Oxygen Uptake Kinetics During Moderate and Heavy Intensity Exercise in Humans: The Influence of Hypoxia and Training Status

Abstract

This study examined the influence of moderate hypoxia on the oxygen uptake (V·O₂) kinetic response (primary time constant and slow component amplitude) during moderate and heavy cycle exercise in twenty-seven male subjects with various training status. Nine endurance trained (21.5 ± 2.6 yr), nine sprint trained (22.9 ± 5.7 yr), and nine untrained controls (24.0 ± 4.4 yr) completed incremental tests to exhaustion in normoxia (inspired gas concentration or FIO₂ = 21 % O₂) and hypoxia (FIO₂ = 13 % O₂) to establish the FIO₂-specific ventilatory threshold (VT) and maximal VO₂. Subsequently, the subjects performed repeated constant work rate cycling exercises during 7 min at moderate intensity (80 % of FIO₂-specific VT) and heavy intensity (midway between the FIO₂ specific VT and maximal VO₂). Pulmonary gas exchange was measured breath-by-breath during all exercise sessions. For both moderate and heavy intensities, the time constant of the primary VO₂ component was significantly (p < 0.05) slowed by ∼ 25 to 30 % in hypoxia compared to normoxia to the same extent in the three groups. Hypoxia produced a more important decrease in the amplitude of the slow component in endurance athletes (- 36 %) than in sprinters (- 30 %) and controls (- 12 %). These results suggest that both primary and slow components of VO₂ kinetics during the adjustment to moderate- and heavy-intensity exercise are sensitive to hypoxia while training status tended to modulate partly the slow component amplitude.