Fat% prediction , part of Body Composition Assessment

ANTHROPOMETRY, or
BODY  COMPOSITION  ASSESSMENT  METHODS.

Scientists and medical specialists for various reasons are interested in the percentages of types of soft tissue, adipose tissue, bone tissue, water, etc. in the composition of the body. A wide range of Body Composition Assessment Methods has been developed for these purposes. Among those are Electromagnetic Scanning (EMSCAN), the application of Ultrasound, the measurement of the natural gamma radiation of potassium (40K, Kalium) and others. Please consult the Overview in  30 ).
For the day to day medical practice a simpler, efficient method for fat% prediction is needed. The skin fold measurement with calipers is frequently used but experience is needed to interpret skin folds at different locations and to base a prediction for the fat%  in the body on the caliper readings.
Recently the Fat Impedance Method has become popular as an efficient tool in the medical practice.
 
The BIOELECTRIC  IMPEDANCE  ANALYSIS
for FAT%  PREDICTION.

Bioelectric Impedance Analysis, BIA is not a Fat Measurement Method in the strict sense. It is a fat% estimate based on an impedance measurement. The distinction is important because both parts cause different errors.
The impedance measurement (electrical resistance is a simple form of impedance; impedance includes the effects of non-conductive  areas like the cell lining, causing capacitive effects) measures a phase shift in an applied alternating current; its frequency can be some 50 kHz. The phase shift is caused by capacitive effects in body tissues. The amount of phase shift depends on the ratio of the fatfree mass (FFM containing body fluids with electrolytes) and the fat_containing_tissue. Fat containing tissue has a low conductivity, it does not contain water.
In this type of impedance measurement two causes of errors may occur.
  • The first is the great difference in skin resistance per person and even with one person in time. This can be overcome by applying the tetrapolar technique, a 4-pole measurement technique that enables the chip in the equipment to eliminate skin resistance from the measured impedance.
  • The second cause is the sequence of various body compositions from one hand through the arm, shoulder, trunk etc to the other hand, or from foot to hand or from foot to foot. The impedance measured is connected with a mix of compositions that is not necessarily equal to the composition of each region. Research is going on in so called "Regional Impedance Measurements".
When a patient suffers from fluid retention a more complex impedance configuration will result. Then multifrequency equipment with sufficiently spread frequencies so that phases differ significantly per applied frequency can present additional information about the body composition.
 
The FAT%  ESTIMATE.

Many research projects were set up to find the relation (correlation coefficient) between BIA_results and the fat%  figures found with anthropometry. From these projects we know that age, sex, height, stature, freqent physical training, pear/apple shape, pregnancy, are important parameters for the fat% / BIA-results correlation. It has resulted in the definition of fat%_BIA profile groups. For each group the fat percentages corresponding with measured Bioelectrical Impedance figures are known. Now it all comes down to finding the right profile group that matches the prospect to be measured.
 
BODY  FAT  MONITORS.

Inexpensive Tetrapolar (single frequency) Fat Monitors are available in two types:
  • The foot scale with four electrodes for heels and balls.
  • The handhold unit with four electrodes for the medial (thumb) and lateral (little finger) parts of the two hands.
The first monitor measures the impedance through legs and lower body. The second obviously measures through arms and upper body.
The choice for one or the other is mainly one for practical reasons.
The footscale has the advantage that it also measures weight. A disadvantage is that persons have to stand on the platform with nude feet (time consuming removal of boots and garments) what requires frequent antiseptic cleaning.
The handhold unit will be hold with bare hands reducing the hygienic aspect to the level of handshaking in a meeting or party.
For both instruments the risk of a false fat% prediction lies in the choice of the reference group.
Monitors have capacity for entering age, sex, stature (height), weight (for the handhold monitor). The memory in the monitor chip holds profiles for each of these combinations. This represents a limited choice from all profiles, so matches will be approximations.
If a wrong entry is used (f.i. male instead of female) the unlikely reading may alert you.
Age can be doubtful information. Depending on the person; the prediction of the monitor may be tried with 10 years added to or subtracted from the administrated age. No entry capacity is available for apple- or pear- shaped obese persons.
Some monitors are even labeled "not for athletes".
    An illustration of the way monitors can be fooled by choosing a wrong profile is found in the Electro Lipolysis treatment. In the Electro- lipolysis  page  is explained that fat is moved, re-placed, not burned by Electro Lipolysis.
    If the treated area is the lower belly, fat will disappear from the lower belly and spread all over the body. This implies that the client's fat distribution profile no longer fits. This can be seen with a Body Fat Monitor. The foot scale monitor will show a lower  fat percentage, as may be expected. The handhold monitor measuring impedance in the upper body is influenced by the additional spread fat and should indicate a higher  fat%. It does!
In the medical practice the emphasis is often on the relative  fat% indication for specific clients (change in relation to treatment) not on absolute  fat%. A frequent question to be answered is: "Does the weight reduction of a treated patient correspond with loss of fat, or loss of water or loss of muscle tissue?" By comparing the loss of weight with the Fat Monitor indication of fat% loss the question can often be answered.
In that situation Body Fat Monitors are very useful.
 
R conS ult  ®
M edBeraad

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