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.