Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men

We analysed the importance of systemic and peripheral arteriovenous O(2) difference ( [Formula: see text] difference and a‐v(f)O(2) difference, respectively) and O(2) extraction fraction for maximal oxygen uptake ( [Formula: see text]). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with [Formula: see text]. Articles (n = 17) publishing individual data (n = 154) on [Formula: see text] , maximal cardiac output ( [Formula: see text]; indicator‐dilution or the Fick method), [Formula: see text] difference (catheters or the Fick equation) and systemic O(2) extraction fraction were identified. For the peripheral responses, group‐mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a‐v(f)O(2) difference and O(2) extraction fraction (arterial and femoral venous catheters) were obtained. [Formula: see text] and two‐LBF increased linearly by 4.9‐6.0 L · min(–1) per 1 L · min(–1) increase in [Formula: see text] (R (2) = .73 and R (2) = .67, respectively; both P < .001). The [Formula: see text] difference increased from 118‐168 mL · L(–1) from a [Formula: see text] of 2‐4.5 L · min(–1) followed by a reduction (second‐order polynomial: R (2) = .27). After accounting for a hypoxemia‐induced decrease in arterial O(2) content with increasing [Formula: see text] (R (2) = .17; P < .001), systemic O(2) extraction fraction increased up to ~90% ( [Formula: see text]: 4.5 L · min(–1)) with no further change (exponential decay model: R (2) = .42). Likewise, leg O(2) extraction fraction increased with [Formula: see text] to approach a maximal value of ~90‐95% (R (2) = .83). Muscle O(2) diffusing capacity and the equilibration index Y increased linearly with [Formula: see text] (R (2) = .77 and R (2) = .31, respectively; both P < .01), reflecting decreasing O(2) diffusional limitations and accentuating O(2) delivery limitations. In conclusion, although O(2) delivery is the main limiting factor to [Formula: see text] , enhanced O(2) extraction fraction (≥90%) contributes to the remarkably high [Formula: see text] in endurance‐trained individuals.