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) y, 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 a) two distinctly different %VO2peak [NORM:45(8)% and HYP1:62(7)%] at the same heat production (Hprod) [NORM:6.7(0.6) W.kg-1 and HYP1:7.0(0.5) W.kg-1]; and b) the same %VO2peak[NORM:45(8)% and HYP2:48(5)%] with different Hprod [NORM:6.7(0.6) W.kg-1 and HYP2:5.5(0.6) W.kg-1]. 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 to HYP2 [∆Tre:0.56(0.22)°C, P<0.01; ∆Tes:0.50(0.30)°C, P<0.01]. As a result of a greater Hprod (P<0.01) in normoxia, and therefore evaporative heat balance requirements, in order to maintain a similar %VO2peak compared to 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 to 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 not different in HYP1, compared to NORM. Likewise, mean LSR [1.11(0.20) mg.cm-2.min-1] was not different (P=0.84) in HYP1 compared to NORM. These data demonstrate, using a within-subjects design, that hypoxia does not independently influence thermoregulatory responses. Additionally, further evidence is provided to support that metabolic heat production, irrespective of %VO2peak, determines changes in core temperature and sweating during exercise.
- heat stress
- core temperature
- Copyright © 2016, Journal of Applied Physiology