Heart rate zones, explained properly

Where 220 minus age came from

The formula appears in a 1971 review by Fox, Naughton and Haskell on physical activity and the prevention of coronary heart disease. It was offered as a convenient approximation of a trend the authors had observed across a scattering of earlier data sets, and it was not presented with a standard error, a confidence interval or a validation sample. It was a line of best fit sketched for clinical convenience, and it became the most widely repeated number in exercise science largely because it can be done in your head.

The deeper problem is not that the slope is wrong by a little. It is that the slope is wrong in a way that varies systematically with age, so the error is not random noise you can shrug off. Because 220 minus age falls a full beat for every year while the better-fitted equations fall about seven-tenths of a beat, the two lines cross at exactly one age and diverge in both directions from there. That crossing point is age 40, which is precisely why the formula feels reasonable to the middle-aged coaches and clinicians who tested it on themselves.

Tanaka, Monahan and Seals settled the matter in 2001. They pooled group mean maximal heart rates from 351 studies covering 492 groups and 18,712 people, then cross-validated the result in a laboratory study of 514 healthy subjects. The meta-analysis produced 208 minus 0.7 times age; the laboratory data produced 209 minus 0.7 times age. Maximum heart rate correlated with age at r = −0.90, and the regression line did not differ between men and women or between people with wildly different habitual activity levels. Their explicit conclusion was that the conventional formula underestimates maximum heart rate in older adults, which has the effect of understating the physical stress of an exercise test and prescribing training that is easier than intended.

The better-validated alternatives, and what they disagree about

Tanaka is the default on this site because it is the broadest evidence base and because it was cross-validated rather than merely fitted. Gellish and colleagues arrived at almost the same place from a completely different direction in 2007: instead of comparing different people of different ages at one moment, they tracked 132 individuals through 908 maximal exercise tests over 25 years, which removes the risk that a cross-sectional sample is simply comparing two different generations. Their longitudinal model produced 207 minus 0.7 times age, one beat below Tanaka at every age and, more importantly, with the same slope.

The HUNT Fitness Study went further again, measuring maximum heart rate in 3,320 healthy Norwegian men and women in a single population and reporting 211 minus 0.64 times age. It found no interaction with sex, physical activity, maximal oxygen uptake or body mass index, and it confirmed that the older equations underestimate measured values in people over about 30. It also did the thing the 1971 paper never did, and published the scatter: a standard error of estimate of 10.8 beats per minute.

That last number is the one that should change how you use any of these equations. A standard error of 10.8 beats means roughly two people in three sit within 11 beats of the prediction and about one in twenty sits more than 21 beats away. A 45-year-old predicted at 176 could genuinely be anywhere from about 155 to about 197 and still be entirely normal. No amount of choosing a better equation fixes this, because the scatter is between individuals of the same age, not between formulas.

Percentage of maximum against heart rate reserve

There are two ways to turn a maximum heart rate into a target, and they are not interchangeable. The percentage-of-maximum method multiplies your estimated maximum by the intensity you want: 70% of 180 is 126 beats per minute. The heart rate reserve method, published by Karvonen, Kentala and Mustala in 1957, works from the range you actually have available. It subtracts your resting heart rate from your maximum to get the reserve, takes the percentage of that, and adds the resting rate back on.

The arithmetic looks like a detail and behaves like a different scale. For a 40-year-old with a Tanaka maximum of 180 and a resting pulse of 60, the reserve is 120 beats. At 70%, percentage-of-maximum gives 126 while Karvonen gives 144, eighteen beats apart, which is most of a zone. The gap is widest at low intensities and closes to nothing at 100%, because both methods necessarily agree at the top.

Karvonen is the better method for one specific reason: it accounts for the fact that your heart rate cannot go below your resting rate, so the bottom of the scale is anchored to you rather than to zero. A well-trained athlete resting at 45 and an untrained person resting at 75 have quite different amounts of room to work with, and percentage-of-maximum pretends they do not. Using the same 40-year-old maximum of 180, 70% of reserve is 140 beats for the athlete and 149 for the untrained person, which is the right direction: the same relative effort, different absolute pulses.

The practical consequence is that a zone label means nothing until you know which scale produced it. A plan written in percentage-of-maximum terms and executed on a watch configured for heart rate reserve will have you training substantially harder than intended, every session, for as long as nobody notices. Our heart rate zone calculator prints both columns side by side for exactly this reason.

What each zone is physiologically for

The five-zone scheme used here follows the percentage bands in ACSM's Guidelines for Exercise Testing and Prescription, and each band exists because something different is happening to the muscle at that intensity. At the bottom, almost all of the energy is coming from fat oxidation in slow-twitch fibres, the circulatory demand is low, and the session costs you very little to recover from. As intensity climbs, faster fibres are recruited, the proportion of energy coming from carbohydrate rises, and eventually lactate production outruns clearance and the effort becomes self-limiting.

The most common mistake in recreational endurance training is spending the whole week in zone 3. It feels productive, because it is uncomfortable. It is also the one intensity that is too hard to accumulate real volume in and too easy to drive meaningful adaptation at the top end, so a week of it produces fatigue without much of either stimulus. Most published endurance programmes deliberately split time between the bottom two zones and the top two, and treat zone 3 as something you pass through.

Note that the zone boundaries in the table below are conventions, not measured transitions. They are round numbers chosen to be memorable and to sit near the physiological events they describe, which is not the same as being those events.

Why lactate threshold, not a percentage, is the real boundary

The physiological event that actually separates sustainable work from unsustainable work is not a percentage of anything. It is the point at which lactate appears in the blood faster than the body clears it. Below that point an effort can be held for a long time; above it, the clock starts. Faude, Kindermann and Meyer catalogued 25 distinct published lactate threshold concepts in their 2009 review, which tells you both that the boundary is real and that defining it precisely has occupied sports science for half a century.

Their framework describes two useful breakpoints during an incremental test: the intensity at which blood lactate first rises above baseline, and the highest intensity at which lactate production and elimination remain in equilibrium, the maximal lactate steady state. The second of these is the one that matters most for pacing, because it is the physiological definition of the fastest effort you can sustain. Across 32 studies reviewed, lactate thresholds correlated strongly and linearly with actual endurance performance, particularly in running.

The catch for anyone using a watch is that the percentage of maximum heart rate at which these thresholds occur varies enormously between people. In untrained individuals the steady state can sit around 75% of maximum; in well-trained endurance athletes it commonly sits closer to 90%. A zone chart drawn from age alone cannot know which of those you are, so its zone 4 boundary may sit either side of your actual threshold. This is not a flaw in the chart so much as an honest limit of what an age-based estimate can do.

If you want the boundary rather than the proxy, there are three routes. A laboratory incremental test with blood sampling gives it directly. A field test (a 30-minute time trial, with average heart rate over the final 20 minutes taken as an approximation of threshold) gets remarkably close for free. Or you can simply calibrate by feel: threshold is the hardest effort at which your breathing stays rhythmic and controlled, and most people can identify it within a few beats after a couple of attempts.

What moves your heart rate without moving your effort

Heart rate is not a measure of work. It is a measure of the cardiovascular response to work, and a long list of things other than workload can change that response. The most predictable of them is cardiovascular drift: during prolonged steady exercise, stroke volume gradually falls and heart rate rises to compensate, so the same pace costs more beats after 45 minutes than it did after 10. Coyle and González-Alonso's review sets out the mechanism, which involves both the redistribution of blood to the skin for cooling and the fall in plasma volume from sweating.

Heat and dehydration accelerate the same process. Exercising in warm conditions diverts a substantial fraction of cardiac output to the skin, and each percentage point of body mass lost as sweat further reduces plasma volume. The result is a heart rate that can sit 10 to 20 beats above its usual value for the same pace on a hot day, which a zone-driven session will misread as unusually hard work and a pace-driven session will misread as nothing at all.

Then there are the ordinary intrusions. Caffeine raises heart rate modestly in most people. A poor night's sleep, a viral illness, alcohol the evening before, psychological stress, a recent large meal, altitude and the phase of the menstrual cycle all move resting and exercising heart rate by amounts comparable to a whole zone. None of these mean your fitness has changed. They mean the relationship between effort and pulse has shifted for the day.

The rule that follows is simple and slightly deflating for anyone who has bought an expensive watch. When heart rate and perceived effort disagree, believe the effort. A morning where zone 2 pace suddenly requires zone 3 heart rate is a morning to go easier, not a morning to push the pace up until the number matches the plan. And a heart rate that is unusually high at rest for several consecutive days, with no obvious explanation, is worth a conversation with a doctor rather than a training adjustment.

• Cardiovascular drift: up to 10 beats over a long steady session at unchanged pace, from falling stroke volume and plasma volume.
• Heat and humidity: commonly 10–20 beats higher for the same workload, because blood is diverted to the skin for cooling.
• Dehydration: each 1% of body mass lost as sweat reduces plasma volume and pushes heart rate up further.
• Caffeine: a modest but real rise in both resting and exercising heart rate for most people.
• Illness, poor sleep, alcohol and stress: all raise heart rate at rest and during exercise, sometimes by a full zone.
• Altitude: a higher heart rate at every submaximal workload, and a lower true maximum, until acclimatisation.
• Beta blockers and some other medications: a substantially lowered maximum, which makes every age-based zone chart invalid.

How to use zones without fooling yourself

Start by accepting the width of the estimate. Use Tanaka or Gellish rather than 220 minus age, print the zones, and then treat every boundary as plus or minus about ten beats. That sounds like it destroys the point of the exercise, but it does not: the value of zones is in the structure they impose on a training week, and a structure that is approximately right is still worth having.

Second, pick one scale and stay with it. Whether you use percentage of maximum or Karvonen matters far less than using the same one in your plan, your watch and your log. If you know your resting heart rate (measured lying still, first thing, over a full minute, on several mornings), Karvonen is the better choice, and our calculator will show it.

Third, replace the estimate with a measurement as soon as it is worth the trouble. A supervised maximal test is the direct route for anyone who has been cleared for one. A hard hill repeat session with a chest strap will get most healthy, already-fit people within a few beats of their true maximum. A 30-minute time trial gives you the far more useful threshold number. Any of these beats an equation, because all an equation knows about you is your birthday.

Finally, hold the number loosely. The best endurance athletes in the world still use perceived effort as the primary control and heart rate as a cross-check, precisely because the pulse lags the effort, drifts through a session and reacts to heat, sleep and stress. A watch that says you are in zone 2 while your legs say zone 4 is reporting a fact about your circulation, not about your training.

Frequently asked questions

Put it into practice

Run your own numbers through the heart rate zones calculator, the calories burned calculator and the TDEE calculator. Related reading: METs and calories burned, TDEE explained and Estimating a 1RM.

Sources

1. Fox SM 3rd, Naughton JP, Haskell WL. Physical activity and the prevention of coronary heart disease. Ann Clin Res 1971;3:404–32. The origin of 220 minus age. pubmed.ncbi.nlm.nih.gov/4945367/
2. Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol 2001;37:153–6. doi.org/10.1016/S0735-1097(00)01054-8
3. Gellish RL, Goslin BR, Olson RE, McDonald A, Russi GD, Moudgil VK. Longitudinal modeling of the relationship between age and maximal heart rate. Med Sci Sports Exerc 2007;39:822–9. doi.org/10.1097/mss.0b013e31803349c6
4. Nes BM, Janszky I, Wisløff U, Støylen A, Karlsen T. Age-predicted maximal heart rate in healthy subjects: the HUNT Fitness Study. Scand J Med Sci Sports 2013;23:697–704. doi.org/10.1111/j.1600-0838.2012.01445.x
5. Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate: a longitudinal study. Ann Med Exp Biol Fenn 1957;35:307–15. pubmed.ncbi.nlm.nih.gov/13470504/
6. Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Med 2009;39:469–90. doi.org/10.2165/00007256-200939060-00003
7. Coyle EF, González-Alonso J. Cardiovascular drift during prolonged exercise: new perspectives. Exerc Sport Sci Rev 2001;29:88–92. doi.org/10.1097/00003677-200104000-00009
8. Shcherbina A, Mattsson CM, Waggott D, et al. Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. J Pers Med 2017;7:3. doi.org/10.3390/jpm7020003
9. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription, 11th edition. The source of the percentage-of-maximum and heart-rate-reserve intensity bands. acsm.org/education-resources/books/guidelines-exercise-testing-prescription/