Fitness Age BMI Math

I believe I have figured out the BMI math for the new fitness age. First off, the BMI it wants you to reach is the exact midpoint of the "healthy" BMI range. This is a little silly as the entire reason BMI ranges exist is that your weight divided by your height is a good rule of thumb but in no way perfect for what your ideal weight should be. Granted, for me personally, said midpoint is actually within a pound of my ideal weight (based on advanced medical scans for accurate body fat percentage and an athletic amount of body fat). Still, that's not going to be the case for many people so perhaps letting people set their own ideal BMI at least within the "healthy" range would probably be an improvement.

Anyway, the other bit of BMI math appears based on the study mentioned in the article: How BMI and Weight Gain Shortens Your Life Expectancy (menshealth.com). It suggests that 1 BMI unit overweight reduces your life expectancy by 7 months and Garmin appears to be moving your fitness age by 0.5 years for each BMI unit. The study link is broken and I haven't had time to search for it via the university database, so it is unclear if there are any other things to consider in the regression equation though it claimed to remove all genetic influences based on the large sample of genetics and parental life expectancy. But from what I've seen, this seems reasonable as far as the gamification of fitness goes.

Top Replies

KrapfenKringel over 3 years ago in reply to ScottSoapbox2 +1

Well the App tells me to get my body fat down to get younger, not my BMI.

There is no way to enter it manually (via tools that Garmin supply), you can import a CSV file formatted like that:

Body
Date,Weight…

All Replies

0 KrapfenKringel over 3 years ago

Isn't BMI just the fallback if there is no bodyfat data?

0 ScottSoapbox2 over 3 years ago in reply to KrapfenKringel

1) I don't know as there is no information that I can find on this new data screen in the app.

2) Is there a way to enter percent body fat? The app just prompts you to enter your weight every few days.

0 KrapfenKringel over 3 years ago in reply to ScottSoapbox2

Well the App tells me to get my body fat down to get younger, not my BMI.

There is no way to enter it manually (via tools that Garmin supply), you can import a CSV file formatted like that:

Body
Date,Weight,BMI,Fat
"2021-09-29","73,1","23,1","18,2"

during import select the correct settings in numbers for the separator , or . and use English as language, otherwise Garmin will reject it.

If you don't have a Garmin scale but a 3rd party one getting those data, there might be some scripts to automate it or payed sites that do this as a service. But without there is only the manual import option via csv file.

0 Dr Phil over 3 years ago in reply to KrapfenKringel

Yes

0 ScottSoapbox2 over 3 years ago in reply to KrapfenKringel

Interesting. My app says to reduce my BMI - perhaps because it doesn't have the percent body fat data.

I just looked at the Garmin scale and the customer reviews are pretty mixed. The electrical resistance method isn't that great for accurate body fat so I'm not sure it's worth picking up just for a slightly different Garmin generated age.

0 silentvoyager over 3 years ago in reply to ScottSoapbox2

My personal experience is that Garmin scale is very inaccurate at measuring body fat percentage. There are multiple threads about that on Garmin Forum if you go into the Fitness section.

0 svetljo over 3 years ago in reply to ScottSoapbox2

well, as far i know there arent any other consumer devices available to "measure" body fat beside the ones using impedance (excluding calipers i guess :-)). going every week for a DEXA scan might not be very convenient if available

but yes, at least in the forum, the garmin index (2) doesnt get much points for exact body fat algorithms - not that happy people will oft come to forums to express their happiness with the product, and yes no other vendor scale exist - such that can easily be synced (for free) to garmin connect :(

so upto you to decide how many $ you are willing to drop for this "generated" age , that might be valid if all else was valid or it might not..... :)

0 KrapfenKringel over 3 years ago in reply to silentvoyager

I'm very curious, I have one of those older Withings and am tired of changes that made the autoimport script fail. It currently sets my fat value at 18%, if I compare sample photos of a persons in my age/gender, that value looks reasonable. So lets see what the Garmin S2 will do with that.