• near-infrared spectroscopy;
  • altitude acclimatization;
  • exercise;
  • cerebral frontal cortex;
  • intercostal muscle

We investigated the effect of hypoxic acclimatization per se, without any concomitant influence of strenuous physical activity on muscle and cerebral oxygenation. Eight healthy male subjects participated in a crossover-designed study. In random order, they conducted a 10-day normoxic (CON) and a 10-day hypoxic (EXP) confinement. Pre and post both CON and EXP confinements, subjects conducted two incremental-load cycling exercises to exhaustion; one under normoxic, and the other under hypoxic (FIO2 = 0.154) conditions. Oxygen uptake (inline image), ventilation (inline image), and relative changes in regional hemoglobin oxygenation (Δ([HbO2]) in the cerebral cortex and in the serratus anterior (SA) and vastus lateralis (VL) muscles were measured. No changes were observed in the CON confinement. Peak work rate and inline image were similar pre and post in the EXP confinement, whereas inline image increased in the EXP post normoxic and hypoxic trials (P < 0.05). The exercise-induced drop in VL Δ[HbO2] was less in the post- than pre-EXP trial by 4.0 ± 0.4 and 4.2 ± 0.6 μM during normoxic and hypoxic exercise, respectively. No major changes were observed in cerebral or SA oxygenation. These results demonstrate that a 10-day hypoxic exposure without any concomitant physical activity had no effect on normoxic or hypoxic inline image, despite the enhanced VL oxygenation.