Online cardiac drift calculator / AeT test

  • Creator
  • #41490

    Hi all,

    I recently wanted to re-test my aerobic threshold, but my training peaks trial ran out. I decided to make the most of all my newly-found time at home and made a tool to calculate cardiac drift from a workout.

    In case anyone else has a use for it, here it is online:

    Drop a TCX file from your last AeT test run onto the page. It will plot your effort, then you can select the area over which to calculate Pa:Hr drift. As far as I understand, if you get a drift value close to 5%, you ran close to AeT. A value much above 5% means you ran faster than AeT, and a value much below 5% means you ran below AeT.

    Let me know if it needs improvements! I’ve only tested with Garmin and Fitbit files.

  • Participant
    Angelos on #41502

    I tried it with Garmin.
    Great job ! Thank you !

    Dada on #41503


    agunn on #41517

    This is awesome. I still have my TP account so I tested it out and the results were pretty close. Thanks!

    Anonymous on #41619


    Thanks so much for doing this. This will make it possible for those without a TP Premium account to still do this drift test.

    We’ll work on incorporating this into our Aerobic Assessment Article with a link to your url. We’ll also credit you for your work.

    Thanks for sharing your knowledge and creativity with the whole UA family.


    Mark on #41698

    I’ve made a profile simply to say thank you, Douglas. Much appreciated!

    moncherwatson on #41906

    Thanks for the kind words everyone! Do let me know if you notice any issues with the software or the instructions.

    And, Scott: thanks for writing the book! I’m a recreational ski mountaineer, but I like how I can use the dry-land training plans to make my weekends more fun. The breadth of the theoretical part is spot on too: when I hear about someone else’s workout structure, I can usually understand where it fits into the bigger picture of endurance training. It’s been a great reference!

    Diana on #42877

    This is awesome– just what I was looking for. Thank you so much for sharing your skills!

    GuillaumeM on #43476

    Hi !
    thank you for that !

    Hrvoje on #48694

    Hi everyone and special thanks to Douglas for making the calculator.
    Since my TP Premium has lapsed this calculator will help a lot.

    I`ve tested it yesterday and I need a bit of help for interpreting the results…
    HRav_H1: 151 bpm
    Pc_H1: 5,56 min/km (10,79 km/h)
    HRav_H2: 151 bpm
    Pc_H1: 6,02 min/km (9,97 km/h)
    Pa:Hr drift [%]: 1,5 (from calculator)

    Since my HRav was the same for both halves of the test (151 bpm) it is easy to see the decrease in pace which is 7,6% and I understood that this should be the actual drift but the calculator is showing me 1,5% drift.

    Could you please help me understand better what is the right way to interpret the results.

    Many thanks and BR,

    slosada on #48947

    To the OP: I just registered to thank you. Using info from Garmin. I use a manual method and this was spot on.

    , dividing the pace 362sec / 356sec = 1.68% but this is after 4 roundings to provide an average for denominator and numerator in both HR and pace.
    So, your “151” in HR can be between 150.5 and 151.4 (and same applies for pace in H1 and H2)

    Let’s pretend the paces are precise: 5:56.000 and 6:02.000 The HR rounding error will give you anywhere between 1.08% and 2.29%

    Hrvoje on #49058

    Thanks @slosada!
    I was calculating with km/h as it is indicated in the calculator description.
    While we are at it; how would you incorporate the HR into the calculation (leaving out the rounding and errors)?
    (Pc2[s]/HR2)/(Pc1[s]/HR1) ?

    Thanks again

    juskojj on #49201


    Can this work with .fit files? I have a wahoo….. or can I convert the file?

    bheemeryck on #52636

    Douglas- Thanks so much for making this available, I was going to pull out the math brain and try to figure out how to do it myself but you saved me many hours!

    Thought I’d share this link as well, apparently to convert a file in strava to .tcx you need to:

    Add “/export_tcx” – without quotes – to the end of your activity page URL. For example, if your activity page is – just add the text to give you and hit enter. This will download a TCX version of your file to the location specified by your browser’s preferences.

    ashanoski on #56613

    Thanks for this handy calculator. I’m just calculating my drift and want to make sure that I’m doing it right. This calculator won’t work with a treadmill workout, unless the distance/pace is calibrated, right? My tcx pace data is definitely off and I don’t know how to edit it and set it to the pace I used on the treadmill. I think I can just look at the change in my heart rate since everything else is constant, right?


    Stella on #65164

    Hi Watson, excellent job with the online calculator. Signed up just to say thanks. It works really well.
    The only suggested improvement would be to display the mean pace as min:sec/km and not min with seconds and a decimal place i.e. in the current version it displays 5.5/km but ideally would like it to display 5 min 30 sec/km


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