Tetrapolar bioelectrical impedance analysis is influenced by time-of-measurement

Abstract

Bio-electrical impedance analysis (BIA) is an attractive method to assess body composition due to its accuracy, time- and cost-effectiveness and simplicity-of-use. Many factors have a confounding influence on the accuracy of the measurement, such as the time-of-measurement once the person assumes a supine position. This occurs due to fluid shifts from a standing to supine position. The purpose of the current study was to determine the effect of assessing body composition at 5-minutes (test) and again at 7-minutes (re-test). Eighty-one college students (21±2 years; 40 men and 41 women) completed the study. Standardised procedures for BIA measurement were followed as outlined in Gonzalez-Correa and Caicedo-Eraso. A paired sample t-test and Bland-Altman analysis were performed between test and re-test. The resistance (R), reactance (Xc) and impedance (Z) increased by 0.8%, 0.6%, and 0.8% from 5 to 7 minutes respectively. Mean values of raw data (R, Xc and Z) and estimated data (total body water, percentage body fat) were significantly different between test and re-test (p<0.01). The Bland- Altman plots revealed systematic bias between measurements. This study emphasises the sensitive nature of time-of-measurement once supine in BIA assessments. The assessment of body composition should occur after 5-minutes once supine.

Keywords: Bio-electrical impedance analysis; Resistance; Reactance; Impedance Body composition