Cardio fitness score updates

[Ali123456]

I did my first run last week. When can I expect my fitness score to be updated? Or do I have to do more than that ? 

[SebWotan]

The Cardio Fitness score barely updates. Mine is at 50-54 since 5 years, sometimes going to 50-50. It is linked to your RHR and except if this one changes a lot, Cardio Fitness score will stay stable. That being said this measure may be imprecise, typically VO2 Max (which is what the Fitness score is supposed to be https://help.fitbit.com/articles/en_US/Help_article/2096.htm ) is measured with instruments. Fitbit is a rough estimation. 

[t.parker · Accepted solution]

@Ali123456 there are certain conditions to be met to acquire a single number score. Fitbit does testing using Cooper test (or its variation). It recommends to run for at least 10 minutes with GPS on relatively flat surface. I would add running with 10 to 12min interval at max effort (all-out). Cooper test takes 12min so as well you may extend recommended by Fitbit 10min to 12min. I run a lot so can't tell how many runs you need to get VO2Max out of it. In theory, you just need one performed just right but I never tried to verify that. Like @SebWotan says, it's just an estimate. For me, it currently shows 60 (which is 60ml/kg) so it's not a range but a single nunber. I'm sure it's not even close to my real aerobic capacity (lab test in March so then will find out).

[Ali123456]

Thanks. I have done the 10 minute on the flat twice now but am not ready to run flat out yet. I still have the 43 to 47 range. I am anticipating it dropping quite a lot as I have a low resting heart rate but am only running at 8kmh currently for 24 minutes 

[t.parker]

@Ali123456 Fitbit doesn't support VO2Max history (so I can't pinpoint which runs affected my score) but Garmin does and it has similar rules in place with one addition - HR must be constantly elevated to 70% of maximum HR or higher. Time of test vary between 10 to 15 minutes (rules may be different per device). If I go back to VO2Max history I see usually races affecting my VO2Max (mostly 5K for which I can go all-out) but not only. Some runs may marginally affect VO2Max but without changing value. There is such metric like "Primary benefit" on Garmin and runs that impact VO2Max show "VO2Max" as primary benefit. My today's Parkrun gave me this benefit, too. All those runs have one thing in common - significant time in Threshold zone and up. Fitbit may need something similar (hence going with or close to max effort). Interesting thing that Garmin doesn't require flat surface as it uses GAP not normal pace to calculate VO2Max. Also, on Garmin I have several runs impacting VO2Max yet without changing an absolute value so that could be the case on Fitbit, too - you may need more than one run (and that renders my previous theory wrong 🙂 ). I had never analysed it before hence my previous conclusion.

[Mscach]

Following. my score wasn’t from  33 in April to the week I started a couch to half marathon running plan. I went the whole pandemic being very sedentary/gained weight. My heart rate sat around 77 during that time and even higher when I was pregnant.  Before then my heart rate sat at 55, and lower depending how active I was. Well after I started run/walking about 9 miles a week with cross training my score dropped to 26! I had an injury so I haven’t recorded a run consistently for 10+ minutes without walking breaks. I also wondered if my score droped because I labeled my workouts as walks the first week. 

[Mscach]

Correction: Score went from 33 to 21 the week I started working out. After a month it’s crawled to 26z