Training zones: how to calculate and use them
Zones split your training into five intensities. Set properly, they tell you how much time you spend in each; set badly, they make you believe an easy run is a tempo run.
Training zones are intensity bands. They are not a fad: they do two very specific jobs — dosing the effort of each session, and letting you add up how much time you accumulate at each intensity over a week. Without that reference, "easy run" and "intervals" end up being whatever you feel like on the day.
Two ways to define zones
Zones come from a reference value, and that is the detail most people skip. There are two usual references:
- Heart rate: zones come from your maximum heart rate, either measured or estimated with the heart rate zone calculator. If you know your resting rate, the heart rate reserve method (Karvonen) applies, which is more accurate because it accounts for the fact that you do not start from zero.
- Pace or power: zones come from your threshold pace, the one you could hold for roughly an hour. It is more stable than heart rate because it does not depend on sleep, caffeine or the time of day. You can get your threshold pace from the pace and race time calculator.
Heart rate reacts with a delay — it takes a couple of minutes to rise and to fall — so for short or changing sessions pace is the better guide. On long runs and in low zones, heart rate tells the truth that pace hides: at 30 °C or going uphill, the same pace is far more effort.
The five zones
The five-zone model is the most widespread and the one Afterpacer uses. Percentages are of maximum heart rate; with the reserve method the bands shift upwards because resting rate has to be added.
| Zone | % max HR | Feels like | What it is for |
|---|---|---|---|
| Z1 · Recovery | 50–60 % | Very easy, nasal breathing | Active recovery, warm-up and cool-down |
| Z2 · Aerobic base | 60–70 % | Conversational | Volume, efficiency and fat use; it supports everything else |
| Z3 · Tempo | 70–80 % | Short sentences | Sustained pace, half marathon and marathon preparation |
| Z4 · Threshold | 80–90 % | Hard, heavy breathing | Lactate threshold; 10K to half marathon |
| Z5 · Max | 90–100 % | Cannot talk | Intervals, VO2max and pace changes |
In Afterpacer the zones are stored as the five bands in the table and applied to every activity: each session shows the time spent in each zone, and the weekly statistics show the accumulated split.
The four mistakes that ruin everything
- Using 220 − age as maximum heart rate. It has a standard error of ±10 to ±12 beats and usually underestimates trained athletes. Get your maximum wrong and every percentage is wrong.
- Copying someone else's zones. Zones are yours: they depend on your maximum heart rate, your resting rate and your threshold, not on your age or your training group.
- Ignoring hills and heat. Zones measure effort, not performance. Going uphill or training at 32 °C pushes heart rate up at the same pace, and that is not you going badly: it is the zone criterion working.
- Never revisiting them. Maximum heart rate and threshold change with fitness. Rechecking every six to eight weeks is enough.
How much time in each zone
For most recreational athletes an approximate polarised split works: 80 % of the time in Z1–Z2 and 20 % in Z3–Z5. The most mistreated zone is Z2: when heart rate drifts into Z3 on a hill, the right move is to slow down rather than negotiate. The point of an easy run is time, not pace.
To see how a zone split looks in a real session, open the demo with a real activity: map, splits, elevation and time in each zone, no account needed.
Frequently asked questions
What is the difference between heart rate zones and pace zones?
Heart rate zones measure the internal cost of the effort; pace zones measure the external result. Heart rate is affected by heat, hills, sleep and caffeine; pace is more stable in short, intense sessions. The usual approach is to run intervals by pace and long runs by heart rate.
Can I use my watch zones?
You can, but check which reference they use. Many watches apply 220 − age unless you have entered your real maximum heart rate, which leaves the zones shifted. If your watch accepts maximum and resting heart rate, set them there and use Afterpacer to review the real split.
How often should zones be recalculated?
Every six to eight weeks during a training block, and whenever you re-measure your maximum heart rate or threshold pace. It is also worth revisiting after a long break.