High power "artifacts" downhill and impact on calculations

[flahutewannabe]

iBike_07_26_2017_1507_19_Miles.ibr

(255.04 KiB) Downloaded 284 times

iBike_07_26_2017_1507_19_Miles.ibr

(255.04 KiB) Downloaded 284 times

iBike_07_26_2017_1507_19_Miles.ibr

(255.04 KiB) Downloaded 284 times

Hi John,

I've been using my PP for a number of months know, and have read a number of your responses to posts about spikes in power when descending under certain situations. I've experienced these "artifacts" myself, particularly when transitions from a negative slope to flat or uphill.

I just returned from a trip to Colorado so had some serious and long descents (files attached). I've also begun usingXert's "What's my FTP?" app for Garmin ... vices.html which calculates FTP while you ride without having to do a specific timed all-out test (not sure if you've been able to experiment with the app in the Velocomp world yet).

I've watched the impact of the downhill "artifact" power on the real-time display so wondering what I can do to get rid of or minimize the number, duration and magnitude of the spikes.

Thanks for the insights, John!

[Velocomp]

The "real time FTP" app reminds me of heart rate straps (and now, tire pressure gauges) that claim to measure power.

They have something in common: garbage in, garbage out.

I remember Hunter Allen telling me how to do an FTP test: "Ride as hard as you can for 20 minutes, until you want to puke".

How in the world can an app infer when you're riding that hard? And for that matter, how many of us really do ride that hard for 20 minutes (or, even better, for one hour)?

I know that I will ride that hard only one time: when I'm doing an FTP test!!!

Your ride file shows that your PP changed angles from miles 2 to 6. You can't use that data for any FTP measurement.

I don't see any unreasonable downhill watts spikes.

If you want to do an FTP test, then ride your a** off for 20 minutes. Use Isaac to get your average power, then take 95% of it.

That number will be 100 times more honest than some silly app.

[flahutewannabe]

Thanks, John. Glad you have an opinion on things

Some folks would say that the PP approach to measuring power is less "kosher" than direct force measurement -- but Velocomp (company) has worked hard to demonstrate otherwise. Not arguing with you, but perhaps the Xert folks have sorted out technical complexities of different approaches to measurement, as have you and your org. I generally put a lot of confidence in DCRainmaker's ability to technically assess products (he's positive on PowerPod for most use cases, and was cautious about the PowerCal HR strap). He's seen good alignment with the Xert app and other FTP measurement so perhaps there is more validity to the approach than it may appear. Then again, he and Coglin got into it in the comments on his review of the "What's my FTP?" app comments.

I wouldn't expect your org to spend much if any time looking at other technologies which measure things other than your sweet spot (no pun intended) of power and related items but I did want you to be aware of the interaction between the power reported by PP and this app.

In terms of power spikes, I'm still a bit confused by what I see on downhills. Since you're not seeing anything out of the ordinary I'll either have to see how a DFPM compares to PP. Or maybe just chill

[Velocomp]

Andy Coggan "wrote the book" on FTP measurement. I understand the basis of the FTP test, and I most surely know how I feel after one!

You are correct that I have not studied anything about the app, nor do I know the assumptions it uses. But when something sounds too good to be true...

[MarkS]

If you search on Google there is research that has been done that shows that FTP can be estimated from full out efforts as little as 3 minutes. Look for Anni Vanhatalo research done in 2007.

Also look at:
http://trainright.com/cts-field-test-wh ... es-not-20/

So Xert is basing their app and other models on established research and practical experience.

[Velocomp]

Ahh...now it makes sense; thank you for the explanation.

The crucial question is this: has the user actually gone "all out" on the bike? Most riders won't do this unless they are forced to do so.

We have a 5 minute FTP test in our Powerhouse Bike app (we also have 20 minute version). I happened to do an FTP test this morning; my FTP has improved by 80W, from 218W to 298W, this year, thanks to Powerhouse Express Fitness plan

It's obvious in my ride file below where the test began. In fact, you'll see the place where a car pulled out in front of me, and I had to stop pedaling for a few seconds...

Honestly, if you go "all out", long enough so that your lungs and legs are maxed out, I'm sure there are ways to estimate FTP. Maybe 3 minutes is long enough; that seems delightfully short to me! In any event, if you feed an app good data, consistent with its assumptions, then I agree you probably can get a decent value of FTP.

But good data is the reason that I hate FTP tests: for the number to be valid I have no choice but to go "all out".

[MarkS]

I agree about the "all out".

I did my updated FTP test yesterday using the Carmichael protocol and the first 8mins definitely felt "all out" being close to the "barf" point. !!!!

[GooseRider]

Mark,

thank you for the mention of the app. This is pretty cool. Also tried their optimum cadence app. interesting.