PROPOSAL OF NEW GUIDELINES FOR PREVENTION OF HEAT DISORDERS DURING SPORTS AND DAILY ACTIVITIES BASED ON AGE, CLOTHING AND HEAT ACCLIMATIZATION / 体力科学

The guidelines for the prevention of heat disorders during sports activities were established 13 years ago in Japan. Since then, various studies on preventive measures against heat disorders have been done, yielding new knowledge about its prevention. It has been reported that the incidence of heat disorders is high in children and the elderly, and heat acclimatization and clothing are the factors involved in this disorder. We proposed to lower the WBGT (wet-bulb globe temperature) limit for warning (discontinuation of hard exercise) from “28°C or more” to “25°C or more” (corresponding to an ambient temperature of 28°C) for non-acclimatized persons, children, the elderly, and persons wearing clothes covering the entire body. We also indicated that heat disorders can occur due to unpredictable causes, because the mechanism is very complicated.

Cold-Induced Vasodilation in Prepubertal Boys, Young and Older Men / 体力科学

The present study was attempted to examine whether the cold-induced vasodilation is affected by maturation and aging. Twelve prepubertal boys (10-11 yrs), 15 young men (18-26 yrs), and 8 older men (66-78 yrs) immersed their middle finger in ice-water for 15 min under air condition of 27°C and 40% RH. Before the immersion, no age-related differences were observed in skin temperature of middle finger (T<SUB>fin</SUB>) . The time required for the first rise of T<SUB>fin</SUB> after the immersion (TTR) was significantly longer in the older men than in the boys and young men. T<SUB>fin</SUB> at the first rise after the immersion (TFR), highest value of Tfin after the first rise (HST) and the mean value of T<SUB>fin</SUB> during the immersion (MST) were significantly lower in the boys than in the young men. The integral value of T<SUB>fin</SUB> from the onset of cold-induced vasodilation to the end of the immersion (CIVD<SUB>index</SUB>) was significantly lower in the boys and older men than in the young men. TTR, TFR, HST, MST, and CIVD<SUB>ifldex</SUB> did not correlate significantly with maximal oxygen uptake, mean skinfold thicknesses at seven body sites, and length and girth of the middle finger. Oral temperature (Tor) did not change between before and after the immersion regardless of age, although the Tar in the boys was significantly higher than in the young and older men. There were no age differences in the relationship of thermal sensation or pain sensation and T<SUB>fin</SUB>. These results suggest that boys and older men have inferior cold-induced vasodilation compared to young men, and that the mechanisms of inferior cold-induced vasodilation are different in these two groups.

Age-Related Differences in Sweat Loss and Fluid Intake During Sports Activity in Summer / 体力科学

In this study, we investigated total sweat rate per unit area of body surface per hour (TSR), the percentage of total sweat loss to initial body weight (%TSL) and the percentage of fluid intake volume to total sweat loss (%FIV) in children (during baseball or basketball practice), young adults (during softball or baseball practice), and the elderly (during gateball practice) in summer. During the practice all participants were given access to drink sports drink or Japanese tea <I>ad libitum</I>. In the basketball group of children no sex difference was observed in TSR, %TSL and %FIV. Although TSR and %TSL in the baseball group of children were significantly higher than in the basketball group due to a higher WBGT, there was no group difference for %FIV. Children drank sports drinks (with carbohydrate-electrolyte) of the similar volume with total sweat loss. The baseball group of children showed a significantly greater %FIV compared to the young adult group regardless of simi lar %TSL, when they drank sports drinks. Children showed a significantly higher %FIV in sports drinks than in Japanese tea, whereas the %FIV of young adults was not affected by the type of beverage. The TSR, %TSL and %FIV of the elderly group were significantly lower than in young adults and children. These results suggest that children can prevent voluntary dehydration by con-suming sports drinks with carbohydrate-electrolyte <I>ad libitum</I> regardless of sex and WBGT, and that periodic drinking should be actively encouraged for the elderly because of their blunted rehydration ability, to prevent heat disorders during sports activity in summer.

EFFECTS OF PHYSICAL TRAINING ON THERMOREGULATORY RESPONSES TO ALTERNATE STRESS OF HEAT AND COLD / 体力科学

The present study was designed to examine the thermoregulatory response to the alternate stress of heat and cold in relation to physical training. A heat stress was given as a 60-minute foot bath in water at 43°C in the air condition of 30°C DB and 60% RH, and a cold stress as a 60-minute exposure to an atmosphere of 20°C DB and 60% RH in summer and 17°C DB and 60% RH in winter. Two experimental conditions of four-hour exposure were set up by combining the hourly heat and cold stress alternately : Condition I was initiated with the heat stress and ended with the cold one, and condition II vice versa. In these conditions, both heat and cold stresses were given twice. In summer, as well as in winter, physical untrained and trained adult males in swimming pants were exposed to alternate heat and cold stress extending for four hours. Rectal and mean skin temperatures were taken every 5 minutes. A ten-minute metabolic rate was measured every 20 minutes during the exposure period. The effect of physical training was generally more remarkable in condition I than in condition II, and in summer than in winter. In condition I, the trained group had a smaller variation in rectal temperature and a smaller rate of variation from a resting value in energy consumption throughout the four-hour exposure than the untrained. The differences between the mean skin temperature in the last stage of the first exposure and that of the second tended to be smaller in the trained group than in the untrained. Reduced differences between these values were noticed in the untrained men after physical training. These results indicate that the effect of physical training was discernible on the thermal adaptability to the alternate stress of heat and cold. It was concluded that physical training generally promoted the acclimatization and enhanced tolerance capacity to heat and cold.

THE EFFECT OF PHYSICAL TRAINING ON COLD TOLERANCE / 体力科学

A study was performed to elucidate the effect of physical training on the cold tolerance in human beings. Physically well trained men (T group) and untrained ones (U group) were exposed to cold stress in summer and winter. Each subject was dressed in experimental clothes and exposed to 10°C DB for 60 minutes in both seasons. Moreover, he was exposed in the semi-nude to 20°C DB in summer and to 17°C DB in winter for 60 minutes. During the period of exposure to cold, rectal and mean skin temperatures and respiratory metabolic rate were measured. To confirm the training effect further, the untrained men were asked to follow an experimental training program of daily routine which consisted of about 7 km outdoor running for 40 consecutive days in July and August. Before and after the training, they were exposed to the same cold stress as in the aforementioned summer experiments and subjected to the same measurement. Resting metabolic rate was higher in the T group than in the U group. Although no significant group differences were shown in the metabolic rate during the period of exposure to cold, the rate of increase from the resting value was lower in the T group than in the U group. There were no group differences in rectal or mean skin temperature during this period. When the untrained men were subjected continually to physical training, the resting metabolic rate was higher and the rate of increase from the resting value during the period of exposure to cold lower after the training than before. It was concluded that physical training could be a means to increase the cold tolerance.