Hi, I'm Dr. Dale Wagner an exercise physiologist, and we're here in the lab
today to do a body composition measurement and we're going to be doing that
measurement using Bioelectrical Impedance analysis. Commonly referred to as BIA.
So BIA sends a low level electrical current through the person's body.
It's so low that the person can't feel it. It's a low voltage, low frequency.
With that electrical current, a large portion of the body is water.
So generally, we are good conductors and the water content in the body is found
in the fat free mass. So the fat mass is essentially anhydrous, or free of water.
And so really the only thing that's impeding the current is the fat mass.
And that's really what we are measuring when we do bioelectric impedance.
We are measruing the impedance, or the resistance, to the electrical current
that's going through the person's body. So the first thing that we are going to do
is we are just going to clean up some areas on our subject's skin.
So that we have a good conduction. And we are going to be placing four electrodes.
So we'll have two electrodes on the wrist and hand, and two electrodes on the ankle
and foot.
We are going to be using the same side of the body for those electrodes.
Traditionally we measuring things on the right side, even though I'm on the left
here that's fine.This is a relatively easy procedure.
It's not difficult for the client or the examiner. So that's probably one of the
benefits of this method. However despite the fact that it's an easy procedure you
still have to be very precise on your landmarks in order to get an accurate
reading. So I'm using some anatomical landmarks here. Bisecting the styloid
processes of the radius. And this one goes down on the proximal phalanx of the middle
finger.
Down here I'm going to bisect the malleoli and then we put this one down at the base
of the toes. Also the client positioning is very important. This method assumes
that we are a series of cylinders. So one cylinder for each leg, one cylinder
for each arm, and a cylinder for the trunk so it's important to keep those cylinders
separate. So you don't want to have the client having any body parts touching.
She's in a good position right now. Also we want to make sure she is not wearing
any metal because of course metal is a good conductor. And so you're not wearing
any metal right? Okay and so that's it. Our set up is all ready.
So we are just going to hookup the electrodes here.
We have red and black leads, just like hooking up a battery on a car basically.
And our red lead is proximal black lead is distal.
And it's very simple from here I just turn on the device and it's going to give me a
resistance reading. And so this is measuring the resistance to the electrical
current going through her body and this number is in ohms.
So right now she has 534 ohms. That number in and of itself just by itself does not
mean anything. But we take that information and we put it into an equation
other information that we would have to know for the equation would be her height.
Her height is critically important because as with any electrical current the
resistance of that current is dependent on the height and the cross sectional
area of the cylinder. And so in this case the electrical current is going through
her arm down the side of her body over to her leg. So we are really measuring the
whole body but half of the body, and then making a prediction based on that
measurement. So certain advantages to this method, as you can see it's simple to use.
Simple to set up. It's easy for both the technician and the client. It's also a
good method for obese people. It's not dependent on body fat. The disadvantages
to this method is it is very dependent on hydration state. Because of the electrical
conductance and the fact that electrical conductance is based on the amount of
hydration a person has. If a person is over dehydrated or if they're super
hydrated, hyper-hydrated, then that could be a problem with the readings. It could
give us an error reading.