VO2max protocol - the gold standard assessment for cardiorespiratory fitness

The Fick equations!

When measuring oxygen in the blood:
VO2 = CO × (a-v O2),
Where CO is cardiac output and a-v O2 is the difference in blood oxygenation between the arteries and veins.

When measuring oxygen in the air:
VO2 = Ve × (FiO2 - FeO2),
Where Ve is ventilatory volume and FiO2 - FeO2 is the difference between the fraction of oxygen in the insired and expired air.

Satin and Astrand. J Appl Physiology. 1967.

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