STUDY ON SEASONAL VARIATIONS OF HEAT TOLERANCE IN YOUNG JAPANESE MALES AND EFFECTS OF PHYSICAL TRAINING THEREON

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1. Physiological responses to heat and heat tolerance were examined in summer and winter on 39 male college students. After having been in the chamber for 30 min, sweating was induced by immersing both legs up to the kness for 90 min a water bath of 42°C in a climatic chamber maintained at 30°C with 70% relative humidity.
2. Heat tolerance was assessed by heat strain cau ed by a certain heating condition. The heat strain was represented by a combination of relative increase in rectal temperature (B) plus relative water loss (A) and salt loss (C). Indices I and S were defined, as reported previously, as (A²+B²+C²) ^1/2 and B/(A²+C²) ^1/2, respectively, to assess the heat tolerance.
3. Sweating reaction in summer was characterized by a relatively smaller salt loss despite a greater water loss, while the rise in rectal temperature was less in summer than in winter.
4. The mean value of Index I showed no significant seasonal differences, being 0.24 in both seasons. The mean values of Index S in summer and winter were 0.81 and 1.42, respectively, the difference being statistically significant.
5. The mean value of Index I for the athlete group, which included college sportsmen, was significantly lower than that of the non-athlete group (0.21 and 0.27, respectively, irrespective of the seasons), while no significant difference was found in Index S between the two groups.
6. Despite the lack of seasonal variation of Index I, the magnitude of individual I showed a good correlation with heat tolerance as judged by the sweating type, n a classification system originally deve oped by Ohara.
7. Based on these results, applicability of the indices for the assessment of individual heat tolerance is discussed.