This paper deals with the features of WBGT, and made them clear in view of heat transfer theory.
The currently used WBGT is an equation obtained from the experiments using subjects. However, it has not been derived from heat balance concerning the human body. It is often said that WBGT is reliable because it is an equation based on the experimental data. Nevertheless, an experimental equation is not always correct. In general, it contains scattering of data and the bias in the conditions of experiments.
Humans produce metabolic heat in the body and release/receive heat to/from the environment. Therefore, the physical law of heat transfer can be correctly applied to the human body and it is probable to derive WBGT equations.
The authors derived two WBGT equations theoretically based on the heat balance equation between the man and the environment. As the results, the characteristics and physiological meaning of WBGT have become clearer. Further, the rational WBGT equations have also been derived. The new ones contain and offer the seven main parameters to be considered, such as air temperature, humidity, air movement, long and short wave radiations, clothing worn and metabolic rate, thus making the estimation of man’s heat stress more strictly.

View full abstract

To examine the effects of heat acclimation states on thermoregulatory responses in agricultural workers, this study investigated the differences in core temperature, hydration states, working times, and working intensity between workers native to subtropical and temperate region who were acclimatized or not acclimated to hot environment during agricultural work in summer. The study was conducted on fine days from August to June in 2005 and 2004 on Miyako Island, Japan. Subjects were 18 male residents of Tokyo (a temperate region) who had newly arrived on Miyako Island for less than 1 week (group N: non-heat-acclimated), 5 male residents of Tokyo who had been working on Miyako Island for more than 2 weeks (group S: short-term heat-acclimated), and 11 male residents of Miyako Island (group L: long-term heat-acclimated).
The total sweat rates of group S and group L were significantly higher than those of group N. Fluid intake of group L was significantly higher than that of group N and S. Degrees of rehydration (fluid intake/total sweat rate, %) was lower (p<0.05) and percentages of dehydration (% of initial body weight) was greater (p<0.05) in group N than in group L. Furthermore, working time was longer and heart rate was lower in group N than in group L. However, tympanic temperature responses during agricultural work were similar between groups. There results suggest that during agricultural work non-heat-acclimated workers are maintaining their core temperature by decreasing work intensity with the longer working time, while dehydration was greater than heat-acclimated workers. Therefore, to prevent heat disorders in agricultural workers native to temperate regions who work under hot environments, proactive measures such as determining the time and amount of rehydration needed must be taken.

View full abstract

To establish the accuracy and precision of deep forehead temperature (Tch) measured by the zero-heat-flow method, Tch was compared with the esophageal temperature (Tes), as an index of core temperature, during 30 min of a cycling exercise at 20% and 50% of maximal oxygen uptake in seven male subjects under 28°C, 24°C, and 20°C environmental temperature conditions. The Tes was measured by placing a thermocouple probe in the esophagus through the subject’s nostril, and Tch was also measured by using Coretemp thermometer probe fixed on forehead. Tch significantly correlated with Tes, correlation coefficient (r²) between two parameters under 28°C, 24°C, and 20°C environmental temperature conditions were 0.555, 0.647, and 0.491, respectively. From the Bland-Altman analysis, the off set (Tes-Tch) and the precision were significantly lower, and also delay time was significantly (p<0.05) longer according to the lowing ambient temperature or exercise intensity. These results suggest that the accuracy and precision of Tch that estimate to Tes were affected by environmental temperature and exercise intensity.

View full abstract

The purpose of this paper is shown the relationship between the ETFe as outdoor thermal environment evaluation index and the human responses in summer outdoor spaces. In order to clarify the effect of the environment stimuli have on the human body, experiments were conducted. For the measurements, observation points were selected with consideration for the condition of the ground surface such as bare ground where the surface is gravel or soil; paved ground such as concrete, asphalt or blocks; green areas covered in plants and water surfaces and with consideration for the condition of the sky factor due to buildings or trees etc. Observation points which were covered by natural factors such as trees and water surfaces etc, were taken as natural scenery observation points. Next, observation points which were covered by artificial factors such as buildings or concrete/block surfaces, were taken as artifical scenery observation points. Then observation points which were covered a mixture of natural factors such as water surfaces etc and artificial factors such as buildings and asphalt pavement etc, were taken as mixed-scenery observation points. Considering the visual environment stimuli in categorization, an investigation was carried out by means of the solid angle of the features acquired from the orthographic projection map for each observation point. The results are the followings. In comparison to visual stimuli given by an artificial scenery composed of buildings and asphalt pavement, the neutral temperature for thermal sensation was 3.5°C lower for visual stimuli given by a natural scenery composed by greenery such as trees and shrubs and an effect mitigating thermal sensation was shown. In comparison with other scenery observation points, the decrease of thermal comfort is small for natural scenery observation points, even if the mean skin temperature increases. Natural spaces composed by greenery such as trees and shrubs are considered to be more valid for improving thermal comfort than the inorganic artificial space composed of concrete and metal etc. The threshold for the human body with regards to thermal environment stimuli in an outdoor space is higher than the thermal environment stimuli in a summer indoor space.

View full abstract

The present study measures rectal temperature, heart rate, body weight loss, and volume of fluid and food intake in a 50-year-old male athlete who ran a 77-km ultra-marathon during the summer. The average dry-bulb temperature, relative humidity and wet-bulb globe temperature (WBGT) during the marathon were 28.5±1.4°C, 53.8±5.2% and 28.9±2.1°C, respectively. The average heart rate and total estimated energy consumption during the entire 10 h and 45 min run were 133±17 beats per min and 6,475 kcal, respectively. Rectal temperature during the run gradually increased and was elevated by 2.6°C by the end of the marathon. Immediately after flushing with cold water over the neck or head during the run, the heart rate immediately increased and rectal temperature slightly decreased at two minutes later. Flushing with cold water therefore helped prevent the core body temperature from rising while running in an ultra-marathon under summer heat. However, the sudden autonomic increase in heart rate as a response to flushing with cold water might be the cause of sudden death that can occur among athletes competing in ultra-marathons under hot environmental conditions.

View full abstract