What is a zone point?

A zone point is a minute of easy training effort. Train for a minute at the bottom of your training range and you earn one point. Train harder and the same minute earns more, up to six. Drop below your lowest training zone — half of your heart rate reserve — and the minute earns nothing at all, because you are not really training at that point.

That is the entire definition. Everything below is why it is built that way.

The rate you earn them at

Your scoring rate is called zone speed, measured in zone points per minute. It rises in a straight line with how far into your heart rate reserve you are — the reserve itself is the fixed range between your resting and maximum heart rate, and it is where your rate sits within that range that changes:

So the hardest minute you are capable of is worth six of the easiest.

That straight line matches how your body works. The share of your heart rate reserve you are using rises one-for-one with the share of your oxygen reserve, as Swain and Leutholtz found in the study described below,2 so each step up the scale stands for an equal step up in the work your heart and muscles are doing.

The scale stops at 6.0, which you only reach at your true maximum heart rate. If a session ever reads higher, your maximum is set too low rather than your effort being superhuman — and ZonePoints notices, remembering the higher rate and offering to raise your maximum so every zone and score lines up again.

Zone speed moves continuously with your heart rate rather than jumping to a whole number when you enter a zone, which is why every row above is a range. Several popular apps do it the other way, in whole steps at a zone boundary — how Fitbit and Apple score the same minute sets the two side by side. Within the ranges above, zone speed reads exactly as you would expect:

• 55% of your reserve is 1.5 points a minute, not 1.
• 65% is 2.5.
• 73% is 3.3.
• 87% is 4.7.

The formula is simply your reserve percentage times ten, minus four:

The solid line is your scoring rate. It has no steps in it: every reading between 50% and 100% of your reserve has its own rate, to one decimal place. The dashed line is what the same effort would earn if a zone paid a whole number, which is how several apps do score it.

There is no cliff at a zone boundary and no bonus for crossing one, because nothing happens there: the zone names are labels printed along a continuous scale rather than steps in it. The app shows your current zone speed to one decimal place for that reason. Drifting from 69% to 71% moves you from zone 2 to zone 3 on the display and moves your scoring rate from 2.9 to 3.1, which is the same small change either way.

How other apps score the same minute

Both of those are reasonable designs, and both answer a different question from this one. A step scale tells you whether a minute was moderate or vigorous. A flat scale tells you whether a minute counted at all. Neither separates a hard minute from an all-out one, which is the distinction a zone point exists to make. The same workout scores differently in every app walks through seven of them, Garmin, Whoop, Strava, Peloton and Orangetheory included.

Why heart rate reserve, and not a percentage of your maximum

Heart rate reserve measures your effort against the range you actually have available, from your resting rate up to your maximum, rather than against your maximum alone. It is the method introduced by Karvonen, whose 1957 longitudinal training study "The effects of training on heart rate" established the reserve formulation still in use.1

Reserve tracks oxygen consumption almost exactly. In "Heart rate reserve is equivalent to %VO2 reserve, not to %VO2max," Swain and Leutholtz found that percentage of heart rate reserve corresponds to the same percentage of VO₂ reserve, and specifically not to the same percentage of VO₂max.2 A percentage of maximum heart rate does not have that property.

This is what makes a zone point a precise measure of total work over time rather than a made-up score. Accumulating effort at a rate proportional to %HRR means the session total is a time-weighted integral of %HRR, which is the same quantity used to measure cardiovascular workload. Two sessions with the same total zone points represent the same amount of work, whether one was short and brutal and the other long and steady.

Why nothing below 50% earns anything

Every scoring system has to decide where training begins, and a system that pays out for walking to the kitchen cannot tell you anything useful about your week.

There is research behind where that line sits. In "VO₂ reserve and the minimal intensity for improving cardiorespiratory fitness," Swain and Franklin re-expressed the intensities of earlier training studies in common units and found that training below roughly 45% of VO₂ reserve was consistently ineffective at raising VO₂max in subjects who started with reasonable fitness.3

In the same paper, among subjects who started with low fitness, no intensity they examined was ineffective, and the lowest they could examine was about 30%.3 So the floor is not a universal law of physiology. It is a threshold that holds for people who already train, and it is set at 50% rather than 45% because a round number at the bottom of zone 1 is easier to reason about than a precise one.

If you are starting from very low fitness, move the floor

That caveat has a setting attached to it. ZonePoints offers two ways of building your zones, and the choice moves the floor.

Heart rate reserve measures from your resting rate upwards, so a 50% floor is halfway between rest and maximum. Heart rate max measures from zero instead, so a 50% floor is simply half your maximum heart rate — a much lower bar. For someone resting at 60 with a maximum of 180, scoring starts at 120 beats per minute under reserve and at 90 under maximum. Work that earns nothing under one method earns points under the other.

That is the right choice if you are returning to exercise, building a base, or doing something genuinely lower in intensity, and it is exactly the group the research says the strict floor was never really about. Change it in Settings under zone calculation method.

Two things to know before you switch. Your whole history is rescored, not just your future sessions, so past weeks are re-judged on the new scale and their totals go up — which is what keeps your own record internally consistent rather than splitting it in two at the date you changed. And your points are no longer comparable with someone using reserve, because you are now measuring against a larger range.

What a total is actually worth

The numbers only mean something once you have a sense of scale.

• A hard workout is around 100 points. That is per session, not per hour. A fast 5 km spent mostly in zones 4 and 5 lands near 100 in about 23 minutes; a longer steady-hard session lands in the same place by a different route. That equivalence is the point of the unit.
• The default weekly target is 200, which is roughly two hard workouts. 300 is about three, 400 about four.
• The World Health Organization recommends 75 to 150 minutes of vigorous activity per week for adults.4 Vigorous sits at roughly 60 to 90% of heart rate reserve, which is a zone speed of 2.0 to 4.9 points a minute — 5.0 is the floor of zone 5 and already past vigorous. At 3 points a minute, a properly hard pace, the WHO range works out at about 225 to 450 points a week. The starting target of 200 sits just below it deliberately, as somewhere to begin rather than somewhere to finish.

What it is not

It is not calories, which depend on your body mass and are an estimate however they are produced. It is not time, because an hour of easy movement and an hour of intervals are not the same training. And it is not comparable to another app's points: nobody agrees what a heart rate zone is, and the same workout scores differently in every app depending on what each vendor decided a minute was worth.

What it is, is one number that answers "have I trained enough this week", where "enough" accounts for how hard the training was.

For how the target works week to week, see your weekly target. For choosing between heart rate reserve and heart rate max, see zone calculation method. Your maximum sets the top of the scale, and if you have never measured it, three formulas and why all of them are wrong will get you a starting estimate.

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(3):307–315. PubMed
2. 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
3. Swain DP, Franklin BA. "VO(2) reserve and the minimal intensity for improving cardiorespiratory fitness." Medicine & Science in Sports & Exercise. 2002;34(1):152–157. PubMed
4. World Health Organization. WHO guidelines on physical activity and sedentary behaviour. 2020. Public health guidance, not a single research finding. who.int
5. Google. "Track Active Zone Minutes or active minutes on your Fitbit device and Pixel Watch." Google Health Help. Product documentation. support.google.com
6. Apple. "Track daily activity with Apple Watch." Apple Watch User Guide. Product documentation. support.apple.com