Nobody agrees what a heart rate zone is

Put on one chest strap, do the same thirty minutes, and let five apps read it at the same time. They will not agree about which zones you were in, or how long you spent there. No sensor is misreading anything — every app is receiving the same beats from the same chest. They disagree because there is no standard for what a heart rate zone is.

This is not rounding at the edges. The same heart rate can be zone 2 in one app and zone 3 in another, and the line between "easy" and "working hard" can sit eighteen beats apart depending only on which app you opened.

Every zone scheme makes four choices

1. A percentage of what? Your maximum heart rate, your heart rate reserve, your lactate threshold, or your power output. The same "70%" means different heart rates under each.
2. How many bands? Two, three, five or seven.
3. Are the bands the same width? Some schemes cut the range into even 10% steps; others use uneven bands tuned to physiological landmarks, so one band covers twice the span of its neighbour.
4. Is the lowest band training at all? In most schemes, it isn't.

Then there is a fifth question, which matters more than any of them and gets discussed far less: what is a minute in each band worth?

What the percentages are of

The two dominant options are a percentage of maximum heart rate (%HRmax) and a percentage of heart rate reserve (%HRR), the gap between your resting and maximum rate. The reserve method comes from Karvonen, Kentala and Mustala's 1957 longitudinal training study, which is why it is still called the Karvonen method.1

They are not close to each other. Take someone who rests at 60 bpm and maxes at 180:

• 70% of maximum heart rate is 126 bpm.
• 70% of heart rate reserve is 60 + (0.70 × 120) = 144 bpm.

Eighteen beats a minute apart, wearing the same label. A rate that is comfortably mid-zone under one method is a serious effort under the other.

The gap is not a quirk of those two particular formulas. Both are the same calculation; they differ only in what they treat as the bottom of the scale. The reserve method starts counting at your resting rate, so a lower resting rate stretches the reserve and drags every boundary down with it. Push that to its limit — a resting rate of zero — and the reserve becomes your entire maximum, which is precisely what the percentage-of-maximum method assumes.

Which is why the two methods are not rival theories so much as the same ruler with different zero points. The reserve method treats the heart rate you never go below as dead space and measures only the range you can actually train in; the maximum method counts that dead space as though it were available effort. That is the whole of the eighteen-beat gap.

Vendors do not even agree with themselves. A Garmin watch offers four bases for the same five zones: "BPM to view and edit the zones in beats per minute", "%Max. HR", "%HRR to view and edit the zones as a percentage of your heart rate reserve", and "%LTHR ... as a percentage of your lactate threshold heart rate".2 Fitbit splits by hardware generation: newer devices define the moderate zone as "Between 40% and 59% of your heart rate reserve", while older ones define the fat burn zone as "Between 50% and 69% of your maximum heart rate".3 Two Fitbits, two answers, same brand.

Apple manages to disagree with itself in public. Its user guide says the zones are "a percentage of your maximum heart rate and are automatically calculated and personalized using your health data",4 while the reporting from the watchOS 9 launch onwards has consistently described the automatic zones as built "based on the Heart Rate Reserve method".14 Those are the two methods that just came out eighteen beats apart. Apple publishes neither the boundaries nor the arithmetic, so from the outside there is no way to settle which account is right — and on the watch you can only edit zones 2, 3 and 4 by hand, which at least tells you the outer two are considered fixed.

How many bands, and where they start

Five is the popular answer, and it is a convention rather than a finding. Fitbit ships three scoring zones plus an uncounted band below them.3 Andrew Coggan's power model, the standard in cycling, has seven levels defined against functional threshold power rather than heart rate at all. The World Health Organization's guidelines get by with two.

More interesting is where the numbering starts. In most schemes, zone 1 is not training:

• Garmin's zone 1 (50–60% HRmax) is "Warm-up", described as "You're walking at a relaxed and easy pace."5
• Polar's zone 1 (50–60% HRmax) is labelled "VERY LIGHT".6
• Strava describes its zones as running "from Zone 1 (active recovery) to Zone 5 (near-maximum effort)".7
• Coggan's zone 1 is literally named Active Recovery.

So in those systems the first band you can genuinely call a workout is zone 2 — the numbering starts one below training, and zone 1 is the thing you do on the way there. In others, including Fitbit's fat burn zone and ZonePoints' Easy zone, the bottom band already asks for real effort.

That disagreement about where the numbering starts is most of why "zone 2" has become the most overloaded term in fitness.

"Zone 2" is at least four different efforts

The second band up, for the same runner resting at 60 and maxing at 180:

Four bands doing the same job in their own scheme, spread across 53 beats a minute. The commonest of them finishes six beats before ZonePoints' even starts, so the two do not overlap at a single heart rate.

ZonePoints' zone 2 lands at 73–80% of maximum heart rate — almost exactly where Polar and Peloton put zone 3.68 Someone moving between the two apps has not changed how hard they train; the label has moved a whole band.

The research does not settle it either. In "Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries", Meixner, Filipas, Holmberg and Sperlich put 50 experienced cyclists through ramp and incremental step tests and located the zone 2 boundary using several accepted markers at once. The coefficients of variation across markers ran from 6% to 29%. The first ventilatory threshold and the intensity of maximal fat oxidation "showed strong alignment" with each other, while "fixed percentages of HRmax and blood lactate thresholds exhibited wide individual differences" — so the two markers that need a laboratory agreed, and the one an app can actually calculate did not. Their conclusion was that a zone 2 worth the name needs personal physiological measurement rather than a percentage.9

Where the schemes stand

%HRmax — five of nine, the commonest choice%HRRMore than one basis, or disputed

Read the shaded column on its own and the popular answer is plain: %HRmax wins on headcount, and it wins largely because it needs nothing but your age. %HRR requires a resting rate the device has to measure and keep current. The cheaper baseline is the one that spread.

The guidelines and the research models disagree along a different axis again.

What a minute in each band is worth

Where the bands sit is only half the disagreement. What an app pays you for a minute inside one is the other half, and it varies more wildly than the boundaries do — a cliff, a step, a cap and a logarithm are all in shipping products. That is its own article: The same workout, five different scores.

Why nothing below half your reserve counts

ZonePoints has no start button. A session begins the moment you cross into zone 1 and pauses when you drop below it, which means the zone 1 threshold is not only a scoring decision — it is the thing deciding whether you are training at all.

That only works if the threshold sits above the noise of ordinary life. The same 60/180 runner one last time:

• 50% of maximum heart rate is 90 bpm. They will hit that climbing a flight of stairs, carrying the shopping in from the car, or getting up off the sofa and walking briskly to answer the door.
• 50% of heart rate reserve is 120 bpm. They have to mean it.

Put the floor at the first number and the app starts a session because someone walked to the kitchen. By Sunday it is reporting hours of "training" that were mostly a commute. The vendors implicitly agree: Garmin's own description of that band is a warm-up at "a relaxed and easy pace",5 Polar calls it "very light",6 and Apple's exercise threshold is explicitly a brisk walk.10 Those are perfectly good definitions of activity. They are not definitions of a workout.

The research puts the useful threshold near the higher number too, though with a caveat worth stating. In "VO2 reserve and the minimal intensity for improving cardiorespiratory fitness", Swain and Franklin re-expressed 18 previous low-to-moderate-intensity training studies in common units and found that intensities below roughly 45% of VO₂ reserve were "consistently ineffective at increasing VO2max" among subjects who started above 40 mL·kg⁻¹·min⁻¹. For less fit subjects nothing they tested was ineffective, down to about 30% VO₂ reserve. Their own summary notes that "evidence for a threshold intensity was not strong".12 Because %HRR and %VO₂ reserve are the same line,11 that 45% converts directly into 45% of heart rate reserve — and ZonePoints puts its floor five points above it, deliberately on the side of "this was definitely a workout".

That is a trade, not a free win. If your goal is to move more rather than to train harder, the lower bar is the more useful one, so ZonePoints ships heart rate max mode as an option: it drops the entry point so a brisk walk or light housework registers and earns points. Which one you want is a question about your goals, and it is covered in how training zones are calculated.

A high floor has one other consequence: it takes a minute or two of real work to cross it, so the clock starts later than the effort does. That is a genuine cost, and your first two minutes don't count — your last two do covers where those minutes go and how the end of a session returns them.

What ZonePoints is not claiming

It would be easy to end by claiming the scheme is the physiologically correct one. It isn't, and neither is anyone else's.

In "What Is Moderate to Vigorous Exercise Intensity?", MacIntosh, Murias, Keir and Weir argue that fixed percentage prescriptions are the wrong tool in principle, because "exercising at a common percentage of V̇O2max or heart rate reserve may represent different magnitudes of disturbance to homeostasis for different individuals", and that "two individuals exercising at 70% of V̇O2max could be exercising in different exercise domains". Their recommendation is to identify intensity from each person's own measured ventilatory or lactate thresholds.13 Meixner and colleagues' 50 cyclists reached the same conclusion from the data.9

They are right, and the verdict applies to every row of both tables above — ZonePoints' included. No percentage-based zone is your physiology, whichever percentage it is a percentage of.

What a zone scheme can be is consistent, and that is what ZonePoints optimises for: one rule applied the same way to everyone, no cliffs and no caps, arithmetic you can check in your head, a floor high enough that the session timer means something, and a number that converts to oxygen and calories without a fudge factor in between.

For people who have had a lab test and know where their own thresholds sit, custom zones is on the roadmap — and deliberately display-only. Your own boundaries will drive the colours, the alerts and the time-in-zone breakdown, while the points stay on the fixed reserve scale. That is the whole reason a score is worth having: move the scale and it stops being comparable with your own history, never mind anyone else's.

The takeaway

There is no standard. There is a five-band convention that most consumer platforms follow, drawn against different baselines, starting at different intensities, and scored on curves that range from a hard cliff to a logarithm.

Knowing which one you are looking at matters more than which one you pick. And if the number is going to be worth anything — comparable week to week, convertible into calories, checkable in your head — the straight line is the version that survives having its arithmetic examined.

1. Karvonen MJ, Kentala E, Mustala O. "The Effects of Training on Heart Rate; a Longitudinal Study." Annales Medicinae Experimentalis et Biologiae Fenniae. 1957;35:307–315. PubMed
2. Garmin. "Setting Your Heart Rate Zones." Forerunner 265 Series Owner's Manual. Product documentation, not a research finding. garmin.com
3. Google. "Track your heart rate with your Pixel Watch or Fitbit device." Google Health Help. Product documentation. support.google.com
4. Apple. "View Heart Rate Zones on Apple Watch." Apple Watch User Guide. Product documentation. Apple Support
5. Garmin. "How You Can Train by Heart Rate Zones Using Garmin." Product documentation. garmin.com
6. Polar. "Polar Heart Rate Zones." Polar Team Pro User Manual. Product documentation. polar.com
7. Strava. "Heart Rate" and "Relative Effort." Strava Help Center. Product documentation. support.strava.com
8. Peloton. "Everything You Need to Know About Using Training Zones." Product documentation. onepeloton.com
9. Meixner B, Filipas L, Holmberg HC, Sperlich B. "Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries." Translational Sports Medicine. 2025;2025:2008291. PubMed
10. Apple. "Track daily activity with Apple Watch." Apple Watch User Guide. Product documentation. support.apple.com
11. Swain DP, Leutholtz BC. "Heart rate reserve is equivalent to %VO2 reserve, not to %VO2max." Medicine & Science in Sports & Exercise. 1997;29(3):410–414. PubMed
12. Swain DP, Franklin BA. "VO2 reserve and the minimal intensity for improving cardiorespiratory fitness." Medicine & Science in Sports & Exercise. 2002;34(1):152–157. PubMed
13. MacIntosh BR, Murias JM, Keir DA, Weir JM. "What Is Moderate to Vigorous Exercise Intensity?" Frontiers in Physiology. 2021;12:682233. Frontiers in Physiology
14. Potuck M. "Heart rate zones on Apple Watch and iPhone: how they work." 9to5Mac, 23 May 2024. Press reporting, not Apple documentation. 9to5Mac