## 4 Discussion
### Models and Equations to Estimate Body Composition  
All the methods to estimate body composition have advantages and defects, and sports-health professionals have to choose methods with a better benefit-to-cost ratio [55]. The anthropometric method is easy, inexpensive, easy to transport, and quick to apply. This method also has sufficient validity and reliability to be considered a useful tool in the assessment of FM in the athlete population [56], but the reliability can be affected by the error introduced by the researcher (varying between 3.0% and 11.0% between a trained/expert and untrained/expert researcher) [57; 58]. One of the problems of the anthropometry method is the existence of multiple equations to estimate body composition, mainly FM [57; 59]. Equations for estimating FM commonly assume a constant value for the density of FM and free FM [53; 57]. While using a constant value for fat mass is generally accepted, free FM has been shown to be influenced by age, gender, and race, which introduces another potential source of bias [60; 61]. Additionally, while several equations have been validated to estimate FM, only [PERSON]'s equation has been validated using a direct method, whereas the others were validated using indirect methods [62]. Therefore, it is possible that there may be errors in estimating FM using these equations. [PERSON]'s equation allows the estimation of subcutaneous adipose tissue, which considers adipose tissue, including in its estimation of other non-lipid components (such as water and proteins) that are part of adipocytes [59; 62].  
Therefore, the use of the sum of skinfolds is effective, especially considering that other methods are affected by factors that are difficult to control and standardize, especially in the clinical setting, such as food intake, hydration levels, or daily physical activity [63; 64].  
Another problem is the level of fractionation of body composition used, specifically the adipose component. There is confusion in using the terms fat, lipids, and adiposity as synonyms when they are not [57]. There are five different levels to understanding how body mass is composed. The first model looks at the number of different atoms, including hydrogen, carbon, oxygen, nitrogen, calcium, phosphorus, and others. The second model considers body mass in terms of the different types of molecules it contains, including lipids, water, proteins, carbohydrates, and minerals. The third model takes into account the different types of matter that make up the body's cells, including fat, water, and solids. The fourth model looks at body mass in terms of different types of tissues, such as adipose tissue, muscle, bone, and connective tissue. Finally, the fifth model considers the body as a whole and breaks it down into different segments, such as the head, trunk, and limbs, to understand how mass is distributed throughout the body [57; 59; 65]. The anthropometric method is possible to approach adiposity using molecular and tissue models [53; 57].  
In conclusion, for the first time to our knowledge, it has been possible to establish indicative reference values for the different body compartments (Figure 3).