I’ve just completed several power interval tests - and I know you advertise that these aren’t needed but I need confirmation that the W figures you show me are the W figures I can produce.
The good news is everything tallies to within a few W except… that’s comparing my estimated FTP from before the test to the test figures. After uploading my test data my estimated FTP has gone down.
A couple of points that I don’t understand.
- I’ve just performed a 20 min FTP test. How can the FTP displayed be anything other than the FTP values I’ve just achieved. That’s the definition of FTP isn’t it? Or am I misunderstanding.
- I felt pretty good (which probably means I didn’t go hard enough) and finished the test with 20 seconds of power ~ 60W above MPA. The android app was “wahooing” me constantly. Its been labelled as a near breakthrough. If 20 seconds at 60 W above MPA doesn’t count as a breakthrough effort then am I misunderstanding that as well?
Can anyone help?
I’m not sure how long the app was running - thats a good point so I’ll make sure I start from scratch in future.
Looking at the activity in a browser (Thu, Apr 18, 2019 5:53 PM) at 29:48 into the activity MPA and Power output coincide at 341. Effort increases until 30:02 where MPA is 306 Power 361. Finally, MPA and power down to 306 at 30:08 as I finish the effort. That makes 20s over MPA with the max difference 55W and four consecutive seconds where Power is over 50W above MPA.
I don’t want to flag the activity. The data is valid and, other than performing an hour FTP test, is as close as I’m going to get to a “real” FTP value. It feels like the data should be used in the calculation of my fitness signature. Besides, how would I know in future which activities to flag and which not to, just flagging the ones that show my performance in a negative light won’t help me train.
I’m impressed that the XERT estimate of FTP before this activity and the re sults of the test only deviate by a couple of W. I’m not really bothered if its a breakthrough or not other than the fact I need to understand whats going on to have confidence in XERT.
The fitness signature extraction is a regression and is designed to allow a minor amount of power above MPA to prevent spikes from causing issues. It should be good to within a few watts in estimating TP.
Pragmatically, TP from a 20min test vs. XERT estimate before the activity differed by about 3W. TP from the 20 min test vs XERT estimate after the activity differed by 6W. For most of the structured training it would mean I would need to be able to judge my effort to within 4W for this to make a difference. I’m not good enough an athlete to do that.
The understanding that I take from this is:
With a regression/breakthrough model, I have to look at the trend and not a single headline figure. The headline figure may be a few W out because of hysteresis or some other artifact of the model.
That if achieving a “breakthrough” is important for my ego, I shouldn’t rely on the android app to tell me but go absolutely flat out whenever I get my MPA anywhere near my current power output (which is easier said than done).