Influence of elbow angle on the reliability and validity of bioelectrical impedance analysis

Abstract

Hand-to-hand bioelectrical impedance (HH BIA) is a low-cost method to estimate percent body fat (%BF). The BIA method is consistently reliable, but questions on validity remain. We have observed anecdotally that elbow position can render consistently different measures of %BF while using HH BIA, thus leading to the question: Does elbow angle influence the validity of measures derived using HH BIA? The purpose of this study was to assess the effect of elbow position (i.e., IN=flexed to 90° versus OUT=fully extended) on the reliability of HH BIA on 44 male and 24 female healthy adults (age=21±2 yrs, BMI=23±3). An additional aim was to assess the validity of the HH BIA %BF on a subset of subjects (n=12) using air displacement plethysmography (BOD POD®) as the criterion measure. The IN position was ~4%BF lower than the OUT position for HH BIA (p=0.05, effect size=0.67). Measures of %BF for both trials for the IN [intraclass correlation coefficient (ICC)=0.99, coefficient of variation (CV)=2.99%] and OUT (ICC=0.99, CV=1.48%) conditions were highly reliable. On the subsample, the OUT (18.3±6.7 %BF) position exceeded both the IN (14.5±7.4 %BF) and the BOD POD® (16.1±7.8 %BF) measures (p<0.05); however, IN and BOD POD® measures of %BF did not differ (p=0.21). These findings support that HH BIA is a reliable measure at both elbow positions; however, %BF estimations vary considerably (~4%) with respect to the criterion measure depending on elbow position. The OUT position was found to overestimate criteria %BF. Further research may reveal an optimum elbow angle position for HH BIA estimates of %BF.