Estimating Maximum Heart Rate
Every zone calculation starts from an estimate of the fastest your heart can beat. The familiar 220 minus age formula has no research pedigree — it was an informal fit to scattered data in the 1970s — but it persists because it is easy to remember.
Formulas
Tanaka: HRmax = 208 − 0.7 × age
Reserve: HRR = HRmax − HRrest
Karvonen target = (HRR × intensity) + HRrest
Tanaka and colleagues derived their equation from a meta-analysis of published studies and it tracks measured maxima more closely, particularly for older adults, where 220 minus age reads too low. Either way, the standard deviation across individuals is around 10 to 12 beats per minute, so treat the number as the centre of a range rather than a hard ceiling.
Why Karvonen Gives Different Numbers
Taking 70% of maximum ignores the fact that your heart never drops below its resting rate. Karvonen works from the reserve — the range you actually have available — and adds your resting rate back on, which shifts every target upward.
The gap is largest for fit people
A trained athlete with a resting rate of 45 has a much larger reserve than someone resting at 75, so the two methods diverge most for them. At 70% intensity the difference can exceed 10 beats per minute.
Measure resting heart rate properly
Take it lying down on waking, before caffeine or standing up, ideally averaged over several mornings. A figure taken sitting at a desk mid-afternoon is typically 10 to 15 beats high and will inflate every Karvonen target.
Consistency matters more than the method
Both approaches are estimates. Pick one, use it for a training block, and track how the same heart rate feels over time — a falling heart rate at a fixed pace is a clearer sign of improving fitness than either calculation.
Training in Zones
Most endurance programmes distribute the majority of training in zones 1 and 2 and reserve a small share for zones 4 and 5. The common failure mode is spending most sessions in zone 3 — too hard to accumulate volume without fatigue, too easy to drive high-intensity adaptation.
Heart rate also lags effort by 30 seconds or more, drifts upward over a long session at constant pace, and rises in heat, at altitude, or when you are dehydrated or under-slept. For short intervals, pace or power is a better guide; heart rate comes into its own for steady work of ten minutes or longer.