What is Aerobic Decoupling?

The squiggly lines and stacks of numbers on Workout Detail charts can be intimidating for people who are new to technical sports training, but luckily one of the most important things they can show you is somewhat easy to identify — even for beginners. What we're looking for is “aerobic decoupling”, and this article explains how to find it, and why it’s important in endurance training and racing.

What is aerobic decoupling, and why should you care?

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 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. Having strong aerobic endurance is essential if you want to perform your best in longer distance races and events, that's why developing your aerobic fitness is the key to successful base training.

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 utilize this powerful analysis process, you need to wear a heart rate monitor when you work out. The popularity of newer forms of fitness sensors occasionally leads to the assumption that heart-rate data is unnecessary. This couldn’t be further from the truth. While heart-rate data is susceptible to being directly influenced by weather, diet, and recovery — it’s invaluable 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. Casual runs or rides at varying speeds and intensities are not the kinds of workouts you want to analyze. To test your aerobic fitness, you need to target an intensity range and maintain it.

Step 1) Determine your current training thresholds

To determine what intensities to target, you must first establish your current thresholds:

• Cycling - You need to conduct a test to determine your current Cycling FTP (a power meter is required).
• Running - Aerobic fitness can be measured with pace or power. To use pace, you need to determine your current Threshold Pace. To use a running power meter, you need to determine your current Functional Threshold Power. You can determine both by executing a single FTP test.

Step 2) Intentionally train at targeted thresholds

• Cycling - Execute training rides at a range of 65% to 75% of your FTP* in order to test your efficiency. 
• Running - If you're using pace, train at a range of 75% to 85% of your Threshold Pace*. If you're using power, train at 65% to 75% of your FTP*.

* = More experienced and fit cyclists and runners should target the upper end of these ranges.

Everyone who does these workouts should have a 20-minute low-intensity warmup period in the beginning, with a few 60-second sprints mixed in. A 10-minute (or longer) cooldown without sprints at the end is also recommended.

Duration: Determining the ideal length of these workouts will vary, depending on how long of a distance you are training for. If the target distance is half-marathon or around 56 miles (90 km) in cycling, your aerobic endurance workouts should be around 60 to 90 minutes in length. For marathons and longer-distance cycling events, this workout should be around 120 minutes. For ultra-distance events, these workouts should be around 3 hours long.

This kind of aerobic analysis is extremely important in long-distances, however, it's not a factor in shorter distances (5k, 10k, etc.). 

Pace vs. Power: Pace has traditionally been used to measure aerobic endurance in running, while power is a relatively new arrival. Both methods provide accurate and actionable results, but power has the advantage of being easier to monitor during the workout itself, especially when running uphill.

Step 3) Analyze the results

As in the screenshot earlier in this article, you want to look at your Workout Detail chart and see if there is a point that your heart rate stops running parallel to your pace and/or power, and decouples. Sometimes this requires using the magnification tool at the base of the chart.

Only analyze the portion of the workout where you maintained your aerobic threshold. Decoupling is always present in the warmup and cooldown segments of a workout, and they are not a concern for this type of analysis.

If your power or pace stay coupled with your heart rate for an entire workout, it's a strong indicator that you're ready to build on your aerobic fitness with the stimulus of specified training (less distance and more speedwork, etc.). If decoupling occurs, you need to do more base training. In running, this typically consists of easy runs, fartleks, sub-threshold tempo runs, and long runs.

Inadequate aerobic fitness isn't the only factor that can trigger decoupling. It can also be caused by dehydration and improper fueling, altitude, weather, and muscle fatigue. When analyzing data, you need to consider all of these elements.

Beyond the chart: Using the Aerobic Efficiency metric

While heart-rate decoupling analysis is an effective way to track your performance, SportTracks provides another way to measure your aerobic fitness. In workouts that have heart-rate data, you get an additional metric called Aerobic Efficiency.

We have a dedicated blog post that fully explains our Aerobic Efficiency metric, but the basic concept is that it's a number that rates your efficiency. The higher the number is, the more efficient you are. If you click on the Total Block for heart rate in a Workout Detail page, you will see your Aerobic Efficiency score.

You can also view your Aerobic Efficiency scores in a list on your SportTracks Workouts page. You can filter this page by sport, and list the temperature of each workout for context. Viewing your AE scores as a list makes it easy to see how your performance trended over time, and how changes in your training potentially influenced your overall efficiency.

In closing...

The ability to track your aerobic fitness is a perfect example of how technology can enhance your training. Workout charts may look confusing at first, but with just a little bit of basic understanding — they become powerful performance improvement tools, even in the hands of a beginner.