Zone 2 (Z2) aerobic exercise is a foundational component of Peter Attia’s methodology for longevity and metabolic health. This steady-state, low-intensity work enhances the function and number of mitochondria, the energy-producing structures within your cells. The ability of mitochondria to efficiently use fat for fuel, known as metabolic flexibility, forms the base of a strong aerobic system. This system benefits overall health and allows for more effective high-intensity training.
Identifying Your Zone 2 Threshold
Before focusing on duration, ensure you are working at the correct intensity. Zone 2 is technically defined as the highest intensity you can sustain while keeping blood lactate concentration below 2.0 millimoles per liter (mmol/L). This level indicates a high rate of fat oxidation, where the body clears lactate as quickly as it produces it. While an at-home lactate meter provides the most precise feedback, it is not necessary for most people.
A more accessible method for gauging this intensity is the “talk test,” which uses your Rate of Perceived Exertion (RPE). When in Zone 2, you should be able to speak in complete, albeit slightly strained, sentences. If you can comfortably carry on a full conversation without effort, you are likely in Zone 1. If you can only speak in short, broken phrases, you have crossed into Zone 3 or higher. This level of exertion generally correlates to an RPE of 4 to 6 on a 10-point scale.
Heart rate can also be used as a proxy, though it is less precise due to daily variation and individual fitness levels. For a general starting point, Zone 2 often falls between 70% and 80% of your maximum heart rate, or you can use the Maffetone formula of 180 minus your age. Heart rate can fluctuate based on fatigue, stress, and sleep quality, making the talk test a more reliable daily indicator for many people.
The Weekly Time Prescription
The recommended total weekly volume for Zone 2 is three to four hours. This is the ideal target for maximizing the longevity and metabolic health benefits of the exercise. Attia suggests that while two hours a week is a good starting point for a beginner, the sweet spot for driving desired cellular adaptations is reached at the three-hour mark and beyond.
This volume is directly tied to mitochondrial biogenesis, the growth of new mitochondria. Spending three to four hours a week in Zone 2 provides the sustained signal necessary to prompt these cellular changes. Lower weekly totals may not provide a strong enough stimulus to elicit the same degree of adaptation, particularly regarding fat oxidation efficiency. Consistently accumulating this volume builds a robust aerobic base, the foundation of cardiorespiratory fitness.
A strong aerobic base improves your capacity to clear lactate, making subsequent high-intensity exercise more effective. This weekly time commitment also enhances insulin sensitivity, a major factor in metabolic health and a countermeasure to age-related decline. The goal is to make the body highly efficient at utilizing its own fat stores for energy, which requires both the correct intensity and sufficient duration.
Optimizing Session Duration and Frequency
To achieve the recommended weekly volume, training must be structured into effective individual sessions. Attia recommends aiming for three to five Zone 2 sessions per week. Crucially, each session should be sustained for a minimum of 45 minutes.
The reason for this minimum session length is that it takes time for the body to fully transition into the desired metabolic state. Sustained exercise beyond 45 minutes ensures that the mitochondria are adequately challenged to stimulate biogenesis and improve their efficiency. Shorter sessions, such as 30 minutes, may not provide the necessary duration to fully signal the body for optimal adaptation.
For many people, a practical structure involves four sessions of 45 to 60 minutes each week to comfortably hit the three to four-hour target. Consistency is more important than intensity for Zone 2; it is better to maintain the correct pace than to push too hard and drop out of the zone. Prioritizing multiple sustained sessions provides frequent signals for the body to adapt, building aerobic capacity that is a strong predictor of long-term health and longevity.