Zone 2 Training

What is zone 2 training?

Zone 2 training is low-intensity, steady-state aerobic exercise performed at the highest effort level where your body still relies almost entirely on mitochondrial oxidative phosphorylation for energy, without significant lactate buildup. In practical terms, blood lactate stays below about 2 mmol/L. You can hold a conversation during zone 2, but not comfortably. This intensity sits below the first lactate threshold (also called LT1 or the ventilatory threshold) and forms the foundation of longevity-focused training as recommended by exercise physiologist Dr. Inigo San-Millan and physician Dr. Peter Attia ^[1].

How to find your zone 2 heart rate

The most accurate way to identify zone 2 is a laboratory lactate test, where blood lactate is measured at increasing intensities to find the point where it first rises above baseline (around 1.8-2.0 mmol/L). Without lab access, the MAF 180 formula from Dr. Phil Maffetone gives a reasonable estimate: subtract your age from 180, adjust for fitness and health status, and train 10 beats below that number up to the result. A simpler approach uses 60-70% of your maximum heart rate or 80-89% of your lactate threshold heart rate. Wearables from Garmin, Apple Watch, or Polar display real-time heart rate zones, though individual calibration through a lactate or VO2 test improves accuracy substantially, since standard formulas can be off by 10-15 beats per minute ^[2].

Why zone 2 training matters for longevity

Cardiorespiratory fitness, measured by VO2max, is one of the strongest predictors of all-cause mortality. A landmark study in JAMA Network Open found that each 1-MET increase (about 3.5 ml/kg/min VO2max) was linked to a 13-15% reduction in mortality risk, regardless of age, sex, or existing conditions ^[3]. The Copenhagen Male Study showed that above-average cardiorespiratory fitness in midlife was associated with nearly five additional years of life expectancy compared to below-average fitness ^[4]. Zone 2 builds the aerobic base that supports a higher VO2max and is the foundation of Peter Attia's "Centenarian Decathlon" concept: building enough cardiovascular and metabolic capacity to stay functionally independent into your 80s and 90s.

Mitochondrial health and metabolic flexibility

Sustained zone 2 exercise drives mitochondrial biogenesis, the creation of new mitochondria, and makes existing mitochondria more efficient at converting fatty acids and glucose into ATP. Over weeks of consistent training, muscle fibers increase both the number and density of mitochondria, which improves fat oxidation capacity and metabolic flexibility. That means your body gets better at switching between fat and carbohydrates as fuel, a hallmark of metabolic health. Better mitochondrial function also supports lactate clearance, reduces insulin resistance, and stabilizes blood glucose ^[5]. A 2022 study found that sedentary adults doing 45 minutes of zone 2 cycling four times per week for 12 weeks increased whole-body fat oxidation by 32% and reduced fasting insulin by 21%, with no dietary changes ^[6].

Zone 2 vs zone 3: why the distinction matters

Zone 3, sometimes called the "grey zone" or "tempo" zone, sits between the aerobic and anaerobic thresholds. It's harder than zone 2 but not hard enough to produce the VO2max gains of true high-intensity work (zone 4-5). The problem: zone 3 generates more fatigue and requires longer recovery than zone 2, while offering fewer of the specific mitochondrial and fat-oxidation adaptations that make zone 2 so valuable. It's also too easy to produce the peak cardiac output adaptations that come from zone 5 intervals. Experienced coaches call zone 3 "no man's land" because athletes who spend most of their time there tend to plateau. The polarized training model, backed by research on elite endurance athletes, avoids this by keeping roughly 80% of training volume in zone 2 and 20% in zone 5 ^[7].

Why zone 2 feels frustratingly slow (and why that's normal)

One of the most common complaints from people starting zone 2 training: it feels embarrassingly slow. Many runners have to walk uphill or do run-walk intervals to keep their heart rate in range. This is completely normal. If you lack aerobic base fitness, your heart rate spikes at relatively low speeds. Heat, caffeine, poor sleep, and stress all push heart rate higher too. The good news: with 3-4 months of consistent zone 2 work, your pace at the same heart rate will measurably increase. Your body is building capillary density, improving stroke volume, and making mitochondria more efficient. Don't fight the process by speeding up. The adaptation only happens when you stay in the zone.

How to practice zone 2 training

Any sustained aerobic activity works: brisk walking, cycling, rowing, swimming, or an elliptical. San-Millan recommends 3-4 sessions per week of 45-60 minutes each, totaling about 3-4 hours weekly ^[1]. Beginners can start at 30 minutes and extend gradually over several weeks. The key is holding a consistent pace within the target heart rate range. The "talk test" is a reliable self-check: you should be able to speak in full sentences, but with some effort. Peter Attia follows an 80/20 model with roughly 80% of total training volume in zone 2 and 20% in high-intensity zone 5 work (such as 4x4-minute intervals), since both provide complementary cardiovascular and metabolic benefits ^[8].

Brain health and zone 2 exercise

Zone 2 training isn't just about the heart and muscles. Moderate-intensity aerobic exercise increases production of brain-derived neurotrophic factor (BDNF), a protein that promotes growth of new brain cells and strengthens existing neural connections. Higher BDNF levels are associated with improved memory, better mood, and lower risk of depression and dementia. A Neurology study of over 1,200 older adults linked regular moderate aerobic exercise with significantly reduced dementia risk. The cardiovascular improvements from zone 2 also enhance cerebral blood flow, delivering more oxygen and nutrients to brain tissue.

What the latest evidence says

A 2025 narrative review in Sports Medicine examined whether zone 2 is truly the best intensity for mitochondrial and metabolic adaptations ^[5]. The evidence shows that zone 2 is highly effective for building aerobic capacity and fat metabolism, but combining it with higher-intensity intervals produces the largest overall VO2max improvements. A separate 2025 expert consensus published in the Journal of Applied Physiology brought together leading sport scientists to define zone 2 boundaries and optimal training protocols, noting significant individual variability in where zone 2 actually falls ^[2]. For people focused on health and longevity rather than competitive performance, the practical takeaway hasn't changed: structure the majority of your training in zone 2 for a sustainable, low-injury approach that delivers real metabolic and cardiovascular returns over time.