How slow is an easy run, really?

What "easy" actually means

An easy run is not a slow version of your race. It is a different kind of effort. You should finish it feeling that you could have kept going for a long time, and that you could do it again tomorrow.

Physiologists describe this as running below your first threshold (often called the aerobic or first ventilatory threshold): the point where your breathing starts to rise faster than your effort. Below it, your body runs mostly on fat and oxygen, produces little fatigue, and recovers quickly. Above it, every extra kilometre costs noticeably more.

You don't need a lab to find this point.

The talk test: the simplest tool you have

Try to say a full sentence out loud while running – something like the first lines of a song or a few sentences of a story.

• You can talk comfortably in full sentences: you are in the easy zone.
• You can talk, but you have to pause for breath: you are around the threshold. Slow down a little.
• You can only manage a few words: this is a workout, not an easy run.

This is not a gimmick. In studies at the University of Wisconsin–La Crosse, the point where speaking first stopped feeling comfortable matched the ventilatory threshold measured in the lab almost exactly, on both treadmill and bike. When speech was no longer comfortable, people were consistently above that threshold.

Why slow running makes you faster

It feels backwards, but there are good reasons:

1. It builds your aerobic engine. Easy kilometres grow the capillaries, mitochondria and heart adaptations that every race distance from 5 km up depends on.
2. It leaves energy for the hard days. If your easy runs are "medium", you arrive tired at your intervals and run them too slowly. Everything drifts to the middle.
3. It lets you run more without breaking down. Volume is one of the strongest drivers of endurance, and easy running is how you add it safely.

When researchers looked at how successful endurance athletes actually train – rowers, cross-country skiers, runners – they found a clear pattern: roughly 80% of their sessions at low intensity and the rest hard, with surprisingly little in between. This became known as the 80/20 or "polarized" approach. Later studies comparing different training mixes in well-trained athletes found that this kind of distribution tended to give the best improvements.

A fair caveat: these numbers come from people who train a lot. If you run three times a week, you don't need to calculate percentages. The message that carries over is simpler: most of your runs should be truly easy, and the hard ones should be clearly hard.

How slow is that in minutes per kilometre?

It depends on your fitness, the weather, the terrain and how you slept, which is exactly why effort beats a fixed number. Still, many runners find that their easy pace is noticeably slower than they expect – often a minute or more per kilometre slower than their 10 km race pace. If that feels embarrassingly slow, you are probably doing it right.

A few practical signs you are too fast:

• Your breathing is audible and you couldn't hold a conversation.
• Your "easy" pace is almost the same every day, regardless of how tired you are.
• You feel flat or heavy on the days you are supposed to run hard.

What about heart rate?

Heart rate can help, but it is less simple than it looks. Formulas like "220 minus your age" are rough population averages and can be wrong by 10 beats or more for an individual. Wrist sensors can also be unreliable at the start of a run or in the cold. If you use heart rate, use it together with the talk test – not instead of it.

Make it easy to run easy

• Run with someone slower, or with a friend you can actually chat with.
• Leave the watch's pace screen off and show time or distance only.
• Pick a hilly or soft route where pace numbers don't mean much anyway.
• Walk the steep uphills if your breathing jumps. That's allowed.
• Accept the slowdown on hot days. Same effort, slower pace.