Key takeaways
Elite endurance athletes do roughly 80% of sessions at low intensity and 20% hard
In a 9-week study of 48 well-trained athletes, the polarised group improved key endurance measures the most
Easy means below about 75% of max heart rate; too much moderate grey-zone running leaves you tired
Watch how elite runners, rowers, cyclists and cross-country skiers actually train, and a pattern appears: most sessions are easy, a few are very hard, and little time is spent in between.
Where it comes from
Stephen Seiler and colleagues analysed the training logs of elite endurance athletes across sports. Counting sessions, roughly 80% were low intensity (below the first lactate threshold — you can hold a conversation) and 20% were hard (at or above threshold, including intervals). Seiler's 2010 review summarised this as a consistent "best practice" distribution among successful athletes.
What studies show
- Stöggl and Sperlich, 2014: 48 well-trained endurance athletes followed nine weeks of polarised, threshold-heavy, high-intensity or high-volume training. The polarised group showed the largest improvements in key endurance measures, including VO2peak.
- Later studies are more mixed: in recreational athletes, several distributions work if total load is right. The consistent finding is that too much moderate "grey zone" running leaves people tired without the stimulus of real intervals.
Why it works
- Easy volume builds the aerobic base — capillaries, mitochondria, a bigger stroke volume — with little fatigue.
- Hard sessions push VO2max and threshold, but need fresh legs to be done well.
- Keeping easy days easy is what allows hard days to be hard.
A sample week (4–6 sessions)
| Day | Session |
|---|---|
| Mon | Rest or strength |
| Tue | Intervals — e.g. Norwegian 4×4 |
| Wed | Easy 40–60 min |
| Thu | Strength + easy 30 min |
| Fri | Threshold — e.g. 3 × 10 min at about one-hour race effort |
| Sat | Easy or rest |
| Sun | Long easy run |
Easy means easy: below about 75% of max heart rate, nasal breathing possible. If your easy pace creeps up, slow down.
Common mistakes
- Running every run at "comfortably hard".
- Skipping strength work (strength training for runners).
- Adding hard sessions while sleep and recovery are poor (HRV and recovery).
Frequently asked questions
What is 80/20 training?
It means doing about 80% of your sessions at low intensity, where you can hold a conversation, and about 20% hard, at or above threshold. Elite endurance athletes across many sports train this way.
Does 80/20 training work for recreational runners?
Studies in recreational athletes are more mixed, and several distributions work if the total load is right. The consistent finding is that too much moderate grey-zone running leaves people tired without the stimulus of real intervals.
How easy should easy runs be?
Below about 75% of your maximum heart rate, at a pace where nasal breathing is possible. If your easy pace creeps up, slow down so your hard days can be truly hard.
Sources
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform, 2010.
- Stöggl T, Sperlich B. Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Front Physiol, 2014.