Aerobic Endurance Analysis

User guide index: https://marcoaltini.substack.com/p/hrv4training-pro-user-guide

The aerobic endurance analysis includes two features: aerobic efficiency and cardiac decoupling. In both cases, aerobic endurance relates to your ability to sustain a given workload. To determine your aerobic endurance we compute the ratio between external load or output (pace or power) and internal load or input (heart rate) across workouts (efficiency) and within a workout (decoupling). Intuitively, a lower heart rate for the same output (pace or power), when consistently shown over periods of weeks, translates into better aerobic endurance.

The ability to track over time this metric makes it easy to determine when meaningful improvements are made, and how long it took, which is useful information.

First, we can select a sport (running or cycling), a timeframe, and a smoothing window, which means that our workouts will be averaged over a moving window that goes from 1 to 4 weeks. Smoothing helps in getting rid of day to day fluctuations that are not representative of longer-term changes in fitness, hence I would recommend using average or heavy smoothing for this feature.

Accounting for confounding factors

Keep in mind that are many factors that can affect the relationship between pace (or power) and heart rate. For this reason, you can choose what data is used to track changes in aerobic efficiency. In particular, via the panel below, you can filter workouts so that the resulting data is more representative of the changes you are interested in.

In particular, you can configure the analysis based on a number of parameters related to the workout, internal load, and environmental conditions:

Pro will show you which workouts are filtered for the last time window included:

Aerobic efficiency

Good endurance athletes tend to have high aerobic endurance, meaning that they can sustain a relatively high workload (for example pace or power), at a relatively low effort (typically measured in terms of heart rate).

To determine your aerobic efficiency we compute the relation between external, load or output (pace or power) and internal load or input (heart rate). Intuitively, a lower heart rate for the same output (pace or power), when consistently shown over periods of weeks, translates into better aerobic efficiency.

Similarly, a higher power or faster pace at the same heart rate is linked to improved aerobic efficiency. By analyzing the relationship between input and output for running or cycling activities, you can easily track aerobic endurance changes over time, as you progress with your training.

Note that there is no ideal (absolute) value when it comes to aerobic efficiency, the whole point is to track progress relative to your historical data and to see how training is progressing.

Below is an example in which I have filtered for zone 2 efforts, as I ran the same route once per week for several weeks, while rebuilding with my training. The analysis captures progress in terms of a faster pace for the same heart rate, in this case:

While aerobic efficiency is in arbitrary units, it can be interesting to see how things change in the medium or long term (these changes would show how cardiorespiratory fitness changes, as in the image above), but also acutely after an effort (these changes reflect fatigue). For example, below, after a marathon, we can see that aerobic efficiency is reduced for the following day’s run, and improves a bit the day after:

You can use the same approach to evaluate the effect of environmental stressors such as the heat or altitude, and keep track of the adaptation process.

Running on a treadmill

Running on a treadmill is different from running outside. Forces are reduced, ventilation is most likely poor, your stride might be a bit shorter, etc.

Additionally, the hardware and software we use to track treadmill workouts and upload them to Strava or TrainingPeaks might estimate our pace with a certain degree of error. As a result, the relationship between heart rate and pace differs from outdoor running, to a point that it can create artifacts in our aerobic efficiency analysis.

For these reasons, we added a new control in the aerobic efficiency analysis in HRV4Training Pro, to let you filter out workouts with zero elevation gain reported, which is typical of treadmill workouts.

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Cardiac decoupling

Cardiac decoupling relates to your cardiac drift during an aerobic effort. What’s your cardiac drift? Basically, your heart rate increases as a result of your body getting fatigued, during the second part of a workout.

To determine your cardiac decoupling, we compute the relation between output (pace or power) and input (heart rate) during the first and second half of a workout.

Intuitively, if your heart rate increases at the same pace during the second part of a workout, or if your pace reduces in an attempt to keep your heart rate below a certain value, it means that your aerobic endurance for the distance is not well developed. Similarly, a ratio close to one or below 1.03–1.05 shows that your heart rate does not drift much during the second part of the workout, which is a sign of good aerobic endurance.

Please note that for this feature to work, you will need to use Strava and log Laps (typically, sport watches log laps automatically to Strava).

I hope you’ll like the new Aerobic Endurance Analysis page and the improvements we implemented.

Please feel free to comment below in case of any questions or feature requests.

Thank you for your support.

Marco holds a PhD cum laude in applied machine learning, a M.Sc. cum laude in computer science engineering, and a M.Sc. cum laude in human movement sciences and high-performance coaching.

He has published more than 50 papers and patents at the intersection between physiology, health, technology, and human performance.

He is co-founder of HRV4Training, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.

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