Estimativa da massa muscular esquelética em mulheres idosas: validade da impedancia bioelétrica

摘要

The objectives of the present study were: a) to determine the agreement between bioelectrical impedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA) for the estimation of skeletal muscle mass (SMM), and b) to analyze the predictive power of anthropometric variables and BIA for the prediction of SMM in elderly women. A total of 120 women (60 to 81 years), living in the southern region of Brazil, were studied. Anthropometric variables (body weight and height) were measured. Resistance and hydration of fat-free tissues were measured by tetrapolar BIA (Biodynamics, BF-310) and by whole-body DXA (Lunar Prodigy DF + 14319 Radiation and DPX-L software, version 7.52.002). Differences between methods were determined using the paired t-test, analysis of residuals and correlation coefficient. The predictive value of the anthropometric variables and BIA was evaluated by multiple linear regression, adopting a level of significance of p < 0.05. No significant difference in the estimation of SMM was observed between methods (p < 0.01). BIA underestimated SMM in mean of 0.8 kg (95%CI: -3.7; 2.0 kg) when compared to DXA. Correlation between methods was high (r2 = 0.75; p < 0.01). Regression analysis demonstrated that the ratio between the square of height and resistance (HEIGHT2/R) explained 80% of the variation in SMM when adjusted to body weight and age, regardless of body fat, lean tissue hydration or body mass index. Thus, the BIA equation tested here is a valid tool for the estimation of SMM in elderly women and its value is best predicted by the regression model including HEIGHT2/R adjusted to body weight and age.