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Zone 2 calculator: easy running heart rate and the 80/20 split

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Zone 2 is the most searched phrase in recreational running of the last few years and the most misunderstood one. This calculator works it out with three methods at once, every method you give data for, so you can see how much they differ. Below it suggests how many runs a week should be easy, explains where 80/20 came from, and shows how to check the zone without any formula.

Enter what you know. Every method with enough data shows its zone 2.

bpm
Maximum heart rate
bpm
Resting heart rate
bpm
Threshold heart rate (LTHR)

Enter your maximum heart rate, maximum and resting, or threshold heart rate to see zone 2.

Runs per week (optional)

Enter your runs per week to see the 80/20 split.

Embed this calculator on your site

Copy the code and paste it into a blog post or your club page. The calculator runs in a frame, and the link below it leads to the full version with sources.

<iframe src="https://easytrackly.app/en/embed/zone-2" title="Zone 2 and 80/20 training" width="100%" height="760" style="border:0;max-width:48rem" loading="lazy"></iframe>
<p><a href="https://easytrackly.app/en/running-calculator/zone-2">EasyTrackly running calculator</a></p>

What zone 2 really is

In physiology zone 2 is effort below the first threshold: blood lactate is barely raised, breathing is calm, and the body covers most of its energy from fat. In a laboratory that threshold is found from lactate or ventilation measurements. Each of the three methods in the calculator only estimates it: percent of maximum from one number, heart rate reserve from two, and threshold heart rate from the 30-minute test, which comes closest to a real measurement. That is why entering all the data gives you three different zone 2 ranges. It is not a bug but a picture of how blurry formulas are.

The talk test

The simplest check of zone 2 needs no watch. A 2004 study by Persinger and colleagues compared the so-called talk test with the ventilatory threshold on a treadmill and a bike: the point at which speaking in full sentences stops being comfortable coincided with the threshold. If you can say a few sentences while running without gasping, you are in zone 1 or 2. If you have to pause every few words, you are above it, whatever the table says.

Where 80/20 came from

Seiler and Kjerland described in 2006 the intensity distribution of well-trained cross-country skiers: about three quarters of sessions in the low zone, almost nothing in the middle and the rest high. This split was named polarized. Stöggl and Sperlich tested it in 2014 in a trial that randomly assigned 48 trained athletes to four training models. The polarized group improved aerobic capacity the most, while the group training mostly around threshold did not improve it at all.

Two caveats. First, the studies concerned athletes training many hours a week; with three runs a week the ratio is a guideline, not a law. Second, later comparisons with the pyramidal model, which gives the middle zone more time, showed no clear advantage for either. The common denominator is one: most of the running has to be genuinely easy.

Why most people run too fast

Zone 3, the "moderately hard" pace, feels productive: you run fast, the fatigue is pleasant and the pace on the watch looks good. The problem is that recovery takes longer afterwards and the hard session the next day comes out weaker. A runner who runs everything "medium" has neither a base nor speed. The calculator suggests a number of easy sessions precisely so they are easier to protect.

Frequently asked questions

Which zone 2 is the real one, since there are three?

The one from threshold heart rate is closest to a measurement, because it starts from a test rather than a formula. If you have no test, take heart rate reserve and check it with the talk test.

Is zone 2 the same as a "conversational run"?

In practice yes. The talk test is a tool that studies have confirmed as a sensible marker of the ventilatory threshold.

Should 80/20 be counted in sessions or minutes?

Seiler counted sessions by their main intensity. The calculator does the same. Counting minutes in zones gives a different picture, because the warm-up and cool-down of a hard session are easy too.

Why does my heart rate in zone 2 rise late in a run?

That is cardiac drift: dehydration and heat raise heart rate at the same pace. On a long run hold the pace from the start and let heart rate go a few beats over the limit.

Sources

Step-by-step guides in the Help Center