Nobody agrees what a heart rate zone is

Record the same thirty-minute workout in five different apps and they will not agree about which zones you were in, or how long you spent in each. None of them is misreading your heart rate — they are all working from the same numbers. They disagree because there is no standard for what a heart rate zone is.

The popular apps and training schemes all define their zones differently. This article sets out what they have in common, where they differ, and why ZonePoints defines its zones the way it does.

What most schemes have in common

Strip away the names and the colours and most schemes share one shape:

• Every boundary is a percentage of a heart rate, so one scheme fits anyone.
• There are five zones. Eight of the nine apps compared below use five; Fitbit uses three.
• They are numbered 1 to 5, easiest to hardest. Fitbit names its zones and Orangetheory colours them, but the rest count up.

Five is a convention rather than a finding. The World Health Organization's guidelines get by with two, moderate and vigorous.

Where they differ

Within that shared shape, two choices can move a heart rate a whole zone.

A percentage of what?

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.

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 whole range from zero to maximum, which is exactly what the %HRmax method assumes.

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.

Is zone 1 training?

In most apps, it isn't:

• 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

So in those apps the first band you can genuinely call a workout is zone 2, and zone 1 is the thing you do on the way there. Garmin does not count it either: its Intensity Minutes are "a 60-second time period spent in either moderate or vigorous physical activity".18

The schemes built to count exercise draw their lowest line at training. The ACSM starts moderate intensity at 40% of heart rate reserve, and the WHO's guidelines count only moderate and vigorous activity. Fitbit's newer devices start their lowest zone at the same 40% of reserve and leave the band below it uncounted.3 ZonePoints does the same: zone 1 starts at 50% of reserve, so every zone is a training zone and anything below them is not training.

What the popular apps use

HRmax — five of nine, the commonest choiceHRRMore 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.

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 device: the Pixel Watch, Fitbit Air, Charge 4 and later, Inspire 2 and later, and the Sense and Versa series define the moderate zone as "Between 40% and 59% of your heart rate reserve", while all other devices define the fat burn zone as "Between 50% and 69% of your maximum heart rate".3 Two Fitbits, two answers, same brand.

Apple's documentation and its watch disagree. The user guide says the zones are "a percentage of your maximum heart rate and are automatically calculated and personalized using your health data".4 A 2025 study of the watch describes the Workout app's zones as "based on %HRR", with the default zones starting at 60% of reserve — already vigorous intensity by the ACSM's definition.15 Press coverage says the same,1416 and the zone limits one owner posted from their watch only add up under the reserve method.17 Apple still publishes neither the percentages nor how it estimates your maximum.

The public health guidelines use intensity classes rather than numbered zones:

Peloton's shortcut

Peloton draws its zones at 65, 75, 85 and 95% of maximum heart rate, not the usual 60, 70, 80 and 90.8 For the same runner, that lands its boundaries surprisingly close to the reserve method's:

Peloton's first boundary is three beats from ours. Adding fifteen points to every percentage is a rough stand-in for the resting rate that the maximum method leaves out. It lifts the boundaries as if everyone rested at about the same rate, and they don't:

Two riders whose resting rates are thirty beats apart get identical Peloton zones. The reserve method starts them fifteen beats apart, because the resting rate is real information: it is the part of the scale each of them never uses. A percentage of maximum ignores it; a percentage of reserve measures it. That is also what the physiology follows. In "Heart rate reserve is equivalent to %VO2 reserve, not to %VO2max", Swain and Leutholtz put 63 adults through incremental cycle tests and found that a percentage of heart rate reserve matched the same percentage of oxygen uptake reserve almost exactly, with a slope of 1.00 and an intercept of −0.1. A percentage of reserve is a percentage of the extra oxygen the effort costs.11

The reserve numbers are the easier ones to carry around, too. Zone 1 starts at half your reserve and each zone adds a tenth: 50, 60, 70, 80, 90. Peloton's 65, 75, 85 and 95 are those steps pushed up by fifteen to make up for the missing resting rate. Measure the resting rate instead, and the round numbers do the job.

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 A 2025 study that located zone 2 in 50 experienced cyclists, using several laboratory markers at once, reached the same conclusion from the data: a fixed percentage of maximum heart rate landed in widely different places from person to person, and a zone 2 worth the name needs personal measurement.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 Watch 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. "Heart Rate Zones." Polar Blog. Product documentation. polar.com
7. Strava. "Heart Rate." Strava Help Center. Product documentation. support.strava.com
8. Peloton. "Peloton's Strive Score Is the Latest Way to Track Your Performance." 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. "Get the most accurate measurements using your Apple Watch." Apple Support. 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
15. Warner A, Vanicek N, Benson A, Myers T, Abt G. "Criterion validity of a newly developed Apple Watch app ('MVPA') compared to the native Apple Watch 'activity' app for measuring criterion moderate intensity physical activity." Digital Health. 2025;11:20552076251326225. PubMed
16. Skwarecki B. "What 'Zone 2' Cardio Actually Means." Lifehacker, 24 April 2026. Press reporting, not Apple documentation. lifehacker.com
17. "How are heart rate zones calculated on my Apple Watch?" Apple Community, 5 December 2024. A user's report of the limits their watch displayed, not Apple documentation. discussions.apple.com
18. Garmin. "Intensity Minute Data Sheds Light on Fitness Habits." Garmin Blog, 13 February 2024. Product documentation. garmin.com