AIBU to tell you that BMI doesn't apply to everyone!

[Randomuser456]

Foreword I know it's a blunt tool, etc, etc ,etc... and I DO exercise more than the average person (don't really ift heavy) but I've always thought my clothes size doesn't match my weight.

Anywho according to the Navy Body Fat formula I'm around 27-28%

A BMI extrapolation would put me at 38%. By reversing that calculation someone with my BF% is around 15kg lighter than my current weight.

Anyway just a public service announcement :)

Quite. A shire horse and a racehorse are both around the same height. Their build is totally different. One weighs twice as much as the other due to their skeletal frame.

I don't understand how there could be (a way to get your body fat measurement from your BMI) and if there were, wouldn't people have similar results for both?

It's in the OP. I googled it out of curiosity.
You're right that it's probably not very accurate!

Mine gave a wildly different result to the navy formula. Although I don't think that's accurate either.

It also seems odd that age makes such a difference (to the navy formula, don't know about BMI). Sure people tend to get heavier as they age, but is that actually healthy? The navy calculator I used actually said I need to gain fat to be within the healthy range! Er no I don't. Yet if I was 15 years younger I'd be spot on. Ludicrous.

Doctors need something though, don't they? People should be able to tell when they're fat just by looking, but some people obviously can't so doctors need some kind of way of telling them that they weigh too much for their height.

Mad is what I'd call it.

"Sure people tend to get heavier as they age, but is that actually healthy?"

Yes, it could be. Older people should have a slightly higher BMI apparently.

I very much doubt the average hobby swimmer could do 3k in an hour. The average person who doesn’t swim regularly would struggle to do a km. you are massively over estimating the average persons fitness!

One hour? It takes me that long to swim 1k! I’m not a fast swimmer but I can keep going and going. But 1 mile is the furthest I think I’ve swum in one go. But thanks for minimising that achievement.

But if you swim 3km EVERY week you will get faster unless you don’t put any effort in to it. So an hour seems reasonable. Or they are doing heads up breaststroke which won’t burn many calories or build much muscle. If you’re saying you swim 3km every week as an example of doing a fair amount of exercise then you’d want to be doing it at a respectable pace 🤷‍♀️.

I’m going to say it again. A significant proportion of the adult population do less than 10 minutes low impact exercise a month. I have emboldened and italicised it so that it’s clearer. A month. Less than ten minutes a month.

a lot of people here living in cloud cuckoo land about how active most people are.

Yes. The research shows that being underweight at 65 and over is associated with an increase in deaths due to any cause:

https://www.omnicalculator.com/health/geriatric-bmi

There’s a massive variation in muscle between gladiator and couch potato. CrossFit is excellent for functional exercise and lifting weights, there’s certainly a few strong looking women at my local CrossFit and they certainly look different (less wobbly) next to my inactive friends. Cycling and running also gives muscular legs too. Runner/cyclist calf muscles can be quite pronounced. Clearly women can’t gain muscle at the rate men do, however with hard work women can gain different degrees of muscle.

But what does that have to do with the PP’s claim that she can’t be overweight - as her BMI suggests - because she swims 3 km a week? A significant portion of the adult population is overweight or obese. Doesn’t mean PP isn’t just because she does more than the “significant portion”.

We all understand what you are saying, it’s just it’s not relevant to the point that doing a couple of hours of exercise a week isn’t going to render you a professional athletes to whom BMI does not apply.

i went for my annual wellness/health check up (one of those exec packages provided by my healthcare) i was poked and prodded and had blood taken and scanned and one of the scans was a body fat/muscle measurer. fascinating stuff.

I would need to be under 5% to compete.

My BMI is obese, and yes I have fat around my middle, but I don’t think I’ve got 3 stone of fat. However I do exercise regularly and lift weights, and I know my bum and thighs are muscular, so I have to assume that I’m not as bad as it looks on the computer.

I'm really shocked about that! 😳

(But I'd struggle to swim a length! Btw)

Yes. But not the (presumably) adult who said they did 3km of swimming per week, as if this made them particularly athletic. There’s a huge gap between adults who do absolutely no exercise and those who do some, but 3km of swimming is far from being a large amount of exercise in itself.

I do think it’s shocking that a significant percentage do virtually no exercise but that doesn’t make a small amount of swimming something to get excited about.

I run regularly and am decent at it. My calfs are super toned and muscly - unfortunately that's the only part that is! 🤣

Nope. 5% you'd be dead.

Unless PP is a man, you're assuming they're a woman.

True I was assuming it was a woman but even a man doesn't need to be under 5% to compete.

If you lift a fair bit and prioritise muscle growth than it’s easy to be in the ‘over weight’ category and look slim and toned, if you were at the higher end of things to start with.
however body fat is really key. Got to be under 28 . If your body fat is in the healthy range or lower you are by definition not fat!

3km of swimming for me and most people is 2 hours of constant exercise. It’s gruelling. Even in an Ironman the swimming part is only 3.8 km which is for people at the peak of fitness. The only reason I think you’re saying it’s easy is because you have little concept of distances. It’s like me saying it’s a piece of piss to run a half marathon every week and that most people can do that (and it’s probably similar in terms of impact on the body).

I’m well aware of how far 3km swimming is, being a swimmer myself. If you swim regularly it isn’t far and wouldn’t take long. It’s the equivalent of those who run Parkrun on a Saturday. Better than not, but it’s 5km and won’t undo a week of being sedentary! The point is: PP seemed to think 3km of swimming was a huge amount. Swimming is very much about technique, and if you can swim that far it isn’t as much effort as it sounds. But not the point of the thread really.