The results of H, Z, Φ, V, and ρ, by sex show consistent reference values for assessing individual deviations in the population mean. Φ increases up to the 15–16 age group and decreases from 17–18 up to 70–89 age groups. The behavior of this bioelectrical parameter in this study could be since during the development and growth of the organism, physiological and morphological changes of the body composition associated with age and with growth, development, and aging occur. This process results in changes in fluid and ion content, as well as in muscle mass, fat mass, and cell mass25.
This finding coincides with that reported by Lukaski and García26, who state that the values of this bioelectrical parameter decrease substantially in aging. Barbosa et al.27, Bosy et al.28 and Dittmar29 in population studies also demonstrated the lower value of Φ, considering a loss of muscle mass.
Ręba30 also considers that Φ provides information on nutritional status, cell membrane integrity, cellular health, and total body mobility. The value of Φ allows tracking nutrition and monitoring recovery and fitness. This bioelectrical parameter characterizes fluid distribution between intracellular and extracellular compartments. This researcher clarifies that Φ has gained interest due to the ability to compare an individual value with normative data, stratified by age and sex, from the healthy population.
Carreira et al.31 explain that Φ has a lower value in populations with associated pathologies. This fact reflects the influence of this bioelectrical parameter on pathological conditions such as infection, inflammation, and various alterations specific to numerous diseases. These researchers suggest that this bioelectrical parameter might be considered a consistent indicator of nutritional condition, regarding disease. They also state that it is a prognostic marker in various chronic pathologies such as cancer.
On the contrary, ρe values in patients are outside the normal range. This suggests the presence of some associated pathology. However, the specific resistivity in biological conductors is not constant and varies depending on the microstructure of the tissue, hydration status, as well as the concentration and type of ions. The predictive action this parameter can be explained from the close relationship between the electrical volume (TBW) of the body, the lengths of all its segments and the specific resistivity of each one, the impedance of the whole body and the fat-free mass32,33.
The ρ parameter results lower in childhood and adolescence, and higher in adulthood. Additionally, this parameter shows higher values in females than in males. This result coincides with that reported by Roman et al. 34, who found that ρ is higher in women than in men, with statistically significant differences. They explain this finding by the fact that in the female sex, there is a considerable amount of total body fat, subcutaneous fat in the extremities, and fat in the individual tissues.
In this sense, Chumlea et al. 35 suggest that this parameter is to recognize the levels of lean mass in individuals. These researchers propose that each tissue has its specific resistance, and the resistivity of a segment or the whole body is the average specific resistance for all the tissues through which the current passes. They propose that electrical bioimpedance and specific resistivity could be a method for estimating body composition.
Also, Chumlea and Guo36 state that variations between tissue and body segment-specific resistances occur due to intra and interindividual differences in body composition.
The results obtained from this study may be due to the existence of intrinsic and extrinsic factors that influence the growth and development of the organism. Among the intrinsic factors are genetic and hormonal factors, and within the latter are nutritional, hygienic, and pathological ones37,38,39.
Any change in tissue physiology can produce changes in the electrical properties of the tissue. This principle is to identify or monitor the presence of different diseases or pathological conditions using electrical bioimpedance40,41.
In the case of individuals with associated pathologies, the normal values of Φ in the female sex suggest that this bioelectrical parameter may not be as consistent in the prognosis of these diseases.
Studies performed by the Electrical Bioimpedance method in patients with different pathologies such as HIV/AIDS, cancer, and cardiopathy among others, show the Φ in normal ranges if these patients are stable and compensated. However, its decrease may suggest that the patient is in the advanced stages of the disease with severe symptoms and signs of decompensation43,44,45,46.