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The purpose of the study was to investigate the degree of subject variability in the peripheral and core temperature thresholds of the onset of shivering and sweating. Nine healthy young male subjects participated in three trials. In the first two trials, wearing only shorts, they were exposed to air temperatures of 5 degrees C and 40 degrees C until the onset of shivering and sweating, respectively. In the second experiment, subjects wore a water perfused suit that was perfused with 25 degrees C water at a rate of 600 cc/min. They exercised on an ergometer at 50% of their maximum work rate for 10-15 min. At the onset of sweating, the exercise was terminated, and they remained seated until the onset of shivering, as reflected in oxygen uptake. In the first two trials, rectal temperature (Tre) was stable, despite displacements in skin temperature (Tsk), whereas in the third trial, Tsk (measured at four sites) was almost constant (30-32 degrees C), and the thermoregulatory responses were initiated due to changes in Tre alone. The results of the first two trials established the peripheral interthreshold zone, whereas the results of the third trial established the core interthreshold zone. The results demonstrated individual variability in the peripheral and core interthreshold zones, a proportional correlation between both zones (r=0.87), and a relatively higher contribution of adiposity in both zones as compared with those of other non-thermal factors such as height, weight, body surface area, surface area-to mass ratio, and the maximum work load.

The clothing area factor (f cl) is defined as the ratio of the clothing surface area to the body surface area. It may play an important role in analyses of heat exchange between the clothed body and the surrounding environment. For practical purposes it has commonly been estimated from a function of clothing insulation although clothing fit is a determining factor in estimating clothing surface area. The significance of clothing fit on f cl was demonstrated by Kakitsuba et al. (1987). In this study, f cl was derived by a photographic method using a 180°OP fish-eye lens camera as used in the previous study. Clothing microenvironment volumes (V m) were measured by two different methods, i.e., a method of measuring the thickness of the clothing microenvironment, and a silhouette method. Subjects wore everyday clothing ensembles: one was relatively tight-fitting and the other was loose-fitting. The f cl values and V m were measured with the subjects standing, sitting on a chair, and sitting on the floor. In addition, the subjects' body volumes (V b) were estimated from anthropological measurements. The results showed that the f cl values varied between 1.05 and 1.31 and were not in accordance with clothing insulation, for which values were consistent (the meanϭ0.52 clo), and that the f cl value can be defined as a function of V m /V b .

In this study, the hypothesis is tested that continuous increases in ambient temperature (Ta) during daytime would give elevated core and skin temperatures, and consequently better thermal sensation and comfort. Rectal temperature (Tre), skin temperatures and regional dry heat losses at 7 sites were continuously measured for 10 Japanese male subjects in three thermal conditions: cond. 1, stepwise increases in Ta from 26 °C at 9 h00 to 30 °C at 18 h00; cond. 2, steady Ta at 28 °C from 9 h00 to 18 h00 and cond. 3, stepwise decreases in Ta from 30 °C at 9 h00 to 26 °C at 18 h00. Oxygen consumption was measured and thermal sensation and comfort votes were monitored at 15 min intervals. Body weight loss was measured at 1 h intervals. While Tre increased continuously in the morning period in any condition, it increased to a significantly greater (p<0.05) 36.9±0.3 °C at 18 h00 in cond. 1 relative to 36.7±0.28 °C in Cond. 2 and 36.5±0.37 °C in cond. 3. Better thermal comfort was observed in the afternoon and the evening in Cond.1 as compared with the other 2 conditions. Thus, a progressive and appropriate increase in Ta may induce optimal cycle in core temperature during daytime, particularly for a resting person.