Ask a coach what most self-trained runners get wrong, and you’ll hear the same answer: easy days aren’t easy enough, hard days aren’t hard enough. Everything blurs into a medium effort that’s too hard to recover from and too easy to improve from.
Heart rate zones are the cheapest fix in running. Here’s what they mean and how to use them.
The five zones, in plain language
Zones are bands of effort, usually expressed as a percentage of your maximum heart rate:
| Zone | Effort | Feels like |
|---|---|---|
| Zone 1 | Very easy | You could sing |
| Zone 2 | Easy | Full conversation, all day pace |
| Zone 3 | Moderate | Talking in sentences, not paragraphs |
| Zone 4 | Hard | A few words at a time |
| Zone 5 | Very hard | No talking, short bursts only |
The counterintuitive part: well-trained runners spend the majority of their time in zones 1–2. The easy running builds the engine; the small dose of zone 4–5 work sharpens it. The zone most runners accidentally live in — zone 3 — is the one that delivers the least return per unit of fatigue.
Why intervals and zones belong together
Interval training is how you visit the high zones on purpose and in controlled doses. A session like 8× (45 seconds hard / 90 seconds easy) is really a zone recipe: spike into zone 4, recover into zone 2, repeat.
The problem is knowing you’re actually doing it. Effort is easy to misjudge — especially early in a run when everything feels smooth, or late when everything feels terrible.
What iRunning shows you
During a run, iRunning shows your live heart rate and the zone you’re in — from your Apple Watch or a Bluetooth heart rate strap. Glance down mid-interval and you know whether “hard” is actually hard.
Afterwards, the run summary includes a time-in-zone breakdown: how many minutes you spent in each zone across the whole session. That’s the honest report card. If your easy run shows twenty minutes of zone 3, you now know exactly what to fix next time — slow down.
Your zones are configurable, so if you know your real maximum heart rate (or your lactate threshold), you can set the bands to match, instead of relying on a generic formula.
A simple zone-based week
- Two easy runs — stay in zone 2 the whole time. Yes, it will feel slow. That’s the point.
- One interval session — for example, 6× (1:00 in zone 4 / 2:00 back down to zone 2)
- One longer run — zone 2, with the last ten minutes drifting into zone 3 if you feel good
Four runs, one of them hard. Do that for eight weeks and your easy pace at the same heart rate will quietly drop — which is what getting fitter actually looks like in the data.