What Zone 2 actually is
Zone 2 is an intensity, not a number on your watch. In physiology it is the effort just below your first lactate threshold: the point where lactate in the blood starts to climb above its resting level. Below it you can keep going for hours, most of the energy comes from fat, and breathing is deeper than at rest but under control. You can still speak in full sentences.
Heart-rate formulas are stand-ins for that threshold. They are handy because a lactate test needs a lab or a finger-prick meter, and rough because the threshold sits at a different share of maximum heart rate for every person and shifts as fitness changes.
Why the four methods disagree
% of maximum heart rate
The common five-zone model puts Zone 2 at 60–70 % of maximum heart rate. It uses only your maximum, and if that maximum is estimated from age, the answer inherits the formula's error: in an independent test on 230 adults, both 220 − age and 208 − 0.7 × age missed the measured maximum by 9–10 beats on average, and by 20 or more for some people. The calculator estimates maximum with 208 − 0.7 × age (Tanaka) and shows 220 − age for comparison. It also ignores fitness. The Norwegian Olympic training scale, built on lactate measurements, puts its comparable easy zone at about 72–82 % of maximum, so for many people the five-zone model's Zone 2 is easier than the physiological one.
Heart-rate reserve (Karvonen)
The reserve is the gap between resting and maximum heart rate. Zone 2 is resting rate plus 60–70 % of that gap. There is no official percentage for Zone 2; 60–70 % is the usual calculator convention, and Karvonen's own 1957 study put the training threshold at about 60 %. Because it starts from your resting rate, it always gives higher numbers than the same percentages of maximum, and each 10 beats of resting rate moves the zone by 3–4 beats. Measure resting rate lying down right after waking, over a few mornings, and use the typical value.
MAF 180
Phil Maffetone's formula starts from 180 minus age and adjusts it for health and training history: subtract 10 after a major illness, surgery or on regular medication; subtract 5 if injured, often ill, or just starting out; add 5 after more than two years of steady progress. The result is the top of the aerobic range, and Maffetone trains in the 10 beats below it, staying close to the top. It comes from coaching experience rather than from lab data. Because it drops a full beat per year of age, faster than the other formulas, it lands close to the reserve method at 30–35 and well below it by 60 (with a resting rate of 60).
Lactate threshold heart rate
Joe Friel's zones are anchored on a field test instead of a prediction: run or ride alone for 30 minutes as hard as you can sustain, press lap after 10 minutes, and take your average heart rate over the last 20 minutes. Zone 2 is 85–89 % of that number for running and 81–89 % for cycling. Because the anchor is measured, it is the most personal of the four; it is under "Have a threshold test" in the calculator.
If you have a lab test or a threshold heart rate, trust it over the formulas. Otherwise start from the band where the methods agree, keep to its lower half on your first sessions, and check it with the talk test.
Is Zone 2 special?
Less than social media suggests. A 2025 review found that the evidence does not support Zone 2 as the best intensity for improving mitochondria or fat burning. Its strength is practical: it is easy enough to do often and for long, so it builds aerobic volume without wearing you out, and most training plans mix it with some harder work.
Check it with the talk test
In Zone 2 you can speak in full sentences without pausing for breath. If you can only get a few words out at a time, you are above it; if you could sing, you are probably below it. Research reviews find the talk test a valid field marker of the ventilatory threshold: the point where talking stops feeling fully comfortable is close to the top of Zone 2. Nose-only breathing is a popular rule of thumb, but a 2023 study found that breathing only through the nose didn't stop people from training harder than they meant to, so treat it as a comfort cue rather than a zone marker.
Chest strap or wrist?
In a 2017 study of 50 adults, a Polar chest strap matched an ECG almost perfectly (agreement 0.996), while wrist devices ranged from 0.92 for the Apple Watch down to 0.67; all of them did worse on an elliptical with moving arm handles. Wrist sensors have improved since, but for intervals, or if your numbers jump around, a chest strap is the safer choice. For steady Zone 2 on a treadmill or bike, a recent watch is usually close enough.
Common questions
Is Zone 2 60–70 % of maximum heart rate?
In the five-zone model that Garmin and Polar use by default, yes. But that model is a convention, not a measurement. Physiological Zone 2, the effort below the first lactate threshold, often sits higher, which is why the heart-rate reserve and MAF methods usually give larger numbers.
How many minutes of Zone 2 a week?
The WHO recommends 150–300 minutes of moderate activity a week for adults, and Zone 2 counts as moderate. Peter Attia, the physician who did most to popularise Zone 2, has called three to four hours a week ideal and about two a good start. The weekly planner splits your available time into easy and hard sessions.
Can walking be Zone 2?
For many people, yes: brisk walking, especially uphill, raises heart rate into Zone 2 without the impact of running. The treadmill incline calculator estimates the incline you need at your speed.
Why is my Zone 2 so slow?
At first, staying in Zone 2 often means jogging very slowly or walking hills. That is normal: as aerobic fitness improves, the same heart rate carries you faster.
Do these numbers work if I take beta-blockers?
No. Beta-blockers and some calcium-channel blockers lower heart rate, so formulas based on age or heart rate don't apply. Ask your doctor; perceived effort and the talk test still work.
Sources
- Tanaka, Monahan & Seals (2001). Age-predicted maximal heart rate revisited. J Am Coll Cardiol. pubmed.ncbi.nlm.nih.gov
- Martin et al. (2025). Exploratory analysis of the accuracy of age-based maximal heart rate equations across cardiorespiratory fitness levels. PLoS One. pmc.ncbi.nlm.nih.gov
- Garmin owner's manual: heart rate zones. www8.garmin.com
- Olympiatoppen intensity scale for endurance training (2024, English). olt-skala.nif.no
- The science of exercise prescription: Martti Karvonen and his contributions. BC Medical Journal. bcmj.org
- Maffetone, P. The MAF 180 Formula. philmaffetone.com
- Friel, J. Joe Friel's quick guide to setting zones. TrainingPeaks. www.trainingpeaks.com
- Coggan, A. Power training levels. TrainingPeaks. www.trainingpeaks.com
- Storoschuk et al. (2025). Much ado about Zone 2: a narrative review assessing the efficacy of Zone 2 training for improving mitochondrial capacity and cardiorespiratory fitness in the general population. Sports Med. pubmed.ncbi.nlm.nih.gov
- Bok, Rakovac & Foster (2022). An examination and critique of subjective methods to determine exercise intensity: the talk test, feeling scale, and rating of perceived exertion. Sports Med. pubmed.ncbi.nlm.nih.gov
- Rappelt et al. (2023). Restricted nasal-only breathing during self-selected low intensity training does not affect training intensity distribution. Front Physiol. pubmed.ncbi.nlm.nih.gov
- Gillinov et al. (2017). Variable accuracy of wearable heart rate monitors during aerobic exercise. Med Sci Sports Exerc. pubmed.ncbi.nlm.nih.gov
- Bull et al. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. pmc.ncbi.nlm.nih.gov
- Attia, P. (2020). Exercising for longevity: Peter on Zone 2 and Zone 5 training. peterattiamd.com
- Eston & Connolly (1996). The use of ratings of perceived exertion for exercise prescription in patients receiving beta-blocker therapy. Sports Med. pubmed.ncbi.nlm.nih.gov