Charge 5 does not support cardio fitness score

[Rambo80]

For months I have gotten a cardio fitness score rather than a range because I run a lot with GPS and get plenty of it on flat routes. A couple of weeks ago I ran to the top of a ski hill and back down. After that my score went from 44 to a range of 46- 50. This made sense to me as almost none of this run was flat and certainly there wasn’t 10 minutes of flat. Since then I have run almost 50 miles on my normal routes on 8 different days. All of these runs have long flat stretches, are 40 minutes minimum and done with GPS. I still can’t get a real score. 
I note that my runs in the app no longer show altitude variation. Not sure if this changed with the recent update of when I switched from Charge 4 to 5. I don’t know if the app is just not reporting altitude changes anymore or if my device isn’t calculating it. That would explain why the algorithm can’t work anymore. 
I have read many times all the stuff about how it gets this score and how I need to run at least 10 minutes and on a flat and all that. 
Any ideas?

[Rambo80]

I went back and looked at old runs and found that the app stopped showing elevation changes during a run when I switched to Charge 5 from Charge 4. That was about 3 months ago so that is unrelated. 

[t.parker]

@Rambo80 to get your score you need to run on a flat surface with GPS (running flat is one of the conditions). It may be that lack of altimeter results in Fitbit not knowing whether you meet this one condition or not (just my theory).

[Rambo80]

I guess no one has an answer. I did try restarting the device and updating the app and such. I guess I'll try support when I have an hour so they can have me uninstall the app and clear the cache and all that.

[Dopovo]

Backing what @t.parker says please remember that Charge 5 doesn't have an altimeter while the predecessor Charge 4 does.

[Rambo80]

I was not aware of that. I'll have to read up on that. The way GPS works, if you get a location you also have altitude so it must be some sort of software limitation. As I think about it I can't see a way to do the math to convert the time signal from various GPS satellites into a location in just x and y without z. 

Anyway, if the 5 can't tell altitude at all that would imply that the 5 cannot do a cardio score since it cannot know if you run flat. Mine gave me a score just fine for over a month. Can anyone confirm that they currently get a cardio fitness score (not a range) from their Charge 5?

[t.parker]

@Rambo80 Fitbit reads elevation only from altimeter.

[Rambo80]

An altimeter? Like from air pressure? I can’t imagine that being accurate enough to know if I am running on a flat or uphill. Especially given that GPS inherently measures altitude. I’m not saying I don’t believe you guys. More that it would be a crazy design to ignore GPS altitude that is just sitting there for free.  Maybe Fitbit should consider updating their help page in the app to explain that Charge 5 can’t do a cardio score. I note that the ski hill run must not have been related. It was a coincidence that I did that run on the day I had been without the Charge 4 for the right amount of time for my old score to expire. 

[Rambo80]

Looking at Charge 5 specs they list when you are looking to buy does not line up with the discussion here. It says for Cardio Fitness Score “Estimate your fitness level using your vo2 max (how well your body uses oxygen during exercise)”. It doesn’t say gives a range based on resting heart rate age and weight. For Floors Climbed it says it tracks floors climbed whether you take the stairs or walk an incline. I wonder how that works with no method of measuring altitude. 

[t.parker]

@Rambo80 it is easy to check. See (if you have any other Fitbit) the elevation of the run given by Fitbit and then upload the same route into Strava (Create Route tool) and see what elevation it's going to come up with. On top of that, there is no calibration of reference altitude. Example from Today, windy 12k run (data from Sense):

Orange - Fitbit raw elevation, Blue - Corrected with GPS data

The reference altitude (see the offset between data points at the same timestamp) is never right (and for some reason, Fitbit never calibrates it).

The highest point (right after the 25min mark) is corrected to 114m (I double-checked it with the elevation finder on the FreeMapTools website which shows the same point as 113m - good enough). Fitbit at the same point shows an elevation of 100m. The lowest elevation in the area (whole area, not just the route, I narrowed down the radius to find the lowest elevation) of the run is 70m and Fitbit goes way below that. Also, the jagged orange line is like that due to wind and rapidly changing barometric pressure. It is not a matter of believing. It's a matter of looking at data.

" For Floors Climbed it says it tracks floors climbed whether you take the stairs or walk an incline. I wonder how that works with no method of measuring altitude." - it doesn't. Charge 5 doesn't count floors climbed.

[Rambo80]

Thanks for the detailed response. I really appreciate it. I don’t have another Fitbit to go check my own data but you did the work for me. My conclusion then is this: Early revs of Charge had no GPS so they needed a pressure sensor so they could estimate altitude. Charge 4 had both but they never got the software done to change from pressure to GPS for altitude estimation. Charge 5 probably eliminated the pressure sensor figuring they would use GPS and they needed the room and cost reduction. Something happened and they never got the software right. That’s why marketing material is wrong. They INTENDED for it to estimate altitude but have not yet gotten it working. It’s probably because the one GPS software guy they have is busy trying to get reliable 2-d positioning to work so no time to worry about 3-d. Or maybe because Charge 5 is so unreliable on GPS in general altitude would be unusable. 

[t.parker]

Nowadays, it's not really the GPS being used to correct elevation but the DEM maps (Digital Elevation Model). If you force a correction in Garmin or Strava platform, the data it uses comes from those maps which are 3D high-resolution scans of terrain. You can do the elevation correction purely with the GPS but this is +120m/-120m accuracy (not that great). Although, that wouldn't matter on the Fitbit platform because there is no way to track real-time elevation during activities so the data could be post-process afterwards and used DEM to correct the elevation. When I found out the Charge 5 was stripped of the altimeter I sort of counted that maybe Fitbit would finally a) fix the reference altitude issue with DEM data, b) use DEM data across all the devices (not only Charge 5) to compensate for missing sensor and in result providing a new feature. That didn't happen. GPS+altimeter+accelerometer is the way to track the elevation in real-time and self-correct some errors but it's far from perfect but often is good enough (I rarely use offline elevation correction on my Garmin devices unless I see a really bad elevation profile due to weather and that happens, too).

[alzmcr]

I have exactly the same problem and I reported to Fitbit now almost 2 years ago when I changed from Charge 3 to Charge 5. Support contacted me and then this was very badly lost and never really come back to me. Now I'm reading this is because the altimeter is missing - pretty ridiculous reason. 

https://community.fitbit.com/t5/Fitbit-com-Dashboard/Account-Data-Export-does-not-have-the-latest-up...