0.04) compared with the Japanese groups. The tropical group who stayed in Japan for > 23 months sweated earlier on the forehead and upper back than those who stayed in Japan < 11 months (P < 0.01 and P = 0.03 for the forehead and upper back, respectively). There was a positive correlation between duration of stay in Japan and total sweat rate (r = 0.58, P <0.05), and negative correlations between duration of stay and sweating onset time on the forehead (r = −0.73, P = 0.01) and on the upper back (r = −0.66, P = 0.02). Other physiological indices measured in this study did not show any difference between the subjects in the tropical group who had lived in Japan for a shorter time and those who had lived there for a longer time.ConclusionsWe conclude that the nature of heat acclimatization of the sweating responses to passive heat exposure that are acquired from long-term heat acclimatization is decayed by a stay in a temperate area, as shown by the subjects in our tropical group. We did not find any evidence of a decay in the other physiological indices, indicating that heat tolerance acquired from long-term heat acclimatization is not completely diminished through residence in a temperate area for less than 4 years, although some aspects of this heat tolerance may be decayed.

Sex differences in thermoeffector responses during exercise at fixed requirements for heat loss

To assess potential mechanisms responsible for the lower sudomotor thermosensitivity in women during exercise, we examined sex differences in sudomotor function and skin blood flow (SkBF) during exercise performed at progressive increases in the requirement for heat loss. Eight men and eight women cycled at rates of metabolic heat production of 200, 250, and 300 W/m(2) of body surface area, with each rate being performed sequentially for 30 min. The protocol was performed in a direct calorimeter to measure evaporative heat loss (EHL) and in a thermal chamber to measure local sweat rate (LSR) (ventilated capsule), SkBF (laser-Doppler), sweat gland activation (modified iodine-paper technique), and sweat gland output (SGO) on the back, chest, and forearm. Despite a similar requirement for heat loss between the sexes, significantly lower increases in EHL and LSR were observed in women (P ≤ 0.001). Sex differences in EHL and LSR were not consistently observed during the first and second exercise periods, whereas EHL (348 ± 13 vs. 307 ± 9 W/m(2)) and LSR on the back (1.61 ± 0.07 vs. 1.20 ± 0.09 mg · min(-1) · cm(-2)), chest (1.33 ± 0.06 vs. 1.08 ± 0.09 mg · min(-1) · cm(-2)), and forearm (1.53 ± 0.07 vs. 1.20 ± 0.06 mg · min(-1) · cm(-2), men vs. women) became significantly greater in men during the last exercise period (P < 0.05). At each site, differences in LSR were solely due to a greater SGO in men, as opposed to differences in sweat gland activation. In contrast, no sex differences in SkBF were observed throughout the exercise period. The present study demonstrates that sex differences in sudomotor function are only evidenced beyond a certain requirement for heat loss, solely through differences in SGO. In contrast, the lower EHL and LSR in women are not paralleled by a lower SkBF response.

Sudomotor activity and heat balance with serial cooling and heating of thermosensors in the esophagus and stomach

This study assessed heat balance parameters and characterized transient sweating responses on the forehead following graded changes in local temperature of the esophagus and stomach from ingesting water of different temperatures. Seven male participants cycled for 75‐min in a temperate environment while ingesting four 3.2 mL·kg−1 boluses of either 1.5°C, 10°C, 37°C or 50°C water, 5‐min before, and 15, 30 and 45‐min after the start of exercise at 50% VO2max. Whole‐body sweat loss (WBSL), rectal temperature (Tre), mean skin temperature (Tsk) and local sweat rate on the forehead (SRhead) were measured throughout. Evaporative heat loss from sweating (Esk), respiratory heat loss, dry heat losses and heat exchange with ingested water were subsequently calculated to estimate net body heat storage (S). Despite no differences in Tre or Tsk, the onset time for sudmotor activity on the forehead was significantly greater with declining fluid temperature (P&lt;0.05), and both mean SRhead throughout exercise and WBSL was significantly lower with 1.5°C compared to 50°C water ingestion (P=0.002). Values for S were significantly greater following 1.5°C water ingestion relative to 50°C (P=0.033), indicating a disproportionate reduction of thermoregulatory sweating, and therefore Esk, relative to the internal heat transfer with 1.5°C water. It is proposed that these data present evidence of independent thermoafferent processes arising from changes in local temperature of the esophagus and/or stomach.Funding for the study was provided by a NSERC discovery grant.

Rate of heat storage does not influence exercise intensity at a fixed rating of perceived exertion

This study investigated whether different rates of decline in self‐selected work rate (W) were mediated by early differences in heat storage. Five males cycled at a W to maintain a perceived exertion of 16 (Borg scale) at 35°C and 25°C. Heat production (Hprod) was estimated via indirect calorimetry. Esophageal (Tes) and skin (Tsk) temperatures, as well as local sweat rates on the lower back (LSRback) and thigh (LSRthigh), were measured throughout. The level of muscle activation in vastus lateralis (VL) was assessed via integrated surface electromyography (iEMG). While dry heat loss was lower at 35°C (P&lt;0.01), sweating responses were elevated, indicated by greater LSRthigh at 2 min (P&lt;0.05), a trend toward greater LSRback (P=0.07), and earlier onsets at both sites (P=0.02). Similar Hprod and rates of change in Tes were found in both conditions (P&gt;0.05), yet at 35°C, exercise time was shorter (35°C: 22.6±4.9 min; 25°C: 32.1±10.4 min; P=0.03), and W (% of initial W) declined more rapidly by 15 min (35°C: 89.2±8.2%; 25°C: 82.2±8.0%; P&lt;0.01). Mean Tsk was lower throughout exercise at 25°C (P&lt;0.01). Similar changes in VL iEMG activity were found at 25°C and 35°C (P=0.28). In conclusion, reductions in W occur without early differences in heat storage between air temperatures, implicating factors other than the rate of heat storage, such as Tsk, in the regulation of exercise intensity.Supported by a NSERC Discovery Grant (O. Jay)

Sweating Is Greater in NCAA Football Linemen Independently of Heat Production

The study's purpose was to investigate whether differences in local sweat rates on the upper body between American football linemen (L) and backs (B) exist independently of differences in metabolic heat production. Twelve NCAA Division I American football players (6 linemen (mass = 141.6 ± 6.5 kg, body surface area (BSA) = 2.67 ± 0.08 m2) and 6 backs (mass = 88.1 ± 13.4 kg, BSA = 2.11 ± 0.19 m2)) cycled at a fixed metabolic heat production per unit BSA of 350 W·m(-2) for 60 min in a climatic chamber (t(db) [dry bulb temperature] = 32.4°C ± 1.0°C, t(wb) [wet bulb temperature] = 26.3°C ± 0.6°C, v [air velocity] = 0.9 ± 0.1 m·s(-1)). Local sweat rates on the head, arm, shoulder, lower back, and chest were measured after 10, 30, and 50 min of exercise. Core temperature, mean skin temperature, and HR were measured throughout exercise. Because metabolic heat production per unit surface area was fixed between participants, the rate of evaporation required for heat balance was similar (L = 261 ± 35 W·m(-2), B = 294 ± 30 W·m(-2), P = 0.11). However, local sweat rates on the head, arm, shoulder, and chest were all significantly greater (P < 0.05) in linemen at all time points, and end-exercise core temperature was significantly greater (P = 0.033) in linemen (38.5°C ± 0.4°C) relative to backs (38.0°C ± 0.2°C) despite a ∼25% lower heat production per unit mass. The change in mean skin temperature from rest was greater in linemen (P < 0.001) after 15, 30, 45, and 60 min, and HR was greater in linemen for the last 30 min of exercise. Football linemen sweat significantly more on the torso and head than football backs independently of any differences in metabolic heat production per unit BSA and therefore the evaporative requirements for heat balance. Despite greater sweating, linemen demonstrated significantly greater elevations in core temperature suggesting that sweating efficiency (i.e., the proportion of sweat that evaporates) was much lower in linemen.

Compensatory hyperhidrosis following thoracic sympathectomy: a biophysical rationale

A side-effect of endoscopic thoracic sympathectomy (ETS) is compensatory hyperhidrosis (CH), characterized by excessive sweating from skin areas with intact sudomotor function. The physiological mechanism of CH is unknown, but may represent an augmented local sweat rate from skin areas with uninterrupted sympathetic innervation based on evaporative heat balance requirements. For a given combination of activity and climate, the same absolute amount of evaporation (if any) is needed to balance the rate of metabolic heat production both pre- and post-ETS. However, the rate of local sweating per unit of skin surface area with intact sudomotor activity must be greater post-ETS as evaporation must be derived from a smaller skin surface area. Under conditions with high evaporative requirements, greater degradations in sweating efficiency associated with an increased dripping of sweat should also occur post-ETS, further pronouncing the sweat rate required for heat balance. In conclusion, in addition to the potential role of psychological stimuli for increased sudomotor activity, the existence of CH post-ETS can be described by the interplay between fundamental thermoregulatory physiology and altered heat balance biophysics and does not require a postoperative alteration in physiological control.

혈압 관리를 위한 4주간의 착의훈련이 고혈압 전단계자의 내열성에 미치는 영향

This study was performed on 5 prehypertensive male participants to investigate the effects of the clothing program for improving the vascular compliance on heat tolerance. The clothing program means the alternate stimulation of the temperature using clothes. The participants wore two different garments with <TEX>$1.5^{\circ}C$</TEX> difference in the temperature inside clothing in a climatic chamber (<TEX>$18.8{\pm}0.2^{\circ}C$</TEX>, <TEX>$38{\pm}3%RH$</TEX>) alternately for 4 weeks. Heat tolerance tests were conducted in the climatic chamber of <TEX>$35.2{\pm}0.5^{\circ}C$</TEX>, <TEX>$54{\pm}3%RH$</TEX> before and after the clothing program. The results were as follows. The <TEX>$\overline{T}$</TEX>sk, Tr and heart rate were lower in the post test than in the pre test (p<.01). The whole body and local sweat rates as well as systolic and diastolic blood pressures had reduced the tendencies in the post test. Participants felt less wet and more comfortable in the post test than in the pre test(p<.01). These results showed that the clothing program through the alternate stimulation of the temperature positively affected the improvement of heat tolerance.

Exercise-Induced Trace Mineral Element Concentration in Regional Versus Whole-Body Wash-Down Sweat

Simultaneous whole-body wash-down (WBW) and regional skin surface sweat collections were completed to compare regional patch and WBW sweat calcium (Ca), magnesium (Mg), copper (Cu), manganese (Mn), iron (Fe), and zinc (Zn) concentrations. Athletes (4 men, 4 women) cycled in a plastic open-air chamber for 90 min in the heat. Before exercise, the subjects and cycle ergometer (covered in plastic) were washed with deionized water. After the onset of sweating, sterile patches were attached to the forearm, back, chest, forehead, and thigh and removed on saturation. After exercise, the subjects and cycle ergometer were washed with 5 L of 15-mM ammonium sulfate solution to collect all sweat minerals and determine the volume of unevaporated sweat. Control trials were performed to measure mineral contamination in regional and WBW methods. Because background contamination in the collection system was high for WBW Mn, Fe, and Zn, method comparisons were not made for these minerals. After correction for minimal background contamination, WBW sweat [Ca], [Mg], and [Cu] were 44.6 ± 20.0, 9.8 ± 4.8, and 0.125 ± 0.069 mg/L, respectively, and 5-site regional (weighted for local sweat rate and body surface area) sweat [Ca], [Mg], and [Cu] were 59.0 ± 15.9, 14.5 ± 4.8, and 0.166 ± 0.031 mg/L, respectively. Five-site regional [Ca], [Mg], and [Cu] overestimated WBW by 32%, 48%, and 33%, respectively. No individual regional patch site or 5-site regional was significantly correlated with WBW sweat [Ca] (r = -.21, p = .65), [Mg] (r = .49, p = .33), or [Cu] (r = .17, p = .74). In conclusion, regional sweat [Ca], [Mg], and [Cu] are not accurate surrogates for or significantly correlated with WBW sweat composition.

Regional Sweating Differs Between Elite American Football Linemen and Backs Independently of Metabolic Heat Production

Evaporative heat loss via sweating is the primary heat dissipation avenue during exercise, particularly in a hot environment. In typical summer football training camps, larger linemen have significantly greater elevations in core temperature than smaller backs. However it is unclear if differences in sweat production are responsible for these higher core temperatures. PURPOSE: Investigate whether differences in local and whole-body sweat rates between football linemen and backs exist independently of differences in metabolic heat production. METHODS: 12 NCAA Division 1 American football players (6 linemen [mass: 141.6±6.5 kg; BSA: 2.67±0.08 m2] and 6 backs [mass: 88.1±13.4 kg; BSA: 2.11±0.19 m2]) exercised at a fixed metabolic heat production of 350 W/m2 for 60-min in a climatic chamber (Tdb: 32.4±1.0°C; Twb: 26.3±0.6°C; Vair: 0.9±0.1 m/s). Core temperature (Tcore) and mean skin temperature (Tsk) were measured throughout. Local sweat rates (LSR) on the head, arm, upper back, lower back and chest were measured after 10, 30 and 50 min of exercise, and whole-body sweat loss was measured using changes in pre and postexercise body weight. RESULTS: Whole-body sweat rate was identical in linemen (8.6±1.8 g/m2/min) and backs (8.6±1.4 g/m2/min); however LSR was significantly greater (P<0.05) in linemen at 4 of 5 sites (head, arm, upper back and chest) after 10-min; at 2 of 5 sites (arm and chest) after 30-min; but no differences were observed for LSR between linemen and backs after 50-min. At the end of exercise, Tcore was significantly greater (P=0.025) in linemen (38.48±0.39°C) relative to backs (38.01±0.24°C). Mean Tsk throughout was similar in linemen (35.34±0.48°C) compared to backs (35.21±0.25°C); however when accounting for differences in starting Tsk, linemen (1.71±0.23°C) had a greater change (P<0.001) than backs (0.82±0.26°C). CONCLUSION: Despite identical whole-body sweating at a fixed heat production per unit surface area, upper body LSR in linemen was greater during the early stages of exercise and presumably lower elsewhere. More profuse upper body sweating in linemen is attributed to greater changes in regional skin temperature. This potentially leads to a greater amount of non-evaporated sweat dripping off the body, a lower whole-body evaporative efficiency and greater elevations in core temperature.

Testing and Evaluation of Three Liquid Cooling Garments for Use During Spaceflight

Extravehicular activity poses several dangers to astronauts. A major concern is the regulation of core temperature and thermal comfort in the context of an impermeable extravehicular mobility unit microclimate and elevated energy expenditure rates for prolonged periods. PURPOSE: To identify the optimal features of each of three liquid cooling garments (MACS-Delphi [MD], Russian Orlan [RO], NASA LCVG [NL]) for maintaining core temperature and thermal comfort during exercise in mild (24°C) and hot (35°C) conditions. METHODS: Four male and two female participants (22-46 years old) performed 10 trials (each with five 20-minute exercise stages and two rest stages) to account for all garment configurations (with/without hood) and temperature regimes. Metabolic (VO2, Ve, RER), temperature (core, skin), cardiovascular (HR, SBP, DBP, SaO2), local sweat rate, and skin wetness data were collected and analyzed during stages five (moderate exercise) and seven (rest). Whole body sweat rate data was collected pre- and post-trial. RESULTS: SBP was lower in MD compared to NL and RO (123.29 vs. 126.92 and 123.29 vs. 128.17mmHg, respectively); HR was lower in MD compared to NL (103.36 vs. 106.66bpm); calf skin temperature was lower in NL compared to MD and RO (28.71 vs. 30.80 and 28.71 vs. 31.68°C, respectively); chest skin temperature was lower in RO compared to MD (27.94 vs. 30.01°C); thigh skin temperature was lower in NL compared to MD and RO (28.29 vs. 31.72 and 28.29 vs. 31.09°C, respectively). Significant differences (p ≤ 0.05) between garments were also found for local sweat rate (groin and upper back), whole body sweat rate and water flow rate. Core temperature was not different between the garments (p > 0.05). CONCLUSIONS: All three garments were similar in terms of regulating core temperature in a safe range during physical exertion in moderate and hot environments but there were variable effects between garments on cardiovascular and other thermoregulatory variables. Future research is needed to identify the roles of adding a cooling hood and/or ventilation system to LCGs in addition to determining optimal water temperature, flow rate, tubing arrangement, and ergonomic design. Supported by NASA Cooperative Agreement NNX07AI90A.