title: Estimation of total body water and extracellular water with bioimpedance in athletes: A need for athlete-specific prediction models.
abstract: OBJECTIVE
  Bioelectrical impedance analysis (BIA) equations can predict total body water (TBW) and extracellular water (ECW) in non-athletic healthy populations. This study aimed: a) to develop BIA-based models for TBW and ECW prediction based on dilution methods in a sample of national level athletes; and b) to validate the new models with a cross-validation approach in a separate cohort using dilution methods as criterion.
  
  
  METHODS
  Two hundred and eight highly trained athletes (21.3 ± 5.0 years) were evaluated during their respective competitive seasons. Athletes were randomly split into development (n = 139) and validation groups (n = 69). The criterion method for TBW was deuterium dilution and for ECW was bromide dilution, where ICW was the respective difference between both. Resistance (R) and reactance (Xc) were obtained with a phase-sensitive 50 kHz BIA device and used for the estimation of TBW and ECW.
  
  
  RESULTS
  Athletic BIA-based models were developed for TBW and ECW [TBW = 0.286 + 0.195*S(2)/R + 0.385*Wt + 5.086*Sex; ECW = 1.579 + 0.055*S(2)/R + 0.127*Wt + 0.006*S(2)/Xc + 0.932*Sex, where sex is 0 if female or 1 if male, Wt is weight (kg), S is stature (cm), and R and Xc are in ohm (Ω)]. Cross validation revealed R(2) of 0.91 for TBW and R(2) 0.70 for ECW and no mean bias.
  
  
  CONCLUSIONS
  The new equations can be considered valid, with no observed bias, thus affording practical means to quantify TBW and ECW in national level athletes.
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal.
authors.forename: Catarina N
authors.initials: CN
authors.lastname: Matias
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal.
authors.forename: Diana A
authors.initials: DA
authors.lastname: Santos
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal.
authors.forename: Pedro B
authors.initials: PB
authors.lastname: Júdice
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal.
authors.forename: João P
authors.initials: JP
authors.lastname: Magalhães
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal.
authors.forename: Cláudia S
authors.initials: CS
authors.lastname: Minderico
authors.affiliation: Department of Pediatrics, Children's Medical Research Institute's Metabolic Research Program, University of Oklahoma Health Science Center, Norman, OK, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Fields
authors.affiliation: Department of Kinesiology and Public Health Education, Hyslop Sports Center, University of North Dakota, Grand Forks, ND, USA.
authors.forename: Henry C
authors.initials: HC
authors.lastname: Lukaski
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal.
authors.forename: Luís B
authors.initials: LB
authors.lastname: Sardinha
authors.affiliation: Exercise and Health Laboratory, CIPER, Faculdade Motricidade Humana, Universidade Lisboa, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal. Electronic address: analiza@fmh.ulisboa.pt.
authors.forename: Analiza M
authors.initials: AM
authors.lastname: Silva
mesh_terms: D000293:Adolescent; D000328:Adult; D056352:Athletes; D001823:Body Composition; D015992:Body Mass Index; D001834:Body Water / Q000737:chemistry*; D001835:Body Weight; D003430:Cross-Sectional Studies; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D011897:Random Allocation; D015203:Reproducibility of Results; D014867:Water / Q000032:analysis*; D055815:Young Adult
chemical_list: D014867:Water
keywords: Athletes; Body composition; Dilution techniques; Extracellular water; Intracellular water; Total body water