Dose-dependent non-thermal modulation of whole-body heat exchange during dynamic exercise in humans

Am J Physiol Regul Integr Comp Physiol. 2023 Nov 13. doi: 10.1152/ajpregu.00203.2023. Online ahead of print.ABSTRACTTo maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate whole-body dry and evaporative heat exchange. These responses are modulated by the rise in body temperature (thermal factors), as well as several non-thermal factors implicated in the cardiovascular response to exercise (i.e., central command, mechanoreceptors, metaboreceptors). However, the way these non-thermal factors interact with thermal factors to maintain heat balance remains poorly understood. We therefore used direct calorimetry to quantify the effects of dose-dependent increases in the activation of these non-thermal stimuli on whole-body dry and evaporative heat exchange during dynamic exercise. In a randomized crossover design, eight participants performed 45-min cycling at a fixed metabolic heat production (200 W/m2) in warm, dry conditions (30°C, 20% relative humidity) on four separate occasions, differing only in the level of lower-limb compression applied via bilateral thigh cuffs pressurized to 0, 30, 60, or 90 mmHg. This model provoked increments in non-thermal activation, while ensuring the heat loss required to balance heat production was matched across trials. At end-exercise, dry heat loss was 2 [1, 3] W/m2 lower per 30 mmHg pressure increment (p=0.006), whereas evaporative heat loss was elevated 5 [3, 7] W/m2 with each pressure increment (p...
Source: American Journal of Physiology. Regulatory, Integrative and Comparative Physiology - Category: Physiology Authors: Source Type: research