Thermoregulatory responses to exercise at a fixed rate of heat production are not altered by acute hypoxia

This study sought to assess the within-subject influence of acute hypoxia on exercise-induced changes in core temperature and sweating. Eight participants [1.75 (0.06) m, 70.2 (6.8) kg, 25 (4) yr, 54 (8) ml·kg–1·min–1] completed 45 min of cycling, once in normoxia (NORM; FIO2 = 0.21) and twice in hypoxia (HYP1/HYP2; FIO2= 0.13) at 34.4(0.2)°C, 46(3)% RH. These trials were designed to elicit 1) two distinctly different %Vo2peak [NORM: 45 (8)% and HYP1: 62 (7)%] at the same heat production (Hprod) [NORM: 6.7 (0.6) W/kg and HYP1: 7.0 (0.5) W/kg]; and 2) the same %Vo2peak [NORM: 45 (8)% and HYP2: 48 (5)%] with different Hprod [NORM: 6.7 (0.6) W/kg and HYP2: 5.5 (0.6) W/kg]. At a fixed %Vo2peak, changes in rectal temperature (Tre) and changes in esophageal temperature (Tes) were greater at end-exercise in NORM [Tre: 0.76 (0.19)°C; Tes: 0.64 (0.22)°C] compared with HYP2 [Tre: 0.56 (0.22)°C, P < 0.01; Tes: 0.42 (0.21)°C, P < 0.01]. As a result of a greater Hprod (P < 0.01) in normoxia, and therefore evaporative heat balance requirements, to maintain a similar %Vo2peak compared with hypoxia, mean local sweat rates (LSR) from the forearm, upper back, and forehead were greater (all P < 0.01) in NORM [1.10 (0.20) mg·cm–2·min–1] compared with HYP2 [0.71 (0.19) mg·cm–2·min–1]. However, at a fixed Hprod, Tre [0.75 (0.24)°C; P = 0.77] and Tes [0.63 (0.29)°C; P = 0.69] were n...
Source: Journal of Applied Physiology - Category: Physiology Authors: Tags: RESEARCH ARTICLE Source Type: research