# measuring ftp?



## steel515 (Sep 6, 2004)

Are these equally accurate?
20 minute TT.
1 hour race.
1 hour time trial.


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## Sumguy1 (Apr 5, 2008)

steel515 said:


> Are these equally accurate?
> 20 minute TT.
> 1 hour race.
> 1 hour time trial.


No. The experts will be along shortly to explain why.


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## iliveonnitro (Feb 19, 2006)

http://alex-cycle.blogspot.com/2008/05/seven-deadly-sins.html


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## kbiker3111 (Nov 7, 2006)

steel515 said:


> 20 minute TT.


Divide by 1.05ish



> 1 hour race.


Only if you use NP and the race is all out.



> 1 hour time trial.


Yes


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## Alex_Simmons/RST (Jan 12, 2008)

iliveonnitro said:


> http://alex-cycle.blogspot.com/2008/05/seven-deadly-sins.html


and the follow up:
http://alex-cycle.blogspot.com/2009/07/sins-of-sins-testing-ftp-2.html


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## kronis (Aug 17, 2008)

hi, if i am doing intervals like 4-5mins for 8 times at a certain high percentage of MAP, do i follow the NP or avr power during that short duration. the NP is about 15-20watts lower than the avr.


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## woodys737 (Dec 31, 2005)

kronis said:


> hi, if i am doing intervals like 4-5mins for 8 times at a certain high percentage of MAP, do i follow the NP or avr power during that short duration. the NP is about 15-20watts lower than the avr.


For any interval average watts would be more germane as NP "smooths" the overall ride data. IIRC, NP is a guestamate of the wattage you would have produced over an entire ride complete with stops, starts, accelerations, etc...You don't want that for any interval. FWIW, I display the 1 second wattage and just try to hold it steady/on target for the duration of the interval.


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## Alex_Simmons/RST (Jan 12, 2008)

kronis said:


> hi, if i am doing intervals like 4-5mins for 8 times at a certain high percentage of MAP, do i follow the NP or avr power during that short duration. the NP is about 15-20watts lower than the avr.


except for the very occasional mathematical oddity in calculations over shortish durations, NP will always be equal to or greater than AP. If it isn't, then either of your NP or AP calculations are wrong.

As for your intervals, that depends on:
- what the purpose of doing them is. 8x5-min is a pretty tough ask if done close to maximal power for the duration, I imagine you are looking at ~ 90% of MAP
- if you are seeking to tax yourself at that level then you do what you can do, 
IOW if you finished the set with relative ease, then lift the power next time, 
if you couldn't do the set or faded badly, then drop the power next time


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## kronis (Aug 17, 2008)

during longer rides, yes my NP will always be higher than my avr power. that's what i thought would happen for my interval workouts, and i had planned the workout wattages based on NP. I used the avr watts and 3 seconds averaging on the edge705 to gauge my intervals so that i can last through the whole workout. it was shagged, i saw the avr power on the meter, i was happy that i hit the targetted watts, but when i uploaded to view the NP, the NP shows a lower value.


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## Alex_Simmons/RST (Jan 12, 2008)

kronis said:


> during longer rides, yes my NP will always be higher than my avr power. that's what i thought would happen for my interval workouts, and i had planned the workout wattages based on NP. I used the avr watts and 3 seconds averaging on the edge705 to gauge my intervals so that i can last through the whole workout. it was shagged, i saw the avr power on the meter, i was happy that i hit the targetted watts, but when i uploaded to view the NP, the NP shows a lower value.


So you are comparing the NP in software (which?) to AP shown on the Garmin.

OK - a few thoughts:

By _definition _AP cannot be greater than NP.

If you are seeing AP>NP for long durations (like I said earlier, a mathematical artifact of the calculations can see AP a watt or two higher than NP for shorter durations), then one or other of the numbers is wrong, that could be because:
- you are using smart recording on the Garmin, which screws with the calculation of NP
- your software isn't calculating NP correctly
- your Garmin is excluding zeros from the averages it displays, hence is not actually showing average power
- something else I haven't thought of!


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## kronis (Aug 17, 2008)

ok i did a trainer workout few hours ago

garmin settings: previously was already 'every second' recording.
zero averaging was off though, which means i should report a higher average watts on the road due to occasional coasting, traffic lights etc.
i think this setting wouldnt affect during trainer workout, because i am pedalling throughout the whole workout, especially during those intervals.

software used is Golden Cheetah.

i did a 17mins warm up on trainer, 10mins spin, slowly increasing the watts every min, then a 5x30sec on (targetted watts), in between 30sec spin. a 2min varying wattage to make up 17 mins. for this, the NP was higher than AP.

from then, all the intervals i did, 5mins x6. all reported NP being lower than AP.


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## kbiker3111 (Nov 7, 2006)

kronis said:


> ok i did a trainer workout few hours ago
> 
> garmin settings: previously was already 'every second' recording.
> zero averaging was off though, which means i should report a higher average watts on the road due to occasional coasting, traffic lights etc.
> ...


I think you're actually referring to Xpower, which isn't NP, they're separate formulas. Xpower will report lower than AP sometimes and thats OK.


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## kronis (Aug 17, 2008)

oh dear, so what is the significance of the Xwatts?

all of my road rides, Xwatts are higher than avr power. which i then assumed is Xwatts = NP.


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## kbiker3111 (Nov 7, 2006)

kronis said:


> oh dear, so what is the significance of the Xwatts?
> 
> all of my road rides, Xwatts are higher than avr power. which i then assumed is Xwatts = NP.


First of all, we need to understand what threaded posting is. See that little pen and paper next to the quote button in the lower right hand corner of the post? Thats the quick reply and it keeps all the posts in one thread, instead of starting a new one each time. 

XPower is trying to accomplish the same thing as NP, but goes about it a different way. They both want to characterize the intensity of your ride (since a ride that spends equal time at 200 and 300 watts is harder than one steady at 250 watts, but have the same AP). I'm not entirely familiar with XP, but it is supposedly more robust than NP by using a varied averaging window. A result is that XP will sometimes show lower values than AP during steady efforts (whether this is by design or accident I don't know). NP has its own issues (non commutability and theoretical negative TSS), so its not like anything is perfect. Both do a pretty good job in practice.


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## Alex_Simmons/RST (Jan 12, 2008)

kbiker3111 said:


> I'm not entirely familiar with XP, but it is supposedly more robust than NP by using a varied averaging window. A result is that XP will sometimes show lower values than AP during steady efforts (whether this is by design or accident I don't know). NP has its own issues (non commutability and theoretical negative TSS), so its not like anything is perfect. Both do a pretty good job in practice.


I thought XP was a simply using an exponentially weighted moving average, compared to the 30-seconds rolling average used in the NP algorithm. Whatever, it's not particularly sensitive to the averaging window used (nor the exponent used).

In any case, it should not report lower than AP for durations of substance. Physiologically that would just be a nonsense.

Like I said earlier, if you are looking at these NP / XP values, then use them for longer efforts, at minimum 20-minutes (and even then you need to be careful how you interpret the data). 

If you are looking at NP/XP for something short, like a 5-min effort, then the maths means the size of the averaging window (30-sec) is a substantial portion of the sample - the algorithm needs 30-sec of data to "kick in" and then it also depends on how it handles the back end of the interval. Hence why NP / XP for short durations really isn't of any particular use.


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## Alex_Simmons/RST (Jan 12, 2008)

kronis said:


> from then, all the intervals i did, 5mins x6. all reported NP being lower than AP.


For the reasons I outlined in my post above, if you are inspecting XP v AP for each 5-min interval separately, then that's meaningless.

What is the AP and XP value for the entire set, which depending on how long your rest intervals were, would be ~ 40-60-minutes long?


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## kbiker3111 (Nov 7, 2006)

Alex_Simmons/RST said:


> I thought XP was a simply using an exponentially weighted moving average, compared to the 30-seconds rolling average used in the NP algorithm. Whatever, it's not particularly sensitive to the averaging window used (nor the exponent used).
> 
> In any case, it should not report lower than AP for durations of substance. Physiologically that would just be a nonsense.
> 
> ...


You're right, he uses an exponentially weighted averaging window, not varying. Nevertheless, its fairly common to get lower XP values for individual intervals, but not the overall ride. I guess it must not weight the beginning of intervals as high as the end, since most people start an interval harder than they finish it.

I still don't understand why no one has approached power analysis as a frequency domain problem. Getting out of the time domain would give much better access to the important information in a workout.


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## kronis (Aug 17, 2008)

Alex_Simmons/RST said:


> For the reasons I outlined in my post above, if you are inspecting XP v AP for each 5-min interval separately, then that's meaningless.
> 
> What is the AP and XP value for the entire set, which depending on how long your rest intervals were, would be ~ 40-60-minutes long?



an example 

avr 291watts xwatts 277watts

rest 1mins


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## Alex_Simmons/RST (Jan 12, 2008)

kronis said:


> an example
> 
> avr 291watts xwatts 277watts
> 
> rest 1mins


If that is for the entire set 40+ min then that's a bug with GC.


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## IAmSpecialized (Jul 16, 2008)

TAG for future.


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