Fitness Age and BMI

We all face this problem. Welcome to the club See here for that problem that garmin hasn't updated in two years.

https://forums.garmin.com/sports-fitness/healthandwellness/f/index-s2-smart-scale/255098/s2-body-fat-not-accurate

To be fair Josh, they did update it 3 monghts ago - with a promise :D But good that you pointed out this Topic for Body Fat on their Scale .. because I do not yet own it and I was actually considering purchasing it to have the 'ecosystem' of Garmin completed. However, if something basic like Body Fat percentage is not working properly, feels like it is not worth buying the Scale for that much Euros. Do you perhaps own it?

Yes. Horribly inaccurate. Garmin $150 scale says 20% BF. My $25 FITINDEX one says 14%. Some people have said the garmin doesn’t even use bioimpedence.  

Josh said:

Garmin $150 scale says 20% BF. My $25 FITINDEX one says 14%.

But which one is correct? We automatically believe the more favourable reading but unless there’s something to measure against it not possible to say which is correct. 

And as for the suggestion that Garmin doesn’t use bioimpedance well that comment can most definitely be treated with a pinch of salt. Does anyone really believe that Garmin will just ‘magic’ a number out of the air. Of course bioimpedance is used to measure body composition. Why else do the instructions tell the user exactly where to stand and not to wear socks? Just for the fun of it? 

How does the Smart Scale measure body composition

Of course people are free to believe what they want to believe in order to support their personal narrative.

But if you check Josh's link above to other Thread a lot of people are stating wrong measurements. One even compared them with Clinical measurement. Also Garmin acknowledged the fact something is wrong, as they are saying they are doing some studies, but unfortunately they are moving too slow.

Welcome back Phillip! It’s pretty clear a lot of people say it’s inaccurate. You are welcome to read the other comments if you don’t believe me. 

I also know I’m not 20% BF. I’ve owned and used several other scales both consumer and other higher grade tools. Google a picture of 20% BF for a simple measure.

1. Last - if you adjust your activity level to “10” in garmin, the BF changes. Garmin uses some sort of BMI calculation ONLY and nobody via the other post can seem to get a a reading based on bioimpedence. I could drink a gallon of water and the measurement of my hydration wouldn’t change. It never changed either since i bought it. Even on my worst days where I’m parched it still shows I’m 59.8% hydrated. The only accurate part of the scale seems to be the scale itself, everything else is a BMI based guess. I don’t need to argue about this with you though, if you are smarter than me on it a mood to debate, go ahead post on the other thread and make your comments, unless you already did ;)

If you do not trust the Index scale, just import the body fat values that you trust more, with the help of a simple csv file in the following format at https://connect.garmin.com/modern/import-data :

Body
Date,Weight,BMI,Fat
"2022-09-23","74.2","23.2","16.6"

Josh said:

Some people have said the garmin doesn’t even use bioimpedence.

And Garmin tells the opposite, directly in the manual ( Garmin Index Smart Scale - Measurements ):

The Garmin Index smart scale uses bioelectrical impedance to calculate your body composition. The device sends a small amount of electrical current (which you will not feel) from one foot through your body to the other foot. The device measures the electrical signal after it passes through your body to estimate aspects of your body composition.

Josh said:

Last - if you adjust your activity level to “10” in garmin, the BF changes. Garmin uses some sort of BMI calculation ONLY

Bioimpedance has absolutely nothing to do with Body Mass Index. It is purely used for assessing body composition. A simple search on the internet will clear up any confusion between BMI and bioimpedance. BMI cannot be used to determine body fat content, bone mass, or lean muscle mass. 

BMI = Body Mass Index which is simply weight in kg divided by height in m squared, which is the calculation Garmin and all other sources of BMI will use. That is why the unit of measure for BMI is kg/m^2. The individual inputs the height, the scales contribute the body mass (aka weight.

Research has shown that you can get a pretty good VO2Max estimate using physiologic parameters (age, weight, sex, ...) and activity intensity, resting heart rate and body fat percentage or BMI to estimate your fitness level, and you VO2Max.

The research turned into marketing this catchy notion of  Fitness Age, including an estimate of your VO2Max based on population statistics.

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

This turned into a free online calculator

https://www.worldfitnesslevel.org

Since the notion of Fitness Age was defined a certain way, including "actionable" parameters, Garmin has implemented the Fitness Age in parallel to their VO2max model. In fact, until 2021, Garmin were using their VO2Max model to give you a fitness age.

A year ago, they switched their Fitness Age model to this newer concept. It is convenient in a sense, because the watch already knows most of the parameters necessary to give you a Fitness Age.

I don't know who is the provider of the Fitness Age model for Garmin, but I don't think it is Firsbeat.Maybe it is this SCOR company.

https://www.garmin.com/en-US/newsroom/press-release/wearables-health/2019-garmin-and-scor-global-life-announce-collaboration-to-enhance-wellness-through-wearables/

For some reason, Garmin's fitness age seems to be limited to 9-years younger ("achievable fitness age"). When I use the online calculator, I get an additional 9-years using the same data.

If you do a lot of exercising, but not in disciplines that produce VO2Max numbers by Firstbeat (eg Strength, HIIT, etc.), you have at least this Fitness Age as a fitness metrics you can act upon.

If you are running or cycling, I believe that the performance-based VO2Max model by Firsbeat is more accurately representing your cardiovascular fitness.