What is the difference between %HRmax, Karvonen, and lactate-based Zone 2?
Three definitions, and only two of them are arithmetic. Percentage of max HR multiplies your max by 60–70%. Karvonen, also called heart rate reserve, takes 60–70% of the gap between your resting and max heart rate, then adds your resting rate back. Lactate-based Zone 2 drops percentages entirely. It puts the ceiling just below your first lactate threshold (LT1), which needs a lab to measure.
| Method | Zone 2 formula |
|---|---|
| % of max HR | 60–70% × Max HR |
| Heart rate reserve (Karvonen) | RHR + 60–70% × (Max HR − RHR) |
| Lactate-based | Just below LT1, measured in a lab |
The first two share the digits 60–70% and share the name Zone 2. They do not share a denominator, so they do not produce the same range.
Same runner, same 60–70%, two answers
Runner: resting HR 50, max HR 190 (heart rate reserve = 140)
| Method | Zone 2 range |
|---|---|
| % of max HR | 114–133 BPM |
| Heart rate reserve | 134–148 BPM |
For this runner the two ranges don't overlap at all. The %HRmax ceiling of 133 sits just under the heart rate reserve floor of 134. Told to train at 60–70%, they've been handed two different workouts about 20 BPM apart.
Why do different sources and devices give different Zone 2 heart rates?
Because the percentage gets published without the scale it belongs to. A page that says Zone 2 is 60–70% has said almost nothing until it says 60–70% of what, and most don't.
Mayo Clinic Press does both at once. Its zone 2 article defines the zone as 60% to 70% of maximum heart rate. It then tells readers to subtract resting heart rate from maximum, multiply by 0.6 and 0.7, and add resting heart rate back. That second procedure is heart rate reserve, not percentage of max, and the article never flags the switch. For a runner with a resting heart rate of 50 and a max of 190, the label and the arithmetic differ by about 20 BPM. Running magazines carry the same split across their zone 2 coverage.
Reusing one set of digits across both scales is a consumer-content habit, not a professional one. ACSM's intensity classifications assign each scale its own numbers.
| ACSM intensity | % heart rate reserve | % max HR |
|---|---|---|
| Moderate | 40–59% | 64–76% |
| Vigorous | 60–89% | 77–95% |
Those are ACSM's categories for apparently healthy adults, published in its 2011 position stand. ACSM doesn't use the label "Zone 2" at all, and its moderate band isn't a Zone 2 definition. The point is narrower and useful: when a governing body maps intensity onto both scales, the numbers come out different, because the scales are different.
Why is the Zone 2 range my watch shows so low?
Because Garmin and Polar default to percentage of max HR, and that method produces the lower of the two Zone 2 ranges. For a runner with a resting heart rate of 50 and a max of 190, the %HRmax default gives 114–133 BPM where heart rate reserve gives 134–148. That's the setting talking, not your fitness.
Whoop applies the same 60–70% band to heart rate reserve instead. That's why its Zone 2 reads higher than a Garmin's for the same athlete. Neither device is malfunctioning. They ship different defaults.
Garmin's manuals document that supported watches can switch heart rate zones from %HRmax to %HRR. Some models also offer a percentage of lactate threshold heart rate. Changing that setting is usually the whole fix. If your easy runs feel absurdly slow at the number your watch gives you, check which method it's set to first.
Why is Zone 2 sometimes 60–70% and sometimes 70–80%?
Because two different things are being called Zone 2. Wearables and RunBeat use 60–70% by formula. The endurance-training register, where the podcast conversation about Zone 2 came from, describes it as roughly 70–80% of max heart rate. That higher band isn't a third formula. It describes work sitting just below the first lactate threshold.
A 2025 expert-panel commentary in the International Journal of Sports Physiology and Performance put 14 experts, working mainly in cycling, on the definition. They defined Zone 2 by threshold rather than by percentage, placing it just below LT1 or VT1. The heart rate they expected there was roughly 70–80% of max, with blood lactate around 1–2 mmol/L. Those figures describe what the intensity typically looks like. They aren't cutoffs.
The same paper shows how the label itself splits. In the three-zone laboratory model, LT1 divides zones 1 and 2 and LT2 divides zones 2 and 3, so "Zone 2" there means everything between the two thresholds. In the five-zone model, Zone 2 sits below LT1. Same words, harder training. Published models use anywhere from three to seven zones.
The practical read: 70–80% of max HR and 60–70% of heart rate reserve describe similar efforts. That's part of why heart rate reserve tends to match how a run actually feels.
Should I use max heart rate or heart rate reserve to set my zones?
Heart rate reserve. It's the method RunBeat uses, and it's the one that reconciles the three competing conventions: the 60–70% device band, the 70–80% endurance register, and the lactate-anchored definition. It also uses your resting heart rate, which percentage of max discards entirely. That lets it tell apart two runners with the same max and very different fitness.
This isn't a claim that heart rate reserve is physiologically more accurate. ACSM classifies moderate intensity as 40–59% of heart rate reserve but 64–76% of max HR, so percentage of max works fine when you use its own numbers. Those numbers just aren't 60–70%.
The honest case for heart rate reserve is narrower and still decisive. The one extra input it needs, your resting heart rate, is free to measure. Its output lands near what the threshold-anchored definitions describe. And runners on forums and in coaching write-ups consistently report that its targets match their perceived effort better than the %HRmax defaults do.
The formula is named for a 1957 study by Karvonen, Kentala, and Mustala. They prescribed intensity as a fraction of the range between resting and maximum heart rate. That study had six subjects. It did not define five zones, did not set the 60–70% band, and did not call itself the Karvonen formula. The zone tables came later.
Zone boundaries are conventions of a model, not constants of your body. Pick one method, apply it consistently, and judge it against how your runs feel.
What max HR and resting HR do I plug into the formulas?
Max HR: the highest heart rate you've actually seen in a genuinely maximal effort within the last year. A hard race finish or a max-effort field test both qualify. A wearable-recorded max from training history works if the effort behind it was real.
If you won't test, 220 minus age is the fallback, and it's the default your watch already uses. Treat it as a placeholder. Age-based formulas carry individual spread of roughly plus or minus 10–12 BPM at one standard deviation. The number describes a population, not you. Replace it with observed data when you have some.
Resting HR: measure it on waking, before getting up, averaged over several days. Your wearable's reported resting average is fine. This input costs nothing to obtain, which is much of the argument for using heart rate reserve.
Max HR feeds both the percentage-of-max formula and the heart rate reserve formula, so an error there moves every zone you calculate. Getting a real reading improves your zones whichever method you settle on.
Sources
- Garber CE, et al. Quantity and quality of exercise for developing and maintaining fitness in apparently healthy adults. Medicine and Science in Sports and Exercise. 2011;43(7):1334–1359.
- Sitko S, et al. What is "Zone 2 training"? Experts' viewpoint on definition, training methods, and expected adaptations. International Journal of Sports Physiology and Performance. 2025;20(11):1614.
- Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate: a longitudinal study. Annales Medicinae Experimentalis et Biologiae Fenniae. 1957;35(3):307–315.
- Device conventions verified against first-party product documentation: Garmin owner's manuals and support pages, Polar's heart rate zones guide, and Whoop's heart rate zone pages.
- Cited as an example of the conflation, not as a source for any number: Mayo Clinic Press, "Zone 2 cardio: what is it and why is it trending online?" Text verified 3 August 2026.