Identifying Athlete Body Fluid Changes During a Competitive Season With Bioelectrical Impedance Vector Analysis

<jats:p><jats:italic><jats:bold>Purpose</jats:bold>:</jats:italic>To analyze the association between body fluid changes evaluated by bioelectrical impedance vector analysis and dilution techniques over a competitive season in athletes.<jats:italic><jats:bold>Methods</jats:bold>:</jats:italic>A total of 58 athletes of both sexes (men: age 18.7 [4.0] y and women: age 19.2 [6.0] y) engaging in different sports were evaluated at the beginning (pre) and 6 months after (post) the competitive season. Deuterium dilution and bromide dilution were used as the criterion methods to assess total body water (TBW) and extracellular water (ECW), respectively; intracellular water (ICW) was calculated as TBW–ECW. Bioelectrical resistance and reactance were obtained with a phase-sensitive 50-kHz bioelectrical impedance analysis device; bioelectrical impedance vector analysis was applied. Dual-energy X-ray absorptiometry was used to assess fat mass and fat-free mass. The athletes were empirically classified considering TBW change (pre–post, increase or decrease) according to sex.<jats:italic><jats:bold>Results</jats:bold>:</jats:italic>Significant mean vector displacements in the postgroups were observed in both sexes. Specifically, reductions in vector length (Z/H) were associated with increases in TBW and ICW (<jats:italic>r</jats:italic> = −.718,<jats:italic>P</jats:italic> < .01;<jats:italic>r</jats:italic> = −.630,<jats:italic>P</jats:italic> < .01, respectively) and decreases in ECW:ICW ratio (<jats:italic>r</jats:italic> = .344,<jats:italic>P</jats:italic> < .05), even after adjusting for age, height, and sex. Phase-angle variations were positively associated with TBW and ICW (<jats:italic>r</jats:italic> = .458,<jats:italic>P</jats:italic> < .01;<jats:italic>r</jats:italic> = .564,<jats:italic>P</jats:italic> < .01, respectively) and negatively associated with ECW:ICW (<jats:italic>r</jats:italic> = −.436,<jats:italic>P</jats:italic> < .01). Phase angle significantly increased in all the postgroups except in women in whom TBW decreased.<jats:italic><jats:bold>Conclusions</jats:bold>:</jats:italic>The results suggest that bioelectrical impedance vector analysis is a suitable method to obtain a qualitative indication of body fluid changes during a competitive season in athletes.</jats:p>