CHANGES IN PHYSIOLOGICAL REACTIONS TO A HOT ENVIRONMENT INDUCED BY CLIMATIC CHANGE AND PHYSICAL TRAINING

Abstract

Fifteen young male Japanese athletes and 15 young male Japanese non-athletes in the sitting-resting position were exposed to a hot environment in winter and summer. Sweating was induced in a climatic chamber of DBT 30 C with 70% relative humidity by immersion of both legs just below the knees in the stirring water bath of 42 C for 90 min after sitting in a chair at rest for 30 min in the chamber. The maximal oxygen uptake, record of 100 m dash and back strength were measured on 16 subjects in summer. Both athletes and non-athletes showed a similar and clear seasonal variation of sweating reaction. Sweating reaction in summer was characterized by a lower salt concentration in sweat in spite of a larger sweat volume. The rise in rectal temperature for both athletes and non-athletes in summer was smaller than that in winter. Athletes showed a smaller sweat volume, lower salt concentration in sweat and smaller rise in rectal temperature than non-athletes both in summer and winter. Heat tolerance of athletes was superior to that of non-athletes in both summer and winter when the heat tolerance was assessed by our index I for the assessment of heat tolerance. A definite tendency towards a small rise in rectal temperature and superior heat tolerance for subjects with lower salt concentration in sweat at a given sweat loss was observed. Positive correlations of heat tolerance to maximal oxygen uptake, the speed of 100 m dash and muscular strength were observed and heat tolerance was more closely correlated to maximal oxygen uptake than the speed of 100 m dash and muscular strength. The reasons for superior heat tolerance of athletes and the subjects with lower salt concentration in sweat were discussed.