RESUMO
The present study was designed to examine the thermoregulatory response to the alternate stress of heat and cold in relation to physical training. A heat stress was given as a 60-minute foot bath in water at 43°C in the air condition of 30°C DB and 60% RH, and a cold stress as a 60-minute exposure to an atmosphere of 20°C DB and 60% RH in summer and 17°C DB and 60% RH in winter. Two experimental conditions of four-hour exposure were set up by combining the hourly heat and cold stress alternately : Condition I was initiated with the heat stress and ended with the cold one, and condition II vice versa. In these conditions, both heat and cold stresses were given twice. In summer, as well as in winter, physical untrained and trained adult males in swimming pants were exposed to alternate heat and cold stress extending for four hours. Rectal and mean skin temperatures were taken every 5 minutes. A ten-minute metabolic rate was measured every 20 minutes during the exposure period. The effect of physical training was generally more remarkable in condition I than in condition II, and in summer than in winter. In condition I, the trained group had a smaller variation in rectal temperature and a smaller rate of variation from a resting value in energy consumption throughout the four-hour exposure than the untrained. The differences between the mean skin temperature in the last stage of the first exposure and that of the second tended to be smaller in the trained group than in the untrained. Reduced differences between these values were noticed in the untrained men after physical training. These results indicate that the effect of physical training was discernible on the thermal adaptability to the alternate stress of heat and cold. It was concluded that physical training generally promoted the acclimatization and enhanced tolerance capacity to heat and cold.
