## 4 Discussion  
The main finding of this study was the usability of BIA\({}_{\rm{8 MF}}\) to estimate the BMC with 82.1% to 90.7% of the DXA BMC explanation (with adjustments on the BIA BMC measurement or by using BIA parameters and/or subjects physical and biological characteristics). Figure 2: Analysis of residual scores of DXA BMC and BMC estimated by Model 1 (**a**), Model 2 (**b**), Model 3A (**c**), Model 3B (**d**), Model 4A (**e**), and Model 4B (**f**). The previous studies that investigated the BIA's usability to estimate the BMC in adults had inconsistent conclusions, showing agreement [11] and disagreement [22; 23; 24; 25; 26] between the BIA estimates and values measured by DXA or inconclusive results [27]. That inconsistency between the studies that investigated the BIA's usability to estimate the body composition was previously shown at systematic reviews, and it was attributed to the use of different types of BIA (BIA\({}_{\text{SMF}}\) or tetrapolar (single or multi frequency)) and an intention to simultaneously validate the method and develop equations and the quality of the research [9; 13]. Regarding the BIA's usability to evaluate the BMC in children and adolescents, only two articles that investigated this association were found (non-systematic review data) [14; 15]. The results from [PERSON] et al. [15] were obtained from the same sample of the present study, and they showed that the BIA equipment internal equation was not suitable to estimate the DXA BMC (estimating 77.5% and 74.4% of DXA BMC with a standard error of 0.035 and 0.038 kg for females and males, respectively). The BIA BMC estimation is obtained by the division of the BIA FFM in the LSTM and the BMC, and while FFM and LSTM values were in agreement with those measured by DXA, the equipment internal equation showed in inability to accurately estimate the BMC [15; 17]. [PERSON] et al. [14] developed equations to estimate the BMC in children and adolescents without an HIV infection diagnosis using BIA parameters and/or the subjects' physical and biological characteristics which were able to estimate 88.6% to 93.2% of the DXA BMC (data regarding SEE were not showed). Those results agreed with the present study that found that the BIA was useful to estimate the DXA BMC also with adjustments to the BIA parameters and/or the inclusion of the subjects' physical and biological characteristics, showing that the equations were able to estimate 82.1% to 90.7% of the DXA BMC (SEE from 0.023 to 0.011 kg, respectively). However, the assumption of the BIA's usability to estimate the BMC in children and adolescents, based solely on the results discussed above, should be made cautiously, considering the limited number of studies on the matter, and the fact that [PERSON] et al. [14] did not show information regarding the SEE and internal or external validation of the developed equations. The BIA body composition estimates starts with the measurements of the resistance and reactance, which are followed by impedance, to estimate the TBW and then, the FFM values [7; 12; 13]. Based on those results, the FM is obtained by the subtraction of the FFM values from the total body mass, and the LSTM and BMC are obtained by the division of the FFM based on an equipment internal equation [12; 13; 17]. The different sets of models of this study considered the estimation process of the BIA, described above, and they were made with the purpose to investigate whether the adjustments in different moments of the BIA estimation process can result in a better BMC estimate. The results showed the improvement of the BMC estimate by the BIA with distinct adjustments: 82.1% of the DXA BMC was explained with an adjustment in the internal equation, but this was 89.9% when the model was based on the body water estimate and the subjects' physical and biological characteristics, and it was 90.7% when the model was based on the body mass and the subjects' physical and biological characteristics.