Should I do Zone 2 cardio?

Zone-2 endurance training (60–70% of max heart rate, conversational pace) is one of the most evidence-supported longevity interventions. It develops mitochondrial density, fat-oxidation capacity, and cardiovascular reserve. Three sessions of 45 minutes per week is the dose with the strongest evidence base.

For almost anyone training for healthspan, Zone 2 is a high-confidence, low-risk foundation. It costs nothing, stacks cleanly on top of strength work and a weekly VO2-max session, and the chain connecting mitochondrial fitness to all-cause mortality is among the best understood on this list. The main failure mode is going too hard: most people drift above Zone 2 and quietly convert an easy aerobic session into a mediocre tempo session.

Audited a tracked voice's Zone-2 podcast episode and reviewed San-Millán's mitochondrial-density literature, then cross-checked the dose and intensity claims against the broader endurance-training and cardiorespiratory-fitness cohort data.

• 01Mitochondrial density: Zone-2 is the dominant training stimulus, supported at the mechanistic and muscle-biopsy level.
• 02Fat oxidation: increases progressively over 8–12 weeks of Zone-2 training.
• 03Cardiovascular outcomes: lower all-cause mortality in cohorts who maintain endurance fitness.
• 04Dose-response: benefit tracks weekly aerobic volume; three 45-minute sessions is a well-supported floor, not a hard ceiling.

Zone 2 requires patience — improvements are weekly, not daily. If you can't hold a full conversation, you're above Zone 2. A chest-strap heart-rate monitor is plenty; the exact zone boundary matters less than staying genuinely easy.