Differing power numbers when uploaded to Garmin Connect

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rstrom
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Differing power numbers when uploaded to Garmin Connect

Post by rstrom »

I just noticed this after uploading today's ride to Garmin Connect

The power numbers shown there are:
Avg Power: 178 W
Max Power: 1,178 W
Max Avg Power (20 min): 188 W
Normalized Power (NP): 205 W
Intensity Factor (IF): 1.025
Training Stress Score (TSS): 347.3
Work: 2,120 kJ


The numbers shown in Isaac are:
Min Avg Max
Power 0 147.1 1320 W
Speed 0.0 20.6 37.7 mi/h
Elev 1158 1316 1633 ft
Slope -8.4 -0.00 6.2 %
Caden 0 88.0 116 rpm
HR 86 143.7 179 bpm
NP:182W
IF:0.83
TSS:277
VI:1.24

The thing that caught my eye was the big differences between the TSS, the IF, and the NP differences.

Any idea what is causing this?

I'll poke around in Garmin Connect to see if I can find it.

Thanks,

Robert
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racerfern
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Re: Differing power numbers when uploaded to Garmin Connect

Post by racerfern »

Robert,

Garmin Connect may not be including zeros. It's impossible to have an IF of more than 1.0 on a ride that's probably close to four hours long. Either there is a basic setting that's wrong, the FTP in Garmin Connect is wrong or their calcs are way off. What does it show on the device because the numbers in Isaac appear to be correct for a long ride. Even the Strava numbers for this ride are in the range of Isaac. The problem is somewhere in Garmin Connect, IMO and Newton and Isaac are on the money.
Fernando
rstrom
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Re: Differing power numbers when uploaded to Garmin Connect

Post by rstrom »

When I went to look in the Garmin Connect settings yesterday the FTP was defaulted to 400w. With that setting the IF should be way lower.

I changed the FTP to 220 and that did not change anything.

I totally agree that the numbers are way off and never questioned the iBike / Strava numbers. I just wanted to see if anyone had seen this and had any idea what was going on.

Robert
Guidob
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Re: Differing power numbers when uploaded to Garmin Connect

Post by Guidob »

I have a Garmin 810 that is getting power data from my Newton. The two show different power numbers for average, NP, peak. If I upload the CSV file from the Newton and the Garmin FIT file to TrainingPeaks the numbers are different for max power at each time duration.

For example the peak 2 minutes, 5 minutes and 6 minute power from the Newton is: 400, 324, and 318 watts. From the Garmin it is: 433, 337, and 330.

For consistencies sake I track the Newton data, but it would be nice to understand why they are so different.
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racerfern
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Re: Differing power numbers when uploaded to Garmin Connect

Post by racerfern »

Please post the .FIT file and the .IBR file.
Fernando
Guidob
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Re: Differing power numbers when uploaded to Garmin Connect

Post by Guidob »

Here are the files. For some reason the bulletin board won't let me upload the FIT file with the FIT extension so I renamed it. I tried different extensions but they didn't work. It has an ibr extension even though it is a FIT file.
Attachments
2013-07-27-07-46-28-fit.ibr
Garmin 810 FIT file
(237.41 KiB) Downloaded 400 times
iBike_07_27_2013_0719_35_Miles.ibr
equivalent ibr file
(661.32 KiB) Downloaded 409 times
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racerfern
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Re: Differing power numbers when uploaded to Garmin Connect

Post by racerfern »

I don't use Garmin Connect, but I do use SportTracks, Golden Cheetah and WKO+. They all show 433,337 and 330 respectively. Assuming you are exporting a csv file and uploading that to Garmin Connect then GC is not reading the file properly.
Fernando
rstrom
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Re: Differing power numbers when uploaded to Garmin Connect

Post by rstrom »

I like my Garmin a lot, but I don't trust the numbers that get uploaded (or interpreted) to Garmin Connect.

On today's ride average wattage is 24w too high and maximum wattage is just shy of 200w too low.

The iBike numbers, WKO+ numbers, and the Strava numbers all agree with each other. With that said, all of those numbers originated from the iBike CSV file.

The Garmin numbers uploaded to the Connect website originate from the Garmin FIT file, not the iBike CSV file. With that said, in theory the numbers should be the same since the wattage information is sent to the Garmin from the iBike.

I suppose that there could be some communication issues? But then again it could just be the way that Garmin reads and interprets the data.

I stick with the other numbers and just upload to Connect because ..... :?: :o :lol:

Robert
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racerfern
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Re: Differing power numbers when uploaded to Garmin Connect

Post by racerfern »

I stick with the other numbers and just upload to Connect because ..... :?: :o :lol:
For the same reason I upload to Strava. There's the social aspect and the real numbers aspect. One to share one to sit down and know your fitness and form. Strava attempts to bridge from fun to fitness but really falls short when you sit down and figure out all the aspects of good hard training.
Fernando
Guidob
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Re: Differing power numbers when uploaded to Garmin Connect

Post by Guidob »

Racefern,
Your analysis is interesting, but not sure how to interpret it yet.
In my case I uploaded both the CSV and Fit file to Training peaks. The CSV file was generated by Newton. The FIT file was generated by Garmin. Training Peaks came up with the 2 sets of results. Using CSV it came up with 400, 324, and 318. Using the FIT file it came up with 433, 337, 330. My guess is that the Garmin is not recording the exact same power at the same exact time. Maybe what is transmitted doesn't match what Newton itself is recording. Another factor might be that Newton is transmitting time filtered results rather than the raw 1 second data. However, that might explain small differences, but not the significant differences I am seeing.

If SportTracks, Golden Cheetah and WKO+ come up with 433, 337, 330 then they are matching the Garmin FIT data and not the CSV data.

Can those programs import both CSV and FIT?

What would be much better is if Newton did the analysis itself. Given all the more complex processing that Newton already does, coming up with a peak power profile versus time either as a plot or in time bins should be pretty easy. Then all the results would be fully under the control of iBIke/Newton rather than depending on a 3rd party.

Has anyone compared the power data from a DFM unit to a Garmin and its native computer? For example, how does the data from an SRM to an SRM display and to Garmin compare? Maybe Garmin is always off, but no one knows since there normally isn't an alternative computer to collect the data. :-)

Guido
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racerfern
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Re: Differing power numbers when uploaded to Garmin Connect

Post by racerfern »

This can get complicated with so many options. I do have to say that Isaac comes up with the same TSS as WKO+. Generally, everything is compared to WKO+.

Sorry, but I don't have a good explanation why the FIT file would match and the exported CSV file from Isaac would not.

SportTracks and Golden Cheetah can import FIT files, WKO cannot.

I don't think you'll ever see venture into peak power profiles, CTL, etc. Take the TSS and put into some trackable form.

That said, although I use various programs I still revert to a good ol spreadsheet. I've attached it. One of the advantages is you don't need to enter some FTP number. You merely take the TSS from Isaac (assuming your FTP is set correctly) and it does the calculations. FYI, thanks to someone on the google groups wattage website for making this available.

Try it. Download it, make a copy in case you mess something up and start putting in TSS numbers. You can make the dates be whatever you want by just changing the date in A3. You only enter TSS in column C, the rest works itself out over a couple of weeks.
Attachments
2008 PMC spreadsheet.rar
(44.82 KiB) Downloaded 443 times
Fernando
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Russ
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Re: Differing power numbers when uploaded to Garmin Connect

Post by Russ »

racefern,

That is a nice spreadsheet, thanks for the post.

For help to other excel novices, like me... it took me a while to figure out how to
put the date into A3. Duh, select the A3 cell and change the date up in the function line.

Then I noticed that it was helpful, for the graph, to either enter my initial ctl and atl
(or guesstimate them after observing the graph) to make the graph more useful in the first
part of the year. Do that on the "starting values" panel.

Thanks again,
Russ
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racerfern
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Re: Differing power numbers when uploaded to Garmin Connect

Post by racerfern »

@Russ:
The easiest way to get the graph to display current correct values is to input the TSS values from the last 45 days.

Also, apologies that I didn't take the time to explain it better. I don't even use the graph. I simply read the CTL and TSB values in their respective column and plan accordingly. The nice thing is that it's a quick and easy way to plan upcoming training for a big event. Simply fill in anticipated TSS for a particular ride on future dates. I would say that most of us know how much TSS given rides will yield.
Fernando
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Russ
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Re: Differing power numbers when uploaded to Garmin Connect

Post by Russ »

racefern,

I may not use the graph much in the future, not sure yet. Guess I am sometimes pedantic.
However, I had the TSS data siting in a column in monthly spreadsheets for the year anyway so
it was easy to start from Jan 01 to current. I have a blood pressure tracking spreadsheet from
the web by a doctor in UK and I had added a few columns of exercise and experimental data.

The reason I got into exercise back in 2002 was health related, then I got hooked :-)

Thanks again,
Russ
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racerfern
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Re: Differing power numbers when uploaded to Garmin Connect

Post by racerfern »

The reason I got into exercise back in 2002 was health related, then I got hooked :-)
Me too!
Fernando
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