The seasonal variation of sweating responses under identical heat stress was investigated to make clear the seasonal acclimatization in daily human life on the experiments. The heat stress of 33°C air temperature, 50% relative humidity laid in the experiments was chosen as a usual daytime condition in summer in metropolitan cities such as Tokyo and Osaka. Five subjects were exposed under the identical heat stress in the climate chamber every two months through the year. Results were discussed on the mean values for five subjects. Although the relation of skin temperature to daily mean air temperature showed a variation of high in summer and low in winter before the heat stress, it rose and showed almost constant value during the heat stress. The seasonal variation of tympanic temperature appeared a little before the heat stress, but disappeared during the heat stress. The seasonal variation of sweating responses was evident, that was high in summer and low in winter. The concluding remarks are as follows: 1) It could be considered that there is a seasonal acclimatization on the threshold temperature for sweat onset. 2) The seasonal acclimatization on sweating is supposed to be caused by the seasonal acclimatization of the threshold temperature. 3) The seasonal acclimatization on sweating could be comprehended in four stages corresponding closely to the daily mean air temperature (Ta). The 1st stage is December-April when Ta<15°C, the 2nd stage is April-August when 15°C<Ta<25°C, the 3rd stage is the term centering on August when Ta>25°C and the 4th stage is August-December when 15°Ca<25°C.
The purpose of this study is to investigate the thermophysiological significance of hydrophilic and hydrophobic properties of underwear materials under the influences of profuse sweating produced during severe exercise in the cold. Two kinds of underwear were used: two layers of cotton underwear with two-piece long-sleeved shirt and full-trousers (C), and two layers of polypropylene underwear with two-piece long-sleeved shirt and full-trousers (P). In addition, the subject put on a two-piece ski suit of 100% polyester including 100% polyester padding. Eight adult females volunteered as subjects in this study. The test was performed in a climatic chamber at an ambient air temperature of 2°C and an air velocity of 0.26 m·s-1. The subject exercised on a cycle ergometer at an intensity of 65% maximal oxygen uptake for 30 min and followed by 60 min recovery. The major findings are summarized as follows: 1) The fall of rectal temperature tended to be greater in P during the recovery. 2) The absolute humidity of innermost layer and middle layer was significantly higher in C than in P during the recovery, but the absolute humidity of middle layer and outermost layer was significantly higher in P than in C during the exercise. 3) Clothing microclimate temperature of innermost at back was significantly higher in C during the exercise and recovery. 4) Metabolic heat production for last 30 min during recovery was significantly higher in P. 5) The degree of skin wettedness sensation and sweating sensation for whole body was significantly higher in P during the exercise. It was concluded that the slower evaporation behavior by absorbing of underwear material in the clothing system has a beneficial influence on thermophysiological responses during severe exercise and its recovery in the cold, although the differences were very small.
The Ama have existed for more than 2000 years in Japan and Korea. They have been diving for seaweed and molluscs. Their traditional way of fishing, with goggles or a mask, but without a wetsuit, is still practised as a result of laws against overfishing. We investigated cardiovascular diving responses, expressed as heart rate (HR) reduction, peripheral vasoconstriction indicated by skin blood flow (SkBF) and mean arterial blood pressure (MAP) during breath-hold face immersion in a group of eight elderly male Ama at Chikura, Japan. Their data were compared to those from three other groups: a) elderly non-divers; b) young divers and c) young non-divers. Our previous studies have shown that young divers show a more pronounced bradycardia than young non-divers. The present study of elderly Ama and elderly non-divers was performed to investigate if this difference persists in old age. We found that, in spite of many years of diving experience, HR reduction of the elderly professional divers observed during face immersion did not differ from that of elderly non-divers, but it was much less pronounced than in the two younger groups. We conclude that even if a well-developed diving response at young age has been reduced to the level of non-divers, the Ama are still able to continue their work of diving in old age. Ama that has been a traditionally female occupation, is mostly practised by men at Chikura today. No young have been recruited for this profession. Therefore, the present Ama are senior and the traditional breath-hold diving will probably cease to exist in the near future. The probable reasons for these changes are discussed.
Environmental and cultural aspects are known to influence particular characteristics of an ethnic group and, as such, are partially responsible for distinguishing an ethnic group from others. This study was designed to compare non-athlete young Japanese and American males on a variety of physiological and fitness characteristics in order to locate and quantify the magnitude of any physiological and fitness differences between the two races. Aerobic capacity based upon bicycle ergometer, resting heart rate, and resting blood pressure, vertical jump, grip strength, and flexibility as measured by sit-and-reach, and trunk-and-neck extension tests were obtained for 20 Japanese and 20 American males whose ages ranged between 19 and 25 years. Cardiovascular and aerobic capacity data indicated that the Americans had higher blood pressure (both systolic and diastolic blood pressures) and higher absolute VO2max than the Japanese. However, the Japanese had a higher relative VO2max value than the Americans. The Japanese had higher values than those of the Americans in the vertical jump and for trunk-and-neck flexibility. Within the limitation of the present study, it can be concluded that the Japanese had a higher lower extremity power and better flexibility in the trunk-and-neck extension compared with the American.
This study was conducted to evaluate physiological reaction and manual performance during exposure to warm (30°C) and cool (10°C) environments after exposure to very low temperatures (-25°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 sansations were measured during the experiment. The effects of severe cold on almost all measurements in the cool (10°C) environment were greater than those in the warm (30°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 removed cold-protective jackets in the cool room (10°C) after severe cold exposure promoted the effects of severe cold. When rewarming in the warm resting room (30°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.
The amplitude of respiratory sinus arrhythmia (RSA) was measured in eight healthy young male students with special reference to the effect of tidal volume (Vt). Under simultaneously controlled respiratory frequency and Vt, the heart rate variability (HRV) of the subjects was measured. While the respiratory frequency was adjusted to either 0.25 or 0.10 Hz, the Vt was controlled at 13 different volumes for each frequency. Linear relationships between RSA amplitude and Vt were observed and close correlations were obtained for 0.25 Hz compared with 0.10 Hz. However, regression equations showed a marked variation among subjects. Furthermore, RSA amplitude was related to vital capacity. Subjects who had lower vital capacity tended to show higher RSA amplitudes at the same Vt. Therefore, the ratio (%Vt) of Vt to vital capacity is a more effective index in normalizing RSA than raw tidal volume. From these results, we have proposed a normalized RSA (RSA amplitude/%Vt) as a new index of autonomic activity that provides a constant value regardless of Vt