Curious why Fitness Age calculation doesn't take VO2max into account as Firstbeat itself suggests to do

Without digging into this deeper (so just throwing this out), the FirstBeat algorithm for VO2Max is using Vigorous activity, resting Heart Rate and weight to determine VO2Max, and Fitness Age is a fun gimmick that falls out as well. Really, IMO Fitness Age is another way of looking at VO2Max but with a fun gimmick thrown on top. Dozens of lookup tables and calculators available for Fitness Age, many based on different calculations and giving different results. I would suggest this is just a terminology choice - both are coming from the same underlying data so they could have shortened the description by saying "VO2Max" rather than the longer choice.

Thanks for the feedback. I'm not sure, since as far as I can understand VO2max is a KPI derived from dynamic metrics such as EPOC or pace/hr curves during workouts and not even just any workout, but only a limited subset of them. Also, it's unclear to me what direct relationship can be established e.g. between VO2max and RHR, thinking that the latter is more influenced in general by being constant in vigorous activities of any kind, including even walking depending on the person and/or the path. Also, despite it's quite intuitive that an overweight person can unlikely have a Superior VO2max, the Body Fat % is hard to link in a direct way to VO2max. Am I overlooking something in these?

Peppe said:

Am I overlooking something in these?

You are not missing anything. In the past, Garmin was using the VO2 Max number to give your a fitness age. They changed a bit more than a year ago and are now calculating the fitness age using parameters that have been found to be excellent predictors... of the VO2 Max. However, they use the parameters only to calculate the fitness age. So it is indeed some sort of new concept.

One benefit is to get a fitness metric when the watch cannot calculate VO2 Max because the person isn't active enough.

This is coming from ~2008 academic research

https://www.ntnu.edu/cerg/vo2max

see another thread here

forums.garmin.com/.../fitness-age-and-bmi

Another well informed reply, thanks Etupes25. I have to admit that I had no idea that such kind of parameters might be used to "guess" (by statistical models) the likely VO2max of a subject. So that quite explains it, though I wonder why they do not directly use the VO2max (or state they do) when available (much the same way the use Body Fat % or just the BMI if not available). Anyway, I've learned something new again, thanks.