What is zone 2 running, and why most people get it wrong
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Zone 2 is the easy aerobic effort you can hold for a long time while still talking in full sentences. In the lab it is defined by blood lactate, which you cannot see on a run, so runners fall back on heart rate formulas or the talk test. The formulas only agree when you give them numbers most runners have never measured. I trust the talk test over any of them, and I explain why below. I spent two years running my easy runs too fast, and my 10km best stayed at 48:30 the whole time.
The definition
One widely quoted definition comes from Peter Attia: the highest effort you can sustain while your blood lactate stays below about 2 millimoles per litre. He calls it an all day pace.
That is a physiological line, not a heart rate or a pace. Measuring it means finger-prick blood samples at stages of rising effort. Everything else you will read, including every number on this page, is an estimate of where that line sits.
The word also means different things depending on who is using it. Sports science papers usually use three zones and Zonna uses five, so zone 2 is not one fixed effort. I sorted out the numbering in why your easy runs aren't easy, and what it costs you.
Why the formulas disagree
Most watches let you set zones from a percentage of maximum heart rate, a percentage of heart rate reserve, or a percentage of lactate threshold heart rate. Garmin's manual lists all three. They are different calculations, so the same runner gets different zones.
Here is mine. My maximum is around 188 and my resting rate is 48. The bands Zonna uses for zone 2 are 70 to 80 percent of maximum, or 60 to 70 percent of heart rate reserve, which is maximum minus resting.
As a percentage of maximum, that is 132 to 150 beats per minute. As a percentage of reserve, it is 132 to 146. They land close because both start from the same maximum. If that maximum is a guess, both are wrong together.
Then there is 180 minus your age, from Phil Maffetone. It gives you a single ceiling, ignores your resting and maximum heart rate, and comes with its own adjustments: subtract 10 or 5 for illness, injury or stalled progress, and add 5 after two years of consistent training.
Anchoring zones to lactate threshold heart rate is closer to the physiology, but it needs a test too. Most of the rest start from a maximum you may never have measured, and I covered how far off the age formulas can be, and how heart rate drifts in heat, on the easy runs page.
The talk test, and why I lean on it
The talk test has research behind it. Work led by Carl Foster at the University of Wisconsin-La Crosse found that speech is comfortable below your first threshold, gets uncertain at it, and fails at the second. A 2022 review in Sports Medicine concluded that the test appears to be a valid measure of both.
Foster is an author of that review as well, so it is not an independent check. The research has limits too. In the original work, one study found some people could still talk at workloads where they were expected not to. Another found it took two to four minutes to lose comfortable speech just above threshold.
So do not judge it from the first minute. Say a few full sentences out loud a few minutes in, and again near the end of the run.
It follows effort rather than a number, so it still works on a hot day.
What zone 2 is not
It is not a pace. The same effort is slower on hills, in heat, or when you are tired.
It is not a single heart rate you can look up. Without a test, any figure is a starting guess.
It is not the whole of training. Easy running is the base and you still need harder work to get faster. Some of what gets posted online treats zone 2 as the entire answer, and I think that is overstated.
How I would use it
Set the effort by feel first. Run at a pace where you can talk in full sentences. It will probably be slower than you want.
Then use your watch to learn, not to give orders. Note your heart rate on a few flat easy runs at that effort, and treat the range you see as your own instead of a formula. That is my method, not something from a study.
When heart rate and effort disagree, go with effort, especially in heat and late in a long run.
If you are new to running, easy running alone will make you faster for a while. If you have been running a while, keep one run a week properly hard. Either way, give the change a month before you judge it. My guide to how slow easy runs should feel has the numbers I use.
Where Zonna fits
Zonna is built around easy running. Most sessions in a plan are easy, and no week has more than two hard ones. It is iOS only, there is no Garmin workout export, and I am the only developer.
The free tier has the 5K, 10K and half marathon plans in full, with no end date. Paid access is £7.99 a month or £59.99 a year, with a two-week trial.
You do not need an app to find zone 2. The talk test and a watch you are willing to ignore will do. If you are choosing an app, I compared the options in the best running app for beginners who go too hard.
My recommendation: set your easy effort by the talk test, check it against your heart rate over a few runs, and treat any formula as a starting guess.
Written by Russ Shear, who built Zonna after running 100km in July 2026 and walking the last 40 of it.