Please cite this article in press as: Matias CN, et al. Total body water and water compartments assessment in athletes: Validity of multi-frequency bioelectrical impedance. Sci sports (2018), https://doi.org/10.1016/j.scispo.2018.11.007 ARTICLE IN PRESS +Model SCISPO-3287; No. of Pages 7 Science & Sports (2018) xxx, xxx—xxx Disponible en ligne sur ScienceDirect www.sciencedirect.com ORIGINAL ARTICLE Total body water and water compartments assessment in athletes: Validity of multi-frequency bioelectrical impedance Évaluation de l’eau corporelle totale et des compartiments d’eau chez les athlètes : validité de l’impédance bioélectrique multifréquence C.N. Matias a,b,* , F.A. Noujeimi c , L.B. Sardinha a , V.H. Teixeira c,d , A.M. Silva a a Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz Quebrada, Portugal b Physiology and Biochemistry of Exercise Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz Quebrada, Portugal c Centro de Investigac ¸ão em Atividade Física (CIAFEL), Saúde e Lazer, Faculdade de Desporto, Universidade do Porto, 91, rua Dr. Plácido Costa, 4200-450 Porto, Portugal d Faculdade de Ciências da Nutric ¸ão e Alimentac ¸ão, Universidade do Porto, rua Dr. Roberto Frias, 4200-465 Porto, Portugal Received 5 June 2018; accepted 27 November 2018 KEYWORDS Athletes; Body water; Water compartments; Multi-frequency bioelectrical impedance; Dilution techniques Summary Bioelectrical impedance provides an affordable assessment of the body’s water compartments: total body water (TBW), extracellular (ECW) and intracellular water (ICW). However, little is known of its validity in athletes. We aim to validate TBW, ECW, and ICW obtained by multi-frequency bioelectrical impedance (MFBIA), using dilution techniques as reference (REF) in athletes. Thirty-six elite athletes (17males and 19females) with a mean age of 18.5 ± 4.1 years were evaluated. TBW, ECW, and ICW were assessed by MFBIA (Tanita MC-180MA) and dilution techniques. TBW REF and ECW REF were obtained by deuterium and bro- mide dilution techniques, respectively, while ICW REF was calculated as their difference. MFBIA underestimated ECW (∼1.3 kg) and overestimated TBW (∼1 kg) and ICW (∼3.5 kg), in relation to criterion. MFBIA explained 96%, 81%, and 83% of the total variability of results obtained from the reference for TBW, ECW, and ICW respectively. Standard error of the estimates ranged between ∗ Corresponding author. Faculdade de Motricidade Humana, Universidade de Lisboa, CIPER, Estrada da Costa, 1499-002 Cruz Quebrada, Portugal. E-mail address: cmatias@fmh.ulisboa.pt (C.N. Matias). https://doi.org/10.1016/j.scispo.2018.11.007 0765-1597/© 2018 Elsevier Masson SAS. All rights reserved.