Heart Rate Zones in Trail Running: How to Calculate Them

“220 minus age”: where the formula comes from, and what it is worth

180. That’s the maximum number of beats per minute that “220 minus age” predicts for a 40-year-old runner, and the figure plenty of training zones are built on. Now do the math on the error: the standard error of this formula runs from 7 to 11 beats per minute [1] [2]. Our 40-year-old’s true max therefore sits somewhere between 170 and 190, and for roughly one runner in three it lands even further away.

The formula is everywhere anyway. The American Heart Association repeats it, with the caveat that its figures are averages to be taken as a general guide [3]. Its history is shakier than its popularity: in 2002, the physiologists Robert Robergs and Roberto Landwehr traced it back and concluded that it comes from no study, but from observations drawn from about ten references, several of which cite a 1971 text by Fox and Haskell as its origin [1]. Their verdict: it has no scientific basis in exercise physiology. A 2024 review adds that it comes from a group of middle-aged men averaging 55 years old, which explains why it overestimates the max of young adults and underestimates it after 40 [4].

Tanaka, Gellish, Nes: closer to the mark, never exact

Several teams have redone the math using real measurements. Hirofumi Tanaka and his colleagues gathered 351 studies, covering 18,712 people, and arrived at 208 − 0.7 × age, which their laboratory test on 514 healthy adults confirmed (209 − 0.7 × age). The line depends neither on sex nor on activity level [5]. Ralph Gellish followed 132 adults whose 908 maximal exercise tests span 25 years: 207 − 0.7 × age [6]. The Norwegian HUNT study, on 3,320 healthy adults, gives 211 − 0.64 × age, with a standard error of 10.8 beats [2].

At 40, the four formulas give 180, 180, 179 and 185: the gap between them is smaller than the error of any one of them. At 60 it reaches 13 beats (160 against 173), because 220 − age falls faster than the others. The American coach Joe Friel, whose zone methods TrainingPeaks publishes, goes further: in his view, 220 minus age is as likely to be wrong as right [7].

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The five zones on your watch: what they mean

Your watch splits effort into five numbered zones. On Garmin, by default, they cover 50 to 100% of your max in steps of 10%, and the brand describes each zone by how it feels [8]. For a max of 180 beats, that gives:

Not every grid looks alike. The American Heart Association talks of 50 to 70% of your max for moderate effort and 70 to 85% for vigorous effort [3]. The talk test costs nothing and bears those figures out: at moderate intensity you can talk but not sing, while at high intensity you can say only a few words without pausing for breath, sums up the CDC [9].

Why spend time in the low zones? In a review of top endurance athletes, the physiologist Stephen Seiler notes that about 80% of sessions are done at low intensity (blood lactate of about 2 mmol/L at most) and about 20% at high intensity, around 90% of VO2maxThe maximum rate at which the body can use oxygen during effort. [10]. These athletes train 10 to 13 times a week. For the rest of us, I take the proportion from it, not the volume.

The Karvonen method: start from the reserve, not the max

The Karvonen method works out the zones from the heart rate reserveThe gap between max heart rate and resting heart rate: the margin the heart has to speed up., that is, your max minus your resting rate [11]. It’s named after the Finnish physiologist Martti Karvonen, whose 1957 study of how training affects heart rate gave the method its name [12].

Take our 40-year-old, with 180 beats at max and 55 at rest: the reserve is 125. Zone 2, at 60 to 70% of the reserve, runs from 55 + 75 = 130 to 55 + 87.5 ≈ 143 beats. Apply the same percentages to the max and the same zone runs from 108 to 126. Between the two methods the figure shifts by 17 to 22 beats, without the runner having changed.

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The algebra explains the shift: the bound equals percentage × max + (1 − percentage) × resting. Resting therefore carries 40% of the result for the 60% bound and 10% for the 90% bound, then nothing at 100%. To measure it, the American Heart Association advises taking your pulse in the morning, after a good night’s sleep, before getting out of bed [3]. Garmin watches also let you enter a personalized resting rate and choose between zones in bpm, % of max, % of reserve or % of threshold [11].

The threshold method: set your zones from a 30-minute test

The third method is Joe Friel’s: start from the lactate thresholdThe intensity above which the body produces more lactate than it clears; the heart rate at that point is called lactate threshold heart rate, LTHR., rather than from your max [7]. The test comes down to four steps:

1. Warm up, then run for 30 minutes on your own, as if racing, as hard as you can sustain for the whole time, without setting off too fast.
2. Press the watch’s lap button at the 10th minute.
3. At the end, read your average heart rate for the last 20 minutes: it’s an approximation of your threshold heart rate.
4. Enter it in your watch: Garmin lets you set this value, or lets the watch detect it during a run [11].

Friel warns that most people start too fast, then slow down, which skews the result. The test gets better with repetition [7]. His running zones are then calculated as a percentage of that threshold. For a threshold of 165 beats:

On the trail: what the watch does not tell you

On a trail, your pulse doesn’t behave the way it does on a track, and three things will skew your zones if you ignore them.

The lag. At the foot of a climb, heart rate takes a while to catch up with the effort: a watch that still shows zone 2 when you’re already out of breath isn’t broken. On a course that strings climbs and descents together, the average per zone quickly blurs. The km-effort helps you compare races, not set a pulse.

The drift. After 10 to 20 minutes of continuous effort, the volume of blood pumped with each beat gradually falls, and heart rate rises to compensate: this is cardiovascular drift [14]. On a long run, your pulse therefore climbs at a constant pace. Temperature, medication and health matter too, notes the Deutsche Herzstiftung [13].

The descent. Your heart slows down there, but your quads take a pounding: the zone says nothing about muscle wear. The first trail training plan doses these efforts without relying on your pulse.

My advice: on a steep climb, walking briskly beats running in zone 4, and your pulse should be read over a steady minute rather than at a single instant. Garmin also points out that you get more from zones with a dedicated heart rate sensor [8]. For the big picture, the beginner’s guide to trail running is still the place to start.

Which method should you choose?

Whichever method you use, stick with it for a few weeks before judging it: changing your settings on every run makes the zones unreadable. And keep in mind the limit common to all of them: a zone is a convention, not a measurement of your body.

A zone is a range of sensations before it’s a number: if the watch and your breathing disagree, believe your breathing and fix the watch.

Worth watching

Compares several ways to estimate maximum heart rate, including 220 minus age, the Tanaka formula and the Nes formula, and covers the limits of the classic rule.

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Julien de Jurquet

Vans, RVs, biking and calculators

Julien de Jurquet writes for Outfarer about camper vans, RVs, biking, and calculators. He reads manuals cover to cover and never lets a number slide without its unit, so your choices rest on math, not promises.

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