Aerobic Decoupling

By Paul Gascoyne

What is aerobic decoupling, and why should you care?

Aerobic decoupling, simply put, 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 to these metrics, they are coupled. If your heart rate drifts, they become decoupled. The point at which your heart rate decouples (if it does at all) can tell you if your body is ready to advance to the next stage of training.

Being able to identify heart-rate decoupling is a very effective way to gauge your current aerobic ability.

If you’re doing a workout where the goal is to maintain a specific pace or power range, decoupling occurs when your heart rate suddenly increases. Decoupling can also appear when you’re doing a workout where the goal is to maintain a specific heart rate zone.

In this case, your pace or power will likely decrease as you maintain the steady heart rate.

How to Identify Aerobic Decoupling

In order to use this powerful analysis process, you need to wear a proper heart rate monitor when you work out, Optical sensor based systems are not accurate enough.

While certainly it is true that heart-rate data is susceptible to being directly influenced by weather, diet, and recovery, it’s also very valuable for determining one of the most critical factors in endurance sports: your aerobic fitness.

The most effective way to gauge your aerobic ability is to intentionally train at specific thresholds for longer durations of time.

To test your aerobic fitness, you need to target an intensity range and maintain it.

Aerobic Decoupling is simply a ratio between Normalised Power and Heart Rate between the first and second part of your workout.

Example: Two Hour Aerobic Cycling Workout

Average Normalized power: 175w

Average HR: 152bpm

Use the lap function on your device or some type of software to split the workout into halves.

First Half: Average Normalized power: 173w

First Half: Average HR 147bpm

Second Half: Average Average Normalized power : 177w

Second Half: Average HR 157bpm

First Half: 173 divided by 147 = 1.18

Second Half: 177 divided by 157 = 1.13(1.18 – 1.13)

divided by 1.18 = 0.04

0.04 x 100 = 4 percent decoupling rate

Now we have a workable equation to check the results of Output Power (w) : Input Heartrate (bpm).

The goal is to be below 5 percent. If it is lower than 5 percent, your body can handle this type of effort and you can move to zone 4 workouts.

If it is higher than 5 percent, you still should spend more time on improving your endurance and tempo zone or take a break as it can be a sign of the body being overloaded.

Do this for a number of long, race-like aerobic endurance rides, and note the ratios. You should notice that the ratios become higher.

Of course, there will be times when the ratio goes in the wrong direction. That’s to be expected for many reasons but the trend over several weeks should be upward.

In a much more simplified form looking at a 4 hour ride:

Ride 1:

Hour 1 – 2 average power 200w = average heart-rate 130bpm

Hour 2 – 4 average power 200w = average heart-rate 145bpm

In this example we experienced aerobic decoupling.

If on the same sort of day (conditions are the same, fatigue level the same etc) you ride the 4 hours the following week

Hour 1 – 2 average power 200w = average heart-rate 130bpm

Hour 2 – 4 average power 200w = average heart-rate 130bpm

Now we have grown the aerobic system. It can handle the additional 2 hours without increased HR.

Note 1: The more variables that change, level of fatigue in the body, changes in temp, different roads etc the harder it is to establish out whether your fitness is changing by looking at drift. But using an indoor trainer with relatively stable conditions will certainly make this test more effective.

Note 2: Be aware that your aerobic fitness is specific to a given duration. So you may remain coupled for 2hrs at race effort, but beyond that begin to decouple. This demonstrates that you have only about 120 minutes of race-specific aerobic fitness. This is fine if you typically race that duration or shorter, but inadequate for Ironman distance, for example.

Iron-distance competitors should decouple no more than 5 percent for four hours while riding at goal effort and for two hours of race-like running. When this is achieved, it can be assumed that the aerobic endurance is well established.

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Paul Gascoyne is a Sport Science & Triathlon/Cycling Coach based in London UK. I have been engaged in coaching and performance teaching for many years, and run a range of Training Camps in Europe for Triathletes and Cyclists, primarily in Crete and Southern Spain. 

I also work as the Performance Director for the largest Boutique Spin Company in the UK as well as delivering Performance Spin Classes for INEOS at their studios in London and on-line around the world. 

With a history in long distance triathlon (7 x Ironman) now behind me I focus on Xterra and Adventure Racing Events in Europe. 

For full info on my services check out www.ucanfitness-coaching.com