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 ( a - v ¯ O 2difference and a‐v f O 2 difference, respectively) and O 2 extraction fraction for maximal oxygen uptake (V ˙ O 2max ). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary withV ˙ O 2max . Articles ( n  = 17) publishing individual data ( n  = 154) onV ˙ O 2max , maximal cardiac output ( Q ˙ max ; indicator‐dilution or the Fick method), a - v ¯ O 2difference (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.Q ˙ max and two‐LBF increased linearly by 4.9‐6.0 L · min –1 per 1 L · min –1 increase inV ˙ O 2max ( R 2  = .73 and R 2  = .67, respectively; both P  < .001). The a - v ¯ O 2difference increased from 118‐168 mL · L –1 from aV ˙ O 2max 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 increasingV ˙ O 2max ( R 2  = .17; P  < .001), systemic O 2 extraction fraction increased up to ~90% (V ˙ O 2max : 4.5 L · min –1 ) with no further change (exponential decay model: R 2  = .42). Likewise, leg O 2 extraction fraction increased withV ˙ O 2max to approach a maximal value of ~90‐95% ( R 2  = .83). Muscle O 2 diffusing capacity and the equilibration index Y increased linearly withV ˙ O 2max ( 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 toV ˙ O 2max , enhanced O 2 extraction fraction (≥90%) contributes to the remarkably highV ˙ O 2max in endurance‐trained individuals.