KEY TAKEAWAYS
This is one of those conversations I have wanted to have for a long time. Dr Iñigo San Millán is the exercise physiologist and coach behind Tadej Pogačar — the rider who has redefined what is possible in Grand Tour cycling — and his work on zone 2 training and lactate metabolism has shaped how an entire generation of coaches thinks about easy riding.
What struck me most was how precise San Millán is about what zone 2 actually means. For him it is not a heart rate range pulled from a formula or a vague instruction to "ride easy." It is a specific metabolic state where blood lactate sits between roughly 1.5 and 2.0 mmol/L and your mitochondria are burning fat as their primary fuel. Stay in that window and you get maximal aerobic development. Drift above it — even slightly — and the stimulus shifts. You end up working harder for a worse adaptation.
That is the trap most of us fall into. We think we are riding easy, but our lactate tells a different story. San Millán explained that the only way to know for certain is a proper lactate test, though the talk test is a decent proxy if lab access is not realistic.
We also talked about fat oxidation — why the ability to burn fat at higher intensities is what separates the best endurance athletes from everyone else, and why the same mitochondrial adaptations that make Pogačar fast also protect everyday people from metabolic disease. It is a rare case where the thing that makes you faster also makes you healthier.
If zone 2 has ever felt confusing or you suspect you are doing it too hard, this conversation will clear it up.
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The written companion to this episode.
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