Heart Rate Zones: What Do They Actually Mean and Should You Be Using Them?
If you have a smartwatch, fitness tracker, exercise bike, or treadmill, there is a good chance you've been told at some point that you are exercising in a particular heart rate zone.
Zone 1.
Zone 2.
Fat burning.
Cardio.
Threshold.
Peak.
It all sounds very scientific. And heart rate can certainly be a useful way to measure and control exercise intensity. The problem is that we often treat the numbers we are given as far more precise than they actually are.
Your watch might tell you that your maximum heart rate should be 170 beats per minute. You then exercise at 175 and wonder whether something is wrong. Or perhaps you are trying to stay in Zone 2, but your heart rate keeps drifting a few beats above the number on your screen.
Should you slow down? Not necessarily. First, we need to understand where these numbers come from.
What is heart rate?
Heart rate is simply the number of times your heart beats each minute. At rest, your body's demand for oxygen and energy is relatively low, so your heart does not need to work particularly hard. Start exercising, and things change.
Your working muscles require more oxygen and nutrients, and carbon dioxide and other metabolic products need to be transported away. One of the ways your cardiovascular system responds is by increasing heart rate. Generally speaking, as exercise intensity increases, heart rate increases with it.
That gives us something extremely useful. A relatively simple way of estimating how hard the cardiovascular system is working.
What are heart rate zones?
Heart rate zones divide exercise intensity into different ranges. There are several systems available, which is partly why people become confused. One of the most commonly used approaches divides exercise into five zones based on a percentage of maximum heart rate.
A typical five zone system might look something like this:
Zone 1: approximately 50 to 60% of maximum heart rate: Very light exercise. This could include gentle walking, very easy cycling, warm ups and recovery sessions. You should be able to breathe comfortably and have a normal conversation.
Zone 2: approximately 60 to 70%: Light to moderate aerobic exercise. You are working, but the intensity should feel sustainable. Conversation should still be possible, although you may notice your breathing becoming deeper. This is the zone that has received a huge amount of attention recently.
Zone 3: approximately 70 to 80%: Moderate to moderately hard exercise. Breathing becomes noticeably harder and conversation becomes more difficult.
Zone 4: approximately 80 to 90%: Hard exercise. This is approaching or moving around the intensities associated with lactate threshold for many people, although an individual's physiological thresholds do not necessarily correspond neatly with generic percentage-based zones. You will normally only be able to speak a few words at a time.
Zone 5: approximately 90 to 100%: Very hard to maximal exercise. This intensity is associated with hard intervals, sprints, and maximal efforts. It cannot normally be maintained for very long.
The exact percentages vary between systems, so don't be surprised if your Garmin, Apple Watch, Polar monitor, exercise bike, and personal trainer give you slightly different zones. That does not necessarily mean one of them is wrong. It simply means they may be using different methods.
What is maximum heart rate?
Maximum heart rate, or HRmax, is approximately the highest heart rate your cardiovascular system can achieve during maximal exercise. And this is where things start getting interesting.
Most people have probably heard this formula: Maximum heart rate = 220 minus your age
So if you are 50: 220 minus 50 = 170 beats per minute. Your estimated maximum heart rate would therefore be 170 bpm.
Simple, right? Unfortunately, human physiology rarely behaves quite that neatly.
Where did 220 minus age come from?
The 220 minus age equation became popular because it is easy to remember and calculate. But it should never be regarded as an accurate prediction of every individual's maximum heart rate.
Research examining measured maximum heart rates has repeatedly demonstrated considerable individual variation around age-based predictions.
One of the most influential studies was published by Tanaka and colleagues in 2001. The researchers analysed data from 351 studies involving 18,712 participants and then cross-validated their findings using laboratory exercise testing.
They proposed a different equation: HRmax = 208 minus (0.7 × age)
For a 50-year-old: 208 minus 35 = 173 bpm. So we already have a three-beat difference compared with 220 minus age.
For a 70-year-old: 220 minus age predicts 150 bpm. The Tanaka equation predicts: 208 minus 49 = 159 bpm. Now we have a nine-beat difference.
Tanaka and colleagues concluded that the traditional equation could underestimate maximum heart rate in older adults.¹ But there is another important point. The Tanaka equation is still an estimate. It is not a measurement.
Your maximum heart rate might be considerably higher or lower
This is probably the most important part of this article. An equation describes what tends to happen across a population. It does not necessarily describe you.
Imagine measuring thousands of people and plotting their maximum heart rates against their ages. You would see a general trend. Maximum heart rate tends to decrease as we get older. But you would not see every 50-year-old producing exactly the same maximum heart rate.
Far from it. Some would be considerably higher. Others would be considerably lower.
Research from the HERITAGE Family Study compared measured maximum heart rates with both the 220 minus age and Tanaka equations in 762 adults. The standard error of estimate was approximately 12 beats per minute for the traditional equation and 11 beats per minute for the Tanaka equation.²
That represents substantial individual variation.
Another study comparing nine different age-predicted equations with maximum heart rates actually measured during treadmill testing found wide limits of agreement for all nine equations. The researchers concluded that the equations demonstrated poor agreement when predicting maximum heart rate at an individual level.³
That does not make the equations useless. It simply tells us what they are… Estimates.
Why can my maximum heart rate be higher than predicted?
Because the equation is predicting an average relationship between age and heart rate. You are not an average.
Imagine a 55-year-old whose formula predicts a maximum heart rate of approximately 165 bpm. During genuinely hard exercise, they might repeatedly record 175 bpm. That does not automatically mean they are exercising beyond some dangerous physiological limit. It may simply mean their actual maximum heart rate is higher than the population-based prediction.
Research in recreational marathon runners, football players and other physically active populations has demonstrated differences between measured and predicted maximum heart rates.⁴ ⁵
The opposite can also happen. Someone's actual maximum might be substantially lower than predicted. This becomes particularly important when we use percentages of maximum heart rate to prescribe exercise.
Why getting maximum heart rate wrong changes all your zones
Suppose we have a 50-year-old. Using 220 minus age: Maximum heart rate = 170 bpm
Using 60 to 70% as our example Zone 2, Zone 2 would be approximately: 102 to 119 bpm
But imagine laboratory testing shows that this person's actual maximum is 185 bpm. Their equivalent range becomes: 111 to 130 bpm
That is a considerable difference. The person could therefore be exercising at 125 bpm, and their watch might tell them they have left Zone 2. But if their real maximum heart rate is 185, that conclusion may be wrong. The reverse is equally important.
If the formula overestimates your maximum heart rate, your prescribed zones may be too high. You could find yourself working much harder than intended simply because the calculation was wrong. This is why I would be cautious about treating automatically generated heart rate zones as absolute physiological boundaries.
Can we calculate heart rate zones more accurately?
There are several options. One is to use a better estimate of maximum heart rate, such as the Tanaka equation:
208 minus (0.7 × age)
Research generally suggests this performs better than 220 minus age in many adult populations, although again it cannot precisely predict every individual.¹ ²
Another option is to use heart rate reserve. This accounts for resting heart rate as well as maximum heart rate.
The calculation is: Heart rate reserve = maximum heart rate minus resting heart rate. We can then prescribe exercise using a percentage of that reserve.
For example: Target heart rate = resting heart rate + (heart rate reserve × desired intensity). Suppose your resting heart rate is 60 and your maximum is 180. Your heart rate reserve is: 180 minus 60 = 120
If we wanted 70% of heart rate reserve: 120 × 0.70 = 84
Then add resting heart rate: 84 + 60 = 144 bpm
This approach recognises that two people with the same maximum heart rate may have very different resting heart rates and cardiovascular profiles.
What about measuring maximum heart rate properly?
If you genuinely need accurate heart rate zones, measuring rather than predicting maximum heart rate is clearly preferable.
A cardiopulmonary exercise test, often called a CPET, performed under appropriate professional supervision can measure your physiological response to progressively harder exercise.
For athletes, properly designed maximal field or laboratory testing can also provide useful information.
But this is important: Not everybody needs to perform a maximal heart rate test.
If you are new to exercise, have cardiovascular disease, experience chest pain, dizziness or unusual breathlessness, take medication that affects heart rate, or have other relevant medical conditions, attempting to discover your maximum heart rate by simply exercising as hard as possible is not something I would recommend without appropriate medical or professional guidance.
For most recreational exercisers, we have other perfectly useful tools.
Do I even need to know my exact maximum heart rate?
Probably not. Unless you are training for a particular performance goal, there is a danger of turning exercise into a maths lesson.
Heart rate is useful. But so is simply paying attention to how exercise feels. One of the easiest methods is the talk test.
At lower aerobic intensities you should generally be able to hold a conversation. As intensity increases, talking becomes progressively more difficult. At very high intensities you may only be capable of saying a few words.
You can also use Rating of Perceived Exertion, usually abbreviated to RPE. On a simple 1 to 10 scale:
1 or 2 feels extremely easy.
3 or 4 feels comfortable.
5 or 6 feels moderately hard.
7 or 8 feels hard.
9 is very hard.
10 is maximal.
Combine RPE with heart rate and you suddenly have much more useful information than either measure provides alone.
Why has Zone 2 become so popular?
Zone 2 training has become something of a fitness buzzword. But low- to moderate-intensity aerobic training certainly is not new. Endurance athletes have used large volumes of relatively easy aerobic training for decades.
The attraction is straightforward. You can accumulate a significant amount of cardiovascular exercise without the fatigue of constantly training at high intensity.
This type of training can help develop aerobic fitness and improve the body's ability to produce energy aerobically. It can also be sustainable. And that matters.
If every cardiovascular workout feels like a near-death experience, there is a reasonable chance you will eventually stop doing it. Not every workout needs to destroy you.
Does that mean Zone 2 is the best exercise?
No. This is where fitness advice often goes wrong. Something useful becomes popular, and suddenly it becomes the only thing anyone should be doing.
Different intensities produce different training demands. Lower-intensity exercise lets you do more total work with less fatigue. Moderate intensity exercise can provide an excellent cardiovascular stimulus. Higher intensity intervals can improve aerobic capacity and performance while requiring considerably less total exercise time. And walking is enormously valuable simply because it is accessible and easy to recover from.
You do not have to choose one. A sensible programme can contain several intensities.
How I would use heart rate zones in practice
Rather than obsessing about individual beats per minute, I would use heart rate as one part of a bigger picture.
For an easier aerobic session, choose an intensity where your heart rate settles into a relatively stable range, and you can still hold a conversation.
For moderate cardiovascular training, increase the intensity so your breathing becomes more noticeable but stays controlled.
For interval training, use periods of harder work followed by sufficient recovery.
And watch what happens over time. This is where heart rate becomes particularly useful. Perhaps you normally cycle at 150 watts with a heart rate of 145 bpm. After several months of consistent training, you can produce the same 150 watts at 135 bpm. Or perhaps you can now produce 170 watts while maintaining the same 145 bpm heart rate.
That tells us something useful about how your fitness is developing.
Do not forget that heart rate changes from day to day
Even if your zones are accurately calculated, your heart rate will not behave identically every day. It can be influenced by things including:
Sleep
Temperature
Hydration
Caffeine
Stress
Illness
Fatigue
Medication
Training status
The type of exercise you are performing
Your heart rate during cycling may also behave differently from your heart rate during running. So if your normal easy run suddenly produces a heart rate ten beats higher than usual, that information can be useful. But it doesn't necessarily mean your fitness disappeared overnight.
Look at the bigger picture.
What about smartwatches?
Modern wearable devices are incredibly useful. They allow ordinary people to collect physiological information that would once have required specialist equipment. But again, do not confuse useful with perfect.
Optical wrist-based heart rate monitors can perform well during steady exercise, but accuracy can vary depending on the activity, intensity, movement and device. If accurate exercise heart rate is particularly important to you, a good quality chest strap will generally give more reliable readings during training.
For most people, however, I would rather see a smartwatch used as a tool to encourage regular exercise than have someone worry because today's Zone 2 session averaged three beats per minute more than yesterday's.
The takeaway
Heart rate zones can be an excellent tool. They can help control exercise intensity, prevent every workout from becoming unnecessarily hard, structure interval training and monitor changes in cardiovascular fitness. But you need to understand them properly.
Your maximum heart rate is not automatically 220 minus your age. That estimate is based on population averages.
The Tanaka equation - 208 minus (0.7 × age) - may provide a better estimate for many adults, but it is still an estimate.
Research shows considerable individual variation between predicted and measured maximum heart rates. Your real maximum could therefore be noticeably higher or lower than the number your watch gives you.
And if your maximum heart rate is wrong, every training zone calculated from it will be wrong too. So use the numbers. But do not become a slave to them. Combine heart rate with breathing, the talk test, perceived exertion and how you actually feel.
Look at trends rather than individual readings. And remember that the ultimate purpose of monitoring your heart rate is not to produce beautiful graphs on your phone. It is to help you train appropriately, consistently and progressively.
Because ultimately, the best heart rate zone is only useful if it helps you exercise.
Alan Griffin
Griffin Fit Personal Training
References
Tanaka H, Monahan KD, Seals DR. Age predicted maximal heart rate revisited. Journal of the American College of Cardiology. 2001;37(1):153 to 156. The authors analysed data from 351 studies involving 18,712 participants and proposed the equation HRmax = 208 minus (0.7 × age).
Sarzynski MA, Rankinen T, Earnest CP, et al. Measured maximal heart rates compared to commonly used age-based prediction equations in the HERITAGE Family Study. American Journal of Human Biology. 2013;25(5):695 to 701. This study reported standard errors of estimate of 12.4 bpm for 220 minus age and 11.4 bpm for the Tanaka equation, demonstrating substantial individual variation.
Shookster D, Lindsey B, Cortes N, Martin JR. Accuracy of commonly used age predicted maximal heart rate equations. International Journal of Exercise Science. 2020;13(7):1242 to 1250. Comparison of nine prediction equations found wide limits of agreement between predicted and measured HRmax.
Nikolaidis PT, Rosemann T, Knechtle B. Age predicted maximal heart rate in recreational marathon runners: a cross sectional study on Fox's and Tanaka's equations. Frontiers in Physiology. 2018;9:226. The study compared predicted and measured HRmax in 180 recreational marathon runners.
Nikolaidis PT. Maximal heart rate in soccer players: measured versus age predicted. Biomedical Journal. 2015;38(1):84 to 89. Measured maximum heart rate differed from values predicted using both Fox and Tanaka equations in competitive football players.
Shargal E, Kislev Cohen R, Zigel L, Epstein S, Pilz Burstein R, Tenenbaum G. Age related maximal heart rate: examination and refinement of prediction equations. Journal of Sports Medicine and Physical Fitness. 2015;55(10):1207 to 1218. Analysis of more than 28,000 maximal stress tests produced HRmax prediction equations while also demonstrating the relationship between age and maximum heart rate.
Roy S, McCrory J. Validation of maximal heart rate prediction equations based on sex and physical activity status. International Journal of Exercise Science. 2015;8(4):318 to 330. The Tanaka equation produced smaller prediction errors than the traditional 220 minus age equation in the population studied.
Lach J, Wiecha S, Śliż D, et al. HR Max prediction based on age, body composition, fitness level, testing modality and sex in physically active population. Frontiers in Physiology. 2021;12:695950. The study found that commonly used prediction equations varied in precision across different groups and that the traditional 220 minus age equation could produce meaningful errors.
Brawner CA, Ehrman JK, et al. Research into maximum heart rate prediction continues to demonstrate that population equations cannot precisely determine individual HRmax. More recent work using additional variables such as resting heart rate, body measurements and blood pressure has improved prediction compared with simple age based formulas, but direct measurement remains preferable when accurate HRmax is clinically or athletically important.