How the zones are calculated
Your lactate threshold heart rate, LTHR for short, is the heart rate at the hardest effort you can hold for about an hour. The zones are shares of it, following the running zones of the coach Joe Friel: zone 1 is under 85%, zone 2 is 85 to 89%, zone 3 is 90 to 94%, zone 4 is 95 to 99%, and zone 5 is everything from your threshold up. Friel splits that last zone into three; this calculator keeps it as one.
How do I find my threshold heart rate?
- Warm up well, then run 30 minutes alone, as hard as you can sustain for the whole 30 minutes. Pace it like a race, not a sprint.
- Press the lap button 10 minutes in.
- Your average heart rate for the last 20 minutes is a good estimate of your threshold.
Do it fresh, on flat ground, in normal weather. Repeat it every couple of months: as you get fitter the pace at threshold rises much more than the heart rate does.
Why use threshold instead of maximum?
Two runners with the same maximum heart rate can have very different thresholds, and it is the threshold that decides what is easy and what is hard for you. It is also safer and more repeatable to test than an all-out maximum.
Using these zones in Kiiro
Kiiro's automatic zones use the maximum heart rate method. To use these instead, switch heart rate zones to Custom in Kiiro's settings and enter the boundaries from the table. They stay fixed until you change them.
Which method should I use?
| Method | You need | Good when |
|---|---|---|
| Maximum heart rate | Your maximum, or your age | You want a quick start. This is what Kiiro uses by default. |
| Heart rate reserve | Maximum and resting heart rate | Your resting heart rate is unusually low or high, so percentages of maximum fit you badly. |
| Lactate threshold | A 30-minute test run | You train seriously and want zones anchored to what you can actually sustain. |
The methods give different numbers for the same person. Pick one and stay with it; do not compare a zone 2 from one method with a zone 2 from another.
Using your zones
- To use them on your watch, see how Apple Watch sets heart rate zones and how to change them.
- For what zone 2 is and why it matters, see Zone 2.
- Kiiro shows your time in zones for every workout and how your weeks split between low, medium and high intensity. See heart rate zones in Kiiro.
