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PostPosted: Wed Aug 25, 2010 9:32 pm 
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Ricky wrote:
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Testing impedance will definitely have a margin of error of at least 5%
So for a 14% BF, a 5% error is 0.7, indicating that her true body fat is between 13.3 and 14.7. I don't think impedance is anywhere near that precise.


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PostPosted: Thu Aug 26, 2010 4:48 am 
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I think he means 5 points. As in 9 to 19%. That seems a little high though.


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PostPosted: Thu Aug 26, 2010 7:15 am 
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Quote:
Ricky wrote:
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The body fat measurement was done using bio-impedance analysis. I know it's not perfect but I would expect it be somewhere around where I'm actually at. I'm naturally lean.


Unless they are using a dunk tank


Ricky,

Hydrostatic weighing in a dunk take is not the "Gold Standard" is been touted to be.

Hydrostatic weighing is based on some small analysis numbers, statistics. The smaller number in a statistical survey, the less dependable the accuracy. Hydrastatic weighing is based on the dissection of five cadavers.

There are other problems with hydrostatic weighing.

Fat Floats

The theory about hydrostic weighing is that fat floats. Thus, the more you float, the greater your precentage of body fat.

A problem with many labs is that they don't measure residual lung volume. The retension of air in your lungs makes you float.

Residual lung volume is measured prior to hydrastatic weighing so a much more accurate measurement of body fat percentage can be obtained.

Bad Idea

Many labs don't measure residual lung volume. The use a "one size" fits all formula. That a Bad Idea.

If residual lung volume is NOT measured prior to hydrastic weighing, the test is worthless.

Protocol NOT Followed

Another problem is the testing protocol is at times is hard to follow. A friend's son was hydrostaticly weighed a while back. They also calipered him, as well.

The calipers determined he had about 7% LESS body fat than the hydrostatic weighing did.

What Was The Problem?

In discussing the his son's hydrostic weighing, he stated that his son was unable to sit on the scale under water and completely expel all of the air in his lungs.

That meant the his son retained more air in his lungs, making him float higher in the water. That indicated he has a higher body fat percentage that he really had.

Thus, the major reason for the 7% higher body fat percentage reading with hydrostatic weighing had to do with his son not being able to follow the protocol.

The lab did NOT measure his son's residual lung volume, either.

Blowing all of the air out of your lungs. Then sitting there for a while under water is hard to do.

I've been hyrostaicly weighed. It took me about four tries to finally be able to sit motionless with no air in my lungs.

Quote:
...the way they are measuring your bodyfat will have a greater margin of error than what you are seeing. Testing impedance will definitely have a margin of error of at least 5%


I am not sure what the "martin of error" is but it is obserd.

Also as I noted in my previous post, the percentage will be lower or higher dependent of if you use the scale you step on or the hand held BIA devices.

If you have more body fat in lower body than your upper body, standing on the scale BIA's will indicate you are "fatter" than you really are.

It is the same for the hand held BIA device.

The opposite is true, too. If you store less fat in you lower body than your upper body, standing on the scale BIA will indicate you are "leaner" than you really are.

Kenny Croxdale


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PostPosted: Thu Aug 26, 2010 8:34 am 
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Kenny Croxdale wrote:
Hydrastatic weighing is based on the dissection of five cadavers.


I assume that the formulas were derived by hydrostatic weighing and subsequent dissection of the cadavers.

It got me thinking that the gold standard for body fat is probably autopsy. I think they can remove all the fat by chemical means, then weigh what's left over.

This is not so good for serial determinations.


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PostPosted: Fri Aug 27, 2010 3:46 pm 
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Ironman wrote:
I think he means 5 points. As in 9 to 19%. That seems a little high though.


I meant +/-5% bodyfat though that's really just a guess, or course. From having it measured myself I can tell you it's been at LEAST that much. The first time I ever had it tested they said my bodyfat was <2% when it was almost certainly over 10 (this was before I even started working out) so it can definitely be higher.

The point being that 11-14% bodyfat (as in the OP) isn't something I'd worry about since that could just be the equipment on that day. It's not just bodyfat distribution that can trow it off but electrolytes, etc. so if you were to drink a bunch of gatorade one day, get tested then the next day drink a bunch of water and get tested right after it'll say you have more fat.

That's just an example; I'm sure there's a lot more.


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PostPosted: Fri Aug 27, 2010 6:40 pm 
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Well, this is a discussion that we have from time to time, and doesn't really contribute to the answer of the OP's question. In these discussions I often ask "why should one care about one's exact BF%?" The answers never seem convincing to me. The best answer is "because I'm a body builder, and body builders care about BF%". There's no good argument for that!


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PostPosted: Fri Aug 27, 2010 7:01 pm 
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Jungledoc wrote:
In these discussions I often ask "why should one care about one's exact BF%?" The answers never seem convincing to me.


Jungledoc,

I agree. Body fat percentage is not a perdictor of performance. Nor is it a absolute in predecting health. A great book that debunks that is "Big Fat Lies".

Quote:
The best answer is "because I'm a body builder, and body builders care about BF%". There's no good argument for that!


Some bodybuilders don't know or care to know what their body fat percentage is.

As one top amateur once told me that he had no idea of what his body fat percentage was. What mattered was how he looked in the mirror and stage in front of the judges.

No bodybuilding judges wants to know any bodybuilders body fat percentage.

Kenny Croxdale


Last edited by Kenny Croxdale on Fri Aug 27, 2010 7:13 pm, edited 1 time in total.

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PostPosted: Fri Aug 27, 2010 7:04 pm 
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Thanks, Kenny. I'll remember that for the next time this argument comes around.


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PostPosted: Fri Aug 27, 2010 7:42 pm 
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Yea, Kenny, that's how I do it. Mirror check and pants check. Can I see more definition in the mirror, and are my pants looser in the waist? That tells me how I'm doing.


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PostPosted: Sat Aug 28, 2010 9:40 am 
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Jungledoc wrote:
Thanks, Kenny. I'll remember that for the next time this argument comes around.


Jungledoc,

A good article that I once read was in regard to athletic performance and body fat percentages.

The article basically noted what I stated, "You canNOT judge an athlete by their body (body fat percentage)"...like judging a book by its cover.

However, another article examined various athletes in sports. Certain ahtletes in certain sports and certain player position in sports like football fall into a body fat percentage range.

Gymnastist and track athletes had lower body fat percentage readings. Some of that due to genetics and some due to their training...burning up calories.

In football, wide receivers and running back had low body fat percentages.

Linemen had much higher body fat percentages.

As I noted in my previous post, measuring body fat percentages is a bit of crap shoot.

As you noted dissection is the most effective method!

Kenny Croxdale


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