The concept of “Zone 2” training has gained popularity in recent years, with proponents claiming it can improve metabolic health and even boost longevity. But is this idea supported by science?
Peter Attia, a physician and podcaster, introduced the concept to a wider audience through his book “Outlive”. He argues that long, slow workouts at a specific intensity level are crucial for metabolic health. However, some scientists question whether this narrow focus is necessary.
The idea behind Zone 2 training comes from Iñigo San Millan’s work on classifying exercise into six different zones based on muscle fuel usage. When exercising in the easiest zone (a brisk walk), you burn mostly fat. As you push harder, your body relies more on carbohydrates and ramps up lactate levels.
Dr. San Millan believes that top cyclists spend most of their training time just below this threshold, which leads to better performance. Training at Zone 2 is thought to improve mitochondrial function, which is associated with positive outcomes like improved insulin sensitivity and athletic performance.
However, scientists have raised concerns about the lack of rigorous testing for these claims. While observational data shows a correlation between Zone 2 training and improved mitochondrial function, muscle biopsies show that intense exercise well above Zone 2 produces bigger effects on mitochondria.
Experts warn that relying solely on Zone 2 training may lead to overtraining or neglecting other types of workouts altogether. Instead, they suggest finding an optimal balance between different intensity levels.
Ultimately, the key to boosting mitochondrial health and improving overall fitness may lie in finding a workout routine that you enjoy and can sustain regularly. As Dr. San Millan notes, “Zone 2 is part of it”, but it’s not the only type of workout worth doing.
Source: https://www.nytimes.com/2025/02/19/well/move/zone-2-exercise-benefits.html