Heart rate zones: what the five bands actually mean
Training zones are percentages of your heart rate reserve, not of your maximum. Here is what each band trains, and why the fat-burn zone is misunderstood.
Every fitness watch reports zones, and almost nobody is told what they are percentages *of*. Get that wrong and the numbers are meaningfully off — often enough to have you training in a different band than the one you intended.
Reserve, not maximum
The naive approach takes a percentage of maximum heart rate. If your max is 190, then 70% is 133 bpm. But that ignores where you start from: a resting rate of 45 and a resting rate of 75 describe very different cardiovascular systems, and the same 133 bpm means something different for each.
The Karvonen method works from heart rate reserve — the gap between resting and maximum, which is the range you actually have to work with. For a 30-year-old with a resting rate of 60: max is 190, reserve is 130, and 70% means 60 + (0.70 × 130) = 151 bpm, not 133. That is a substantial difference — nearly a full zone.
The five zones for a 30-year-old, resting 60
| Zone | Effort | Heart rate | What it trains |
|---|---|---|---|
| 1 — Warm-up | 50–60% | 125–138 bpm | Recovery, blood flow, warming up |
| 2 — Easy / "fat burn" | 60–70% | 138–151 bpm | Aerobic base, endurance, fat oxidation |
| 3 — Aerobic | 70–80% | 151–164 bpm | Cardiovascular fitness, stamina |
| 4 — Threshold | 80–90% | 164–177 bpm | Lactate threshold, race pace |
| 5 — Peak | 90–100% | 177–190 bpm | Speed, VO₂ max, short intervals |
The fat-burn zone is the most misread label on any watch
Zone 2 is labelled "fat burn" because at low intensity a higher proportion of your energy comes from fat rather than carbohydrate. That is true, and it is routinely misunderstood as burning more fat overall.
Proportion is not total. Working harder burns more calories per minute, so a greater absolute amount of fat can be burned in a higher zone even though the percentage from fat is lower. And over a day, total energy balance is what moves body composition — not which fuel was oxidised during one particular hour.
How age fits in
Maximum heart rate is usually estimated as 220 minus age. It declines predictably, so zones shift down over the years:
| Age | Estimated max | Zone 2 (resting 60–72) | Zone 4 |
|---|---|---|---|
| 20 | 200 bpm | 144–158 bpm | 172–186 bpm |
| 30 | 190 bpm | 138–151 bpm | 164–177 bpm |
| 40 | 180 bpm | 134–146 bpm | 157–169 bpm |
| 50 | 170 bpm | 130–140 bpm | 150–160 bpm |
| 60 | 160 bpm | 125–134 bpm | 142–151 bpm |
The 220-minus-age rule is a population average with real individual variation — roughly ±10–12 bpm. If your watch insists you are exceeding your maximum during hard efforts, the formula is more likely wrong than your heart. A properly supervised test gives a far better number.
What resting heart rate tells you
Measured first thing in the morning before getting up, resting heart rate is one of the more useful numbers in amateur training. It falls as fitness improves, because a stronger heart moves more blood per beat. Tracking the trend over months is a genuine fitness signal.
A resting rate several beats above your normal for a few days often precedes illness, or indicates incomplete recovery from hard training. Many athletes use it as their main "should I train hard today?" check, and it works better than how motivated you feel.
Using zones without overthinking them
Most endurance plans put the large majority of time in zones 1–2 and a small share in zones 4–5, with relatively little in the middle. The common amateur mistake is the opposite — training everything at a moderately hard zone 3 that is too taxing to do often and too easy to drive adaptation. Easy days genuinely easy, hard days genuinely hard.
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