Whole-body heat exchange in black-African and Caucasian men during exercise eliciting matched heat-loss requirements in dry heat.

Abstract

What is the central question of this study? Black-African descendants are thought, by some, to possess genotypic adaptations conducive to survival in hot climates. We therefore assessed whether Canadian residents of black-African descent display enhanced whole-body total heat loss (evaporative plus dry heat exchange) in comparison to Caucasian Canadians during exercise eliciting matched heat-loss requirements in dry heat. What is the main finding and its importance? Neither whole-body total heat loss nor body heat storage differed significantly between groups, irrespective of the exercise intensity. Our findings indicate that genotypic adaptations associated with ethnicity do not appreciably modify whole-body heat exchange during exercise-heat stress. Ethnicity has long been thought to modulate thermoregulatory function; however, an evaluation of whole-body heat exchange in men of black-African descent and Caucasian men (white-European descendants), born and raised in the same climate, during exercise eliciting matched heat-loss requirements remained unavailable. We therefore used direct calorimetry to assess whole-body total heat loss (evaporative plus dry heat exchange) in young (18-30 years of age), second-generation (or higher) black-African (n=11) and Caucasian (n=11) men. Participants performed three 30min bouts of semi-recumbent cycling at fixed metabolic heat productions (and therefore matched heat-loss requirements between groups) of 200 (light), 250 (moderate) and 300Wm-2 (vigorous), each followed by 15min recovery, in dry heat (40°C, ∼13% relative humidity). Across all exercise bouts, dry (P=0.435) and evaporative (P=0.600) heat exchange did not differ significantly between groups. As such, total heat loss during light, moderate and vigorous exercise was similar between groups (P=0.777), averaging [mean (SD)] 177 (10), 217 (13) and 244 (20)Wm-2 in black-African men and 172 (13), 212 (17) and 244 (17)Wm-2 in Caucasian men. Accordingly, body heat storage across all exercise bouts (summation of metabolic heat production and total heat loss) was also similar between the black-African [568 (142) kJ] and Caucasian groups [623 (124) kJ; P=0.356]. We demonstrated that, when assessed in young, second-generation (or higher) black-African and Caucasian men during exercise eliciting matched heat-loss requirements in dry heat, ethnicity did not significantly modulate whole-body dry and evaporative heat exchange or the resulting changes in total heat loss and body heat storage.