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Bioimpedance Analysis : Accurate?


#1

Is it accurate enough compared to a 9-sites bodyfat callipers test??


#2

No.
First, the only 100% accurate method is an autopsy, so any other method will have some error. What these tests should be used for is finding consistency so you can track progress.

The good thing about skinfolds is if you have the same tester they can be rather consistent. Electrical impedence since it heavily involves water balance, if your hydration levels change from test to test (which is easy to do), then it can throw off the readings.

I would use it when skinfold is possible.


#3

The search function is your friend.


#4

Bioelectrical impedance is based on the fact that the lean tissue of the body is much more conductive due to its higher water content than fat tissue. Electrodes are attached to the body at the extremities and a small 500-800 micro-amp, 50 kilohertz signal measures the body's ability to conduct the current. The more lean tissue present in the body the greater the conductive potential, measured in ohms.

The first commercial bioimpedance units utilized "linear regression" formulas to predict body fat based on biological data input into a single equation. Units which utilize these linear regression equations tend to be somewhat valid for a "normal" population, but under-predict body fat for obese subjects and over-predict body fat of lean subjects. The standard errors of estimate for these equations are ?5% to ?6.4. in normal populations.

As far as calipers, the assumption is that substantial fat is proportional to overall body fat and thus by measuring several sites total body fat may be calculated. There are over 100 different equations available to estimate body fat with the use of skin fold calipers. This wide variety of equations is the problem with the accuracy of this methodology. The validity of skin fold measurements is at best ?6%. Because of the inaccuracy associated with skin fold calipers, many credible organizations such as the U.S. Army and the Los Angeles Police Department have abandoned the use of them.

In my opinion, and from experience, a well done test with bioelectrical impedance is more accurate, though it's a pain in the ass since the hydration status is more of a problem. I use it though. I do it in the morning after going to the bathroom and before eating or drinking anything. While it might not be 100% accurate, doing it under the same conditions will reflect the changes made. This rule will apply to pretty much any bodyfat testing.


#5

Agreed...remember electricity is very LAZY and will try and find the easiest path to its ground. Water, dry or moist skin,time of day always affects it. Not an accurate method...

Water immersion..#1
Calipers #2

Kerwyn.


#6

A consumer bioelectrical-impedance scale manufacturer recommends testing before an evening meal, on the basis that 1) the subject is normally-hydrated (they say that people tend to be dehydrated upon waking in the morning) and 2) it's a moderately fasting state, to reduce the contribution of stomach contents in the impedance measurement.

Measurement first thing in the morning seems more practical to track BF% trends, as long as one recognizes the BF% reading will be slightly higher due to the dehydrated state.


#7

I don't think BIA is any good, honestly. As someone mentioned, it's very dependent on hydration status, and I've seen it fluctuate even over the course of a few minutes. Seems to me the mirror is a hell of a lot better option.


#8

Thanks for your input guys, that is pretty interessting.

After some research, I would have access to a DEXA test (absorptiometry) and DELTATRAC (for caloric needs) They are supposed to be very precise but I don't know the price, so I guess they are much more expensive than callipers.

Anybody have any experience with these tests?

Thanks again.