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Using The Karvonen Formula To Optimise Heart Rate Training Zones

Heart rate training zones provide a very accessible and effective way to measure, monitor, and assess how hard you are training. Think of them as a way to quantify the physiological stress of exercise.

Essentially, they allow you to monitor and control your exercise intensity by keeping your heart rate within specific training zones. 

Heart rate training is something I was first introduced to way back in the 90s — long before gps watches, power meters, and the plethora of fitness tech that’s now flooded the market. At the time it seemed like a giant leap forwards from just recording running time on my stop watch, or lap times during track interval running workouts. Whilst fitness tech has moved on in leaps and bounds, heart rate monitors have held strong as one of the most valuable additions to any fitness training program. They’re also now built into many fitness watches — Apple, Garmin, Polar, Fitbit, etc.

In this article, we take a look at:

  • Why heart rate monitors are one of the best ways to monitor intensity
  • How to work out your heart rate zones — percentage of maximum heart rate vs the Karvonen Formula method
  • The surprising difference between the two methods
  • Why the Karvonen Formula method is better
  • Extra considerations with heart rate monitoring

Why Use Heart Rate Training Zones?

Whilst there are several ways to monitor exercise intensity — heart rate, speed, pace, power, perceived effort and even muscle oxygen saturation — heart rate has several major advantages.

1. Heart rate chest monitors have very high accuracy

First, it’s one of the most accurate measures of intensity: heart rate chest straps, such as those provided by Garmin and Polar, are research proven to provide a top level of accuracy. And even in the early days they were considered comparable to clinical heart rate monitoring.

One point to note: this is less true for some wrist based heart rate monitors.

While these can be accurate during activities like cycling or walking, they’re pretty hit and miss during more dynamic activities like running. In fact, any activities where there’s increased arm movement. Personally, I’ve had mixed results with these, especially during interval workouts.

That said, some wrist based heart rate monitors — like the Apple Watch — have proved to have a high level of accuracy.

A recent study (1) comparing the Polar H7 Chest Strap with several wrist based heart sensors found the Polar H7 to have the best heart rate accuracy. Whilst, the wrist watches had reduced accuracy the Apple Watch demonstrated a high level of accuracy. The researchers concluded that for endurance athletes a chest based heart rate monitor or the Apple Watch provided the best accuracy.

2. Heart rate provides a measure of physiological stress

Second, heart rate provides a direct measure of your physiological stress, making it very useful when other measures of work intensity are less effective. As an example controlling intensity by power can be extremely useful for maintaining a consistent work rate, but it doesn’t account for changes in physiological stress — changing temperatures and even day to daily variations in your own physiological condition (illness, tiredness, stress etc) can all affect this. In contrast, heart rate provides a measure of physiological stress rather than a measure of your work rate (power, speed, etc).

By monitoring heart rate, you can adjust work rate to take account of increased physiological stress such as when heart rate is higher due to increasing temperatures, stress, fatigue, illness, etc.


What are Heart Rate Training Zones?

So, we’ve seen that heart rate training zones can be useful for monitoring and controlling exercise intensity, but what are they?… Put simply, they’re a way of quantifying exercise intensity by relating intensity to specific heart rate zones. Whilst there are a few different ways to define heart rate zones, we’re going to examine the two most common approaches and consider the benefits of each approach.

The first approach is to set heart rate based on a percentage of maximum heart rate.

Percentage of Maximum Heart rate

At the most basic level, we can define intensity based on a percentage of your maximum heart rate. 

The advantage here is that it’s very straightforward — you simply multiply your maximum heart rate by a given percentage. For example to find 70% of your maximum you multiply your maximum heart rate by 0.7.

Ideally, we base this on your actual maximum heart rate. However, we can predict this based on the following formula (2):

Maximum heart rate = 220 – your age. 

While this provides a reasonable level of accuracy, this is based on population averages, and there can be wide individual variation.

Another factor here is that this is less accurate amongst lifelong athletes, who typically record maximum heart rate values above age predicted values. There are some additional formulas — which we won’t look at here — that provide a better prediction of maximum heart rate for certain populations (lifelong athletes, over 40s, etc). However, if you’re an athlete or seriously into your fitness, you’ll likely have a good idea of what your maximum heart rate is.

So, once you know (or have estimated) your maximum heart rate (HRMax), you can then work out heart rate training zones based on percentages of your maximum.


Five Heart Rate Training Zones

Below are the five most commonly described training zones – used by Polar, Garmin etc – based on HRMax:

  • Zone 1 (Very light/Recovery) = 50-60% of HRMax
  • Zone 2 (Light/Easy) = 60-70% of HRMax
  • Zone 3 (Moderate) = 70-80% of HRMax
  • Zone 4 (Hard) = 80-90% of HRMax
  • Zone 5 (Maximum) = 90-100% of HRMax

Negatives with this method

Whilst these zones can be useful, by basing intensity solely on maximum heart rate, there are a few drawbacks:

1. It doesn’t account for individual differences

First, it doesn’t consider your resting heart rate, so it doesn’t account for individual differences in fitness and conditioning.

In particular, this doesn’t consider the range of your working heart — the difference between your resting and maximum heart rate — we’ll look at this shortly.

2. The heart rate zones are wide

Second, when we use this method, the heart rate zones are wide. As an example, if you have a maximum heart rate of 200bpm then each zone covers a range of 20bpm.

If we take Zone 3 as an example: there’s a big difference between exercising at 70% HR max and 80% HRmax — 140 vs 160bpm — yet it’s all classed as moderate intensity.

3. The Heart rate zones don’t always match the true intensity

Another factor here: if you’re highly trained with a great level of aerobic conditioning, then these zones don’t always match the described intensity. Let’s take zone 1 as an example — described as very light/recovery. Most endurance athletes, or anyone with a good level of aerobic fitness, would likely find 50-60% of heart rate max too easy, even for recovery training. And, in reality, if you’ve got excellent aerobic fitness, then 60-70% of HR max is more in line with the recovery intensity of well-trained athletes.

At the other end of the spectrum — someone with a high resting heart rate would find that zone 1 is barely above their resting heart rate.

So, how can we improve on this?… We can make the training zones more specific by also taking account of resting heart rate.


Karvonen Formula

With this method we calculate the training zones from the percentages of heart rate reserve. 

What is heart rate reserve?

This is the amount that your heart rate can rise from your resting heart rate to your maximum.

Heart Rate Reserve (HRR) = Maximum HR – Resting HR

You can find your resting heart rate by measuring this first thing in the morning.

To find your heart rate reserve, you simply subtract your resting heart rate from your maximum heart rate.

Then to work out your training zones you multiply your heart rate reserve by the given percentage (70, 80, 90% etc) and then add back on your resting heart rate. 

Karvonen Formula Calculation

Karvonen formula calculation: Target Heart Rate Training Zone = Resting HR + ( % Intensity x [maximum HR – resting HR]).

Karvonen formula example:

  • Maximum heart rate = 200bpm
  • Resting heart rate = 50bpm
  • Calculate the 70% target heart rate

First determine the heart rate reserve: Maximum heart rate – resting heart rate

In this example 200bpm – 50bpm = 150bpm.

Second, you then multiply heart rate reserve by the percentage intensity.

So, to find the 70% range:

First you change 70% to a decimal (0.7), then you multiply 150 by 0.7 which equals 106bpm.

Finally, you add back on your resting heart rate to find your 70% heart rate training intensity: 106 + 50 = 156bpm.


Karvonen Formula vs Percentage of Heart Rate Max

So, how do the two methods compare?… Let’s start by comparing the percent heart rate max against the Karvonen formula using two examples. Here we’re going to consider:

  • An elite athlete with a low resting heart rate (40bpm)
  • Someone with a healthy resting heart rate (60bpm)
  • In each case they have a maximum heart rate of 200bpm

Here I’ve calculated the zones for each and put this in graphical form to really highlight just how big a difference there is.

Note the difference between the percent heart rate max method and Karvonen method for the individual with a resting heart rate of 60bpm!

Karvonen Formula vs percentage of maximum heart rate
Intensity Percentage
Maximum
Heart Rate
MHR = 200bpm
Karvonen
Formula
MHR = 200bpm
RHR = 40bpm
Karvonen
Formula
MHR = 200bpm
RHR = 60bpm
50-60%  100-120bpm 120-136bpm 130-144bpm
60-70% 120-140bpm 136-152bpm 144-158bpm
70-80% 140-160bpm 152-168bpm 158-172bpm
80-90% 160-180bpm 168-184bpm 172-186bpm
90-100% 180-200bpm 184-200bpm 186-200bpm

What can we take from this?

So, the first point here is that by using the percent of heart rate max method, the training zones would be identical regardless of resting heart rate. 

Second, whether you have a high or low resting heart rate, the Karvonen Heart rate training zones are higher than the %HRmax zones.

Third, individuals with a smaller heart rate reserve (higher resting heart rate) have to reach higher heart rates for each of the training zones. Why is that?… Put simply, because they have a higher resting heart rate, their exercising heart rate needs to be higher to achieve a desirable increase above resting.

From this you can see just how significant the difference is between the standard heart rate zones method (used by many fitness trackers) and the more effective Karvonen formula.

One point to note here: whilst the Karvonen Formula tends to be more effective for lower intensity training zones (Zone 1, Zone 2), careful attention needs to be placed on higher intensities. If we look at the examples above zone 4 and zone 5 heart rates are higher for the individual with a higher resting heart rate. In reality a highly trained athlete with a low resting heart rate will find it a lot easier to sustain a higher percentage of maximum heart rate.


To sum this up…

To sum this up, heart rate monitoring is an excellent way to measure and control training intensity. And allows you to adjust training intensity to account for changes in physiological stress. However, to get the most from this we need to account for individual differences in fitness and conditioning. Compared with using percentages of maximum heart rate, the Karvonen formula provides a much more effective method for quantifying intensity.

One final point here: basing intensity around a percentage of heart rate — whether it’s maximum heart rate or the Karvonen formula — is useful, however it’s important to recognise that this doesn’t always equate to the same relative intensity in different individuals. As mentioned, a well trained athlete could sustain a high percentage of maximum heart rate for considerably longer than someone who is less well-trained. For this reason, heart rate zone percentages often need adjusting based on an individuals fitness level. In particular, careful attention needs to be paid to higher intensity training zones.

One effective approach for well trained athletes, is to establish heart rate training zones based on your lactate threshold. This is particular useful for optimising training and reducing the risk of overtraining.

You can read more about this method on the following page: aerobic base training

Next time out we’ll take a closer look at the different heart rate zones you can use in your own training.

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References

  1. Pasadyn SR, Soudan M, Gillinov M, et al. Accuracy of commercially available heart rate monitors in athletes: a prospective study. Cardiovasc Diagn Ther. 2019;9(4):379-385. doi:10.21037/cdt.2019.06.05
  2. Fox 3rd, S. M., Naughton, J. P., & Haskell, W. L. (1971). Physical activity and the prevention of coronary heart disease. Annals of clinical research3(6), 404-432.