Zone 2 Training Explained: Best Intensity for FatMax & Endurance

Zone 2 training is one of the most discussed topics in endurance sports right now, but what actually is Zone 2 and why does it matter so much? Zone 2 training refers to training at an intensity that is below the first lactate threshold, LT1. At this intensity, the body is primarily using fat as a fuel source and the aerobic system is the dominant energy pathway.

The lactate production rate is low enough that the body can clear lactate as fast as it produces it, so blood lactate stays at or near baseline levels. The reason Zone 2 has become so popular is that it provides a strong aerobic stimulus without accumulating significant glycolytic stress. This means it can be done frequently without impairing recovery, and over time it drives mitochondrial adaptations that improve fat oxidation capacity and overall aerobic efficiency.

The challenge with Zone 2 training is that the correct Zone 2 intensity is highly individual and cannot be accurately determined from a simple heart rate formula or a percentage of threshold power. In INSCYD, Zone 2 is defined based on the actual metabolic data. It corresponds to the intensity range where fat combustion is maximized, which is the FatMax zone, and where lactate remains at baseline.

For some athletes this might be at 60% of threshold power. For others with a different metabolic profile it might be at 75% or even 80%. The only way to know the correct intensity is to test the athlete.

Using INSCYD you can determine the individual Zone 2 range with precision and ensure that when your athlete is told to do Zone 2, they are actually doing Zone 2 and getting the adaptation you want.

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