Effects of acute hypoxia on the VO2 max of trained and untrained subjects

The purpose of this study was to compare the responses of highly trained (TR) and untrained (UT) subjects' maximal oxygen uptake (VO2 max) while breathing a hypoxic gas mixture. Two groups of healthy volunteers were recruited: (1) trained subjects (n = 8), VO2 max = 67.2 +/- 4.0 ml kg-1 min-1; (2) untrained subjects (n = 8), VO2 max = 45.4 +/- 5.5 ml kg-1 min-1. Both groups were administered maximal cycle ergometer tests under hypoxic (13% O2, 87% N2) and normoxic conditions (21% O2, 79% N2). A pulse oximeter (Ohmeda 3700) was used to estimate arterial haemoglobin saturation (SpO2). The trained group had lower values for SpO2 at maximal exercise (TR = 67.0 +/- 7.1%; UT = 77.5 +/- 9.0%) and greater reductions in VO2 max while breathing the hypoxic gas mixture was linearly correlated with the subjects' normoxic VO2 max (ml kg-1 min-1: r = -0.91). These results indicate that highly trained subjects experience greater percent decrements in SpO2 and VO2 max while breathing a moderately hypoxic gas mixture compared to untrained subjects, and may explain some of the variable decrease observed when VO2 max is measured at simulated altitude.