Maximum heart rate came up again in running communities last week: you can't “train” it up, and it declines with age. That's true. But people often draw the wrong practical conclusion from it — that since the maximum depends on age, you can simply calculate it with a formula. A new study from Norway shows what that shortcut costs anyone who trains by heart rate.

What the researchers did

Ausland, Kelemen and Stephen Seiler — one of the architects of the polarised training concept — from the University of Agder (Norway) (Frontiers in Sports and Active Living, April 2026) ran an online survey of endurance athletes around the world.

After implausible answers were filtered out, 4375 people remained: 42% cyclists, 27% runners, 15% triathletes, plus rowers and cross-country skiers.
Average age was 43, with 15 years of training experience and about 10 hours of training a week.
Participants were asked to report the highest heart rate they had ever seen during a maximal effort in training or a race.
This “field” maximum was compared with two classic formulas: Fox (220 − age) and Tanaka (208 − 0.7 × age).

What they found

The average real maximum was 183 beats per minute. The Tanaka formula gave an average of 178, the Fox formula 177.
Both formulas systematically underestimate the maximum: Tanaka by 4.8 beats, Fox by 5.8.
Individual spread is much larger than the average error. For 95% of participants, the Tanaka formula's error fell between −18.5 and +9.1 beats, and Fox's between −20.2 and +8.6.
The link between maximum and age is strong (r = −0.60), but age explains only about a third of the differences between people.
No differences were found between men and women.
The more years of training experience, the lower the maximum (r = −0.34) — but experience is strongly linked to age.
Resting heart rate barely depended on age, but was lower in those who trained more per week (r = −0.23).

An example. A runner is 45. The Fox formula gives 175, Tanaka about 177. If his real maximum is 190 — hardly unusual given this spread — then a “threshold” zone (about 85–90% of maximum) calculated from the formula will be 10–13 beats below the true one. He'll think he's working at threshold, when in fact he's doing a comfortable tempo run.

Why the lab isn't a cure-all either

A treadmill VO₂max test is considered the “gold standard”. But the authors point to a classic study by Ingjer: in a single incremental test, peak heart rate comes out 5–6 beats lower than with a protocol of repeated maximal efforts. A VO₂max test is stopped when oxygen uptake plateaus or the person refuses to continue — not when heart rate has hit its ceiling.

Maximum heart rate is not a constant but the result of a specific protocol: it is affected by warm-up, fatigue, motivation, heat and the sport. On a bike it is usually lower than when running — more in our article on heart rate zones in running and cycling.

Limitations

All data are self-reported. We don't know what device people used to measure heart rate: an optical wrist sensor can “lock on” to cadence instead of heart rate and produce a phantom maximum — this error is covered in our article on cadence lock.
The sample was recruited through social media — motivated, data-minded athletes, not a cross-section of all athletes.
The study is cross-sectional: it cannot tell us whether training changes the maximum itself. The “more years of training — lower maximum” link is almost certainly explained by experienced athletes simply being older.
There are no data on performance or VO₂max, so recreational and high-level athletes cannot be separated.

How to apply this

A formula is a starting point, not the answer. If you train by percentages of your maximum, an error of 10–15 beats shifts every zone.
Check your own data first. Look at your maximums over the last six months in races and hard intervals — but only from a chest strap. A single spike from an optical sensor, especially early in a session, is best discarded.
The field test the authors suggest: a warm-up of 10–30 minutes, then 2–3 maximal efforts of 3–4 minutes, ideally uphill. The highest value you see is your working maximum. Do it rested, not after a hard week.
Safety. Only do a maximal test if you are healthy and already used to intense work. Beginners, people over 40 with risk factors and anyone who experiences chest pain or palpitations should get a medical check-up first.
Re-test every year or two — your maximum slowly declines with age.
An alternative is to base your zones not on your maximum but on your heart rate at the lactate threshold: for most people this is more accurate. You can recalculate your zones in the zones generator.

The bottom line

In 4375 endurance athletes, the “220 − age” and Tanaka formulas underestimate maximum heart rate by an average of 4.8–5.8 beats.
Individual error reaches 15–20 beats low and up to 9 high: enough to mix up your zones.
A lab VO₂max test can also underestimate your maximum by 5–6 beats.
The most reliable method is repeated maximal efforts after a good warm-up, using a chest strap.

Sources: Ausland Å., Kelemen B., Seiler S. “An exploratory study of maximal heart rate determination in endurance athletes: laboratory testing vs. field based”. Frontiers in Sports and Active Living, 2026;8:1806303. DOI: 10.3389/fspor.2026.1806303 · Tanaka H., Monahan K.D., Seals D.R. “Age-predicted maximal heart rate revisited”. Journal of the American College of Cardiology, 2001;37(1):153–156. DOI: 10.1016/S0735-1097(00)01054-8