You might have heard of it, but there is also a good chance that you are unfamiliar with the specifics of this concept. "Heart rate decoupling", sometimes also called Aerobic Decoupling (AD) has been around for a while. Especially in running, heart rate decoupling has been used for some time as an effective tool for training sessions analysis. But you can also use it in cycling. We will explain what it is and how to use it in this article.

Heart rate decoupling is actually not a very complicated calculation. You divide your training into two parts and calculate the ratio between power and heart rate over both halves. Then you divide these two numbers to get the difference between these two ratios.

Relationship between power and heart rate.

But what does this number say? It simply shows the heart rate at which the body has to work to deliver the same power. In other words, it shows the decrease in power at the same heart rate. But why is this data point interesting? Assuming that heart rate reflects the amount of work the body does, it shows that when the body gets tired, it has to work harder to deliver the same watts. The idea of heart rate decoupling is that there is a relationship between heart rate and power. With the aforementioned equation you can see whether heart rate and power run parallel to each other or whether the heart rate differs from the power.

Heart rate decoupling shows the effect of fatigue.

This value shows the heart rate at which your body is tired. Now that you know this, you can compare different workouts to see if you are getting better. But before you compare all workouts, you have to look out for some pitfalls. For starters, the relationship between heart rate and power is quite reliable up to your aerobic threshold. Above this point (where fat burning is at its maximum), the relationship becomes less reliable. Your aerobic threshold is normally between 80 and 95% of anaerobic threshold or FTP. Heart rate decoupling should not be used for training sessions with many intervals above the aerobic threshold and that makes heart rate decoupling especially suitable for analyzing longer endurance rides.

The delay in heart rate.

There is also a delay in the heart rate when the intensity changes where power shows the change immediately. So if the intensity is very variable you can see this clearly in power graphs but much less so in the heart rate chart. For this reason, for heart rate decoupling you will need to use workouts that are uniform, without too many intervals and changes in intensity. Also, the training should have a certain length to be able to see the slowing of the heart beat frequency. In order to get a reliable picture, the training should last at least one hour.

Heart rate numbers can be misleading.

Another pitfall are the many conditions that can affect the heart rate that have nothing to do with fatigue. Coffee or other products containing caffeine can lead to a higher heart rate at the same power levels. So if you stop halfway through your workout for a nice espresso, this can distort the heart rate readings. A few nights of poor sleep can also affect the heart rate. During your workout this will increase and your heart rate will drop again. But because the heart rate was high in the beginning, this can lead to a negative value for heart rate decoupling. Dehydration has an even greater effect on the heart rate. When your body has too little fluid, the heartbeat and power will no longer run in parallel. But this also works the other way around. If you suspect dehydration you can use the value from heart rate decoupling to determine the degree of dehydration.

What is a good heart rate decoupling?

So if you keep these in mind, what numbers are we looking at? Normally a value below 5% for heart rate decoupling during an endurance ride is considered good. Of course, the length of the workout has a big influence on that value. The duration of the ride should match your personal goals. If you train for a particular race or ride that lasts longer than four hours, the first step is to achieve a heart rate decoupling of less than 5% over an endurance ride of three hours. Once that has been achieved, your endurance capability is at a level that you can add some more intensive workouts to your schedule. But if you don't reach that 5% yet, it's advisable to train a bit more on your endurance first. Heart rate decoupling is very useful at the beginning of your training plan. It helps you to determine whether you are ready for the second phase of training which contains more intensive training, or whether it is better to work a bit longer on your basic condition in the first phase of your training plan. Always keep in mind that you use low-intensity workouts for your analysis that are at least one hour long. And when you want to compare two workouts to determine your progress, compare two workouts with more or less the same intensity and under the same conditions.