Effects of short hypoxic pre-exposure on physiological responses to subsequent hypoxic exercise

Abstract

In mountain climbing, short pre-exposure to hypoxia at the midway point of a high mountain is often carried out before heading to a higher altitude. However, the effects of such exposure have not been examined experimentally. This study aimed at investigating the effects of short pre-exposure to hypoxia on physiological responses to subsequent hypoxic exercise. Thirteen male sea-level residents participated in 2 tests. Both tests consisted of 60-min normobaric exposure followed by 15-min stepwise incremental ergocycle exercise (five workloads) under hypoxic conditions (fractional inspired oxygen concentration [FiO₂] = 0.167). Conditions during normobaric exposure were hypoxic (FiO₂ = 0.167) or normoxic (FiO₂ = 0.209). Results of the two-way analysis of variance (oxygen concentration × exercise intensity) showed significant oxygen concentration effects on heart rate (HR), carbon dioxide production (VCO₂), and rating of perceived exertion during hypoxic exercise. Significant interaction effects were found in minute ventilation and VCO₂. Post hoc tests compared these parameters after hypoxic exposure with those after normoxic exposure at each workload, and only showed a significant difference in HR at workload 2. A significant negative correlation was observed between peak oxygen uptake (VO₂) measured in normoxia and ratio of arterial oxygen saturation (SpO₂) after hypoxic exposure to that after normoxic exposure at workload 5. The present study could not clearly show through post hoc tests the significant effects of short hypoxic pre-exposure on physiological responses to subsequent hypoxic exercise, while it indicated that those with relatively higher peak VO₂ showed a greater decrease in SpO₂ during hypoxic exercise after hypoxic exposure than after normoxic exposure.