Whole-body Sweat Research Articles

Thermoregulatory Efficiency is Increased after Heat Acclimation in Tropical Natives

To evaluate the effects of heat acclimation on sweat rate redistribution and thermodynamic parameters, 9 tropical native volunteers were submitted to 11 days of exercise-heat exposures (40+/-0 degrees C and 45.1+/-0.2% relative humidity). Sudomotor function was evaluated by measuring total and local (forehead, chest, arm, forearm, and thigh) sweat rates, local sweat sodium concentration, and mean skin and rectal temperatures. We also calculated heat production (H), heat storage (S), heat exchange by radiation (R) and by convection (C), evaporated sweat (E(sw)), sweating efficiency (eta(sw)), skin wettedness (w(sk)), and the ratio between the heat storage and the sum of heat production and heat gains by radiation and convection (S/(H+R+C)). The heat acclimation increased the whole-body sweat rate and reduced the mean skin temperature. There were changes in the local sweat rate patterns: on the arm, forearm, and thigh it increased significantly from day 1 to day 11 (all p<0.05) and the sweat rates from the forehead and the chest showed a small nonsignificant increase (p=0.34 and 0.17, respectively). The relative increase of local sweat rates on day 11 was not different among the sites; however, when comparing the limbs (arm, forearm, and thigh) with the trunk (forehead and chest), there was a significant higher increase in the limbs (32+/-5%) in comparison to the trunk (11+/-2%, p=0.001). After the heat acclimation period we observed higher w(sk) and E(sw) and reduced S/(H+R+C), meaning greater thermoregulatory efficiency. The increase in the limb sweat rate, but not the increase in the trunk sweat rate, correlated with the increased w(sk), E(sw), and reduced S/(H+R+C) (p<0.05 to all). Altogether, it can be concluded that heat acclimation increased the limbs' sweat rates in tropical natives and that this increase led to increased loss of heat through evaporation of sweat and this higher sweat evaporation was related to higher thermoregulatory efficiency.

Accumulation of 2H2O in plasma and eccrine sweat during exercise-heat stress

The purpose of this research was to characterize the movement of ingested water through body fluids, during exercise-heat stress. Deuterium oxide ((2)H(2)O) accumulation in plasma and eccrine sweat was measured at two sites (back and forehead). The exercise of 14 males was controlled via cycle ergometry in a warm environment (60 min; 28.7 degrees C, 51%rh). Subjects consumed (2)H(2)O (0.15 mg kg(-1), 99.9% purity) mixed in flavored, non-caloric, colored water before exercise, then consumed 3.0 ml kg(-1) containing no (2)H(2)O every 15 min during exercise. We hypothesized that water transit from mouth to skin would occur before 15 min. (2)H(2)O appeared rapidly in both plasma and sweat (P < 0.05), within 10 min of water consumption. The ratio (2)H(2)O/H(2)O (D:H) was 47.3-55.0 times greater in plasma than in back sweat at minutes 10, 20, and 30 (DeltaD:H relative to baseline). At elapsed minute 20, the mean rate of deuterium accumulation (DeltaD:H min(-1)) in plasma was 14.9 and 23.7 times greater than in forehead and back sweat samples, respectively. Mean (+/-SE) whole-body sweat rate was 1.04 +/- 0.05 L h(-1) and subjects with the greatest whole-body sweat rate exhibited the greatest peak deuterium enrichment in sweat (r(2) = 0.87, exponential function); the peak (2)H(2)O enrichment in sweat was not proportional (P > 0.05) to body mass, volume of the deuterium dose, or total volume of fluid consumed. These findings clarify the time course of fluid movement from mouth to eccrine sweat glands, and demonstrate considerable differences of (2)H(2)O enrichment in plasma versus sweat.

Peripheral sweat gland function is improved with humid heat acclimation

1. The purpose of this study was to determine if humid heat acclimation improves thermoregulatory function at the level of the eccrine sweat gland. 2. Mean rectal temperature and heart rate were significantly ( p<0.05) reduced by 0.5 °C and 17 bpm, respectively, during an 8-day heat acclimation protocol in 13 male subjects. 3. Whole-body sweat rate was also significantly increased 20% during the same time period. The most important new finding was that humid heat acclimation produced a significant 63% increase in pilocarpine-induced sweat rate. These results strongly suggest that heat acclimation improves sweat gland function via a peripheral mechanism.

Thermoregulatory Responses to Constant versus Variable-Intensity Exercise in the Heat

To compare the thermoregulatory responses between constant (CON) and variable-intensity exercise (VAR) in a dry-hot environment (36 degrees C, 29% relative humidity, and 2.5 m x s(-1) airflow). In a random order, seven endurance-trained, heat-acclimated subjects cycled either at 60% VO2max (CON) or alternating 1.5 min at 90% VO2max with 4.5 min at 50% VO2max (VAR). Total work output (915 +/- 100 kJ) and exercise duration (90 min) were identical in both trials. Net metabolic heat production was not different between trials (394 +/- 12 vs 408+/- 11 W x m(-2) for VAR vs CON). However, heat storage (60 +/- 3 vs 48 +/- 4 W x m(-2)), the increase in rectal temperature (1.6 +/- 0.1 vs 1.3 +/- 0.1 degrees C), and final heart rate (HR; 147 +/- 5 vs 141 +/- 4 beats x min(-1)) were all higher for VAR than for CON (P < 0.05). During VAR, averaged forearm skin blood flow (S(K)BF) was lower, whereas whole-body sweat rate (1.23 +/- 0.1 vs 1.11 +/- 0.1 L x h(-1)) and dehydration (2.8 +/- 0.1% vs 2.5 +/- 0.2%) were higher than during CON (P < 0.05). Final blood lactate during VAR was higher than during CON (3.5+/- 0.4 vs 2.1 +/- 0.3 mmol x L(-1); P < 0.05). Ninety minutes of variable-intensity exercise in a hot environment increases heat storage and fluid deficit in comparison to the same amount of work performed in a constant-load mode. VAR increases not only thermal (i.e., heat storage) but also cardiovascular (i.e., heart rate) and metabolic (i.e., blood lactate) stresses, which makes it less advisable than CON when the goal is to minimize physiological stress.

Effect of Heat Acclimation on Sweat Minerals

This study examined the impact of 10 d of exercise-heat acclimation on sweat mineral concentrations. Eight male subjects walked on a treadmill at 3.5 mph, 4% grade for 100 continuous minutes or until rectal temperature reached 39.5 degrees C on 10 consecutive days in an environmental chamber set at 45 degrees C, 20% relative humidity. Arm sweat samples were collected during the first 30 min of exercise-heat stress on days 1 and 10 using a polyethylene arm glove. Final core temperature and HR values were significantly lower (P < 0.05) on day 10 versus day 1. Whole-body sweating rates increased by approximately 6% (P = 0.12). Sweat sodium concentration on day 10 (36.22 +/- 7.22 mM) was significantly lower than day 1 (54.49 +/- 16.18 mM) (P < 0.05). Sweat mineral concentrations of calcium (approximately 29%), copper (approximately 50%), and magnesium (approximately 43%) were also significantly lower on day 10 versus day 1 of heat acclimation (P < 0.05). A trend for lower sweat iron (approximately 75%; P = 0.07) and zinc (approximately 23%; P = 0.10) concentrations were observed from day 1 to day 10. The estimated hourly sweat mineral losses (arm concentration x whole-body sweat rate) were reduced for calcium (approximately 27%), copper (approximately 46%), and magnesium (approximately 42%) (P < 0.05), but not iron (75%) or zinc (approximately 16%) (P > 0.05), from day 1 to day 10. Exercise-heat acclimation conserves arm sweat mineral concentrations and possibly whole-body sweat losses of calcium, copper, and magnesium, and may reduce sweat iron and zinc concentrations.

Sweat secretion from the torso during passively-induced and exercise-related hyperthermia

Thermal sweating from the human torso accounts for about half of the whole-body sweat secretion, yet its intra-segmental distribution has not been thoroughly examined. Therefore, the aim of the current study was to provide a detailed description of the distribution of eccrine sweating within the torso during passively-induced (water-perfusion garment: 40 degrees C) and progressively increasing, exercise-related thermal strain (36 degrees C, 60% relative humidity). Sudomotor function was measured in ten males using ventilated sweat capsules (3.16 cm(2)) attached to twelve sites on the ventral (four), lateral (three) and dorsal (four) torso, and upper shoulder surfaces. Sweating increased asymptotically in all sites, with the final core temperature averaging 39.7 degrees C (+/-0.1) and heart rates being 181 b min(-1) (+/-2). During exercise, the mean torso sweat rate averaged 1.35 mgcm(-2)min(-1), with sweating from the lateral torso surfaces generally being the lowest. Each of the between-site comparisons with the lateral torso differed significantly (P < 0.05), except for comparisons with the chest (P = 0.051) and shoulder (P > 0.05). The intra-segmental differences between the lateral torso and the chest, abdomen, upper- and lower-back areas were significantly accentuated during exercise. From these data, it is evident that the torso is another region that does not have a uniform distribution of thermally-induced sweating. Thus, it is no longer acceptable for researchers, modellers, sweating manikins engineers or clothing manufacturers to assume that the sweat rates for all local sites within any body segment are equivalent.

Is sweat rate during steady state exercise related to maximum oxygen uptake?

The purpose of this study was to investigate whether whole-body sweat rate induced by exercise (SR ex) at the same oxygen uptake could be correlated with individual maximum oxygen uptake (peak oxygen uptake ( V ˙ O 2 peak ) ). A secondary purpose was to examine the relationship between SR ex and local sweat rate induced by pilocarpine on the forearm at rest (SR pilo). Nine healthy young males ( V ˙ O 2 peak 55.2 (12.3) mL min −1 kg −1, mean (SD); 43.3–76.1 mL min −1 kg −1, range), acclimatized to a tropical climate had their sweating stimulated in two situations: (1) exercise-induced whole-body sweat by 120 min of cycling exercise at a constant submaximal oxygen uptake of 1.65 L min −1 or (2) pilocarpine-induced sweat on the right forearm with 0.5% pilocarpine hydrochloride (1.5 mA, 5 min) at rest. The SR ex was not correlated with V ˙ O 2 peak ( r = - 0.53 , p = 0.14 ). In addition, there was not correlation between SR ex (0.38 (0.03) mg cm −2 min −1) and SR pilo (0.36 (0.20) mg cm −2 min −1) ( r = 0.23 , p = 0.57 ). These results suggest that whole-body sweat rate during exercise at the same oxygen uptake in a temperate environment is not related to V ˙ O 2 peak . Furthermore, the eccrine sweat gland does not respond similarly for local pilocarpine or exercise stimuli.

Effect of partial body cooling on thermophysiological responses during cycling work in a hot environment

1. We measured rectal ( T re), tympanic ( T ty), and skin ( T sk) temperatures, skin blood flow (SkBF), local and whole-body sweat rate (SR), heart rate (HR), and thermal sensation in seven men during bicycle exercise for 40 min, with and without two types of cooling. 2. An increasing rate in T ty was suppressed by the ice cooling, but not in T re. By the fan cooling T ty was lowered 0.3 °C. Δ[ T re– T ty] was markedly higher with the fan cooling than with the ice cooling or control. 3. Local SR, SkBF and HR were significantly inhibited by both types of cooling, but whole-body SR was not lowered. However, enhancement of evaporative efficiency was observed with the fan cooling. There were improvements of thermal sensation during exercise after both types of cooling. 4. As apparent thermoregulatory responses-to-core temperature ( T core) relation, the relation differed between the control and both cooling trials. Δ [ T re– T ty]-to- and T re-to-local SR relation slopes were altered in both cooling trials as compared with the control. In all trials, the slope of SkBF– T ty relation was suddenly reduced at approximately 37.5 °C. 5. It is concluded that the present study confirms the effectiveness of partial cooling on the human body. We suggest that the beneficial effects of the cooling on the body should be taken into account when designing an adequate training program.

Thermoregulation during Exercise in Individuals with Spinal Cord Injuries

The increased participation in wheelchair sports in conjunction with environmental challenges posed by the most recent Paralympic venues has stimulated interest into the study of thermoregulation of wheelchair users. This area is particularly pertinent for the spinal cord injured as there is a loss of vasomotor and sudomotor effectors below the level of spinal lesion. Studies within this area have examined a range of environmental conditions, exercise modes and subject populations. During exercise in cool conditions (15-25 degrees C), trained paraplegic individuals (thoracic or lumbar spinal lesions) appear to be at no greater risk of thermal injury than trained able-bodied individuals, although greater heat storage for a given metabolic rate is evident. In warm conditions (25-40 degrees C), trained subjects again demonstrate similar core temperature responses to the able-bodied for a given relative exercise load but elicit increased heat storage within the lower body and reduced whole-body sweat rates, increasing the risk of heat injury. The few studies examining a wide range of lesion levels have noted that, for paraplegic individuals where heat production is matched by available sweating capacity, excessive heat strain may be offset. Studies relating to tetraplegic subjects (cervical spinal lesions) are fewer in number but have consistently shown this population to elicit much faster rates of core and skin temperature increase and thermal imbalance in both cool and warm conditions than paraplegic individuals. These responses are due to the complete absence or severely reduced sweating capacity in tetraplegic subjects. During continuous exercise protocols, the main thermal stressor for tetraplegic subjects appears to be environmental heat gain, whereas during an intermittent-type exercise protocol it appears to be metabolic heat production. Fluid losses during exercise and heat retention during passive recovery from exercise are related to lesion level. Future research is recommended to focus on the specific role of absolute and relative metabolic rates, sweating responses, training status and more sport- and vocation-specific exercise protocols.

Possible Biphasic Sweating Response during Short-term Heat Acclimation Protocol for Tropical Natives

The aim of the present study was to evaluate the sweat loss response during short-term heat acclimation in tropical natives. Six healthy young male subjects, inhabitants of a tropical region, were heat acclimated by means of nine days of one-hour heat-exercise treatments (40+/-0 degrees C and 32+/-1% relative humidity; 50% (.)VO(2peak) on a cycle ergometer). On days 1 to 9 of heat acclimation whole-body sweat loss was calculated by body weight variation corrected for body surface area. On days 1 and 9 rectal temperature (T(re)) and heart rate (HR) were measured continuously, and rating of perceived exertion (RPE) every 4 minutes. Heat acclimation was confirmed by reduced HR (day 1 rest: 77+/-5 b.min(-1); day 9 rest: 68+/-3 b.min(-1); day 1 final exercise: 161+/-15 b.min(-1); day 9 final exercise: 145+/-11 b.min(-1), p<0.05), RPE (13 vs. 11, p<0.05) and T(re) (day 1 rest: 37.2+/-0.2 degrees C; day 9 rest: 37.0+/-0.2 degrees C; day 1 final exercise: 38.2+/-0.2 degrees C; day 9 final exercise: 37.9+/-0.1 degrees C, p<0.05). The main finding was that whole-body sweat loss increased in days 5 and 7 (9.49+/-1.84 and 9.56+/-1.86 g.m(-2).min(-1), respectively) compared to day 1 (8.31+/-1.31 g.m(-2).min(-1), p<0.05) and was not different in day 9 (8.48+/-1.02 g.m(-2).min(-1)) compared to day 1 (p>0.05) of the protocol. These findings are consistent with the heat acclimation induced adaptations and suggest a biphasic sweat response (an increase in the sweat rate in the middle of the protocol followed by return to initial values by the end of it) during short-term heat acclimation in tropical natives.

Comparison of sweat rate during graded exercise and the local rate induced by pilocarpine

Centrally stimulated sweat rate produced by graded exercise until exhaustion was compared to the local sweat rate induced by pilocarpine, often used as a sweating index for healthy individuals. Nine young male volunteers (22 +/- 4 years) were studied in temperate environment in two situations: at rest and during progressive exercise with 25 W increases every 2 min until exhaustion, on a cycle ergometer. In both situations, sweating was induced on the right forearm with 5 ml 0.5% pilocarpine hydrochloride applied by iontophoresis (1.5 mA, 5 min), with left forearm used as control. Local sweat rate was measured for 15 min at rest. During exercise, whole-body sweat rate was calculated from the body weight variation. Local sweat rate was measured from the time when heart rate reached 150 bpm until exhaustion and was collected using absorbent filter paper. Pharmacologically induced local sweat rate at rest (0.4 +/- 0.2 mg cm-2 min-1) and mean exercise-induced whole-body sweat rate (0.4 +/- 0.1 mg cm-2 min-1) were the same (P > 0.05) but were about five times smaller than local exercise-induced sweat rate (control = 2.1 +/- 1.4; pilocarpine = 2.7 +/- 1.2 mg cm-2 min-1), indicating different sudorific mechanisms. Both exercise-induced whole-body sweat rate (P < 0.05) and local sweat rate (P < 0.05) on control forearm correlated positively with pilocarpine-induced local sweat rate at rest. Assuming that exercise-induced sweating was a result of integrated physiological mechanisms, we suggest that local and whole-body sweat rate measured during graded exercise could be a better sweating index than pilocarpine.

Acute effects of dehydration on sweat composition in men during prolonged exercise in the heat.

To determine whether acute exercise-heat-induced dehydration affects sweat composition, eight males cycled for 2 h at 39.5 +/- 1.6% VO2peak on two separate occasions in a hot-humid environment (38.0 +/- 0.0 degrees C, 60.0 +/- 0.1% relative humidity). During exercise, subjects ingested either no fluid (dehydration) or a 20 mmol L(-1) sodium chloride solution (euhydration). The volume of solution, calculated from whole-body sweat loss and determined in a familiarization trial, was ingested at 0 min and every 15 min thereafter. Venous blood was collected at 0, 60 and 120 min of exercise and sweat was aspirated from a patch located on the dominant forearm at 120 min. Following the 2-h cycling exercise, sweat [Na+] and [Cl-] was greater (P < 0.05) in the dehydration trial (Na+ 91.1 +/- 6.8 mmol L(-1); Cl- 73.3 +/- 3.5 mmol L(-1)) compared with the euhydration trial (Na+ 81.1 +/- 5.9 mmol L(-1); Cl- 68.5 +/- 3.3 mmol L(-1)). In addition, dehydration invoked a greater serum [Na+] (142.2 +/- 0.7 mmol L(-1); P < 0.05), [Cl-] (105.8 +/- 0.6 mmol L(-1); P < 0.05) and [K+] (5.27 +/- 0.2 mmol L(-1); P < 0.05) over the euhydration values for [Na+], [Cl-] and [K+], respectively (138.9 +/- 0.6, 102.9 +/- 0.5 and 4.88 +/- 0.1 mmol L(-1)). Plasma aldosterone was also significantly higher during exercise in the dehydration trial compared with the euhydration trial (53.8 +/- 3.8 vs. 40.0 +/- 4.3 ng dL(-1); P < 0.05). Acute exercise-heat stress without fluid replacement resulted in a greater sweat [Na+] and [Cl-] which was potentially related to greater extracellular fluid [Na+], plasma aldosterone or sympathetic nervous activity.

Effects of mild heat exposure on sleep stages and body temperature in older men.

The purpose of this study was to examine the effects of mild heat exposure on sleep stages and body temperature in older men. Ten healthy male volunteers with a mean age of 69.2 +/- 1.35 years served as subjects. The experiments were carried out under two different sets of conditions: 26 degrees C 50% relative humidity (RH) and 32 degrees C 50% RH. The subjects slept from 2200 hours to 0600 hours with a cotton blanket and wearing short-sleeve pajamas and shorts on a bed covered by a sheet. Electroencephalogram, electro-occulogram and mental electromyogram recordings were made through the night. Rectal and skin temperatures were measured continuously. No significant differences were observed in sleep onset latency. In time spent in each sleep stage, wakefulness was significantly increased at 32 degrees C than at 26 degrees C. The total amount of wakefulness increased and rapid eye movement sleep (REM) decreased at 32 degrees C compared to 26 degrees C. The fall in rectal temperature was significantly suppressed and the mean skin temperature was significantly higher at 32 degrees C than at 26 degrees C. These results suggest that, for older men, even mild heat exposure during the nighttime sleep period may increase thermal load, suppress the decrease of rectal temperature, decrease REM, and increase wakefulness and whole-body sweat loss.

Whole-Body Sweat Rate during Graded Exercise Testing and Sweat Rate during Prolonged Exercise

Whole-Body Sweat Rate during Graded Exercise Testing and Sweat Rate during Prolonged Exercise

Whole-Body Sweat Rate during Graded Exercise Testing and Sweat Rate during Prolonged Exercise

2143 Sweating capacity has been measured by pharmacological induction (cholinergic agents) and during prolonged exercise. A recent study showed correlation between sweat rate (SR) induced by pilocarpine through iontophoresis and SR during graded exercise testing until exhaustion (GET). Therefore, it is interesting to know whether GET could be a reliable predictive index of the sweating capacity in others exercising situations. PURPOSE: Measure the whole-body SR during GET and during a prolonged exercise (PRO) in the same individuals. Methods: Nine healthy male volunteers (22,3 ± 3.6 yrs; 176.3 ± 5.9 cm; 69.2 ± 7.6 kg; body surface area (BSA): 1.85 ± 0.1 m2; VO2peak: 57 ± 12 mLO2.kg−1.min−1) performed two exercises bouts in thermoneutral environment (18.4 ± 0,4 °C and 19 ± 0.6 °C WBGT, GET and PRO, respectively). The GET consisted of 25W of power increments every 2 min on a cycle ergometer until exhaustion. During PRO the volunteers cycled 2 hours at a constant power (500 kcal.h−1). Whole-body SR was calculated by the difference of the body mass after exercises, divided by BSA and by the duration of exercise. Results: The SR in GET (4.1 ± 1.3 g.m−2.min−1) was similar to SR in PRO (4.1 ± 1.0 g.m−2.min−1) and there was a significant correlation between the SR during GET and PRO (r = 0.79, r2 = 0.62, p = 0.01). Conclusion: The PRO stimulated the sweating in a proportional way to GET, which suggests that the measurement of sweating during a graded exercise testing could be a predictive index of the sweating capacity in a thermoneutral environment. Supported by: CAPES, CNPq, FAPEMIG, SNE

Effects of head cooling on human sleep stages and body temperature.

The purpose of this study was to confirm the effect of head cooling on human sleep stages and body temperature. Nine healthy male volunteers with a mean age of 25 +/- 3.77 years served as subjects. The experiments were carried out under three different sets of conditions: 26 degrees C, relative humidity (RH) 50% (26/50); 32 degrees C, RH 80% (32/80); and 32 degrees C RH 80% with the use of a cooling pillow (32/80 HC). The subjects slept from 2300 hours to 0700 hours with a cotton blanket, wearing short-sleeved pyjamas and shorts on a bed, which was covered with a sheet. Electroencephalograms, electro-ouclogram, and mental electromyelograms were recorded through the night. Rectal temperature (Tre) and skin temperature (Tsk) were measured continuously. Whole-body sweat and the tympanic temperature (Tty) were measured before and after sleep. Wakefulness significantly increased at 32/80 than at 26/50; however, no significant difference was observed between 32/80 HC and 26/50. Tre and mean Tsk were higher both at 32/80 and 32/80 HC than at 26/50. The whole-body sweat loss was significantly greater and Tty in the morning was higher at 32/80 than 32/80 HC and 26/50. These results suggest that head cooling during sleep may help to decrease the whole-body sweat rate during sleep under humid heat conditions.

WEARING A CAP, THERMAL BALANCE, AND THERMAL SENSATION DURING RUNNING IN A WARM ENVIRONMENT

Head cooling during exercise in a warm environment removes 20% of the metabolic heat produced, reducing physiological strain, rectal temperature, sweat rate, and thermal discomfort. Wearing a cap during long distance running races in a warm environment is common. Theoretically, wearing a cap during running in a warm environment may impede body heat loss, increasing body core temperature and thermal discomfort, but this is unclear based upon the scientific literature. PURPOSE: To determine if wearing a cap alters thermal balance and thermal sensation during running in a warm environment. METHODS: Eight (6 males, 2 females) well-trained runners ran for 1 hour at 67% VO2 max in a warm environment (Tdb = 31 °C, relative humidity = 41%) wearing (CAP) or not wearing (NOCAP) a white cotton/polyester cap. During both running trials, subjects consumed 2 ml kg−1 of water every 15 minutes. Thermal balance was assessed using continuous monitoring of rectal (Trec) and skin temperatures (Ts, weighted mean: forehead, chest, lower back, forearm, palm, thigh) as well as measurement of whole-body sweat loss and thermal sensation of the head and overall body (10-point scale). RESULTS: Mean (± SEM) Trec rose steadily from 36.81 (± 0.24) °C to 38.16 (± 0.15) °C during NOCAP and from 36.76 (± 0.19) °C to 38.27 (± 0.29) °C during CAP. There were no significant differences in Trec or Te (p > 0.05) between groups. One hour of running in a warm environment elicited a whole-body sweat loss of 1.23 (± 0.11) liters during NOCAP and 1.30 (± 0.13) liters during CAP with no differences (p > 0.05) between treatments. Ratings of thermal sensation for the head and overall body indicated that subjects felt warm during both NOCAP and CAP, with no differences (p > 0.05) between running trials. Heart rate increased similarly to 164 (± 3.88) and 166 (± 8.38) beats min−1 during the last 5 minutes of NOCAP and CAP. Rating of perceived exertion averaged 12.5 (± 0.73) and 13.38 (± 1.15) during the last few minutes of NOCAP and CAP, respectively, with no differences (p > 0.05) between groups. CONCLUSION: Wearing a cap during prolonged, moderate intensity running in a warm environment does not significantly alter thermal balance, thermal sensation, or physiological stress. Therefore, such a practice should not compromise endurance performance or increase the incidence of thermal injury.

SWEAT AND SODIUM LOSSES IN CRAMP-PRONE PROFESSIONAL FOOTBALL PLAYERS

Severe, debilitating muscle cramping is often associated with large fluid and sweat sodium losses. Our purpose was to determine whether or not sweat [Na+] and large fluid losses were associated in cramp-prone professional football players (N = 3). Players were referred for testing due to frequent cramping problems and were interviewed for history of severe muscle cramps in the lower extremities or whole body during pre-season preparation. Since pre-collegiate play, all players had experienced frequent, intense muscle cramps during explosive movements. Change in bodyweight and site-specific sweat patches were used to measure gross sweat loss and estimate mean whole-body sweat rate and sweat electrolyte values during one hour of cycle exercise (workload ≈ 150 W) in a warm environment (80°F, 50% RH) while wearing shorts.TableThese players showed large inter-individual variability in sweat rates and sweat [Na+]. Longer practices in full uniform and in hotter, more humid conditions than those of our one-hour study are likely to increase the risk for larger sweat and sodium losses and the potential for heat-related illness and cramping. While the association between muscle cramps and fluid/sodium losses has yet to be fully elucidated, these data do support that large fluid and sodium losses may be evidenced in players with a history of muscle cramps.

Variations in regional sweat composition in normal human males

This project aimed to quantify the regional distribution of sweat composition over the skin surface and to determine whether sweat constituent concentrations collected from regional sites can estimate whole-body concentrations. Ten males cycled for 90 min in a 20°C (50 % relative humidity) environment at 45 % peak aerobic power. Sweat was collected from eleven skin regions and the whole body, using a wash-down technique. Strong relationships were evident between the regional and whole-body sweat [Na+] and [Cl-], such that the thigh and calf exhibited greater correlation coefficients than area-weighted means derived from four and eight skin regions. Therefore, in this particular protocol the whole-body sweat [Na+] and [Cl-] could be predicted from regional sweat collections. Relationships between sweat constituents were evident for sweat [Na+] and pH, and sweat [K+] and [lactate] when data were pooled between skin regions and subjects. To our knowledge this is the first investigation to report a positive relationship between sweat [K+] and [lactate]. The exact mechanism responsible for the positive relationship between sweat [K+] and [lactate] is uncertain although it is speculated to occur at the secretory coil.

Variations in regional sweat composition in normal human males.

This project aimed to quantify the regional distribution of sweat composition over the skin surface and to determine whether sweat constituent concentrations collected from regional sites can estimate whole-body concentrations. Ten males cycled for 90 min in a 20 degrees C (50% relative humidity) environment at 45% peak aerobic power. Sweat was collected from eleven skin regions and the whole body, using a wash-down technique. Strong relationships were evident between the regional and whole-body sweat [Na+] and [Cl-], such that the thigh and calf exhibited greater correlation coefficients than area-weighted means derived from four and eight skin regions. Therefore, in this particular protocol the whole-body sweat [Na+] and [Cl-] could be predicted from regional sweat collections. Relationships between sweat constituents were evident for sweat [Na+] and pH, and sweat [K+] and [lactate] when data were pooled between skin regions and subjects. To our knowledge this is the first investigation to report a positive relationship between sweat [K+] and [lactate]. The exact mechanism responsible for the positive relationship between sweat [K+] and [lactate] is uncertain although it is speculated to occur at the secretory coil.