How do impedance scales measure our fat mass

The impedance scalesalso known as bioimpedance scalesthey don’t just measure our weight but also give us an overall picture of our body composition, also measuring ours fat massthe lean mass, the mass of our skeleton and the amount of water inside our body but also more specific information such as the ratio between essential fat and adipose fat. This information is useful for establishing dietary regimens, physical training, and health monitoring in clinical settings.

How an impedance balance works

Impedance scales use the basic quantities of electrical engineering which, together with empirical algorithms, estimate further body parameters.

The theory behind these devices is the bio-impedance measurementor the analysis ofbioelectrical impedance (BIA, from the English Bioelectrical Impedance Analysis) of the human body. This analysis is widely used in body composition assessment due to the high speed of information processing, as it is a non-invasive method that generates information through portable, easy-to-use and relatively inexpensive equipment, estimating fluid distribution bodies in the intra- and extra-cellular spaces.

L’electrical impedance it is a fundamental concept in the electrical engineering it describes how much a circuit resists current flow when a voltage is applied to its terminals. It is quite similar to the concept of electrical resistancebut it is a generalized concept as it takes into account not only the effects of electrical resistance but also the effects of capacity and of inductances present in the circuit (the so-called reactances). These reactive effects are only appreciated in circuits powered by quantities that vary over time (alternating quantities) and increase or decrease as the frequency varies. These effects do not exist in electrical circuits powered by direct current (at steady state).

The human body, from an electrical point of view, behaves like a conductor It therefore has its own electrical impedance, composed of resistance and capacitive reactance. This impedance, however, is not always constant in the human body but is very variable and depends on various factors, such as: hydration, state of health, stress, amount of muscle mass, fat mass, rather than on external environmental conditions. and by the path that the current takes within the body itself.

Bioimpedance scales, in addition to having the standard sensors for measuring body weight, have some metal plates on the support surface (the more advanced ones also have dumbbells to hold in the hand, as in the cover image) which act as real electrodes. By climbing on the scales (obviously barefoot and possibly naked) the scales imprint on the body of the person, standing on the scales, a very weak and imperceptible electric current, high frequency and low voltage. The same electrodes measure the potential difference that arises between the two feet, thus determining the impedance value. Once the body impedance has been measured, this data, combined with the measured weight plus a series of further data and information that are requested by the scale itself or by the application that manages it (such as sex, age, height, the physical activity carried out, etc.), applying some empirical formulas to estimate indirectly all the evaluable parameters previously described.


The uses of impedance scales

The best professional impedance scales are helpful tools necessary for monitoring body composition in contexts such as diet, physical training or medicine. They can help track progress toward health and fitness goals, providing a more comprehensive view of your body than just weight.

These devices are then employed and used by professionals in the field of nutrition to determine the basis on which to build any diet regime or to monitor its evolution over time, rather than as a personal trainer and in sport in general to monitor the physical state of an athlete or someone who simply does personal physical activity.

Finally, bio-impedance measurement is also used in clinical field, for example for the monitoring of some chronic diseases, providing complementary data on the clinical course of patients followed in the medium and long term. In this case the bioelectrical impedance analysis is not performed with scales but with dedicated medical equipment capable of providing more precise and reliable values.

How reliable are impedance scales?

The accuracy of impedance scales can vary based on several factors, including hydration and food consumption. Furthermore, the data they provide, as previously mentioned, does not directly measure fat mass or lean mass, but these values ​​are indirectly deduced based on empirical estimates. Therefore, the use made of these scales is for simple general monitoring without intending to be a precise diagnostic method.

It is therefore important to reiterate that these scales provide useful information on your physical state but do not replace professional medical advice. It is always advisable to set up a physical activity program appropriate to your body rather than a diet consult your doctor or healthcare professional first expert. In order to correctly interpret the data it is necessary to have a good knowledge of the fundamentals of this method, the correction equations used and the resources that the method can offer for the evaluation of body composition.