Effective training control in the endurance domain takes into account heart rate, exercise duration and your subjective sense of effort.
Dividing training into zones based on the maximum heart rate is a proven, practical and entirely sensible method – especially in endurance training.
However, anyone who wants to make their training control even more individual can go a step further. This is exactly where the Karvonen formula comes into play.
It does not replace the previous considerations; rather, it builds on them and makes them more individual.
From maximum heart rate to heart rate reserve
Training intensity is often given as a percentage of the maximum heart rate.
For example: training at 70–80 % of HRmax.
This method is based on the individual upper performance limit and allows structured load planning.
The Karvonen formula supplements this approach with an additional physiological variable: the heart rate reserve.
Here it is important to distinguish:
The heart rate reserve describes the difference between maximum heart rate and resting heart rate:
Heart rate reserve = HRmax – HRrest
The Karvonen formula is then the calculation model that uses precisely this reserve to determine training zones.
Put differently: the heart rate reserve is the foundation – the Karvonen formula is the tool.
Why the resting heart rate makes a difference
Two people can have the same maximum heart rate of, for example, 190 bpm – and yet be loaded differently at the same training heart rate.
The difference often lies in the resting heart rate.
Example:
Person A
- HRmax: 190 bpm
- HRrest: 50 bpm
Person B
- HRmax: 190 bpm
- HRrest: 75 bpm
Although both have the same HRmax, their heart rate reserve differs markedly.
Person A has a larger “working range” in which the heart can increase its performance.
As training progress advances, this difference becomes even more significant: in adulthood the maximum heart rate barely changes and tends to decrease over the years, while the resting heart rate adapts markedly through regular endurance training and usually falls. Precisely in well-trained people, taking the HRrest into account therefore plays a central role in precise training control.
If one worked exclusively with percentages of the maximum heart rate, this difference would remain unaccounted for.
This is exactly where the Karvonen formula comes in.
The Karvonen formula in practice
The calculation is as follows:
Training pulse = (heart rate reserve × intensity factor) + resting heart rate
The intensity factor corresponds to the desired training zone, for example 0.70 for 70 % intensity.
Calculation example
Assume:
- HRmax: 195 bpm
- HRrest: 60 bpm
Heart rate reserve: 195 – 60 = 135 bpm
Training at 70 % intensity:
135 × 0.70 = 94.5 94.5 + 60 ≈ 155 bpm
For comparison: 70 % of 195 would be 136 bpm.
The difference of almost 20 beats per minute can be relevant in training practice – especially in base training or for ambitious goals.
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Physiological background
The resting heart rate is an indirect marker of training status and the efficiency of the cardiovascular system.
A low resting pulse often goes hand in hand with:
- a higher stroke volume
- improved cardiac economy
- stronger parasympathetic regulation
When this baseline value is integrated into the training calculation, a more realistic picture of the relative load emerges.
The Karvonen formula thus takes into account not only the performance limit, but also the individual starting point of the system.
For whom is the Karvonen formula particularly useful?
For many health-oriented trainees, percentages of the maximum heart rate are entirely sufficient.
The Karvonen formula becomes particularly interesting when:
- training zones are to be controlled very precisely
- performance development is planned systematically
- there are large differences in resting heart rate
- training is periodised and built up over the long term
It allows a finer gradation – particularly in the lower and middle intensity range.
Despite precision, interpretation remains decisive
As already emphasised in previous articles: the heart rate is a reactive marker.
Lack of sleep, stress, heat, lack of fluids or hormonal fluctuations influence it.
The Karvonen formula, too, cannot eliminate these factors; it does, however, create a more differentiated starting basis.
If your calculated training zone is around 155 bpm, but this effort feels unusually hard, this very deviation gives you valuable information about your current load capacity.
Here the circle closes with subjective perception, which must likewise be taken into account in every training session.
Conclusion – Precision as a supplement, not a substitute
The Karvonen formula does not replace training control via the maximum heart rate, but makes it more precise. It supplements the orientation to the maximum heart rate with the heart rate reserve and makes training zones more individual.
Whether simple percentages or a differentiated calculation – what remains decisive is the ability to understand numbers in context and to connect them with one's own sense of effort.
Modern training control does not mean calculating as complexly as possible. It means using the right tools at the right time.
