Training zones: measuring effort without kidding yourself
The three-zone model, where 80/20 comes from, how to estimate your threshold with a field test, and why most recreational runners train in a grey zone that achieves nothing.
Zones are not watch bureaucracy: they are how you make sure the easy is genuinely easy and the hard is hard enough. The most repeated mistake in recreational running is training every day at a medium comfortable-uncomfortable pace that fatigues like a quality session and stimulates like an easy run.
The three-zone model
| Zone | Physiological reference | How it feels | What it is for |
|---|---|---|---|
| Z1 — Low | Below the first threshold | Conversation flows | Aerobic base, volume, recovery |
| Z2 — Threshold | Between threshold 1 and 2 | 3–4 words at a time | Holding pace, half and full marathon |
| Z3 — High | Above the second threshold | Broken breathing | VO₂max, aerobic power |
Elite distance runners train about 80% of the time at low intensity
The classic review on intensity distribution describes a converging pattern in national and international endurance athletes: ~80% of sessions at low intensity and ~20% dominated by high-intensity work, with very little time in the middle zone. It is not a law; it is what elite practice converges on.
The polarised model wins narrowly, and not on everything
A 2024 systematic review with meta-analysis found polarised distribution is slightly superior for VO₂peak (SMD 0.24), mostly in interventions shorter than 12 weeks and in highly trained athletes, but with no clear differences in time trials, time to exhaustion or threshold. In plain terms: “mostly easy with some very hard” is a reasonable guide, not a demonstrated superiority over other distributions.
How to know which zone you are in
- 1
Feel and breathing (always available)
Long sentence = Z1. Three or four words = Z2. One word or none = Z3. It is the cheapest method and the one that adapts best to heat, fatigue or hills.
- 2
Pace per kilometre (good on the flat)
Precise and objective, but useless uphill, on trails or in wind: pace drops even as effort rises. In those cases effort decides, not the watch.
- 3
Heart rate (good for long sessions)
It takes 1–2 minutes to respond, so it is no use for short intervals. It rises with heat, dehydration and accumulated fatigue (cardiac drift): on a long run, holding heart rate means dropping pace.
“220 − age” zones are a poor estimate
The formula has an individual error of more than ten beats. If you are going to use heart rate, anchor the zones to your threshold heart rate measured in a test, not to an age formula.
A field test to anchor your zones
Common coaching practice, not a laboratory protocol: after 15–20 minutes of warm-up, run 30 minutes at the hardest pace you can sustain, on the flat and alone. The average pace and average heart rate of the last 20 minutes are used as an estimate of your threshold. From there:
- Z1 (easy)
- Threshold pace + 45 to 90 s/km
- Z2 (tempo)
- Threshold pace ± 5 s/km
- Z3 (intervals)
- Threshold pace − 15 to 25 s/km
Most of your weekly volume.
Blocks of 8–20 min.
Intervals of 3–5 min.
If you would rather start from a recent race result, VDOT tables convert a 5K or 10K time into equivalent training paces; it is the most widely used reference for not making your paces up (VDOT calculator).
Takeaways
- Three zones are enough to decide: easy, threshold, high.
- The elite pattern is ~80% easy / ~20% hard; as a guide it works, as dogma it does not.
- Anchor your zones to a 30-minute test, not to “220 − age”.
- Uphill, in heat or on trails, perceived effort rules, not pace.
- The grey zone — neither easy nor hard — is where most training time gets wasted.
Sources for this chapter
- [1]Seiler S (2010). What is best practice for training intensity and duration distribution in endurance athletes?. International Journal of Sports Physiology and Performance. review
- [2]Silva Oliveira P, Boppre G, Fonseca H (2024). Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes’ Endurance Performance: A Systematic Review with Meta-analysis. Sports Medicine. meta-analysis
- [3]Daniels J (VDOT O2) (2026). Calculadora VDOT: ritmos de entrenamiento equivalentes por marca. VDOT O2. resource