Heart Rate Drift Test

Without doing a gas exchange test, this is a way of determining your Aerobic Threshold (AeT). The test involves running for an hour, after a sufficient warm-up, at a heart rate that you think you think is close to your AeT for 1 hour. The rate at which your pace declines over time determines how close you are to running at your actual AeT.

The specific protocol involves using Training Peaks to calculate the variation, but the protocol as outlined at Uphill Athlete is as follows:

  1. Run, preferably on a flat (or very gently rolling) course at what feels like an easy aerobic pace. If you have a good idea of what your AeT is, then target that heart rate for the beginning of the test.
  2. Once your heart rate stabilizes for 2–3 minutes after at least a 15-minute warm-up, start the recording feature on your GPS watch.
  3. Record for 60 minutes while doing your best to keep your heart rate close to that initial heart rate number.
  4. Upload the data to TrainingPeaks.
  5. Open the workout in TrainingPeaks and click the “Analyze” button. In the window to the right of your workout graph you will see Pa:Hr X.XX%. This decoupling metric compares the pace-to-heart-rate ratio of the first half of the workout to that of the second half. Note the number and skip ahead to “Reading the Results.”

And interpreting the results:

You want to see some decline in your heart rate, but nothing dramatic. If you see none (less than 3.5%) than your picked a target too low. If you see too much (> 5%) then you picked a number too high. Re-test to see how you're progressing.