Zone 2 is everywhere in longevity content right now - but the research says VO2 max matters more

The biology behind Zone 2 is real. At 60-70% max heart rate your body preferentially recruits Type I muscle fibers, mitochondrial density increases, fat oxidation is maximized. Inigo San-Millan's work at the University of Colorado showed that metabolically healthy individuals oxidize fat at significantly higher rates in Zone 2 compared to people with metabolic dysfunction - and that training there can partially restore that capacity.

The issue is what gets left out of the Attia/Huberman version of this conversation.

A 2025 narrative review in the International Journal of Sports Physiology and Performance found that for people training fewer than six hour per week, higher intensity exercise produces equal or greater mitochondrial adaptations than Zone 2 in less time. The 80/20 polarized model was built for athletes logging 12-20 hours weekly - not recreational exercisers with three hours to spare.

More importantly, VO2 max is a stronger predictor of all-cause mortality than the mitochondrial benefits Zone 2 is primarily credited for. Data from the Cooper Center Longitudinal Study across 122,000 participants shows moving from the bottom quartile to the median of cardiorespiratory fitness cuts mortality risk by roughly 50% - exceeding the risk reduction from controlling blood pressure, cholesterol, or smoking. And higher intensity training drives VO2 max improvements more effectively than low intensity work.

Zone 2 isn't wrong. It's just probably not the priority it's been sold as for most people in this community