[Christian]

Hi pvoosen,

I thought about your post and I would agree:
When performing a 1 hour drift test and comparing the mean HR of both halfs, then the ratio it is equivalent to the HR drift per 30 minutes.

The duration of the entire test and specifying the slope of the HR drift curve seems to be a source of confusion. I hope I can illustrate this with the above chart. In fact, we are always talking about the same slope but in different units.

As Shashi said it is more reliable to compare two means than to compare two single data points. At TrainingPeaks they say “Aerobic Decoupling values for efforts under 20 minutes in duration aren’t as valid” (https://help.trainingpeaks.com/hc/en-us/articles/204071724-Aerobic-Decoupling-Pw-Hr-and-Pa-HR-and-Efficiency-Factor-EF-). So in my drift tests I compare means and try to go as long as possible. Afterwards I adjust the percentage according to the duration of my test, to be able to compare drift tests of different duration. I assume TrainingPeaks does this duration adjustment of their pa:hr metric under the hood.

I hope I could help a bit. 🙂
Christian