Workout To Keep FTP Number Refreshed?


I’m in a bit of a down phase, not training as much as I was earlier. My FTP number in Xert is of course going down because Xert degrades it as time goes by if you don’t do any maximal efforts. Is there a specific workout I can do maybe once a week to keep my FTP in Xert refreshed? I’m ok with it going down as I don’t train enough but I want it to be based on real efforts as opposed to just a degradation formula.


I have a goto 15-20 minute effort that I use outdoors for inducing breakthroughs. It works well for me in the sense that it is physically difficult, but mentally manageable and also kind of fun. You’ll probably want to experiment to find what you like:

I ride near my LTP (zone 2/3) and sprint hard (for about 5 to 10 seconds) every 2-3 minutes.


Indoors, I’ll usually do something more structured. I like to do 40/20’s at 150% / 40% (of TP) for 6 reps and then hold a 7th effort at 150% as long as possible.

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If it’s a short term thing, switch to off season and no decay. Otherwise, throw in a workout as suggested by @commonerg once in a while, or search the workout library for ‘breakthrough’.

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I like to use the British Cycling version of the MAP test.

Start at 100 Watts and increase in steps of 25 Watts each minute until failure:

What I would like to understand is how breakthroughs at different intensities actually affect how the fitness signature is changed. Take two scenarios:

  • 2 minute MMP until exhaustion
  • 20 minute MMP until exhaustion

Is the first more likely to see a bump in HIE and the second in TP?

It would be a nice feature to be able to see what the change in fitness signature would be for a breakthough effort in the workout designer.


What the extraction process does is somewhat unpredictable given the complexity of the math but it essentially tries to map the slope of power fatigue during max efforts. How the signature parameter changes are weighted based on how deep you go and refined based on this slope. Hence it is always best to try and hold MPA when you reach your limit.

Thanks for that. Very interesting and I guess the reason why you can’t make a prediction based on a workout you haven’t actually done yet.


One possibility is to generate some simulated .fit files with constant wattage at 20mmp and 2mmp for various durations:

20mmp for 20:10, 20:20, 20:30…
2mmp for 2:03, 2:05, 2:07…

Upload one of the files to Xert and see how the model updates the parameters, then just delete the activity and try the next one.

I would like to run these scenarios, but I can’t seem to find a convenient way to created simulated fit files. Anyone know a way? Is the .fit format simple enough that this can be done by hand in a text editor?

@xertedbrain would this be a difficult feature to build into the workout creator? “predicted signature after workout”

Is there any advantage to the 25w per minute over the 20w per minute of the Zwift ramp test? Just curious.

Ramp tests unfortunately aren’t very great for determining your fitness because of this reason. The calculations used to determine FTP from these tests are entirely protocol dependent (some ramps are 20W/min, others are 30W/min; some start at 0W, others start at 100W, etc…). Further, because they only have a few, short seconds of maximal effort right at the end of the ramp, they can be difficult to determine the input from HIE and TP, which becomes easier/more apparent to Xert as you increase the maximal effort time, and go deeper.


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It wouldn’t really be useful since how you demonstrate fatigue is what’s important and this can only be modeled when you know the signature. Trying to model fatigue to obtain the signature requires advanced notice of what the future signature would be… sort of defeating the exercise…

I don’t think so: As Scott said it’s all protocol dependant, and to be honest, they’re not really very good for actually determining FTP. I like them as breakthrough workouts just to keep my signature from decaying too much at this time of year.

I’ve found that myself, and find that during the TT season here in the UK my signature becomes more accurate with my race efforts. What I tend to do over winter is six or seven 30sec on/15 off then try and hold above TP until I feel I’m fading then do a pitiful sprint. Usually gets me at least a silver breakthrough and is fairly accurate if the workouts that follow the adjustments are anything to go by. Never tried it on the trainer though, I’m just after someway of refreshing my signature during the winter months if I’m struggling to get out due to the rubbish weather.

My advice(because well we all have some). If I want to confirm my signature I put in maximum efforts of different duration in my workouts even on different days when I feel ready. This updates/confirms my signature. My experience has been is that the default decay rate holds true for me with maybe sprint/peak power efforts being a little off.

Since my numbers fall in line with the predictions I don’t worry about the accuracy anymore. You may find out that you are different and making the max efforts will enrich your personal knowledge.

Ramp tests do seem to be “in” right now. I’ve seen many people say that British cycling prescribes 20 watts/min ramp for elite men 15 for elite women and (inexplicably) 25 for non-elite men. I suppose for Xert, it doesn’t really matter.

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I agree it wouldn’t be that useful beyond experimenting to get some additional intuition about the Xert model.

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Thanks everyone. Very enlightening thread, at least for me.

Cheers and happy Xerting.