Padrão de distribuição de vetores de impedância bioelétrica em adolescentes atletas

Abstract

The Bioimpedance Vector Analysis (BIVA) can be used to qualitatively compare total body water and body cell mass independently of specific models and predictive equations. This thesis aims to describe BIVA patterns for adolescents athletes according to sex and handgrip strength (cross-sectional study) and according to sex and nutritional status (longitudinal study). For such objective, two databanks will be analyzed. In both, values of bioelectrical impedance (Z), resistance (R), reactance (Xc) and phase angle (PhA) were obtained using a single frequency bioimpedance analyzer (RJL®). Fat-free mass (FFM) and total body water (TBW) were estimated using predictive equations. The first study aimed to investigate vector disposition considering sex, age and handgrip strength. 273 adolescents (male, n = 161) involved with different sports participated. Female adolescents presented higher values of R (5.5%, p = 0.001), R/height (3.8%, p = 0.041), Z (5.3%, p = 0.001), and fat mass (53.9%, p = 0.001). Male adolescents presented higher values of FFM (5.3%, p = 0.021) and PhA (3.1%, p = 0.033). In both stratifications (age and handgrip strength), for both sexes, BIVA ellipses shifted to left in RXc graphs in relation to younger (≤13 years) and to lower strength (<median), presenting patterns related to higher TBW and body cell mass. Discrimination of older and higher strength individual evidenced by confidence ellipses possibly represents differences in biological maturity evidencing influences of age and strength in vector disposition in BIVA. The second study aimed to identify vector disposition in a longitudinal study considering sex and body mass index (BMI). 138 adolescents athletes (male, n = 83) participated. All adolescents were submitted to BIA in baseline (T0) and one year follow-up (T1). Confidence ellipses presented significative Mahalanobis distances (D) differentiating between normal weight and overweight participants (p<0.01). In female adolescents, D were 1.3 (T0) and 1.19 (T1); in male, 1.37 (T0) and 1.32 (T1). Paired confidence ellipses did not differentiate only overweight female adolescents (D= 0.43, p= 0.20). Tolerance ellipses showed mean vector migrations related to cell mass in female, and to total body water in male. BIVA was able to identify adolescents according to BMI in T0 and T1. Sex and BMI are relevant factors to be considered in longitudinal studies to follow adolescents throughout development.