Phase angle and bioelectrical impedance vector analysis in the evaluation of body composition in athletes

Aims: To analyze the association of classic and specific bioelectrical impedance vector analysis (BIVA) and phase angle with reference techniques for the assessment of body composition in athletes. Methods: 202 athletes of both sexes (men: 21.5 ± 5.0; women: 20.7 ± 5.1) engaged in different sports were evaluated during the in-season period. Bioelectrical resistance (R, ohm) and reactance (Xc, ohm) were obtained with a phase-sensitive 50 kHz bioelectrical impedance analysis device. The classic and specific BIVA procedures, which respectively correct bioelectrical values for body height (R/H and Xc/H, ohm/m) and body geometry (Rsp and Xcsp, ohm cm), were applied. Dual energy X-ray absorptiometry was used as the reference method to assess fat-mass (FM), fat-free mass (FFM) and %FM. Deuterium dilution and bromide dilution where used as the criterion method for total body water (TBW) and extracellular water (ECW), respectively. Intracellular water (ICW) was calculated as TBW minus ECW. Results: Specific bioelectrical values (Rsp, Xcsp, Zsp) were positively correlated with FM and %FM (%FM; Zsp men: r = 0.569, p < 0.001; Zsp women: r = 0.773, p < 0.001). Classic values (R/H, Xc/H, Z/H) were negatively correlated with FM and FFM, but were correlated with %FM only in men (Z/H men: r = −0.214, p = 0.013; Z/H women: r = 0.218, p = 0.097). As to body fluid, classic BIVA showed strong associations (Z/H men: r = −0.880, p < 0.001; Z/H women: r = −0.829, p < 0.001) with TBW, whereas Zsp was not correlated. Phase angle was negatively correlated with ECW/ICW ratio in both sexes (men: r = −0.493, p < 0.001; women: r = −0.408, p < 0.001) and positively with ICW (men: r = 0.327, p < 0.001; women: r = 0.243, p = 0.080). Conclusions: Specific BIVA turns out to be more accurate for the analysis of %FM in athletes, while it does not correctly evaluate TBW, for which classic BIVA appears to be a suitable approach. Phase angles, and hence both BIVA approaches, can detect ECW/ICW changes