Training
Heart rate zones, honestly
Almost everyone training by heart rate is using zones built on a formula invented as a rough guide in 1971. Since zones are percentages of that estimate, an error at the top moves every boundary beneath it.
A 45-year-old’s Zone 2, three ways
Same person, same session. A ten-beat error in maximum heart rate moves the top of Zone 2 from 117 to 131.
Almost everyone training by heart rate is using zones built on a formula invented as a rough guide in 1971, which can be wrong by ten or twelve beats in either direction. Since zones are percentages of that number, an error at the top moves every boundary underneath it.
This is fixable, and it does not require a laboratory. But it does require knowing what the numbers you have been given actually are.
What a zone is
Heart rate zones divide your range of effort into bands, usually five, each describing a different kind of training. The intent is sound: effort is easier to hold honestly when it has a number attached, and most people ride and run their easy days too hard.
Walking pace. Conversation completely unaffected. Useful between hard days, and easy to skip because it does not feel like training.
You can hold a full conversation, in sentences, slightly aware of your breathing. The zone most people are looking for and most people overshoot.
Short sentences only. Comfortably hard. Productive, but it is where easy sessions go to quietly become moderate ones.
A few words at a time. Sustainable for a while with real concentration. This is interval territory, in measured doses.
No talking. Minutes at most. Small amounts, and not on a day when everything else already hurts.
The formula problem
Those percentages are of your maximum heart rate — and your device almost certainly estimated that with 220 minus your age.
That formula was never a research finding. It is generally traced to a rough guide from 1971, reportedly a line drawn by eye through a scatter of around 35 data points. It stuck because it is easy to remember.
The better-supported replacement comes from Tanaka and colleagues in 2001, built on a meta-analysis of 351 studies covering 18,712 people:
Maximum heart rate ≈ 208 − (0.7 × age)
At 20 the two formulas nearly agree. They diverge with age: at 60, “220 minus age” gives 160 while Tanaka gives 166. The older formula tends to overestimate maximum heart rate in younger adults and underestimate it in older ones.
Tanaka is better. It is still an estimate, with a reported standard error around seven beats per minute, and individual variation at any given age is wide — two healthy 40-year-olds can genuinely differ by twenty beats.
Why a small error moves everything
Zones are percentages. Get the maximum wrong and every boundary underneath it moves by the same proportion.
| Max HR from | Estimate | Zone 2 becomes |
|---|---|---|
| 220 − age | 175 | 105–123 bpm |
| Tanaka | 177 | 106–124 bpm |
| True max 10 beats higher | 187 | 112–131 bpm |
| True max 10 beats lower | 167 | 100–117 bpm |
That spread — 100 to 131 for the top of the same person's Zone 2 — is the difference between an easy aerobic hour and a tempo session labelled as an easy one. Over a training block, that distinction matters more than almost anything else you could adjust.
Most people are not failing to train in Zone 2. They are training in Zone 3 while a formula tells them it is Zone 2.
The other thing nobody mentions
There is more than one zone system, and they produce different numbers from the same body.
- Percentage of maximum heart rate. The common consumer default. Simple, and it ignores your resting heart rate entirely.
- Percentage of heart rate reserve (the Karvonen method), which works from the span between your resting and maximum heart rate. Generally considered the better of the two, and it gives noticeably higher boundaries for the same zone.
- Percentage of lactate threshold heart rate, used in most serious endurance coaching, anchored to a tested value rather than an estimated one.
So “Zone 2” is not one thing. If your coach's Zone 2 and your watch's Zone 2 disagree by fifteen beats, neither is necessarily wrong — they may simply be different systems wearing the same label.
How to fix your zones in one session
You do not need a laboratory. You need either a better anchor or a check that does not involve numbers at all.
-
Replace the formula with Tanaka
208 minus 0.7 times your age. If your device lets you set maximum heart rate manually, this is a free improvement over the default.
-
Use the talk test as the real calibration
In true Zone 2 you can speak in full sentences while slightly aware of your breathing. If you are down to short phrases, you are in Zone 3 whatever the display says. This beats any formula.
-
Find your actual maximum, carefully
A supervised field test — a long hard hill repeated to genuine exhaustion — will get closer than any equation. Not advisable if you are new to training, unwell, or have any cardiac history. Ask a doctor first if you are unsure.
-
Switch to heart rate reserve if you can
Using the span between your resting and maximum heart rate personalises the zones with a number your band already measures well.
-
Allow for the day
Heat, dehydration, poor sleep and illness all shift heart rate at the same effort — cardiac drift of five to ten beats on a hot afternoon is ordinary. On those days, trust effort over the number.
A note on wrist accuracy during intervals. Optical sensors are at their weakest during rapid changes in intensity, which is exactly what interval sessions are made of. For steady Zone 2 work a wrist reading is fine. For sprints, a chest strap is a genuinely different class of measurement — and how you wear the band matters more than usual.
The talk test is free, needs no battery, and is more accurate than the number your watch inherited from 1971.
How Mesh approaches zones
Mesh 2.0 measures heart rate continuously and records time spent at each intensity, with your resting heart rate as a personal anchor rather than age alone. Being screenless, there is no number flashing on your wrist mid-interval to chase — you train by effort and read the session afterwards.
That order is deliberate. Effort is the thing you can actually control; the zone is a description of it after the fact. See how the app presents it, or read the full Mesh 2.0 specification.
Questions people actually ask
What should my heart rate be in Zone 2?
Conventionally 60 to 70% of your maximum heart rate — but that depends entirely on your maximum being right, and for most people it was estimated with 220 minus age.
The more reliable check needs no numbers: in true Zone 2 you can speak in full sentences while slightly aware of your breathing. If you are down to short phrases, you are in Zone 3 regardless of what the display says.
Is 220 minus age accurate?
No. It is generally traced to a rough guide from 1971 — reportedly a line drawn by eye through about 35 data points — rather than to a study. It tends to overestimate maximum heart rate in younger adults and underestimate it in older ones.
The better-supported alternative is Tanaka: 208 minus 0.7 times your age, from a 2001 meta-analysis of 351 studies covering 18,712 people. At 60, the old formula gives 160 and Tanaka gives 166.
How do I find my real maximum heart rate?
A supervised field test gets closer than any formula — typically a long, hard hill effort repeated to genuine exhaustion, with the highest reading taken as your maximum.
This is not advisable if you are new to training, currently unwell, or have any cardiac history or risk factors. Speak to a doctor first if you are unsure. For most people, using Tanaka plus the talk test is the sensible compromise.
Why does my coach’s Zone 2 differ from my watch’s?
Probably because they are different systems using the same word. Percentage of maximum heart rate, percentage of heart rate reserve (Karvonen) and percentage of lactate threshold heart rate all produce different boundaries from the same body.
Heart rate reserve uses the span between your resting and maximum heart rate and generally gives higher boundaries than percentage of maximum for the same zone label.
Why does my heart rate drift up at the same pace?
Cardiac drift. Heat, dehydration, fatigue and poor sleep all raise heart rate at a given effort, and five to ten beats on a hot afternoon is ordinary rather than alarming.
On those days, trust perceived effort over the number. Holding a zone by slowing down is usually the right call; forcing the pace to keep the number is not.
Are wrist heart rate readings accurate enough for interval training?
For steady work, generally yes. For intervals, less so — optical sensors are weakest during rapid changes in intensity, which is precisely what intervals consist of.
If you train seriously by zones, a chest strap is a meaningfully different class of measurement. For everything else, a well-fitted band is fine.
Sources
- Tanaka, Monahan and Seals, Age-predicted maximal heart rate revisited, Journal of the American College of Cardiology, 2001 — meta-analysis of 351 studies covering 18,712 subjects; maximum heart rate ≈ 208 − (0.7 × age); reported standard error of estimate around seven beats per minute.
- Background on the origin of the 220-minus-age formula, widely reported as a rough guide dating to 1971 derived by inspection from a limited set of data points rather than from a dedicated study.
- Karvonen heart rate reserve method — zones calculated from the span between resting and maximum heart rate rather than from maximum alone.
- Investigating sources of inaccuracy in wearable optical heart rate sensors, npj Digital Medicine, 2020 — measurement error in wrist photoplethysmography increasing during dynamic changes in activity intensity.
Figures are quoted as reported by the cited sources. All age-based maximum heart rate formulas are population estimates with wide individual variation — two healthy people of the same age can genuinely differ by twenty beats per minute, so no formula should be treated as your personal maximum. Maximal effort testing carries risk: do not attempt it if you are new to exercise, unwell, pregnant, or have any history of or risk factors for heart disease without speaking to a doctor first. This article is general information and is not medical advice.
Mesh 2.0
Wear less.Know more.
A screenless band that tracks your heart rate, sleep and BioFuel — then stays out of the way. Available now across Pakistan.