Finding Your Zones
Maximum heart rate is estimated as 220 minus age, then zones are carved from the reserve between resting and max. The Karvonen method adds resting heart rate back in, personalizing bands for fitter hearts that beat slower at rest.
A 35-year-old with a 62 bpm resting rate gets an aerobic zone of roughly 148–160 bpm — meaningfully different from the cruder percentage-of-max method.
What Each Zone Is For
Zone 1 (50–60%): recovery and warm-up. Zone 2 (60–70%): the aerobic base — fat oxidation, mitochondrial density, and the zone endurance athletes obsess over. Zone 3 (70–80%): steady cardio, sometimes overused as a 'grey zone'.
Zone 4 (80–90%): threshold work that raises sustainable speed. Zone 5 (90–100%): maximal intervals that push VO2 max. The evidence-backed split: ~80% of sessions easy, ~20% hard.
When Zones Lie
Beta blockers and other medications cap heart rate, making zones unusable until adjusted with a clinician. Heat, caffeine, sleep debt, and stress shift heart rate at the same effort.
Fall back on the talk test: Zone 2 is fully conversational, Zone 4 is single sentences, Zone 5 is no talking at all.
Sources
FAQ
What heart rate should I train at?
60–70% of max for most sessions, with 20% of workouts at 80–95% — the 80/20 distribution backed by endurance research.
Is 220 minus age accurate?
It is a population estimate, ±12 bpm for individuals. A lab or field test gives your true max; Karvonen zones soften the error.
Which zone burns the most fat?
Zone 2 burns the highest proportion of fat as fuel, but total calories still decide weight loss — which is why a mix of zones wins.
Important disclaimer: This guide is educational information, not a substitute for professional professional advice. Discuss your individual situation with a qualified professional.