# Zone 2 training

Zone 2 training is sustained aerobic exercise at or just below your first lactate threshold (LT1, around 1.5 to 2.0 mmol/L). That is often roughly 60 to 70% of your max heart rate, though the exact percentage varies. Lactate testing or the 'talk test' is more accurate. At this intensity, fat oxidation supplies most of your energy, in your slow-twitch fibers, with carbohydrate use rising near the top end. Regular Zone 2 work builds mitochondrial density, capillaries, and metabolic flexibility.

## Sources

- San-Millán I, Brooks GA. (2018). Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals. Sports Medicine. https://doi.org/10.1007/s40279-017-0751-x
- Faude O, Kindermann W, Meyer T. (2009). Lactate threshold concepts. Sports Medicine. https://doi.org/10.2165/00007256-200939060-00003

---

_Canonical: https://longevity-switzerland.com/en/glossary/zone-2-training · Part of Longevity Cities · Updated 2026-06-22_