## 5 Conclusions  
BIVA is a quantitative analytical method for the study of body composition based on the measurement of tissue electrical impedance. It is currently employed in clinical practice because of its rapidity, ease of use, harmlessness, high reproduction rate, and lack of active patient cooperation. All these aspects are common to both BIVA and BIA; however, in addition, BIVA does not presume anything about body compartments, weight, geometry or hydration status, so it does not present the limitations of the two-compartment model for BC evaluation and thus produces fewer estimation errors to quantify TBW or BC. Because of to the excellent results of BIVA in clinical practice, it is here proposed for use in sports. Recent studies have shown that BIVA can be applied to monitor athletes by using both quantitative and qualitative parameters, as a new regression equation has been developed specifically for athletes [25], and the impedance vector distribution is similar to that of elite athletes, with clear differences from the general population [28; 32].  
As shown in the examples provided, BIVA is consistent with somatotype and coherent with BC interpretation; however, BIVA also provides information about hydration and BCM. Furthermore, there is evidence that it can also detect dehydration caused by intense exercise and posterior rehydration more efficiently than conventional methods. In conclusion, the application of BIVA in the evaluation and monitoring of athletes could improve BC studies in sports if used and interpreted correctly. However, further validation of BIVA for different sports and disciplines is necessary, which is equally useful to develop reference tolerance ellipses for the athlete population (by sport, age, gender, and race).  
Conceptualization, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Data curation, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Formal analysis, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Investigation, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Methodology, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Resources, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Software, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Supervision, M.P.R.d.R. and B.d.M.S.; Validation, M.P.R.d.R. and B.d.M.S.; Writing--Original draft, S.d.l.C.M., M.P.R.d.R. and B.d.M.S.; Writing--Review & editing, S.d.l.C.M., M.P.R.d.R. and B.d.M.S. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Somatotype** & **BIVA Nomogram** \\ \hline BMI (kg/m\({}^{2}\)) & 37.5 & 18.5–24.9 \\ SOMATOTYPE (Endo/Meso/Ecto) & 3.9/4.1/2.3 & 3.6/ 4.9/1.9 \\ FFM (kg/\%) & 83.8/70.8 & 47.0 (6.1)/— \\ FM (kg/\%) & 34.7/29.3 & 15.7 (4.9)/24.6 (4.8) \\ Phase angle & 6.7 & 6.8 \(\pm\) 0.8 \\ \hline \hline \end{tabular}  
* BMI: body mass index; Endo: endomorph; Meso: mesomorph; Ecto: ectomorph; FFM: fat-free mass; FFM: fat mass.
* Reference values: BMI [48]; somatotype [25]; phase angle [49].  
\end{table}
Table 6: Descriptive characteristics of the female athlete performing rugby.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by Clinical Research Ethics Committee (CEIC) of Valladolid-East Health Area (Protocol code: PI 16-512 of 17 January 2017).  
**Informed Consent Statement:** Written informed consent was obtained from all subjects that participated in the study.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The research team thanks all volunteers who participated in the study for their collaboration.  
**Conflicts of Interest:** The authors declare that there is no conflict of interest.