Heat balance during 1hr exercise at 450 kpm/min was measured on 5 healthy male students wearing only shorts in a climatic chamber of 13°C and r.h. 60% at the minimum phase (5 : 00-7 : 00), the rising phase (11 : 00-13 : 00), the maximum phase (17 : 00-19 : 00) and the falling phase (23 : 00-1 : 00) of body temperature.
Heat production was nearly constant, 194 to 209w/m2 at all phase both in summer and winter. Evaporative heat loss was lowest at the minimum phase and highest at the maximum phase. In all phases, evaporative heat loss was 14-29% higher in summer than in winter. Dry heat loss was not significantly different summer and winter. Body heat storage was high at the minimum phase, low at the maximum phase and higher in winter than in summer. The threshold rectal temperature for the onset of sweating was lower at the maximum phase than at the minimum phase by 0.65°C in winter and by 0.70°C in summer.