Peter Attia, referencing data from the Cleveland Clinic, has highlighted that moving from the bottom fitness quartile to the second quartile reduces all-cause mortality risk by approximately 50% — a larger risk reduction than quitting smoking. A 2022 study in JAMA Network Open tracking 750,000 US military veterans found that low cardiorespiratory fitness was associated with a 4.09 times higher all-cause mortality hazard ratio compared to very high fitness. No other single variable, including smoking, high blood pressure, diabetes, or obesity, produced a comparable effect size.
What VO2 Max Actually Measures
VO2 max is the maximum rate at which your body can consume oxygen during maximal exercise, expressed in millilitres of oxygen per kilogram of bodyweight per minute. It reflects the integrated efficiency of your cardiovascular system, pulmonary function, haemoglobin capacity, mitochondrial density, and skeletal muscle oxidative capacity. A low VO2 max means the entire oxygen delivery and utilisation chain is operating below its potential.
Going from unfit to moderately fit reduces your risk of dying more than any other single health intervention available.
Improving VO2 Max
- Zone 2 cardio (conversational pace) for 150–180 minutes per week as the aerobic base
- High-intensity intervals (4×4 minute efforts at 85–95% max heart rate) once or twice weekly
- Norwegian 4×4 protocol has the strongest evidence for VO2 max improvement
- Nasal breathing during lower-intensity sessions to improve CO2 tolerance
- Consistency over years, not months — adaptations compound across decades