Introduction
Bioelectrical impedance analysis (BIA) is a physical method used to determine the exact composition of a living organism. 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 mass
- The extracellular noise mass
General information
This procedure is rarely used in medical practice to help with a diagnostic procedure, as the usual methods (X-ray, MRI) are suitable for this purpose. It is more often used for people who are interested in knowing their body fat percentage or who are interested in their exact percentage of muscle mass. Professional athletes, especially in the field of bodybuilding, often use it to evaluate their progress scientifically and 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), BIA can be used to give the patient a better self-image of his sick body. However, this is rarely used in practice, as such treatment tends to favour psychological and social factors and a rational argument based on facts and figures does not provide the patient with any clarification. You might also be interested in the topic: Body composition
Principle of bioelectric impedance analysis
From a physical point of view, the impedance of the organism under investigation is measured with the help of an alternating current of about 0.8mA and a 50kHz frequency. To do this, electrodes must be attached which create a magnetic field and further electrons which detect the voltage and the phase shift. The phase shift is nothing else than the shift of two equal functions, or curves to each other.
Trained personnel is required to attach the electrodes, which will place them in exactly the right position. In this context, one also speaks of four-wire measurement, since the electrodes provide four conductors 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 capacitances Xc.
Since every body is different in its composition, different resistances are also measured, which provide information about the tissues and organs of the body, as well as the electrolytes. In this case this refers to the ions inside and outside a cell, for example sodium and potassium. However, the physical basis for this is not only the measured resistance R, but also the so-called Xc value, which can determine the number of body cells as well as their quality.
The quality of the cells is mainly characterized by a high Xc value, because if a high value is present, it can be assumed that the cells are intact and healthy and do not show any deficient states, such as malnutrition. When assessing these deficient 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 calculated ratio of our previously measured values.
If this phase angle is particularly large, then the state of health of the examined athlete is excellent: he or she has a particularly large musculature, is athletic and well nourished. However, if the phase angle is very small, then malnutrition is very common, the athletic and general muscular condition of the patient is very low and therefore the risk of various diseases is very high. At first glance, BIA can be used to assess whether hormonal disorders, hypothyroidism/overactive thyroid and heart disease are present.
In addition, it is possible to limit its measurements to individual body compartments in the evaluation. For example, fat or muscle mass can be measured specifically in the extremities, i.e. the arms and legs. You might also be interested in the topic: Determination of body fatHowever, it should be mentioned that physical-medical measuring methods always only allow for a generally valid statement – the patient or person must be seen as an individual and therefore the results of an impedance analysis must be individually evaluated in each case with the specific medical history of a person. This means that even a very good athlete with muscles and little body fat can develop diseases and this result is not a free ticket for an unhealthy lifestyle.
