Stephen Seiler
and 80/20.

Who is Stephen Seiler

Seiler studied how rowers, cross-country skiers, cyclists and runners at the top level actually spread their training across intensities. Instead of asking what should work, he looked at what the winners did. The answer was remarkably similar across sports: most sessions are easy, a minority are hard, and the middle is used sparingly.

The 80/20 rule

Counted by sessions, roughly 80 percent of an elite endurance athlete's training is done at low intensity, below the first lactate threshold. About 20 percent is done at or above threshold. Counted by minutes, the easy share is often even higher, because hard sessions are short.

Seiler describes it with a three-zone model: zone 1 below the first threshold, zone 2 between the thresholds, zone 3 above the second. That is not the same as Zone 2 in the five-zone model many watches use. Our heart rate zones guide explains both.

Polarized vs threshold vs pyramidal

"Polarized" means most work very easy, some very hard, little in the middle. "Pyramidal" means most easy, a fair amount at threshold, less at the top. Seiler's own work shows that many elites train pyramidally in parts of the year and more polarized near competition. The common factor is not the exact shape. It is that the easy days are really easy.

The problem with most recreational runners

Recreational runners tend to do the opposite: most runs at a medium effort that feels productive. Seiler calls it the black hole, we call it the grey zone. It is too hard to recover from and too easy to drive big adaptations. The result is tired legs and slow progress.

What normal runners can take from it

• Count your sessions. With five runs a week, one hard session plus maybe a long run with some faster finish is enough. The rest is easy.
• Make easy days slower. Use a heart rate ceiling from the zone calculator or the MAF calculator.
• Make hard days count. When you go hard, go properly hard, in a structured session from the interval library.
• Volume is the base. 80/20 only works when there is enough easy running. See aerobic base.

Sources: Seiler S, 2010, What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform 5(3):276-291. Seiler S, Kjerland GO, 2006, Scand J Med Sci Sports 16(1):49-56.