Experimental Support for the Theory of Diffusion Limitation of Maximum Oxygen Uptake
In spite of many years of investigation, the question of what determines maximum oxygen uptake (V̇O2max) remains controversial. While it has been suggested that V̇O2max is not limited by oxygen supply (Jobsis and Stainsby, 1986), the preponderance of experimental evidence suggests the contrary. Thus, increasing oxygen supply by breathing hyperoxic gas mixtures produces small but measurable increments in maximum V̇O2max (Welch, 1983). Other forms of increasing convective oxygen delivery to muscle also result in increased V̇O2max. Thus, as reviewed by Gledhill (1982), blood transfusion acutely increases V̇O2max. In the opposite direction, it is well-known that V̇O2max can be acutely reduced by breathing hypoxic gas mixtures, and in the extreme with chronic hypoxia, V̇O2max can be reduced to some 25% of sea level values when the inspired PO2 is equivalent to that of the summit of Mt. Everest (Ward et al., 1989). It would thus seem reasonable to conclude that oxygen supply is in fact limiting maximum V̇O2, at least within an experimentally feasible range of investigation. The question then becomes: where in the oxygen transport pathway from the atmosphere to the mitochondria within the muscle are these limits set?
KeywordsOxygen Delivery Maximum Oxygen Uptake Measured Muscle Individual Subject Data Perfusion Heterogeneity
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