Comment by inopinatus
12 days ago
Many of those metrics are population or sampling measures and are confounded by many factors at an individual level. The most notorious of which is BMI; it is practically a category error to infer someone's health or risk by individual BMI, and yet doing so remains widespread amongst people that are supposed to know better.
Instrumentation and testing become primarily useful at an individual level to explain or investigate someone's disease or disorder, or to screen for major risk factors, and the hazards and consequences of unnecessary testing outweigh the benefits in all but a few cases. For which your GP and/or government will (or should) routinely screen those at actual risk, which is why I pooped in a jar last week and mailed it.
An athlete chasing an ever-better VO2max or FTP hasn't necessarily got it wrong, however. We can say something like, "Bjorn Daehlie’s results are explained by extraordinary VO2max", with an implication that you should go get results some other way because you're not a five-sigma outlier. But at the pointy end of elite sport, there's a clear correlation between marginal improvement of certain measures and competitive outcomes, and if you don't think the difference of 0.01sec between first and third matters then you've never stood on a podium. Or worse, next to one. When mistakes are made and performance deteriorates, it's often due to chasing the wrong metric(s) for the athlete at hand, generally a failure of coaching.
> The most notorious of which is BMI; it is practically a category error to infer someone's health or risk by individual BMI, and yet doing so remains widespread amongst people that are supposed to know better.
BMI works fine for people who aren't very muscular, which is the great majority of people. Waist to height ratio might be more informative for people with higher muscle mass.
As a person who has been told I'm "morbidly obese" for decades now, I will say that doctors at almost every level look at your chart not you. I've been told time and time again that until I get my weight under control, my health will suffer.
I'm 5'8" and weigh on average 210lbs. My BMI isn't even morbidly obese, it is 31, which is just "regular" obese, but on top of that, a DEXA scan shows that I am actually only 25% body fat, with only 1lb of visceral fat.
Doctor's don't care about that, they see on the Epic chart that my BMI is > 30 and have to tell me some spiel about a healthier lifestyle so they check check off a checkbox and continue to the next screen.
I'd consider 5'8 and 210lbs morbidly obese. An average male at 5'8 should generally weigh about 150lbs and no more than 164lbs.
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Huh. The standard in your case is to measure waist circumference if BMI is high. Did no doctor do that? As long as you are below 40” or 37” if Asian you are considered good to go.
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> Doctor's don't care about that
Literally all of them?
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I mean those stats arent good...
No. BMI does not work as a diagnostic measure for general population. The range of "normal" BMI values does depend at least on genetic lineage, gender and individual development history. Fine to compare two scandinavian lineage men, but if you compare e.g. a dutch man with an african woman oh boy, you error margins would be mid-to-high single digit units
> Waist to height ratio
Again, while not a bad metric per se, translates poorly between cohorts.
My understanding is that it doesnt even do that, because it creates false negatives for the so called skinny fat body type: significant visceral fat mass, which is what we are concerned about, but not much muscle or peripheral fat mass, thereby not being flagged by BMI screens, even though they are at risk.
> BMI works fine
An individual learns nothing from its calculation and it has no clinical value. I receive more constructive feedback from an auntie jabbing me in the chest and saying "you got fat".
> the great majority of people
There is wide morphological variety across human populations, so, no.
I dunno, basing life decisions off a metric that has a fudge factor built into it to make the regression work feels sub-optimal to me.
BMI underestimates in most cases and your body fat is higher then the chart would predict.
When people say "oh BMI isn't accurate" it means you are more overweight then it suggests unless you are literally an extreme body builder.
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