Heart rate zone training has moved from elite sports science into mainstream fitness, driven partly by the popularity of “Zone 2” training in endurance and longevity circles. Understanding what each zone actually trains helps you exercise with intention rather than guessing at effort.
The most common estimate, though not perfectly precise for every individual, is:
Max heart rate (MHR) = 220 − age
For a 40-year-old, that estimates a max heart rate of 180 bpm. This formula has known limitations — actual max HR can vary by 10–20 beats from the estimate depending on genetics and fitness level — but it is a reasonable starting point for setting training zones without lab testing.
| Zone | % of max HR | What it trains |
|---|---|---|
| Zone 1 — Recovery | 50–60% | Active recovery, warm-up, cool-down |
| Zone 2 — Fat burn / aerobic base | 60–70% | Builds aerobic base, mitochondrial density, fat oxidation |
| Zone 3 — Aerobic | 70–80% | Improves cardiovascular efficiency, moderate endurance |
| Zone 4 — Threshold | 80–90% | Raises lactate threshold, race-pace training |
| Zone 5 — Max effort | 90–100% | VO2 max, anaerobic power, short high-intensity intervals |
Zone 2 training — a pace where you can still hold a conversation but are clearly working — builds your aerobic base by increasing mitochondrial density and improving your body’s ability to burn fat as fuel. It is deliberately not exhausting; the effectiveness comes from consistent volume over weeks and months, not single-session intensity.
Endurance athletes often spend 70–80% of total training volume in Zone 2, reserving high-intensity Zone 4–5 work for a smaller portion of weekly training — a ratio sometimes called “polarised training.”
The Karvonen formula adjusts for your individual resting heart rate, which the simple 220-minus-age method ignores entirely:
Target HR = ((Max HR − Resting HR) × %intensity) + Resting HR
This matters because two people with the same max heart rate but very different resting heart rates (say, 50 bpm for a trained athlete vs 75 bpm for a sedentary person) have meaningfully different real training zones despite an identical max HR estimate.
Zones are only as good as the number feeding them, and heart-rate measurement has real quirks worth knowing:
Wrist sensors lag and wobble. Optical wrist sensors are decent at steady efforts but struggle with intervals, cold weather, and anything that flexes the wrist (rowing, lifting). For training that depends on accurate zones, a chest strap remains meaningfully more reliable.
Expect cardiac drift. On long efforts in the heat, heart rate creeps upward at a constant pace as you dehydrate and your body works to cool itself. A run that starts mid–Zone 2 can end in Zone 3 without you speeding up — drifting a little is normal, not a signal to keep slowing forever.
HR lags effort. Heart rate takes 30–90 seconds to respond to a change in intensity, which makes it a poor guide for short intervals — by the time it reads Zone 5, the rep may be over. Use pace or power for short work, and heart rate for steady sessions.
When in doubt, use the talk test. Full sentences comfortably = Zone 2; short phrases = Zone 3–4; single words = Zone 5. It's crude, free, and immune to sensor error.
Heart rate zones turn "how hard am I working" from a feeling into a measurable, trainable target. Calculate your own zones — adjusted for your resting heart rate — with our heart rate calculator.
Common culprits: heat, dehydration, poor sleep, caffeine, stress, or simply running your easy days too fast — the most widespread training error. If easy pace still reads high after slowing down and resting well, mention it to a doctor.
Yes — beta blockers in particular lower both resting and maximum heart rate, making formula-based zones inaccurate. If you take heart-affecting medication, base training on perceived effort or get zones set with medical guidance.
Check them first. Many devices default to percentages of a formula-estimated max. Entering your true resting heart rate and any known max from hard efforts — as the calculator here does — makes the zones noticeably more personal.
Put these numbers into practice with our free calculator — no sign-up required.
Open Heart Rate Calculator