Cardio Fitness Score on Charge 2

pupntot

I was just wondering if anybody has any understanding of this feature and how accurate/inaccurate it is?

Mine seems to be directly related to the fluctuations in my resting heart rate, which can vary by 10 bpm either way!

heybales

https://help.fitbit.com/articles/en_US/Help_article/2096

It's an estimate using BMI (height/weight) appearing to be good or bad for your gender/age, along with resting HR.
Polar uses a rough level of time in workouts weekly too. Garmin has finer levels.
I think Fitbit uses the Polar method, since it's a published study that showed slightly better accuracy compared to Garmin.

It's about as good an estimate you'll get using those stats. And is generally good up to very fit level than it starts underestimating worse and worse.

But just as BMI being good or bad was never intended for individuals but rather population stats - it can be thrown off a lot.

Because you can be pretty fit and have a bad BMI, but at least resting HR would show that still fit.
You can also have a high muscle mass and have a bad BMI, but low BF%, and be very fit. That would fool it.

The VO2max figure they calculate is then used for HR-based calorie burn during workouts.

Mine per formula was about 15 mL/min/kg lower than lab tested. So pretty bad estimate.

And as you noticed - true VO2max would never fluctuate that fast from day to day, so it's more of a fun figure for them, an average thing to view going up or down.