Effects of 6-h exposure to low relative humidity and low air pressure on body fluid loss and blood viscosity.

The purpose of this study was to investigate the effects of 6-h exposure to low relative humidity (RH) and low air pressure in a simulated air cabin environment on body fluid loss (BFL) and blood viscosity. Fourteen young healthy male subjects were exposed to four conditions, which combined RH (10% RH or 60% RH) and air pressure (NP: sea level or LP: equivalent to an altitude of 2000 m). Subjects remained seated on a chair in the chamber for 6 h. Their diet and water intake were restricted before and during the experiment. Insensible water loss (IWL) in LP10% condition was significantly greater than in NP60% condition; thus, combined 10%RH and LP conditions promoted a greater amount of IWL. The BFL under the LP condition was significantly greater than that under the NP condition. Blood viscosity significantly increased under LP conditions. Increases in red blood cell counts (RBCs) and BFL likely contributed to the increased blood viscosity. These findings suggest that hypobaric-induced hypoxia, similar to the conditions in the air cabin environment, may cause increased blood viscosity and that the combined low humidity and hypobaric hypoxia conditions increase IWL.

Decay of heat acclimation during exercise in cold and exposure to cold environment.

Sixteen male students exercised for 14 days (1 h/day) in the heat for heat acclimation (HA). During deacclimation (DA) one group exercised in the cold (EXG, n=8) for 60 min/day (morning) and was exposed to the cold for another hour (afternoon) for 14 days. The other group was exposed to the cold (EPG, n=8) for 1 h each in the morning and afternoon (Ta: 18.0 degrees C, RH: 58%) over the same period. All returned to exercise in the heat for reacclimation (RA) for 10 days. Subjects were tested on days 1, 16, 21, 32, 36 and 44 on a bicycle ergometer for 60 min at 60% of VO(2max) in the heat (Ta: 31.1 degrees C, RH: 70%). Rectal temperature (T (re)) and heart rate (HR) at 40 min of exercise were used to determine the decay/gain of HA, which was calculated using the formula described by Pandolf et al. (Ergonomics, 20:399-408, 1977). After HA (day 16) T (re) and HR decreased significantly. During DA, EXG showed decay in T (re) of 24 and 35% and HR of 29 and 35% on days 21 and 32, respectively. For EPG the corresponding decay was of 2 and 9% for T (re) and 17 and 17% for HR. After 10 days of RA, EXG showed gains of 11% in T (re) and 12% in HR, while EPG showed gains of 47% in T (re) and 38% in HR. In conclusion, EXG had greater decay during DA and lower gains in RA compared to EPG. However, the differences between groups were significant only for T (re) after 4 days of DA.

Physiological responses and manual performance in humans following repeated exposure to severe cold at night.

We evaluated human physiological responses and the performance of manual tasks during exposure to severe cold (-25 degrees C) at night (0300-0500 hours) and in the afternoon (1500-1700 hours). Thirteen male students wearing standard cold protective clothing occupied a severely cold room (-25 degrees C) for 20 min, and were then transferred to a cool room (10 degrees C) for 20 min. This pattern of exposure was repeated three times, for a total time of exposure to extreme cold of 60 min. The experiments were started either at 1500 hours or 0300 hours and measurements of rectal temperature, skin temperature, blood pressure, performance in a counting task, hand tremor, and subjective responses were made in each condition. At the end of the experiment at night the mean decrease in rectal temperature [0.68 (SEM 0.04) degree C] was significantly greater than that at the end of the experiment in the afternoon [0.55 (SEM 0.08) degree C, P < 0.01]. After the second cold exposure at night the mean increase in diastolic blood pressure [90 (SEM 2.0) mmHg] was significantly greater than that at the end of the second cold exposure in the afternoon [82 (SEM 2.8) mmHg, P < 0.01]. At the end of the second cold exposure at night, mean finger skin temperature [11.8 (SEM 0.8) degrees C] was significantly higher than that at the comparable time in the afternoon [9.0 (SEM 0.7) degrees C, P < 0.01]. Similarly for the toe, mean skin temperature at the start of the second cold exposure at night [25.6 (SEM 1.5) degrees C] was significantly higher than in the afternoon [20.1 (SEM 0.8) degrees C, P < 0.01]. The increased skin temperatures in the periphery resulted in increased heat loss. Since peripheral skin temperatures were highest at night, the subjects noted diminished sensations of thermal cold and pain at that time. Manual dexterity at the end of the first cold exposure at night [mean 83.7 (SEM 3.6) times.min-1] had decreased significantly more than at the end of the first cold exposure in the afternoon [mean 89.4 (SEM 3.5) times.min-1, P < 0.01]. These findings of a lowered rectal temperature and diminished manual dexterity suggest that there is an increased risk of both hypothermia and accidents for those who work at night.

Japanese and Korean elderly people's evaluation of clothing colors for elderly people.

This study evaluated the clothing colors in the elderly. We took photos using the elderly as models, displayed them on a computer screen, and produced 75 colors of the clothing in the elderly using computer graphics. The 75 colors were evaluated by Japanese and Korean elderly women. We compared the ideal colors for and the colors actually worn by elderly people in Japan and Korea. Japanese and Korean elderly women differed concerning their ideal clothing color and their most often worn color. The images concerning clothing colors also differed between the two groups, suggesting differences in their views related to clothing. Japanese elderly women tended to view clothing as a means of expressing their individuality, while Korean elderly women tended to view clothing as a means of expressing their character.

Effects of bathing and hot footbath on sleep in winter.

The effects of daily bathing and hot footbath (immersion of feet in hot water) in winter on the sleep behavior of nine healthy female volunteers were studied. Subjects were assigned to three sleep conditions: sleep after bathing (Condition B), sleep after hot footbath (Condition F), and sleep without either treatment (Control). Polysomnograms (consisting of electroencephalograph, electrooculograph, and electromyograph) were obtained, and body movements during sleep were measured while monitoring both the rectal and skin temperatures of subjects. In addition, subjective sleep sensations were obtained with a questionnaire answered immediately by the subjects on awakening. The rectal temperature increased by approximately 1.0 degree C under Condition B, but this elevation was not observed under Condition F compared with Control. In contrast, the respective increases in the mean skin temperature of participants subjected to bathing and hot footbath were greater than those of Control, although these temperature differences became negligible 2 h after subjects went to bed. The sleep onset latency was shortened under both conditions compared with Control. Body movements during the first 30 min of sleep in Control were greater than under the other conditions. Rapid eye movement (REM) sleep decreased under Condition B compared with Condition F, and stage 3 was greater under the latter condition compared with Control. As such, the subjective sleep sensations were better under the two treatment conditions. These results suggest that both daily bathing and hot footbath before sleeping facilitates earlier sleep onset. A hot footbath is especially recommendable for the handicapped, elderly, and disabled, who are unable to enjoy regular baths easily and safely.

Japanese and Korean female students' evaluation of elderly people's clothing colors.

This study evaluated the clothing colors in the elderly. We took photos using the elderly as models, displayed them on a computer screen, and produced 75 colors of the clothing in the elderly using computer graphics. The 75 colors were evaluated by Japanese and Korean female students. We compared the ideal colors for and the colors actually worn by elderly people in Japan and Korea. Korean students tended to evaluate high value colors positively, while Japanese students tended to evaluate low value colors positively. When asked to choose the ideal clothing color for elderly people, the choices differed between the Korean student group and the Japanese student group. The images held concerning these colors also differed between the two groups. When selecting the ideal color to be worn by elderly people, Japanese students attached importance to taste, brilliance, functionality and comfort. On the other hand, Korean students attached importance to commonness and inactivity when selecting the ideal clothing color for elderly people. Thus, in the present study, the evaluation of the clothing colors for elderly people differed between Japanese and Korean students.

Short-term longitudinal changes in subcutaneous fat distribution and body size among Japanese women in the third decade of life.

This research clarified the changes in body shape among Japanese women aged in their 20's, by measuring the subcutaneous fat distribution over the whole body and its circumference at certain points. The subjects, 13 healthy women, were measured twice, once in their early 20's and 5 years later in their late 20's. Subcutaneous fat thickness was measured at 14 points on the body using the B-mode ultrasound method and the body size was measured directly at 8 points on the body using a steel measure. Subcutaneous fat thickness tends to increase with age, except at the cheek, neck, bust and leg. Significant increases were detected especially at lower parts of the trunk such as the waist and infragluteal region. Meanwhile, despite the significant change in subcutaneous fat thickness, the circumferences measured did not change, and also weight tended to decrease with age. Based on this finding, except for fat, body mass, such as muscle and bone, decreases with age due to decreased exercise and changes in calorie intake. Cluster analysis of the accumulation patterns of subcutaneous fat indicated that there were the following 3 patterns of subcutaneous fat accumulation from the early 20's to the late 20's. I. Accumulation on the whole trunk (bust, abdomen, waist and back) and upper arm--trunk/upper arm accumulation pattern. II. Significant accumulation around waist--waist accumulation pattern. III. Even accumulation at abdomen, side abdomen, hip and lower hip--abdomen/hip accumulation pattern.

Bathing before sleep in the young and in the elderly.

In this study we investigated the effects of bathing on the quality of sleep in 30 elderly people (ages 65-83 years) and in 30 young people (ages 17-22 years) in their homes. Room temperature did not vary significantly during the nights that data were acquired, ranging from 8 to 12 degrees C. After bathing and at the beginning of sleep, the mean (SE) rectal temperatures of the young and the elderly were 37.8 (0.08) and 37.5 (0.07) degrees C, respectively, and were higher by 0.7 (0.13) and 0.6 (0.07) degrees C, respectively, than when the subjects had not bathed. At the beginning of the sleep after bathing in the young subjects, skin temperature was 32.5 (0.24) and 1.5 (0.34) degrees C higher than when those subjects had not bathed. In the elderly, however, there were no significant differences in skin temperature with and without prior bathing because they used electric blankets during sleep. After bathing, the young people reported "warmth" in their hands and/or legs, while the elderly more often reported "good sleep" or "quickness of falling asleep". During the first 3 h of sleep, body movements were less frequent after bathing for both the young and the elderly subjects. The results suggest that a bath before sleep enhances the quality of sleep, particularly in the elderly.

Perceived, actual, and seasonal changes in the shape of the face, hands and legs.

In this study, we measured the shape of the face, legs, hands and fingers during the course of a day to determine the amount of swelling. We examined the relationship between the perception of swelling and the degree of actual swelling, and considered the influence of seasonal factors. The topology of the face was measured using the 3D curved shape measuring apparatus, VOXELAN, while the circumference of the legs and fingers and the volume of the hands were also recorded. The measurements were used to determine the amount of change in each parameter, which was then used to determine the degree of swelling. The subjects for the experiment were 10 healthy Japanese women aged 24 to 30 years of standard build (BMI: 19.3-25.0). Measurements were carried out twice a day in the mornings and afternoon, first between 8:30 and 10:00 a.m. and then between 4:00 and 5:30 p.m. At each measurement session, subjects were asked if they perceived swelling to have occurred. We investigated the relationship between the degree of actual swelling and the reported perception of swelling. We also investigated the influence of seasonal factors by conducting the same tests on the same subjects in summer (August 1997) and in winter (February-March 1998). The relationship between perceived and actual swelling differs depending on the part of the body. For the face, actual swelling correlates strongly with perceived swelling. This trend is particularly noticeable for the upper eyelids. For the thigh and lower leg, on the other hand, there was no significant difference. The frequency with which subjects reported the perception of swelling varied depending on the area of the body, and was generally extremely low for the thighs, hands and fingers. With respect to seasonal variation, swelling in the face, hands and feet tended to be more pronounced during the summer. In the facial region, the biggest difference was in the lower eyelid, where swelling increased more than five times. This level of variation suggests that the atmospheric temperature is the main factor affecting swelling.

Thermal responses from repeated exposures to severe cold with intermittent warmer temperatures.

This study was conducted to evaluate physiological reaction and manual performance during exposure to warm (30 degrees C) and cool (10 degrees C) environments after exposure to very low temperatures (-25 degrees C). Furthermore, this experiment was conducted to study whether it is desirable to remove cold-protective jackets in warmer rooms after severe cold exposure. Eight male students remained in an extremely cold room for 20 min, after which they transferred into either the warm room or the cool room for 20 min. This pattern was repeated three times, and the total cold exposure time was 60 min. In the warm and cool rooms, the subjects either removed their cold-protective jackets (Condition A), or wore them continuously (Condition B). Rectal temperature, skin temperatures, manual performance, blood pressure, thermal, comfort and pain sensations were measured during the experiment. The effects of severe cold on almost all measurements in the cool (10 degrees C) environment were greater than those in the warm (30 degrees C) environment under both clothing conditions. The effects of severe cold on all measurements under Condition A except rectal temperature and toe skin temperature were significantly greater than those under Condition B in the cool environment but, not at all differences between Condition A and Condition B in the warm environments were significant. It was recognized that to remove cold-protective jackets in the cool room (10 degrees C) after severe cold exposure promoted the effects of severe cold. When rewarming in the warm resting room (30 degrees C), the physiological and psychological responses and manual performance were not influenced by the presence or absence of cold-protective clothing. These results suggest that it is necessary for workers to make sure to rewarm in the warm room outside of the cold storage and continue to wear cold-protective clothing in the cool room.

Physiological responses of men and women during exercise in hot environments with equivalent WBGT.

Eight Japanese men and women participated in this study. They were randomly exposed to two environments: hot-dry; HD (Ta = 40 degrees C, rh 30%, wet bulb globe temperature (WBGT) = 32 degrees C) and hot-wet; HW (Ta = 31 degrees C, rh = 80%, WBGT = 32 degrees C) for 110 min. During the exposure, they rested on a bicycle ergometer for 20 min during rest and 30 min during recovery, then they pedaled it with an intensity of 40% VO2 max for 60 min. Tre, Tsk, and HR were recorded every minute. Total sweat loss and dripping were measured by independent bed balances which was connected to a computer processing with an accuracy of 1 g throughout the experiment. Sweat sodium concentration at forearm and back sites were collected by sweat capsule technique. These results showed that delta Tre, Tsk, evaporated sweat, dripping sweat, body heat storage of both sexes in HD were significantly higher than these in HW during exercise. HR of men in HD at the end of recovery was slightly higher than that of women. Whereas the sweat sodium concentration at forearm and back sites in both sexes remained unchanged either in HD or HW environment, it was found that HD was more stressful than HW environment under equivalent WBGT.

Physiological responses of women during exercise under dry-heat condition in winter and summer.

Fourteen young Japanese women were exposed to a dry-heat condition (Ta = 40 degrees C, rh = 30%) both in winter and summer. During an exposure for 110 min, they were rested on a bicycle ergometer for 20 min, exercised with an intensity of 40% Vo2 max for 60 min and recovery for 30 min. Their rectal and skin temperatures, and heart rate were determined every minute. Total sweat loss and dripping sweat were recorded throughout the experiment by independent bed balances which connected to a computer processor with an accuracy of 1 g. Sweat capsule with filter paper was used to measure sodium concentration on the forearm and back sites. Rectal temperature was not significantly different between winter and summer. Mean skin temperature was significantly higher in summer than in winter during exercise while heart rate was significantly lower in summer than in winter. Sweat evaporation and dripping in summer showed a tendency to increase much more than these in winter, but there were not significantly different. Sweat sodium concentration were significantly lower in summer than that in winter. It was found that sweating responses were not influenced by seasonal variation during exercise in dry-heat except the sweat sodium concentration.

Effects of the thermal conditions of the dressing room and bathroom on physiological responses during bathing.

The effects of the thermal conditions of the dressing room and bathroom on the physiological responses during bathing were assessed. Six female students participated in this experiment. Three climate chambers were used as a living room, a dressing room and a bathroom. The living room was thermoneutral and maintained at 25 degrees C, while the thermal conditions of the dressing room and bathroom were as follows: (A) cold (10 degrees C), (B) cool (17.5 degrees C) thermoneutral (25 degrees C). The subjects wore standard clothing (0.65 clo). Heart rate (HR), blood pressure, rectal (Tre) and skin temperature, and subjective thermal sensation were recorded. 1) Marked increases in systolic blood pressure (SBP) after undressing and redressing in the dressing room and during washing were observed under the cold conditions. 2) A significant negative correlation was found between the dressing room temperature and increased SBP compared to before bathing (r = -0.684, p < 0.01, n = 18). 3) After exposure, mean skin temperature (Tsk) showed marked differences among the three conditions despite the rest taken under the same thermal conditions. 4) A significant negative correlation was found between Tsk and the increase in SBP of after undressing relative to that before bathing (r = -0.695 p < 0.01, n = 18). These findings suggested that 25 degrees C was the most appropriate temperature for the bathroom and dressing room, since the increase in blood pressure was minimum and subjective thermal sensation was neutral (neither cool nor warm) to warm under this thermal condition, and 17.5 degrees C at which the increase in blood pressure was within the physiological fluctuation range (+/- 10 mmHg) is the minimum tolerable temperature.

Physiological and subjective responses to standing showers, sitting showers, and sink baths.

The purpose of this study was to investigate physiological and subjective responses during and after bathing in three different bathing methods. Eight healthy males bathed for 10 minutes, and then rested for 30 minutes. Three kinds of bathing methods - standing shower, sitting shower and sink bath - were adopted in this experiment. Water temperature and flow volume of the showers were kept at 41 degrees C and 11 liter/min, while water temperature of the bath was kept at 40 degrees C. Rectal temperature, skin temperatures and heart rate of the subjects were measured continuously during bathing and the subsequent 30-minute rest. Blood pressure and votes for thermal sensations were recorded before bathing, after 5 and 10 minutes of bathing, and 5, 10, 20 and 30 minutes after bathing. The following results were obtained. 1) Although rectal temperature rose, on the average, by 0.15 degrees C in all bathing methods, there were no significant differences among the three bathing methods at any time in the experiment. 2) Mean skin temperature (Tsk) during the sink bath was significantly higher than that in the standing or sitting shower. After bathing, Tsk of sink bath was slightly higher than those of the remaining conditions, but did not significantly differ among the bathing methods. 3) Heart rate increased gradually during all the bathing methods, however, only HR in the standing shower exceeded 100 beats/min which was significantly higher than those of the two remaining bathing methods. 4) Blood pressure (BP) decreased rapidly during the sink bath in contrast to an increased BP in the sitting and standing showers.

Thermal conditions in the bathroom in winter and summer, and physiological responses of the elderly during bathing.

Thermal conditions in the bathroom and physiological responses were examined during winter and summer. The subjects were 22 male and 20 female elderly people, between 65 and 88 years old living in 25 houses in Gunma Prefecture, Japan. Heart rate, blood pressure, skin temperature and thermal sensation were measured during bathing. Changes in thermal sensation due to bathing were assessed in the living room and dressing room on a 9-point scale. Then they were asked about the purposes of bathing and the facilities of bathroom and dressing room. The results are summarized as follows: 1. The purpose of bathing in winter was to warm up for more than 80% of the subjects. In summer, all subjects felt refreshed by bathing. Eighty-five percent of the subjects took a bath every other day in both seasons. 2. Fifty-two percent of the bathrooms had no ventilating fans and 32% had no exclusive dressing rooms. 3. The average room temperature in the dressing rooms was 13-14 degrees C in winter. Thermal sensation was 'cool', 'slightly cold' or 'cold' for more than two-thirds of the subjects when they were partially nude, and there were no heaters in most dressing rooms. 4. The heart rate increased steadily, and reached a maximum value in a partially dressed condition in both seasons. 5. In winter, a marked increase of systolic blood pressure was observed in the partially nude condition. There was a significant difference between the before bathing condition and partially nude condition in winter.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of repeated exposures to severely cold environments on thermal responses of humans.

This study was conducted to investigate the effects of different exposure rates on thermal responses with the total cold exposure time the same under each of the conditions. After resting in a warm room (25 degrees C) for 10 minutes, six male students wearing standard cold protective clothing entered an adjoining cold room (-25 degrees C). Each 5-, 10- and 20-minute cold exposure was repeated 12, 6 and 3 times, respectively. Each cold exposure was followed by a similar duration of rest at 25 degrees C. Total cold exposure time was the same under the three conditions. Rectal temperature, skin temperatures, blood pressure, 17-hydroxycoyticoids (OHCS), counting task and subjective responses were measured. At the end of the cold exposure skin temperatures in the shorter exposures were higher than those in the other conditions, except on the foot. Discomfort due to cold was less in the shorter exposures and manifestation of discomfort was delayed. However, there were no differences among the three conditions in the fall of rectal temperature and urinary excretion of 17-OHCS, which are good indices of cold stress. Moreover, increase in blood pressure and decrease in counting task due to cold were not different among the three conditions. Even though the cold exposure time for each stay was short, when cold exposures were repeated frequently, cold stress of the whole body and decrease in manual task performance were the same as in the longer cold exposure.

Physiological reaction and manual performance during work in cold storages.

Subjects were 10 workers (Group R) working in two cold storages (air temperature was between -20 degrees C and -23.2 degrees C), and eight workers (Group C) working in a general storehouse (air temperature was between 12 degrees C and 15.2 degrees C). They were all male workers operating forklift-trucks. Average (SE) age for Group R was 41.4(1.3) years and for Group C was 47.3(1.6) years. Hand tremor, handgrip strength, pinch strength, counting task, flicker value, peak flow rate and blood pressure were measured five times (before work, at 10 a.m., before lunch, at 3 p.m. and after work) per day. Blood samples were collected before lunch. Free fatty acid (FFA) of Group R was significantly higher than that of Group C. There were no significant differences in handgrip strength, pinch strength, counting task, flicker value and peak flow rate between Group R and Group C. However, changes in hand tremor and diastolic blood pressure for Group R were significantly greater than those for Group C. Only for Group R, there was a significant relationship between FFA and the hand tremor values measured the second time. Work loads of Group R would be increased by not only the extreme coldness but also large temperature difference between the inside and the outside of the cold storages. The actual forklift work in these cold storages did not cause a distinct reduction in manual performance, but caused an increase in stress which would be expressed as an increase in catecholamine excretion.

Body movements of the elderly during sleep and thermal conditions in bedrooms in summer.

The frequency of body movement in the elderly and young people during sleep was measured in order to investigate the effect of hot thermal environments on sleep in summer. Simultaneously, room temperature and humidity were also measured. In the morning after measuring body movements, the subjects completed a questionnaire about their night's sleep. The results obtained were as follows: 1) The time of going to bed and rising in the elderly was significantly earlier than the young. 2) The elderly had a tendency to judge their sleep as "good", however, there were no significant differences between the two groups. 3) The room temperature for the elderly during sleep ranged from 25 to 28 degrees C (mean 26.5 degrees C). On the other hand, it was between 20 and 30 degrees C (mean 27.1 degrees C) in the young, which was significantly higher than that of the elderly. 4) Body movement in the elderly during sleep was significantly greater than those in the young. 5) A significant relation between body movement and room temperature was found within each group. Under conditions of less than 28 degrees C of room temperature, there were significantly higher rates of body movement in the elderly.

Thermal responses of 6- to 8-year-old children during immersion of their legs in a hot water bath.

Twenty-three children (12 boys and 11 girls) and 13 female students served as the subjects in summer. The children were from six to eight years old. The subjects were seated in a hot room of 30 degrees C and their legs were immersed in bath water of 42 degrees C for 30 minutes. Total sweat rate, local sweat rate on the back, rectal temperature, skin temperatures at eight sites, heart rate and blood pressure were measured during the experiments. Total sweat rate of both groups was similar, but local sweat rates of the children were significantly smaller than those of the students. Although the degree of increase in rectal temperature from immersion in the hot bath were similar, the increases of heart rate and skin temperatures on the thigh and forearm were greater in children. These results suggest that the thermoregulatory ability of children during heat exposure is similar to that of young female adults. However, it is found that for heat loss, children resort more to vasodilation than sweating during heat exposure as compared to adults. The children were divided into two groups according to whether the children were exposed to air cooling systems in summer in their infancy or not. There was no significant inter-group differences in physiological responses during immersion in the hot water bath. It is found that the ability of Japanese children to tolerate heat was not reduced distinctly by the frequent use of an air cooling system in infancy.

Thermoregulation during heat exposure of young children compared to their mothers.

The study was conducted to investigate the thermoregulation of young children compared to that of adults. A group of 19 children (ages 9 months-4.5 years), with only 3 children aged 3 years or above, and 16 adults first rested in a thermoneutral room (air temperature 25 degrees C relative humidity 50%, air velocity 0.2 m.s(-1)). They were then exposed to a hot room (air temperature 35 degrees C, relative humidity 70%, air velocity 0.3 m.s(-1)) next door for 30 min, and then returned to the thermoneutral room where they stayed for a further 30 min. The rectal temperature (Tre), skin temperatures (Tsk) at seven sites, heart rate (HR), total sweat rate (Msw,t), local sweat rate (Msw,l) and the Na+ concentration of the sweat were measured. There was no significant difference in Tre between the children and their mothers in the rest phase. However, the Tre of the children increased as soon as they entered the hot room and was significantly higher than during the control period, and than that of the mothers during heat exposure. Mean Tsk, forehead, abdomen and instep Tsk were significantly higher in the children during both the thermoneutral and heat exposure. The Msw,t was significantly higher and Na+ concentrations in the sweat on the back and upperarm were significantly lower for the children during the heat exposure. They had a greater body surface area-to-mass ratio than the mothers by 64%, which indicated that they had advantages for thermal regulation. However, the sweating and Tsk responses of the children were not enough to prevent a rise in body temperature. These results would suggest that the young children had the disadvantage of heating up easily due to their smaller body sizes and there may be maturation-related differences in thermoregulation during the heat exposure between young children and mothers.