What “easy” actually means
Easy is an effort, not a pace. The test is simple. You can talk in full sentences, and you could keep going a lot longer than you are about to.
That test works everywhere. On a hill. In the heat. On a bad day. A pace that feels easy in October at 8 °C is not easy in July at 28 °C. The talk test knows that. Your watch does not.
What the research really says
The pattern is real. The rule people built on top of it is not.
When researchers look at what trained runners actually do, about 80 % of their sessions are easy. That holds across sports and across decades 1. Reviews of distance runners find the same shape 23. So do reviews of elite runners 4.
So far so good. This is a solid description of how good runners train.
The problem is the next step: “therefore you must do it, and anything else is worse”. That step has been tested. It does not hold up.
The individual studies are thinner than their reputation. The one most often quoted was a pilot on twelve runners 7. The only trial run on recreational runners found no significant difference 8.
None of that makes easy running pointless. It makes the honest claim narrower. A big base of easy volume is how runners survive the training that does change them, and nothing has been shown to beat it. That is a good reason. It is not the same as “polarized is optimal”.
Why it holds up anyway
Three reasons, from most certain to least.
- It lets you run more. Volume only helps if you can repeat it. Intensity is what stops you repeating it.
- It leaves room for the hard sessions. Two real sessions a week need five days that are not hard. Run those five at medium and you get neither.
- It survives real life. Easy-by-effort adjusts itself on a bad day. Easy-by-pace turns a bad day into a failure or an injury.
One thing we will not claim: that easy running is what raises your VO2max. The trials do not support that. Repeating it would be a slogan, not a finding 9.
How to know you are actually running easy
Three checks, in order of usefulness.
- Say a full sentence out loud. If it comes out in pieces, this is not an easy run. Free, and it works in any weather.
- Rate the run afterwards, not during. Wait twenty minutes, then score the effort on a fixed scale with the wording in front of you. That is a usable signal 10. Scored from memory the next day, it is not.
- Watch your own trend. How the legs feel and how the session went track your response to training better than most of the numbers people buy devices for 11.
The three ways this goes wrong
| What happens | Why | What it costs |
|---|---|---|
| Easy runs get faster | The proper easy pace feels too slow to bother with | The whole week becomes medium: too hard to recover from, too easy to gain from |
| Hard sessions get softer | You arrive tired from the easy runs | The sessions meant to change you stop changing you |
| You count minutes, not sessions | It looks better that way | A week that is 80 % easy by session can be far less by time 1 |
The first one is the most common and the hardest to see. Nobody notices a single run fifteen seconds per kilometer too fast. Six weeks of them is a different plan from the one you were given.
Questions people actually ask
Do I have to hit 80/20 exactly?
Heart rate or feel?
I only run three times a week. Does this apply?
How slow is too slow?
References
Every figure above rests on one of these studies. Author and year are enough to find the paper.
- Seiler (2010)
- Campos (2022)
- Kenneally (2018)
- Casado (2022)
- Rosenblat (2019)
- Rosenblat (2025)
- Esteve-Lanao (2007)
- Muñoz (2014)
- Joyner (2008)
- Foster (1998)
- Saw (2016)
