Zone 2 cardio is more important for longevity than any high-intensity workout you will ever do

Zone 2 is defined as the highest intensity at which you can maintain a conversation — roughly 60–75% of maximum heart rate, and the intensity at which blood lactate remains below 2 mmol/L. At this intensity, mitochondria are the primary energy producers. Over months and years of consistent Zone 2 training, mitochondrial biogenesis occurs: existing mitochondria increase in size and efficiency, and new mitochondria proliferate within muscle cells.

The most powerful anti-ageing training tool available is also the least glamorous: going slowly, for a long time, consistently.

The Minimum Effective Dose

• 150–180 minutes of Zone 2 cardio per week is the evidence-based threshold for meaningful mitochondrial adaptation
• Sessions of 45–90 minutes are more effective than shorter sessions at building mitochondrial density
• Heart rate monitor or lactate meter to verify you are in Zone 2, not Zone 3
• Walking briskly, cycling at moderate pace, rowing, or swimming all qualify
• Nasal-only breathing is a practical proxy for Zone 2 — when you need to open your mouth, you have left Zone 2