Is Zone 2 Killing Your Performance?

Over the last few years, Zone 2 has become almost unavoidable.

Coaches, podcasts, and articles return to it again and again, framing it as the foundation, the holy grail, the thing everyone was supposedly missing. Train easy. Stay aerobic. Accumulate volume. Zone 2 has been positioned as the answer.

And for good reason. It works.

Except most people aren’t actually training in it.

Zone 2 does matter. When it is performed correctly, it works exactly as advertised. The problem is that most people don’t know where theirs actually is.

The vast majority of Zone 2 prescriptions people follow are not measured. They are inferred. Estimated using percentages of max heart rate, heart rate reserve, pace charts, or watch-generated zones. Some methods look more sophisticated than others, but none of them directly identify the physiological boundary that defines true Zone 2.

They are guesses.

At best, these estimates loosely approximate aerobic work across large populations. At worst, they give people false confidence that they are training “easy” when they are not.

And yet those numbers are treated as definitive.

Zone 2 is not a vibe and it is not a percentage. It is a physiological state, defined by work below your first ventilatory threshold, VT1. This is the point where aerobic efficiency begins to decline and the cost of producing energy starts to rise.

Below VT1, breathing remains controlled, fat oxidation is high, and work can be repeated day after day without excessive fatigue. Above it, carbohydrate reliance increases and stress accumulates quietly, even if the effort still feels manageable.

VT1 is individual.

It does not sit at a fixed percentage of max heart rate. It does not line up neatly with pace. And it cannot be reliably inferred from an algorithm.

Two athletes with the same max heart rate can have VT1 separated by twenty beats. Two athletes running the same pace can be operating in completely different metabolic states. Yet both are often told they are “in Zone 2” because a number on a screen says so.

That number is rarely personal.

Miss VT1 by even a small margin and the session changes entirely.

What most people call Zone 2 is usually just above it. The work feels controlled. It feels sustainable. It feels like the right thing to be doing.

Physiologically, it isn’t.

Sit there long enough and nothing really moves. Training volume increases, but thresholds don’t. People feel fit, but not fast. Recovery just about keeps up, which allows the mistake to be repeated.

Zone 2 is not the problem.

Relying on inaccurate methods to define it is.

If your “easy” work is based on formulas, charts, or algorithms, you are training on assumptions, not physiology. Until Zone 2 is anchored to a measured threshold, it remains an estimate, no matter how sensible it looks.

Zone 2 isn’t killing your performance.

Training to the wrong definition of it might be.