The Body Composition Machine

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We live in a society fixated on numbers, even when it comes to health and fitness. Often when you begin a fitness program, regardless of the goal, the first task is to take a set of body composition measurements: height, weight, waist girth, percent body fat, etc. Some of these measurements may be used to accurately monitor success while others may grant you false accomplishment or failure.

One common instrument that can be found in many health and fitness clubs measures your percentage of body fat. Sometimes referred to as the body composition machine or the body fat machine, you may recognize these devices as electrodes that are placed on the body or a type of scale that you stand on. Other machines have two handles to grasp or a combination of a scale and handles.

All of the above-mentioned variations are very similar and all attempt to accurately estimate the percentage of body fat through what is scientifically known as Bioelectrical Impedance Analysis (BIA). While the name might sound complicated, the theory behind BIA is actually quite simple to understand.

BIA sends an electrical current through your body and measures the current¡¯s opposition to flow. As we all know, water is an excellent conductor of electrical current, and muscle, believe it or not, is 70 to 75% water. Fat is anhydrous and is, therefore, a poor conductor of electrical current. So, the theory behind BIA says the easier the flow of the current, the more water you have, reflecting a greater proportion of muscle and less fat.

As you may have guessed, the major opportunities for error with BIA revolve around your state of hydration. Measurements will be inaccurate if the test is performed after drinking and eating a regular meal because the resistance of the current will be much less and the test will underestimate the percentage of body fat. Dehydration would obviously have the opposite effect and would overestimate body fat.

The second major source of error arises when the test is performed immediately after exercise. The body¡¯s water contains electrolytes, which are excellent conductors of current. With exercise you lose more water than electrolytes, leaving you with a higher than normal concentration of electrolytes. Therefore, the body composition test will underestimate your body fat as there is much less resistance to the electrical current.

In general, measurements taken with the BIA method may vary by up to 5% within a matter of hours. This might not seem like much, but in terms of body fat this could mean the difference between being categorized as completely healthy and being categorized as obese.

If you are set on having your body fat measured, talk to your trainer and discuss other possible methods. If you wish to use the BIA method, recognize that while it is a quick, noninvasive and comfortable method, accuracy depends on your adherence to specific guidelines which should be fully explained to you ahead of time.

You should always be tested on the same version of the machine as different versions will give you different readings. The method that involves grasping two handles sends an electrical current through your upper body only, leaving out body fat in the lower region. Conversely, the scale-like instrument you stand on measures lower body fat but ignores the upper body. The method that involves electrodes placed on the hand and foot measures the total body and might therefore be considered more indicative of total body fat.


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