Reliability and concurrent validity of Futrex and bioelectrical impedance

Thirty Caucasian males (aged 19-32 yr) participated in this study designed to investigate the reliability of multiple bioelectrical impedance analysis (BIA) and near-infrared spectroscopy (Futrex, FTX) measurements and the va lidity of BIA and FTX estimations of hydrostatically (UW) determined percen t body fat (%BF). Two BIA and two FTX instruments were used to make 6 measu rements each of resistance (R) and optical density (OD) respectively over a 30 min period on two consecutive days. Repeated measures ANOVA indicated t hat FTX and BIA, using manufacturer's equations, significantly (p<0.01) und er predicted UW by 2.4 and 3.8 %BF respectively. Standard error of estimate (SEE) and total error (TE) terms provided by regression analysis for FTX ( 4.6 and 5.31%BF respectively) and BIA (5.65 and 6.95%BF, respectively) were high. Dependent t-tests revealed no significant differences in either FTX or BIA predictions of %BF using two machines. Intraclass reliabilities for BIA and FIX estimates of UW %BF across trials, days, and machines all excee ded 0.97. A significant random error term associated with FTX and a signifi cant subject-by-day interaction associated with BIA was revealed using the generalizability model. Although FTX and BIA estimates of UW %BF were relia ble, due to the significant underestimation of UW %BF and high SEE and TE, neither FTX nor BIA were considered valid estimates of hydrostatically dete rmined %BF.