Understanding Training Data (part 2)

Following from my previous post, this time we dive further into the “data lake”. If you are into IT you will see what I did there! Luckily I don’t make my living as a comedian! So without further preamble…

Heart Rate Decoupling.

Heart Rate (or more correctly Aerobic) decoupling is when your heart rate drifts away from the power or pace you’ve been maintaining in a workout. When your heart rate is running parallel, and tracking either of these metrics, they are described as coupled. If your heart rate drifts upwards when power or pace is reduced, they are then said to be decoupled. The point at which your heart rate decouples (if it does at all) can tell you a lot about your current level of aerobic capacity. Which for endurance athletes is an important marker.

Why Care?

As an endurance athlete you appreciate that having a well developed aerobic system is important to your event capability. You invest time performing a variety of different training sessions aimed at improving your aerobic energy system. But how do you know that you are progressing and how do you know what level you have reached? One method is to track your ability to produce more power / run faster, for lower heart rates. Heart Rate decoupling gives you an additional analytical tool to help you answer the question.

What to look for

Quite simply, over time are you able to hold a faster pace for longer periods of time with no noticeable decoupling? If the answer is yes then, tick, all good you are progressing. Next consideration is to then find the pace at which you do see decoupling happening and compare that to your target event pace.

One point of note, other factors can impact when decoupling may occur including hydration, nutrition, residual muscle fatigue and even mood. So do consider these factors when reviewing your data.

Types of workout session

Pretty much any session that prescribes either a constant HR zone or constant Pace. Hill reps, sprint intervals and the like would not lend themselves to this kind of analysis. But if you were, for instance, running 3 x 2km @ low Zone 2 HR, part of the post run analysis might be (1) did you achieve a consistent HR in each of the three intervals? If so (2) did you run at a very similar pace in each interval?

In this snapshot taken from a recent run you can quite clearly see that I was running within my aerobic capacity. Able to hold a pace (which will have been a slow easy pace) regardless of the changes in terrain. As I ran down the first decent you can see the red line drop below the green pace line (as clearly it was easier to hold that pace on a decent. And then running up the next climb an increase in HR. But importantly as the terrain levelled out HR coupled to pace again quickly.

If six / nine weeks later I ran the same route again, produced a similar level of coupling BUT ran faster then I would know that my aerobic base was continuing to improve and my training was being effective.

TrainingPeaks offers you a further metric to conveniently summarise the level of decoupling within a workout and that is the Pa:HR percentage. In this example I have taken a 30min BRICK run which was run at Threshold Pace or better. You can see the “or better” part didn’t happen!

The IF value is 1.05 showing that this was broadly at Threshold HR. But for our purposes in this post we are more concerned with the Pa:HR which is shown to be 5.49%.

What do the Pa:HR values mean?

According to TraininPeaks (who have modelled this against MANY different athletes), an aerobically fit endurance athlete will experience a decoupling rate of less than 5% when working at what should be a “sustainable” pace / power output. My observation of different athletes supports this. This run was after a 2hr turbo session, so already fatigued and probably dehydrated. In isolation this means little (you need more context), but when this session is repeated in six weeks time you would then hope to see a similar 5% coupling, but a faster time. This would then evidence “improvement”.

To Summarise

There is no silver bullet in endurance training. The skill is in taking a variety of inputs (quantitive and qualitative) and then using all of these to compose a picture. To that end, you now have another tool in you toolbox.