Cardio Fitness Score dropped unexpectedly

[EamusH]

I've been using FitBit since 2014 and I have a LOT of data that I've put through it. I wear the device all time.

At 54 years old my VO2 max score of 54 is great and I've worked hard to get it. BUT there are issues with how your software derives this number and how it changes. Two things I'd like some feedback on please;

With a score of 54, last Sunday I went on a slow recovery run for 10k. When I came back my score had dropped to 48! This is nuts. With YEARS of trend data this just should not happen. I've been on 2 fast 5km runs since and my score has only gone back up to 50 when both of those runs (and therefore the recovery times) were over exactly the same terrain as before and at the same speed. This just isn't right.

Secondly, my score only seems to be affected when I run. I've done over 200 WattBike sessions in the last 18 months alone (as well as countless road bike sessions) and I know that my VO2 max has improved immeasurably during this time but the app is completely ignoring this even though all the data is meticulously saved as a session in the app every time.

How come? It'd be great to get some helpful feedback. Thanks!

Moderator Edit: Clarified Subject.

[MarcoGFitbit]

Hello @EamusH have a warm welcome  to the Fitbit Community, it's great to have you on board. 

I appreciate your participation in the Forums and for sharing your experience with us. Please take in consideration that your cardio fitness score is determined by your resting heart rate, age, sex, weight, and other personal information. For best results, make sure your weight is correct in your Fitbit profile. Also, wear your tracker or watch to sleep for a better resting heart rate estimate. Your cardio fitness score will be shown as a range unless you use GPS for runs.

If your Fitbit device connects to GPS, we can provide a more precise estimate of your score using the relationship between pace and heart rate during your runs. This is because individuals with higher VO2 Max have a lower heart rate while running at the same pace compared to individuals with lower VO2 Max. If you're able to run at a comfortable pace for at least 10 minutes, track a run with GPS. We recommend running on flat terrain as much as possible since only the flat sections of your run count towards your score estimate. You may need to go on several runs that are at least 10 minutes in length to affect your score.

As you mentioned your cardio fitness score dropped suddenly after a run, it's possible that specific run was not tracked correctly, did you start the activity using your device? If so, which device are you currently using and did you use connected GPS with it? This will be very helpful for us to check this further. 

Finally, note that your cardio fitness score only takes in consideration your runs and to improve it, try the following tips for the best estimate:

• Go for long runs (at least 10 minutes long) on flat terrain.
• Complete multiple runs to help improve accuracy.
• Run at a faster pace if you’re able to do so. You don’t have to run at maximum speed but higher-intensity runs provide a more accurate estimate.

Thanks for your patience and understanding, if there's anything else we can do for you, please feel free to reply. 

[Gainn]

It's not really that accurate because it seems so heavily weighted towards resting heart rate. All it takes is a bad infection that raises your resting rate, or a couple of really busy days where you are constantly active and it drops like a stone.

I've stopped paying it any attention. 

[davepass]

i would just ignore it, my resting heart rate is between 48 and 53, i run 3 times a week, my fitbit shows vo2 at 49 and some time 35, its useless. one extreme to another.