Body fat scale
A body fat scale is a personal scale , the use of four electrodes to the body fat measuring the human body. The electrodes are attached to the base of the scale so that one (bare) foot stands on one or two electrodes.
The measurement accuracy is relatively low. The measurement results vary with different scales. A full bladder or dehydration due to physical exertion can seriously falsify the results. You can only get a reasonably reliable statement if you always measure at the same time of day under the same conditions. Well comparable conditions are usually achieved every morning after using the toilet or before showering (dry skin). Ultimately, only monitoring of personal change is possible in this way.
The caliper method is usually used by doctors as a more reliable method for measuring the absolute body fat percentage .
Measuring principle (simple)
Usually the complex resistance of the body is determined with a four-wire measurement. A small alternating current (<2 mA) is impressed via two electrodes and the voltage drop is measured on the other two electrodes. The influence of the contact resistance from the electrode to the skin is minimized by the measurement process. The different water content of fat and muscle tissue causes different complex electrical resistances. A computer integrated into the scales can use an electrical equivalent model of the human body to calculate the approximate body fat percentage from resistance values at various alternating current frequencies . By providing additional information (weight, gender, age), the percentage of body fat and muscle mass can be derived.
Measurement inaccuracies can occur with simple body fat scales. Changes in the conductivity of the skin surface due to moisture play a role here. This moisture affects the ohmic part of the measured impedance . The number of measurements, the frequencies used, the measurement resolution of the phase shift and the substitute model used affect the accuracy.
The general problem with such scales is that the current is passed from one foot to the other and thus only the body fat percentage is measured down the hip. Statistical conclusions about the fatty tissue above must be made based on further information (age, gender).
Measuring principle (extended)
Body fat scales with additional electrodes are now also available for private use. As a result, the values can be determined much more precisely, as more measured and less extrapolated data are used. All distances between the four measuring points are first measured individually and then calculated. The surface moisture of the skin can also falsify the measured values here.
Other measurement methods
The caliper method
The caliper method is mostly used by doctors and specialists, because incorrect use falsifies the result. Here, the grease measuring pliers on z. B. the biceps or shoulder area measured three times the thickness of the fatty tissue under the skin. This results in the values for the body fat percentage.
The densitometry
Also called underwater weighing. The buoyancy of a body is measured in a vessel full of water and the body fat percentage is determined via the density.
The ultrasonic measurement
Ultrasound measurements can be carried out on the whole body and calculated using a program on the KFA computer.
Near-infrared light spectroscopy
This method is based on the absorption capacity of the different types of tissue at the point to be measured. For example, fat absorbs most of the infrared rays while non-fat areas let the radiation pass through.
