Zone 2 Cardio
Zone 2 training explained. Aerobic base building, fat oxidation, mitochondrial health, and longevity. Featuring Iñigo San Millán, Galpin, and Attia.
Low-intensity aerobic training that builds mitochondrial density, metabolic flexibility, and cardiovascular base without excessive fatigue
Zone 2 cardio is the foundation of metabolic health and longevity-focused training. The evidence is overwhelming: low-intensity aerobic work builds mitochondrial density, improves fat oxidation, enhances cardiovascular function, and reduces all-cause mortality. Most people do far too little Zone 2 and far too much high-intensity work.
The highest-ROI training investment for longevity and metabolic health. Aim for 3-4 hours per week at an intensity where you can hold a conversation but prefer not to.
Science & Mechanisms
Mechanisms:
- Stimulates mitochondrial biogenesis via PGC-1α activation
- Increases Type I (slow-twitch) muscle fiber oxidative capacity
- Improves fat oxidation (ability to use fat as fuel)
- Enhances stroke volume and cardiac output
- Lowers resting heart rate over time
- Improves metabolic flexibility (ability to switch fuel sources)
- Builds capillary density in working muscles
Key research:
- San-Millán & Brooks (2018): Zone 2 training optimizes lactate clearance by training mitochondria to use lactate as fuel
- Seiler (2010): Elite athletes train 80% low intensity, 20% high intensity (polarized model)
- Mandsager et al. (2018): Higher cardiorespiratory fitness reduces all-cause mortality with no upper limit of benefit
- Holloszy (1967): Foundational study showing endurance training doubles mitochondrial content
- Iellamo et al. (2000): Low-intensity training improves HRV and autonomic function
Effect sizes:
- Mitochondrial density: Large effect with consistent training
- Fat oxidation: Large effect (metabolic flexibility improves significantly)
- VO2max: Moderate effect (Zone 2 alone improves it, high-intensity adds more)
- All-cause mortality: Strong inverse relationship with cardiorespiratory fitness
Limitations:
- Benefits require consistency over months and years
- Most people train too hard and miss Zone 2 benefits
- Requires heart rate or lactate monitoring to stay in zone
- Boring for some people (low intensity feels "too easy")
Episodes
Simon Hill sits down with Dr. Inigo San Millan, an assistant professor at the University of Colorado and one of the world's foremost experts on metabolic health and exercise phy...
In this follow-up conversation, Simon Hill and Dr. Inigo San Millan take a deep dive into lactate -- debunking the long-held myth that it is a toxic waste product and revealing ...
Simon Hill and exercise physiologist Drew Harrisberg unpack practical takeaways from Hill's previous deep-dive with Dr. Inigo San Millan on zone 2 training. The conversation cov...
Dr. Inigo San Millan discusses his research connecting zone 2 training, mitochondrial function, and cancer metabolism. He explains how skeletal muscle acts as an endocrine organ...
Sarah Macklin interviews Dr. Inigo San Millan on why mitochondrial function represents the next frontier beyond VO2 max for understanding health and longevity. San Millan explai...
Sean from Upside Strength interviews Dr. Inigo San Millan, professor at the University of Colorado and performance director for Team UAE (coach of Tour de France winner Tadej Po...
Brett McKay interviews hybrid athlete and coach Alex Viada on why most people skip zone 2 cardio entirely, jumping straight from rest to zone 3 and missing significant health an...
Compounding pharmacist Kris Gravant breaks down zone 2 cardio training for the general population, explaining why it has become the most discussed training zone in longevity cir...
Dr. Stephen Cabral simplifies heart rate training zones for the general population, cutting through the complexity of different zone systems and formulas. He presents a practica...
Dr. Stephen Cabral makes the case for adding cardiovascular training alongside weight training for longevity, acknowledging his own bias toward weights as a strength and conditi...
In the inaugural episode of Perform, Dr. Andy Galpin delivers a comprehensive guide to understanding and improving cardiovascular fitness. He opens with a deceptively simple que...
Dr. Andy Galpin explains how to improve VO2 max and build endurance. Covers the physiology of aerobic capacity and training methods to enhance it.
One minute of vigorous exercise equals 4-10 minutes of moderate activity for health outcomes. Just 3-9 daily minutes of hard effort cuts cardiovascular mortality by 40-50%. High...
Dr. Andy Galpin covers evidence-based strategies for improving heart health, training VO2 max, and optimizing sleep. Heart disease is the leading cause of death - Andy shares wh...
Build your weekly fitness around 150-200 minutes of zone 2 cardio (conversational pace, nasal breathing) plus strength training. Alternate emphasis every 10-12 weeks. Long zone ...
Three weeks of bed rest causes worse cardiovascular decline than 30 years of aging. The flip side: exercising 4-5 days per week preserves youthful heart structure, and the Norwe...
Each unit increase in VO2 max adds roughly 45 days to life expectancy. The Norwegian 4x4 protocol (four 4-minute intervals at 95% max heart rate) is one of the most effective wa...
Andrew Huberman breaks down the science of endurance into four distinct categories: muscular endurance, long-duration endurance, high-intensity anaerobic conditioning, and high-...
Dr. Andy Galpin delivers a comprehensive solo episode on lactate metabolism, tracing the science from its discovery in sour milk in 1708 through George Brooks' lactate shuttle h...
Dr. Herman Pontzer discusses his groundbreaking research on how humans really burn calories. Challenges conventional thinking about exercise and metabolism with evolutionary insights.