FACTORS LIMITING MAXIMAL OXYGEN-CONSUMPTION IN HUMANS

The factors limiting V̇O max in humans are analyzed according to a multigfactorial model derived from the O2 conductance equation. In this context, alveolar ventilation (V̇a) and lung O2 transfer (Gl) are not considered to be limiting, at least at sea level, because changes in V̇a and/or in Gl are not accompanied by changes in V̇Omax due to the shape of the O2 dissociation curve. Thus, the limits of V̇Omax are shared between blood O2 transport (Fq′) and a peripheral factor. This last includes tissue O2 transfer (Ft′) and mitochondrial O2 utilization (Fm′). In untrained subjects at sea level, blood O2 transport is found to be responsible for ∼70% of the overall to limits to V̇Omax (Fq′ = 0.7), the rest depending on the peripheral factor. Fq′, a well as the sum of Ft′ and Fm′, are unchanged after training or upon return to sea level following exposure to chronic hypoxia (altitude higher than 5000 m) In the latter condition, however, since tissue O2 transfer, which sea sets Ft′ is facilitated, and mitochondrial O2 utilization, which sets Fm′, is impaired, Ft′ is reduced and Fm′ increased as compared to control condition and/or after training. © 1990.