Whole-body heat exchange in black-African and Caucasian men during exercise eliciting matched heat-loss requirements in dry heat.Exp Physiol 2019EP
• 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 + dry heat exchange) compared 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 + dry heat exchange) in young (18-30 years), second-generation (or higher) black-African (n = 11) and Caucasian (n = 11) men. Participants performed three, 30-min bouts of semi-recumbent cycling at fixed metabolic heat productions (and therefore matched heat loss requirements between groups) of 200 (light), 250 (moderate), and 300 W/m2 (vigorous), each followed by 15-min 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) W/m2 in black-African men, and 172 (13), 212 (17) and 244 (17) W/m2 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 demonstrate 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. This article is protected by copyright. All rights reserved.