Abstract
Twelve healthy male nonathletic university students were selected as subjects. Anthropometric measurement and a work capacity test using a bicycle ergometer in a climatic chamber of 30°C and 60% R. H. were carried out in summer and winter. Observations of the physiological responses of the subjects were made while pedalling a bicycle ergometer at a constant work load of 50% Vo2max and at a cycling rate of 50 rpm for 30 min in a climatic chamber of 30°C and 60% R.H., in summer. The subjects took the same exercise for 13 successive days except the day after training, for 6 days in a climatic chamber of 30°C and 60% R.H., after the work capacity test was tested in winter. Body weight and skinfold thickness showed a tendency to decrease in summer. Vo2max per body weight was considerably greater in summer than in winter though this difference was statistically not significant. Na concentration in sweat and the increase in heart rate during exercise were significantly lesser in summer than in winter. Sweat volume induced by exercise increased and rise in rectal temperature during exercise showed a tendency to decrease in summer. Increase in heart rate during exercise was decreased significantly by physical training. Sweat volume during exercise tended to increase and rise in rectal temperature during exercise tended to decrease progressively during physical training. Decrease in heart rate during exercise induced by physical training was greater than that induced by climatic heat acclimatiztion, while decrease in Na concentration of sweat due to climatic heat acclimatization was greater than that observed during physical training. Indices representing the magnitude of strain including relative increase in heart rate, relative rise in core temperature and relative water loss are proposed for the assessment of work capacity in heat.
