20min rFTP test, vs. 9/3min vs. 3/9min | 80/20 Endurance

20min rFTP test, vs. 9/3min vs. 3/9min

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    Hi folks,

    I was wondering if you ever compared the 3 tests mentioned above. On the 80/20 resources side it is recommended to run a 20min TT and use 95% of the average power as rFTP. Easy enough, just like cycling.

    Stryd recommends a 9min – 3min test to find out the critical run power, which by my understanding is not the same as the rFTP. Still, how does the outcome of that test compare to the 20min test? I feel a 9min – 3min effort is easier than a 20min TT.

    Lastly, Jim Vance, on the TP website, recommends a 3min – 9min test. 90% of average of both equal the rFTP in watts. Now, that sounds interesting, too. Same question: how does that compare to the other two?

    Running With Power: How to Find Your Run FTP



    In my experience, the 3/9 or 9/3 test results in a higher CP than a 20 minute time trial.

    My tendency is to be disproportionately faster on shorter distances. So doing a 3/9 or 9/3 test has resulted in an overestimated CP. When this happens, I end up pushing too hard on the easy runs, which has hurt my aerobic development. For people with this tendency, Steve Palladino recommends doing a 3/10 or even a 3/12 test. I decided on the 3/12 test along with a 5K time trial and then used my auto-CP to set up my training zones. If you’re faster than a 20 minute 5K (which I’m not), then the 20 minute TT might be better.

    David Warden

    This discussion is an example of accuracy vs precision. An rFTP test does not need to be precise, but it should be accurate.

    I’m comfortable with Jim’s method as an alternative to finding rFTP. In fact, we used to list it in our documentation.

    The issue with Stryd’s Critical Power is that it is a moving target, unique to each athlete. It’s anywhere from CP20 to CP60. It may be that it is a superior method than using a static rFTP protocol, it just is not compatible with the zone system 80/20 has established.



    David – Is it possible to let the Stryd auto-calculate the CP and then derive rFTP from their “power duration curve”? (whatever is shown at 60min for example)

    David Warden

    Yes, if you trust the auto-calculation from Stryd, this is a reasonable alternative. I’d still propose a formal test is more accurate than an estimated CP, but in the spirit of my previous post, it’s going to be close enough.



    If you can put in some longer duration best effort runs, this will help in generating a more accurate rFTP for that duration. I don’t know how fast you are, but a 10K time trial would probably help.


    I’d agree – races have really made my stryd power curve fairly accurate. I have some 5k’s, 10k’s and half marathon efforts (although the half’s were in IM70.3). However Stryd models that my standalone half marathon power should be higher – which makes sense.

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