Cardio Fitness score

[mjv5460]

How much faith should we put into the cardio fitness score?

It told me my score is fair to average for men in their 40s.

Meanwhile, it's not unusual for me to bike 40km on a heavy mountain bike, walk 25,000 steps across Manhattan, then get up at 5 AM the next day to do 45 minutes of weight training, followed by an additional 4 days of workouts throughout the rest of the week.

I don't know of that many 40 year olds that can do that...

[t.parker · Accepted solution]

@mjv5460 cardio score is pretty much your running VO2Max. If you don't run (with GPS on a relatively flat surface) then Fitbit will still make attempt to estimate your VO2Max but it's not really following the main testing protocol. You may find out more here . Basically, to get your cardio score more accurate you have to run with GPS (and pretty much perform Cooper Test, although I don't know why Fitbit shortens the testing protocol to 10 minutes). Whether it will be accurate? Probably not. Watches are quite bad at estimating your VO2Max. I'm 42 and my running VO2Max is 58mL/(kg·min) (lab test but not very recent, I expect some drop since then), Garmin gives me 57mL/(kg·min) for running and 58mL/(kg·min) for cycling and Fitbit gives me 61mL/(kg·min). Probably Fitbit is overestimating it quite a lot. I run a lot so Fitbit has lots of runs to work with in order to estimate my VO2Max. There is some degree of accuracy but on the other hand, one can't know it unless one performs a lab test to know reference VO2Max. Now, do I care? Not really. It's just a number and it's an estimate that as well may be far from reality.

[YachatsMike]

I found this thread on a search before I was about to ask the same question.  Looking at your post where you say  that your lab test V02max is 58 ml/kg/min and your Fitbit score is  61,   That sounds like pretty good correlation to me.