The Seiler 3-zone model
Stephen Seiler studied how elite endurance athletes train and found the same pattern everywhere: three zones split at the two lactate turnpoints, roughly 80% of sessions easy and 20% hard. Distribution matters more than exact borders.
Zone 1 sits below the first lactate turnpoint (LT1, ~2 mmol/L): aerobic base. Zone 2 spans LT1 to LT2 (~4 mmol/L): useful but easy to overuse. Zone 3 lies above LT2: VO₂max intervals. Keep Zone 1 easy so Zone 3 lands 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 'gray zone' between thresholds, useful but easy to overuse. Polarized training deliberately minimizes 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 'gray zone' between thresholds, useful but easy to overuse. Polarized training deliberately minimizes 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
Of ten weekly sessions, about eight easy in Zone 1 and two hard in Zone 3. The most common amateur mistake is drifting into Zone 2 on easy days, which blunts recovery and adaptation. If in doubt, slow down.
Polarized training pairs with any zone calculator 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 training sessions should be low intensity (below the first lactate threshold) and 20% high intensity (above the second). Seiler found this pattern across elite rowers, runners, cyclists and skiers.
What are the three zones in polarized training?
Zone 1 is easy work below the first lactate turnpoint (LT1). Zone 2 is the gray zone between LT1 and LT2. Zone 3 is hard work above LT2. Polarized training fills Zones 1 and 3 and minimizes 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 progress on almost any structure.
Why avoid the middle zone?
The middle zone is tiring enough to limit recovery but not intense enough to maximize high-end adaptation. Too much time there leaves you chronically fatigued yet under-stimulated. Keep easy days easy so hard days can be 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.