VALIDATION OF A BIOIMPEDANCE EQUATION FOR ESTIMATING FAT-FREE MASS OF SPINAL CORD INJURED ADULTS 319

Abstract

This study developed and cross-validated a bioimpedance (BIA) equation for estimating the fat-free mass (FFM) of 91 spinal cord injured (SCI) adults, 18 to 73 years. Dual energy x-ray absorptiometry was used to obtain reference measures of FFM. Resistance and reactance were measured with an RJL (model 101A) bioimpedance analyzer. BIA equations were developed and cross-validated using regression analysis. Subjects were randomly divided into validation (n = 61) and cross-validation (n = 30) groups. The combination of height2/resistance, body weight, age and gender accounted for a significant proportion of the variability in FFM (R2 =.83, SEE = 3.5 kg). The predictive accuracy of this equation was acceptable, with R2=.87, SEE = 3.2 kg, E = 3.5 kg. The average predicted FFM (50.7 kg) did not differ significantly from reference FFM (50.5 kg). Thus, we recommend using this BIA equation for estimating the FFM of SCI adults: FFMBIA = 18.874+ Ht2/R (0.367) + weight (0.253) - age (0.081) - gender (5.384),(gender code: male = 0, female = 1)