There is no doubt that sweating, changes in body temperature and changes in circulatory function are main physiological changes induced by heat exposure and that these physiological changes may be used to assess a so called “heat tolerance” of each person. It will be natural to inquire what combination of these physiological changes is the best index for the evaluation of “heat tolerance”.
It may be presumed that there is an underlying factor which is called as “heat tolerance” and that this factor controls various physiological changes induced by heat exposure simultaneously. If this hypothesis is true, the factor which may be expressed as a transformed variate of various physiological changes must be the best index for the evaluation of “heat tolerance”.
The above hypothesis has been tested by applying a statistical method called “principal components analysis” to the data on several physiological changes when young healthy male subjects were compelled to exercise in a warm bath.

Physical fitness of 900 volunteers over 60 years of age were analyzed using a 6-item battery test to obtain fundamental data on the fitness status of the aged Japanese. The test battery consisted of stepping, vertical jump, grip strength, breath holding, body flexion and one-leg balancing, and could be performed safely with relatively mild physical stress in the elderly after simple screening by measurement of resting blood pressure and oral check on mobility problems of the knee and the hip. Males showed significantly higher values in vertical jump, grip strength and breath holding, while females showed significantly higher values in body flexion. There were no sex differences in stepping and one-leg balancing. Lowing trend was found in the score with age in all items except breath holding, but the extent of the reduction differed among the measure elements of fitness. Most of measured items showed significant correlations each other. The values obtained with this test are considered to be useful for future analysis of the fitness of aged people and also to determine the exercise appropriate for them.