Hypoxia gradually augments metabolic and thermoperceptual responsiveness to repeated whole‐body cold stress in humans

NEW FINDINGS What is the central question of this study? In male lowlanders, does hypoxia modulate thermoregulatory effector responses during repeated whole-body cold stress encountered in a single day? What is the main finding and its importance? A ∼10 h sustained exposure to hypoxia appears to mediate a gradual upregulation of endogenous heat production, preventing the progressive hypothermic response prompted by serial cold stimuli. Also, hypoxia progressively degrades mood, and compounds the perceived thermal discomfort, and sensations of fatigue and coldness. ABSTRACT We examined whether hypoxia would modulate thermoeffector responses during repeated cold stress encountered in a single day. Eleven men completed two ∼10 h sessions, while breathing, in normobaria, either normoxia or hypoxia ( PO2 : 12 kPa). During each session, subjects underwent sequentially three 120 min immersions to the chest in 20°C water (CWI), interspersed by 120 min rewarming. In normoxia, the final drop in rectal temperature (Trec ) was greater in the third (∼1.2°C) than in the first and second (∼0.9°C) CWIs (P