Two runners, same age, same maximum heart rate, get handed the same zone chart — and for one of them the chart is simply wrong. The difference is resting heart rate, and it is exactly what the Karvonen method accounts for and the simple percentage method ignores. This article works through both systems with the same athlete, shows where the numbers diverge, and helps you decide which one your training should obey.
Both systems also share an ancestor problem worth naming: they were designed around laboratory populations — young, male, trained — and exported to everyone. The formulas have been re-validated broadly since, but the episode is a good reminder that a zone chart is a map drawn from other people’s terrain.
The two formulas
The simple system slices maximum heart rate into bands: Zone 2 at 60–70% of max, and so on. The Karvonen system, published by Finnish researcher Martti Karvonen in 1957, slices the heart-rate reserve — the gap between resting and maximum — and adds resting back: target = resting + percentage × (max − resting). Both systems use the same zones on paper. They diverge because a percentage of the whole range is not the same as the same percentage of the usable range, whenever resting rate is well above zero — which is always.
Key takeaways
- Percentage-of-max ignores resting heart rate
- Karvonen zones sit higher for fit, low-resting-HR runners
- The fitter you are, the more the simple chart undercooks your zones
One athlete, two charts
Take a 38-year-old with a maximum of 182 and a resting rate of 52. Percentage-of-max puts Zone 2 at 109–127 bpm. Karvonen, working from a reserve of 130, puts it at 130–143. Those are different workouts: the simple chart has her jogging at the top of recovery while the Karvonen chart has her at genuine endurance effort. Now give the same age a resting rate of 74: the two systems nearly converge (reserve 108; Zone 2 ≈ 139–150 by Karvonen versus 109–127 by percentage — still apart, but the practical gap narrows differently across zones). The divergence grows precisely with fitness, which is why trained runners grumble that generic charts feel too easy.
| Athlete | Resting HR | Zone 2 (of max) | Zone 2 (Karvonen) |
|---|---|---|---|
| Fit runner | 52 bpm | 109–127 | 130–143 |
| Beginner | 74 bpm | 109–127 | 139–150 |
Which one, when
Karvonen deserves your trust if you know two things honestly: a real resting heart rate (measured in bed across several mornings, not glanced at a watch at your desk) and a defensible maximum. It personalises zones to the engine you have. The percentage method wins on simplicity and on days when inputs are shaky — and both methods lose to a measured maximum from a hard race or test, which beats every formula. This site’s zone calculator runs both systems on your numbers so the difference is visible rather than theoretical.
Resting heart rate: the number that moves
Resting heart rate is not a fixed trait; it is a slow weather report on your life. Aerobic training lowers it over months — five to fifteen beats across a year of consistent work is common — while illness, poor sleep, alcohol, heat and accumulated fatigue raise it, sometimes overnight. That mobility is precisely what makes Karvonen zones alive: recalculated with a current resting figure, the zones track the athlete’s development automatically. It is also the method’s trap. A resting rate captured during a stressful, under-slept week inflates the reserve calculation and pushes every zone too high; the fix is boring and essential — a rolling average of calm mornings, updated when life genuinely changes gear.
Many watches now estimate resting rate continuously. Their figures are serviceable for this purpose if they sample sleep, and questionable if they sample your desk.
Zones drift within a single workout
Even with perfect boundaries, heart rate is a lagging, drifting instrument. It takes a minute or more to respond to a pace change, so interval training by heart rate alone chases its own tail; and across a long run at constant pace, heart rate creeps upward — cardiovascular drift — as dehydration and heat accumulate, typically 5–10 beats over two hours. The zone did not change; the cost of the pace did, which is arguably the heart rate doing its job honestly. Runners who understand drift stop treating a rising heart rate at even pace as a malfunction, and start reading it as the session’s true price arriving.
This is also why the zone calculator and the training pace calculator belong together: pace sets the target, heart rate audits it, and neither is believed alone on a hot day.
A worked week under both systems
Take the athlete from this article — max 182, resting 52 — and schedule her Wednesday: forty minutes of Zone 2. By the percentage method she runs at 109–127 bpm, a pace she describes as ‘barely running’. By Karvonen she runs at 130–143, a pace she describes as ‘properly easy’. Now measure the training effect over a season: the Karvonen runner accumulates hundreds of kilometres at genuine endurance intensity; the percentage runner accumulates them at recovery intensity and plates her threshold work on top, wondering why progress stalls. This is not a rounding error; method choice, compounded over months, is a training programme in itself.
The symmetric error exists for the beginner with resting 74 using a Karvonen chart carelessly set from a wrist-watch ‘resting’ figure recorded at his desk (say 61, flattered by sitting): his zones inflate beyond his fitness and Zone 2 becomes tempo. Both errors have the same cure — honest inputs, the talk test as referee — which is why this site’s zone page prints both systems side by side: disagreement between them is itself information about your inputs.
The talk test, the oldest validator
Before chest straps there was conversation. Recovery and endurance efforts allow full sentences; tempo allows phrases; threshold allows a few words; maximal effort allows none. When your zones and your speech disagree, believe your speech and re-measure your resting rate — the commonest cause of zone nonsense is a resting figure recorded during a stressful week and then treated as permanent physiology.
Common mistakes
- Using a desk-bound ‘resting’ heart rate in the Karvonen formula
- Trusting 220 − age to the beat when it carries a ±10 bpm spread
- Running Zone 2 by heart rate on a hot day and calling the slower pace lost fitness
Questions this raises
If it uses percentage of an age-estimated max, its zones are the simple system with all its caveats. Most watches let you enter a measured max or resting rate; doing so meaningfully improves them.
Heart rate rises with temperature and dehydration at any given pace. The zones are still describing your cardiovascular load honestly — it is the pace that must yield.
Put a number on it.
Two ways to draw the same five zones can disagree by ten beats. Here is the reserve method, the simple method, and the resting heart rate that decides between them.
Open the Heart Rate Zone Calculator