BMI Calculator or Device Question

hhof

I just read a blog about fitness data, it had a section on BMI and had a BMI calculator, of course I tried it out. What I am trying to figure out is what is the difference between the BMI measuring devices they use at the gym and the calculator. If you can just calculate it on a calculator, what is the purpose of holding the hand held device? Any one know?

AnvilHead

BMI and bodyfat percentage are two completely different calculations and not related to each other in any way. BMI is based purely off weight - two people with the exact same BMI could look completely different. A 5'10", 180 pound guy who's 35% BF and a 5'10", 180 pound guy who's 8% BF are completely different things. One will be fat and soft, the other will be ripped and muscular.

As a side note, the device you hold at the gym is a BIA (body impedance analysis) device, and they are not very accurate (to say the least). It measures body fat percentage (not BMI), but the readings aren't considered to be reliable.

hhof

Thank you. So what do you think a person should pay attention to? Or do you think it even matters?

Sabine_Stroehm

For what it's worth, sometimes impedance machines like at the gym are INCORRECTLY referred to as BMI, but as AnvilHead has said, that's not true, they are BIAs very likely. And as noted, aren't generally very reliable.

The standard BMI calculators are accurate, in that it's just a mathematical formula. The number is technically correct. But they have their own limitations. Again, as anvil notes.

AnvilHead

hhof wrote: »

Thank you. So what do you think a person should pay attention to? Or do you think it even matters?

It depends. For somebody who's morbidly obese, it's worthwhile to simply look at getting to a healthier weight (which correlates with BMI). For somebody who's already somewhere close to a normal/healthy weight and wants to look better/more athletic, BF% is of far more importance. Just as with the examples given above, I'd much rather be a slightly higher BMI with lower BF% (which will mean looking 'cut' with more muscle mass) than a lower BMI with higher BF% (which would be skinnier but loose/droopy/saggy looking due to less muscle mass and more fat).

A 5'10, 150 pound guy with 30% BF would have a BMI of 21.5 - well within the "normal/healthy" range. But with that 35% BF, he'd be "skinny fat" and saggy looking, with no visible musculature.

A 5'10, 185 pound guy with 10% BF would have a BMI of 26.5, which puts him in the "overweight" category. But he'd be lean and muscular, most likely with six-pack abs showing. He'd also have less of the health risks associated with high body fat.

Which sounds better to you?

hhof

Thanks for explaining all that to me. I have only really been interested in my health for about a year now and am just started to understand nutrition and fitness. Of course my answer would be the second one. I see a lot of people loosing weight quickly and looking saggy, it doesn't look healthy at all.

AnvilHead

hhof wrote: »

Thanks for explaining all that to me. I have only really been interested in my health for about a year now and am just started to understand nutrition and fitness. Of course my answer would be the second one. I see a lot of people loosing weight quickly and looking saggy, it doesn't look healthy at all.

Exactly. Which is why it's better to:

1) Lose weight more slowly, at a less severe deficit.

2) Incorporate strength training during your weight loss, to help preserve lean body mass.

Too many people are completely obsessed with that number on the scale and all they're interested in doing is getting that number down to wherever they want it to be as soon as possible, by whatever means. The thing is, you don't walk around with your scale reading blinking above your head for everybody to see - but your bodyfat percentage has a very visible effect upon your appearance.

Many people say "I'm not worried about it, I'll just start lifting and gain the muscle back after I get to my goal weight". What they don't realize is that gaining muscle is a slow, difficult process - and it also involves gaining back some fat along with the muscle. That's an unavoidable fact. You will inevitably lose some muscle mass while losing weight, but strength training, a smaller deficit and adequate protein intake will help minimize it. It's beneficial to hang on to every bit of muscle you can because it's a whole lot easier to retain it than it is to gain it back afterward.

antennachick

^ great post totally agree!