Bioelectrical Impedance Analysis (BIA)


Bioelectrical Impedance Analysis (BIA) is a physical process that is used to determine the exact composition of a living being. The parameters that can be measured are:

The water in the body

  • The fat-free mass
  • The lean mass
  • The fat mass
  • The body cell size
  • The extracellular mass


This procedure is rarely used in medical practice to help with a diagnostic procedure, as the common methods (X-ray, MRT) fulfill their purpose here. Rather, it is used for people who are interested in knowing their body fat percentage or who are interested in their exact muscle mass percentage. Professional athletes, especially in the field of bodybuilding, often resort to this in order to be able to scientifically evaluate their progress and to be able to design their training accordingly.

In addition, it can provide information about whether a health-critical condition is present: In the case of anorexia (a form of anorexia) or obesity (obesity), the BIA can be used to give the patient a better self-image of his sick body. However, this is rarely used in practice, since psychological and social factors tend to be preferred in such a treatment and a rational argumentation with facts and figures does not give the patient any clarification.

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Principle of bioelectrical impedance analysis

From a physical point of view, an alternating current of around 0.8 mA and a 50 kHz frequency is used to measure the impedance of the organism to be examined. To do this, electrodes must be attached that build up a magnetic field and additional electrons that detect the voltage and the phase shift. The phase shift is nothing other than the shift of two identical functions or curves to one another. Trained specialists are required to attach the electrodeswhich attaches them in exactly the right position. In this context, one also speaks of four-wire measurement, since the electrodes provide four wires that measure according to Ohm's law. (Voltage = resistance times current)

The variables that are measured here are the resistance R, the membrane capacitance or the sum of all membrane capacities Xc. Since every body is different in its composition, different resistances are measured, through which one gets information about the tissues and organs of the body, as well as the electrolytes. In this case, this means the ions inside and outside a cell, e.g. sodium and potassium. However, the physical basis here is not only the measured resistance R, but also the so-called Xc value, which can determine both the number of body cells and their quality.

The quality of the cells is primarily characterized by a high Xc value, since if a high value is present, it can be assumed that the cells are intact and healthy and do not show any deficient conditions such as malnutrition. When assessing these deficiency states, the physical term phase angle also comes into play: This is the proportion of the Xc value, i.e. the sum of the membrane capacities, in the total resistance R - i.e. a mathematical ratio of our previously measured values.

If this Phase angle is particularly large, then the state of health of the athlete examined is excellent: he particularly has a lot of muscles, is athletic and well nourished. If the However, the phase angle is very small is then very common Malnutrition and malnutrition before, the athletic and generally muscular condition of the patient is very low and therefore there is a risk of various diseases.

The BIA can be used to assess at a first glance whether there are hormonal disorders, hyperthyroidism or hyperthyroidism and heart disease. It is also possible to limit your measurements to individual body compartments during the evaluation. For example, the fat or muscle mass in the extremities, i.e. the arms and legs, can be measured.

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However, it should be mentioned that physico-medical measurement methods only ever allow one general statement - The patient or person must be seen as an individual and so the results of an impedance analysis must be evaluated individually with the special medical history of a person. This means that even a very good athlete with muscles and little body fat can develop diseases and that result is not a ticket to an unhealthy lifestyle.


A crucial factor in purchasing a home scale is that Number of electrodes. When the scales without electrodes works, that's how it is usually imprecise, because the current looks for the shortest path and this goes directly through the legs, so it is only measured here. However, if two additional electrodes are attached, the current also works its way through the arms and the middle of the body, making the measurement result much more accurate.

As described, the measurement itself is very convenient and suitable for home use and also provides sufficient results. The measuring principle described above is slimmed down in the home version, because the membrane capacity is usually not taken into account in these devices. In addition, the measurement does not take place lying down, but standing up, as with a standard scale to measure its weight. These different devices thus also have very different prices.

Cost of a bioelectrical impedance analysis

In contrast to the BIA procedure, which some practices carry out and which takes place while lying down, there is also the Possibility to use a body fat scalewhich basically works on the same principle. However, this is far more inaccurate and it does not even reveal cell density or hormonal disorders. Depending on the number of adhesive electrodes, their accuracy can increase. The advantage with it is that it is much easier to use because the patient only has to stand on it and a presentable result is displayed immediately. The scale is also much cheaper to buy. (Costs: Available from 50 euros for private households, in various configurations, but sometimes also much more expensive).

A conventional BIA that only comes with trained specialist staff may be operated and where the Measurement lying down takes place can still be found in some practices today, but has become a rarity due to the rapid technical progress and the associated home measurement method. The costs for such a device, however, amount to several hundred euros for a single measurement and As a rule, the health insurance company does not cover this.

Devices used in bioelectrical impedance analysis

When buying, you should pay attention to customer reviews, as the different devices can also deliver very different results. As already described above, as different as the costs are, as different are the devices and their functions: With some devices, the visceral fat, i.e. the fat in the organs, can be determined, with others not. Most devices can determine the body mass index, but a few do not deliver this performance. Here the buyer has to decide for himself whether he wants to calculate it himself (weight: size ^ 2).

In addition, some devices are suitable up to 150kg, others up to 180kg. In a clinic for obese (adipose) patients, this can be partly important. In addition, some devices have memory, while others do not. If a memory is available, sometimes 4 people can be saved, while others can store 10 or more people, which makes operation easier. Most devices are about the same size and weight. However, accuracy is probably what most users care most about. Here the accuracy varies from “very accurate” to “satisfactory” or just “okay” in other areas.

First and foremost, you should buy such a device if you are interested in your muscle percentage, but if you want to get a very precise result, want to know your membrane capacities and also want to know about its phase angle (ratio of membrane capacity to total resistance), you should get one Use a body monitor from a doctor's office, which works as described above, which is not suitable for home use for reasons of cost.

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