Oct 02, 2015

Aerobic Efficiency Explained

Measuring cardio efficiency in running and cycling

Top performing endurance athletes are very efficient. They produce a large amount of output (in the form of forward speed or power) at a minimal aerobic cost. One important part of fitness performance training is to improve your efficiency. The more efficient you are, the better you're going to perform in races. Knowing how your aerobic efficiency is improving (or not...) is a key factor in planning your training and setting performance expectations for competition.

How can we measure improvement in aerobic efficiency?

Pros have access to performance assessment labs, and a team of professionals that can run the tests. Most of us aren't so fortunate. Luckily, with SportTracks all you need is a GPS or bike power meter and a heart rate monitor. With these two sensors we can calculate your aerobic efficiency (AE), allowing you to track and monitor improvement.

Aerobic efficiency is a new metric we display in two places:

1. On the workout detail page in the top "total blocks" you'll find aerobic efficiency located in the heart rate block. Click or tap the block to cycle to the aerobic efficiency metric.

2. On the workouts list page you can add the new aerobic efficiency column to monitor changes across a season (or years) for a particular sport and type of workout.

Aerobic efficiency theory and practice

The theory behind aerobic efficiency is simple: it measures the ratio of intensity to effort. For running, intensity is indicated by your pace: higher pace = higher intensity. For cycling intensity comes from your watts: higher watts = higher intensity.

In all sports the effort in this calculation is measured by your average heart rate. We know from basic physiology that as your intensity increases your heart rate must also increase - muscles require more oxygen supplied by your heart. On the other hand, a more efficient athlete will be able to maintain a higher intensity with lower effort, resulting in a higher AE ratio.

Effective training will show a visible improvement in aerobic efficiency. Conversely, if over a season you see that your workouts with consistent intensity are requiring more effort (decreasing AE), it may indicate problems in aerobic endurance.

A few important notes when you're looking at trends in aerobic efficiency:

  • Aerobic efficiency is best measured on longer, steady aerobic workouts (sub lactate/anaerobic threshold). AE numbers for interval workouts may not be relevant.
  • Because intensity is measured by speed or power, different sports will have different AE numbers. Be sure to filter your workout list by sport and workout type (using the text filter).
  • As much as possible you should compare AE numbers on similar courses (terrain, road surface) in similar conditions (weather, nutrition, sleep/fatigue) since these things will effect both the intensity and effort. This is one of the benefits of being able to filter and analyze your workouts by Weather in SportTracks.
  • There is no absolute AE number you can use to compare performance across athletes. Each athlete will have different numbers, and improvements should be recognized as relative changes in the number for an individual athlete.

Training tips

Endurance training guru Joe Friel recommends doing regular aerobic threshold workouts as a way to assess efficiency changes. Basically this is a standard duration run/ride (say, 30 minutes) at 28-32 BPM below LT HR.

Once you've completed your workout, add a tag to the notes such as "#AETest". You can now use the text filter on the workouts page to list only those workouts with "#AETest" for a particular sport. Make sure you've added the aerobic efficiency column and sort the list by date. If fitness is improving, you should see your AE number go up over weeks or a season.

Doing these tests periodically and using the aerobic efficiency metric in SportTracks can be helpful if you're not able to find the time (or money) to go to a proper performance assessment lab.


Very interestng metric. For a few of my most recent runs (the ones I can remember well enough, since I don't usually take notes), the relative differences between AE values seem consistent with how I subjectively felt.

One small issue: in the workouts list, AE column is not sortable like the others. Or is this by design?

And while we're at it, any chance of having a gear column added to the workouts list? (it can be a simple enumeration, or even only the first one, nothing fancy) I keep forgetting to set gear to my workouts and I would love to have a way to see quickly spot the missed ones.


Great new metric, thanks a lot Aaron and ST team!!. It would be interesting to check consistency between this and Vo2max improvement.

Jorge, espero que estes bien! both metrics doesn´t develope in a pararell way along a training cycle, And are not dependant, Each one takes Different times for improving, you can develop one and then the other or for any reason improve only one of them depending on the demands of your particular race event . They are in different effort levels. VO2Max is in a harder zone than Aerobic Efficiency,

great idea!!

I'm definitely going to do a couple of these test to see how i'm doing... I would assume you would get the best results doing them indoors on either a trainer or a treadmill??

I wanted to add the "#AETest" tag which you mentioned to my student's workout after it was completed, but can't do that in the Notes section of their workout. Can that only be done by the student or by the coach only when creating the work?

Workout data including notes can only be edited by the athletes performing the workout.

You're free to add comments if you like, or message your athlete to ask them to tag workouts or edit other data such as name and description, etc.

How about tracking AE over time? What about AE for running? Will this be a new metric when the Running Power meter metrics are added? :)

You can track the Aerobic Efficiency metric over time using the same charts (on the Analysis page) and tabular view (on the Workout page) that you use for tracking other performance metrics over time. It's fully integrated into the platform.

Run power metrics were incorporated a couple months ago. Also fully integrated and available across the platform. If you use Stryd, you'll also get run dynamics data (vertical oscillation, cadence and ground contact time).

It's all available now.

Oh awesome! Thanks for the response! :)

Hi ST Team: Was just looking back at this post and wondered if rAE (running Aerobic Efficiency) can also be measured using power (watts) when using a Stryd power meter with either a Garmin using the Stryd IQ app and/or with the Suunto Ambit 3/Spartan watch? I believe that SportTracks.mobi can log power from these devices (or from their web based data interfaces). I like the power number better than the HR number and it may be useful/helpful to calculate rAE and bAE (biking AE) using the same metrics, whenever power data is available.

As far as I can tell, rAE is calculated using Power when you run with a Stryd. I started running with one in May and since then my rAE has been on a different scale. This is cool apart from one thing - I cannot compare rAE from May onwards with values calculated before I had the Stryd. This would be useful so I wonder does anyone know the respective formulas for power and pace?

For speed: 47 * speed (meters per second) / average heart rate
For power: power (watts) / average heart rate

I find it strange that SportTracks still does not include elevation gain into its calculation of training effort (when no heart rate information is available) or efficiency.

In trail running the rule of thumb is: 100 vertical meter are equivalent to 1 km.
When I do stair training, I may do 600 vertical meters over a distance of 4 km in 65 minutes. This effort comparable to a 10k run. At a heart rate of 130, Sporttracks gives me an efficiency of 0.93 for the 10k run, but only 0.37 for the stair training.

Would be such an easy correction in the formulas!

Where does the 47 come from in the calculation for AE using speed?

Is it just to normalize it to a value comparable with that calculated using power? If it is a conversion factor from power to speed would it not depend on weight and grade (for uphill running) or are these factor negligible?

Splendid thank you!

Is there any way we could add custom fields in the future? For example a formula to show speed based rAE alongside power based?

as a beginner with sporttracks.mobi
I am using TE (training effect) with sporttracks3, is there a posssible relation between TE vs AE ?

Not really...

Training Effect is a mix of Effort (Training Load) and HRV (Heart Rate Variation) along with some magic sauce from First Beat. It is more related to intensity and fatigue rather than cardio efficiency.

Here is the white paper on the calculations, if you're interested:



My aerobic efficiency values seemed to have rocketed recently and I do not understand why this would be the case. For example, in the following two runs I would expect the AE to be the same/similar and yet it is not.

Pre-change.... 20miles @ 7:10/mile. Avg HR: 155. AE=1.15
Post-change.... 18miles @ 7:09/mile. Avg HR: 154. AE= 2.38


Between these runs, I have changed the watch I am using to record data, but given that this is a pace/HR metric I cannot understand why that might impact on the results.

Any explanation / thoughts?

The aerobic efficiency metric calculated in Sporttracks remains useless, as it continues to neglect the effort from elevation gain. I had mentioned this in a post a few months ago. No response at that time, and no change in the calculation of aerobic efficiency.

The fact that elevation gain is not taking into account shows up in other metrics as well. For example, the cal/hr numbers are also way off. They also seem to be pace based, not heart rate based. Again, all workouts with lots of elevation gain are completely off. Example:
Run: 7:30min/k, avg HR 134, 700kcal/hr
Hills: 13:40min/k, avg HR 141, 271kcal/hr
How can a tougher effort with a higher heart rate result in a much, much lower caloric burn rate.

Similarly, the 'level pace' field shows numbers which make me wonder how this pace is calculated. E.g. on a recent run I did 10k with 1000m up and down again. ITRA calculates this as being equivalent to 20k. I.e. my true pace of 14min/k should therefore equate to 7min/k flat. Sporttracks show a level pace of 13:10min/k.

If elevation is not factored into the calculation of the different metrics, they are pretty much meaningless. And it would be very easy to adopt the rule of thumb used by ITRA: 100m elevation gain = 1km.

There is a lot I like about Sporttracks, but these weird decision to neglect elevation gain in the calculation of efforts really puts me off.

For metrics such as aerobic efficiency, level pace, and calories per hour, SportTracks uses the standard formula developed by sport scientists and published in books and research journals - metrics proven to be useful to millions of athletes and coaches. We don't invent new calculations for these metrics for two reasons: a) we don't have the scientific depth to prove the increased utility of invented calculations, and b) it would confuse folks that are accustomed to the existing definitions of how these metrics are calculated.

New metrics that incorporate elevation gain sounds like a delightful idea! You can submit your ideas to our customer idea tracker here:

SportTracks Customer Ideas

As far as calories per hour, the calories burned figure comes straight from the watch, so it's subject to the on-watch algorithms which will differ by vendor and even model. Calories Per Hour is a simple division of total calories by duration. There's no magic; you can do the calculation manually with pencil and paper.

If you have other technical questions about metric calculations, you can open a support ticket by email. The support folks are there to help you.