Thermal Behavior During Exercise Alleviates Thermal Discomfort Despite Exacerbating Increases in Core Temperature

Abstract

PurposeIncreases in metabolic heat production during exercise stimulate perceptions of thermal discomfort as core and skin temperatures, and skin wettedness increase. Thermal discomfort is the precursor to thermal behavior. Employing thermal behavior during exercise may reduce thermal discomfort by attenuating the rise in core temperature. However, this remains unknown. We tested the hypothesis that thermal behavior attenuates the rise in core temperature and alleviates thermal discomfort during exercise.MethodsTwelve healthy subjects (24 ± 3 y, 6 females) performed two trials in which they completed 60 min of recumbent cycling exercise at a fixed rate of metabolic heat production (217 ± 28 W/m2) in a 27 ± 0°C, 48 ± 6% relative humidity environment. In both trials subjects wore a water perfused suit top. In the control trial, 34 ± 0°C water circulated through the top during the trial (CON). The experimental trial allowed for thermal behavior (BEH) where subjects were instructed to maintain their upper body thermally comfortable throughout. In BEH, subjects thermally behaved by pressing a button to receive cool water (2 ± 1°C) through the water perfused suit top for 2 min, which was followed by a 1 min wash out period. Mean skin (10 site) and core (telemetry pill) temperatures, mean skin wettedness (8 site), skin blood flow (forearm, laser Doppler), and local sweat rate (ventilated capsule) were measured continually. Local sweat rate was measured under (on mid‐axillary line) and outside (on anterior thigh, n=7) of the water perfused suit top. Whole body thermal comfort was recorded every 10 min. Water perfused suit top temperature provided an index of thermal behavior. Data are presented as mean ± SD as the absolute change from the values acquired pre‐exercise.ResultsMetabolic heat production was not different between trials (P=0.44). The increase in core temperature was greater in BEH vs. CON at 50 and 60 min (both by +0.1 ± 0.3°C, P<0.01). Mean skin temperature was reduced in BEH vs. CON from 20 min (by −0.5 ± 0.7°C, P<0.01) onwards (P<0.01). Mean skin wettedness was greater in BEH vs. CON from 30 min (by +0.01 ± 0.03 a.u., P<0.01) onwards (P<0.01). Water perfused suit top temperature was reduced in BEH vs. CON from 10 min (by −5.6 ± 7.0°C, P<0.01) onwards (P<0.01). Mid‐axillary sweat rate was attenuated in BEH vs. CON from 10 min (by −0.1 ± 0.12 g/cm2/min) onwards (P<0.01), and thigh sweat rate was attenuated at min 20 (by: −0.1 ± 0.2 g/cm2/min) and 60 (by −0.2 ± 0.2 g/cm2/min). Forearm skin blood flow was not different between BEH and CON at any time (P=0.20). Increases in whole body thermal discomfort were attenuated in BEH vs. CON within the first 10 min (by −0.4 ± 0.4 a.u., P=0.04) onwards (P<0.01).ConclusionsEmploying thermal behavior that reduces mean skin temperature during exercise alleviates thermal discomfort despite exacerbating the rise in core temperature and skin wettedness. Reductions in sweat rate may contribute to the greater rise in core temperature when employing thermal behavior. These findings may question the role of skin wettedness in stimulating thermal behavior during exercise.Support or Funding InformationSupported by lululemon athletica inc.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.