VO2 Max
topic
VO2 max (maximal oxygen uptake) is the gold standard measure of cardiorespiratory fitness — the maximum rate at which the cardiovascular and respiratory systems can deliver oxygen to working muscles and those muscles can utilize it for ATP production — measured in mL/kg/min and declining approximately 1% per year after age 25 without training intervention. It is determined by cardiac output (heart rate × stroke volume), oxygen extraction efficiency (arteriovenous O2 difference), and skeletal muscle mitochondrial density.
Role
VO2 max is the most important objective health metric most people have never measured and most doctors have never ordered — despite its all-cause mortality prediction being stronger than any blood biomarker in the clinical literature. Peter Attia's analysis of the hazard ratios shows that moving from the lowest to above-average VO2 max quintile reduces all-cause mortality risk by approximately 45% — a magnitude that dwarfs any pharmaceutical intervention and that is achievable through consistent aerobic training in 12–24 weeks. The majority of people optimizing cholesterol, blood pressure, and glucose while never measuring or training VO2 max are managing secondary risk factors while ignoring the primary one.