Abstract
The purpose of these experiments was to compare the effects of breathing air (79%
N2-21% O2) and a normoxic helium oxygen gas mixture (He-O2) (79% He - 21% O2) on maximal oxygen uptake (V̇2 max) and work tolerance during both incremental and high-intensity constant load
exercise. First, eight subjects underwent two separate short incremental cycle ergometer
exercise tests until the subject could not maintain the desired power output. Second,
four subjects exercised to exhaustion on two separate occasions at a constant exercise
intensity (100% V̇O2 max). Each exercise protocol required the subject to breathe air on one test and
a normoxic He-O2 mixture on an additional occasion. Data analysis revealed higher (P < 0.05) minute ventilations, an increased time to exhaustion, and a greater V̇O2 max during He-O2 breathing in both exercise conditions. Small but significant (P < 0.05) differences existed in the percent hemoglobin saturated with O2 (% SO2) at exercise demands greater than 120 W during the incremental experiment and during
each minute of the constant load test with He-O2 giving the higher value. These data support the hypothesis that breathing a normoxic
He-O2 gas mixture during exercise elevates V̇O2 max and increases exercise tolerance. Further, although it appears that breathing
a He-O2 mixture results in higher %SO2 during intense exercise, the increase in arterial O2 content is small and probably does not fully account for the higher V̇O2 max observed under these conditions.
Key words
helium - V̇O2 max - exercise tolerance - hemoglobin saturation - normoxia
