FEMALES DISPLAY DIFFERENT HEAT BALANCES TO MALES WHEN MEASURES ARE CORRECTED FOR SMALLER BODY SIZE

Dorman, L. E., Jay, O., Gagnon, D., Webb, P., DuCharme, M. B., Reardon, F. D., & Kenny, G. P. (2008). Sex differences in human heat balance at the same intermittent work loads. ACSM 55th Annual Meeting Indianapolis, Presentation Number, 1934.

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This study used whole-body calorimetry to determine differences in heat balance when males (N = 6) and females (N = 6) work intermittently at the same absolute work load. Ss completed three 30-minute bouts of semi-recumbent cycling separated by 15 minutes of seated rest at 30C within a modified Snellen whole-body air calorimeter. Changes in the rates of evaporative heat loss and dry heat loss were determined by direct calorimetry. The specific heat capacity of the tissues was calculated with a DEXA scan. Rectal temperature was measured continuously.

There were no significant gender differences in metabolic heat production and total heat loss throughout exercise and recovery. Females also had a similar absolute evaporative heat loss to males, however it was relatively higher when corrected for the smaller body surface area at the end of all three exercise bouts. There were no significant differences between the genders in change in body heat content but when taking the females' smaller mass and lower specific heat capacity into account, significant differences were seen at the end of all three exercise bouts. Rectal temperature was also significantly higher in the females at the end of each exercise bout.

Implication. Males and females had the same absolute metabolic heat production and total heat loss, but females showed a higher evaporative heat loss when corrected for body surface area. Females showed progressively greater changes in mean body temperature across all three exercise bouts due to their lower body mass and specific heat.

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