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.
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.