Zone 2 training: the complete guide
Zone 2 is the aerobic base most plans get wrong, because most plans calculate it instead of measuring it. Here's what a threshold test changes, and the error margin the shortcuts carry.
Zone 2 is the easy, conversational pace that builds your aerobic base — the foundation underneath every harder session you do. The problem isn't the concept. It's how most apps calculate your Zone 2 heart rate: as a percentage of an estimated maximum, using a formula built from population averages, not your body.
Three ways to find your Zone 2, ranked by accuracy
- Measured threshold (LT1) — from a talk test or lab threshold test. Reflects your actual physiology.
- Heart rate reserve — uses your known resting heart rate. A reasonable middle ground.
- Percentage of estimated max heart rate — the last resort, and the most common method in consumer apps. Error margin: roughly ±11 beats per minute.
That ±11 bpm isn't a rounding error. Mixing these three methods up shifts most people a full training zone or two — meaning a session logged as "easy aerobic" might actually be moderate-intensity work that never lets your aerobic system adapt the way Zone 2 is supposed to.
“The app should tell you which method it used to set your zones. If it doesn't say, assume it's the least accurate one.”
Why the base matters more than the hard sessions
Zone 2 trains mitochondrial density and fat oxidation — the engine that everything else, including your hard sessions, draws on. Skipping it in favor of constant high intensity is a common way plateaus happen: the top end has nothing left to build on.
This article is educational and does not diagnose, treat, or replace advice from a qualified doctor. If something here is relevant to your own results, it's worth discussing with a clinician.