Bioimpedance parameters in adolescent athletes in relation to bone maturity and biochemical zinc indices

Phase angle (PA) is derived from resistance and reactance determined by bioimpedance analysis (BIA) and it appears to relate to cellular stability and integrity. Interpretation of PA values could be complemented by bioelectrical impedance vector analysis (BIVA), which relates to body hydration and structure. Body composition, age, sex, and nutrients are known to stabilize cell membranes, such as zinc, have been related to PA although information is scarce in adolescent athletes. The aim of the present study was to assess the association of body composition, skeletal maturity and zinc biochemical indices with phase angle and bioelectrical impedance parameters, in forty male adolescent soccer athletes (13.4±0.6years). BIA was performed with a single-frequency tetrapolar analyzer. PA and BIVA were determined using resistance and reactance BIA data. Plasma and erythrocyte zinc concentrations were measured using inductively coupled plasma-optical emission spectrometry. Body composition was determined by dual-energy X-ray absorptiometry, and bone age by hand X-ray measurements. PA was higher in adolescents classified by bone age as "Early" (6.8±0.9°) compared to "Late" (5.7±0.5°) (p<0.05). PA correlated with bone age (r=0.562), BMI (r=0.382), fat-free mass (r=0.468), and erythrocyte zinc (r=0.379) (p<0.05). BIVA confidence ellipses were sensitive to skeletal maturity status. Phase angle was higher in adolescents with erythrocyte zinc concentration above the median (>0.66μmol.g hemoglobin^-1) compared to those below the median. Multiple linear regression analysis showed that bone age (B=0.254, p=0.001) and erythrocyte zinc concentration (B=1.168, p=0.047) were significantly related to PA in this group, and accounted for 34% of its variability. Our results indicate that bone age and zinc erythrocyte contribute to PA values in the young male soccer athletes and that BIVA is influenced by skeletal maturity status in this group.