And Why That’s Not a Contradiction
Zone 2 training works.
It builds aerobic capacity, improves efficiency, and allows runners to accumulate volume without constantly flirting with injury. For most endurance athletes, it is the foundation that makes everything else possible.
The problem is not Zone 2 itself.
The problem is what happens when Zone 2 becomes the entire language of training.
At a certain point, many runners stop using Zone 2 as a tool and start using it as a shelter.
Zone 2 feels productive because it is controlled.
The pace is manageable. The effort is predictable. Recovery is reliable. Weeks stack cleanly on top of each other, and the body responds well — at least on the surface.
This creates a powerful feedback loop:
If it feels good and progress continues, why change anything?
And for a long time, that logic holds.
Until it doesn’t.
The limitation of Zone 2 is not visible while training is going well.
It appears when conditions change.
The marathon does not test the body in a fresh, efficient state. It tests it after hours of accumulated fatigue, mechanical degradation, and neuromuscular stress. The system you bring to the final kilometers is not the same one you trained in during most of your easy runs.
Zone 2 prepares the body to work efficiently when everything is still relatively intact.
The later stages of long races demand the ability to function when efficiency is already compromised.
If that ability has never been trained, it cannot be summoned on race day.
This is why runners who rely almost exclusively on Zone 2 often experience a very specific pattern: strong control early, followed by a gradual loss of responsiveness that feels difficult to explain.
The heart is not failing.
The fueling plan is not necessarily wrong.
The pacing might even be reasonable.
What is missing is structural resilience — the capacity to maintain usable mechanics when fatigue has already altered the system.
Zone 2 does not fail here.
It simply stops being sufficient.
The danger is subtle because Zone 2 rarely produces obvious warning signs. Training weeks feel solid. Long runs are completed successfully. Recovery metrics look good. Nothing suggests that something is missing.
But what is missing is not volume or discipline.
It is exposure.
Exposure to controlled discomfort.
Exposure to running well when it no longer feels automatic.
Exposure to managing fatigue rather than avoiding it.
This does not mean turning every session into a struggle.
It does not mean abandoning aerobic work.
And it certainly does not mean training harder for the sake of suffering.
It means recognizing that comfort cannot be the primary filter for deciding whether a stimulus is useful.
Training that always ends before it becomes structurally challenging teaches the body exactly one thing: how to perform until the moment things start to matter.
Zone 2 should remain the base.
But a base is not a ceiling.
When it becomes the place where all uncertainty is removed, adaptation slows quietly. The system becomes excellent at confirming what it already knows how to do — and increasingly fragile when asked to do something slightly different.
This is not a flaw in the method.
It is a mismatch between the method and the demands of the event.
In Fino al km 38 andava tutto bene, this idea is explored not as a critique of Zone 2, but as a reminder of its limits. The book looks at why doing everything “right” can still lead to predictable breakdowns — and how those breakdowns are usually prepared long before race day.
Zone 2 works.
Until the race asks for something else.
You can find the book here:
https://a.co/d/678Qvyn