Studies on heat tolerance of subtropical natives after migration to a temperate zone.

Abstract

Anthropometric measurements and observations of physiological responses to heat were made in the autumn on 20 young male Japanese who were born and reared in the main islands of Japan (group M), 20 young male Japanese who were born and reared in Okinawa, subtropical zone, and who have lived in the main islands of Japan, temperate zone, for less than three years (group O). In winter the same tests were made on 25 subjects in group M and 17 subjects in group O. Group O showed lower skinfold thickness and less body fat content than group M. Both groups showed lower skinfold thickness and less body fat content in autumn than in winter. Group O was characterized by lower sweat rate and lower Na concentration in sweat for a given rise in body temperature. In both groups, greater sweat loss, lower Na concentration in sweat and smaller rise in body temperature were observed in autumn than in winter. Group O showed higher heat tolerance than group M when assessed by our numerical index for the assessment of heat tolerance. It was assumed that capacity of non-evaporative heat dissipation for group O was superior to that for group M, and the efficiency of sweat for cooling body in group O was better than that in group M. Differences in anthropometrical characteristics and physiological responses to heat between the two groups might reflect more advanced heat acclimatization of subjects in group O when compared with those in group M.