The Seiler 3-zone model
Sports scientist Stephen Seiler studied how elite endurance athletes actually train and found a consistent pattern: a three-zone intensity model split at the two lactate turnpoints, with roughly 80% of sessions easy and 20% hard. The model is intensity-distribution-first, it cares less about the exact zone boundaries than about how much time you spend low versus high.
Zone 1 sits below the first lactate turnpoint (LT1, ~2 mmol/L), where you build aerobic base. Zone 2 spans LT1 to the second turnpoint (LT2, ~4 mmol/L), useful but easy to overuse. Zone 3 lies above LT2, where VO₂max-driving interval work happens. The discipline is keeping Zone 1 genuinely easy so the hard Zone 3 sessions land with full quality.
Estimate your 3 zones
We approximate your lactate turnpoints (LT1, LT2) from HRmax. For real thresholds, use a lactate or time-trial test.
LT1 (aerobic threshold)
152bpm
≈ 82% HRmax
LT2 (anaerobic threshold)
165bpm
≈ 89% HRmax
| Zone | Range | What it trains |
|---|---|---|
| LIT | Zone 1, Low intensity ≤ 152 bpm | Aerobic base; the ~80% of training that should feel easy. Below the first lactate turnpoint (LT1). RPE 2–4, conversational, nose-breathing. |
| THR | Zone 2, Threshold 152–165 bpm | The 'grey zone' between thresholds, useful but easy to overuse. Polarized training deliberately minimises time here. RPE 5–7, comfortably-hard to hard. |
| HIT | Zone 3, High intensity ≥ 165 bpm | Above the second lactate turnpoint (LT2). The ~20% of hard interval work that drives VO₂max gains. RPE 8–10, hard to maximal. |
LIT · Zone 1, Low intensity. Aerobic base; the ~80% of training that should feel easy. Below the first lactate turnpoint (LT1). RPE 2–4, conversational, nose-breathing.
THR · Zone 2, Threshold. The 'grey zone' between thresholds, useful but easy to overuse. Polarized training deliberately minimises time here. RPE 5–7, comfortably-hard to hard.
HIT · Zone 3, High intensity. Above the second lactate turnpoint (LT2). The ~20% of hard interval work that drives VO₂max gains. RPE 8–10, hard to maximal.
- Seiler's polarized model uses just three zones split at the two lactate turnpoints. Elite endurance athletes spend roughly 80% of sessions in Zone 1 and 20% in Zone 3, with little Zone 2.
- These LT1/LT2 estimates from HRmax are rough. For real thresholds, use a lactate test or derive LT2 from a 30-minute time-trial (your LTHR ≈ LT2).
How to apply 80/20
Count by sessions or by time: of ten weekly sessions, about eight should be easy Zone 1 and two hard Zone 3. The most common mistake amateurs make is running easy days too hard, drifting into Zone 2, which blunts both recovery and adaptation. If in doubt, slow your easy days down.
Polarized training pairs naturally with heart-rate or pace zones from the calculators on this site. Use LTHR zones or MAF to anchor the easy end, and VDOT interval paces or FTP power zones for the hard end.
Frequently asked questions
What is the 80/20 rule in training?
The 80/20 rule says roughly 80% of your training sessions should be low intensity (below the first lactate threshold) and about 20% high intensity (above the second threshold). Stephen Seiler's research on elite endurance athletes found this distribution repeatedly across rowing, running, cycling and skiing.
What are the three zones in polarized training?
Zone 1 is easy work below the first lactate turnpoint (LT1). Zone 2 is the 'grey zone' between LT1 and the second turnpoint (LT2). Zone 3 is hard work above LT2. Polarized training fills Zone 1 and Zone 3 while deliberately minimising time in the middle Zone 2.
Is polarized training better than threshold training?
For well-trained endurance athletes, several studies show polarized training produces equal or greater gains in VO₂max and performance than threshold-focused plans, with less fatigue. Beginners often progress on almost any structure; the polarized advantage grows as training volume and experience increase.
Why avoid the middle zone?
Moderate 'comfortably hard' work (Zone 2) is tiring enough to limit recovery but not intense enough to maximise high-end adaptations. Spending too much time there (the common 'grey zone' trap) leaves athletes chronically fatigued yet under-stimulated. Polarized training keeps easy days easy so hard days can be truly hard.
Sources
- Seiler & Kjerland (2006). “Quantifying training intensity distribution in elite endurance athletes.” Scand J Med Sci Sports 16:49–56.
- Stöggl & Sperlich (2014). “Polarized training has greater impact on key endurance variables than threshold, high-intensity or high-volume training.” Front Physiol 5:33.