PP %BF Tables are totally bogus!
 

In verifying Disneybebe's calculations, I noticed something rather disturbing on PP (and hopefully PPLP has corrected this).

I am VERY sceptical about the validity of the basic approach.

For Women, notice that the %BF measurements do not take into account anything other than the hip and waist measurements (in addition to height). Does it not seem reasonable that we could find two 5' 7" women who had the same measurements and yet one is a large framed body builder with thick muscles and the other is a small framed couch potato with thick fat? Yet both would yield the same %BF by these calculations.

%BF measurements using girth measurements are questionable to begin with - but if you are only using them as a rough estimate of where you are, they are OK. But the simpler the calculation, the worse the validity of the results.

In addition to being way too simplistic - only taking two girth measurements into account - I have a serious problem with this particular approach from another standpoint. The conversion constants are linear and this makes no sense whatsoever since volume is a power relationship.

The abdominal constant is (inches)*(0.71)
The hips constant is (inches)*(1.4) - 8.52
The height constant is (inches)*(0.61)

This makes no physical or logical sense whatsoever. Given how these numbers are used, this says that if a woman's waist increases by 1", that her body fat percentage increases by 0.71. It says that it doesn't matter whether her waist went from 20 to 21 inches or from 40 to 41 inches. Yet the amount of additional fat that can be added in the latter case is at least twice as much.

The method for males is even worse. While it does take into account frame structure (that's the purpose for the wrist measurement since the wrist has very little muscle or fat on it) and the weight, from there it goes into the dumpster immediately.

Notice that it doesn't take into account the person's height at all. For example, let's say that two guys each weigh 180 pounds. Each has a 30" waist and a 6" wrist. According to this chart, they each have the same percentage of body fat. Even though one might be a 5' tall pear shape and the other a 6' tall apple shape. Make sense to you?

Does it make sense to completely ignore the apple/pear shape in determining %BF after spending a whole bunch of time talking about how important it is?

I am VERY dissappointed in the Eades' for this.

Body %
 

Bill,

I posted a piece in Protein Power on a similar subject titled "Lean Body weight" and was able to find out how BF% are estimated.

I was curious too. BF% are apparently only an estimate based on a significant sample of men any women where known body fat percentage, determined by density in water, is compared to general measurements.

This explains how the various measure can differ. You and I would be less fat as women! Do you like my new shoes?

Re: PP %BF Tables are totally bogus!
 

It's actually worse than that, Bill. The formula for women also doesnt use the wrist measurement - which has been identified as an indicator of frame size and a determining factor in calculating % of BF.

These numbers should always be taken with a grain of NuSalt - unless you can get a proper test at a research facility (underwater testing) BF % should be used as a reference point only - use the same method to check on progress. The results are, however, not to be taken as carved in stone.

Nat

yup, bill. As I said in my response to rust's post, I just did several BF calculations based on measurements, using on-line calculators. I'm clearly somewhere between 19 and 34%--lol. Quite a range!

By calipers (& a very experienced caliper-wielder) a month ago, I was 27 point something BF; now I'm using that same LBM calculation to figure out my BF as the pounds decrease. Every three months or so, I'll go back to the same person and get a new BF measurement and adjust my stats here to match.

thanks so much for doing those calculations and giving solid evidence of where the PP formula fails!

Re: PP %BF Tables are totally bogus!
 

[QUOTE]Originally posted by wbahn
[B]In verifying Disneybebe's calculations, I noticed something rather disturbing on PP (and hopefully PPLP has corrected this).

Hi Bill,
Did I do any calculations? I need to use a calculator to add up my daily carb-intake & I'm on a 20g-30g/ day stage :D
Bebe :wave:

I was kinda hopin' you wouldn't notice that.

Yeah, it was actually someone else's calculations but by the time I noticed that the two day edit window was past. So, like so many of my mistakes, this one is immortalized for eternity. Or until the server crashes hard.

Dear Bill,
Actually I was flattered that u thought I was capable of such complicated calculations, hehe :D
I must say that I'm way impressed by your quick replies to both threads today. U sure do type fast ;)
Bebe :wave:

It's not that I'm a fast typist, I just had nothing better to do than sit in front of a computer because I traveled halfway across the state of Colorado to test a client's chip that I designed for them and it turns out that FedEx screwed up the shipment and they didn't arrive. FedEx actually changed the address from what the shipper put on there to an old address that hasn't existed for a couple of years. So I sat around waiting for the package to be redelivered and it never was.

A very unproductive day, but I did get some "quality time" on the forum.

Funny - I just got PP out of the library last night and did the calcs and thought the same thing (re: only using hip/waist for %BF.) One thing I didn't like was the instruction to measure your waist at navel level. That might work for men, but my waist is considerably higher than my navel!

Apparently, it's nearly impossible for the pencil heads to come up with an accurate formula for %BF, because we're all too different.

Thus, I'm going to go mainly by how I feel, how my clothes fit, and how much butt I can pinch. :D

You are right - it is basically impossible to come up with a PRACTICAL means of accurately computing %BF based on measurements.

What the measurements are trying to do is estimate your body volume - which is all you are doing when you measure your submerged weight using the accepted gold standard for %BF computations.

The more measurements you make, the better the estimate. But to get decent results you would probably have to take measurements at least every six inches up your body - by the time your took your arms into account you are talking about something like twenty measurements. Even then you are still going to have to estimate the volume things like the hands and feet.

Kristine...

Your waist is considerably higher than your navel? In my case, I think my navel has drifted considerably south of my waist! LOL

Question for all you Aussies and other S. Hemi types.

Does the above post mean the same to you as it does to me?

On your maps, what direction is normally "up"?

navel contemplations
 

Having found my navel (I am an "inny") my waist is definately below. I still have an overhang supported by my belt. Men have a different shape.

My PP calculation is 33% BF. I agree that it perhaps bears only a passing resemblance to the truth. But its the best I have got at the moment until someone attacks me with calipers.

*LOL*

Lisa, my waist is about 2 inches above my navel, basically at my ribcage. During my short-lived attempt at learning to sew, I found that I had to alter the patterns for a high waist.

My skirts "migrate" up until they're around my ribcage, and pants... well, they try and it's really uncomfortable!

non-medical terms for aging bodies
 

Rustpot...

In America (at least where I'm from here), they call that overhang "Dunlop's disease". It's where you belly "done lops over your belt". LOL Being a female, I also am starting to suffer from "Furniture disease". After 40, you chest has the tendency to drop into your drawers. :D