Reliability and Concurrent Validity of Futrex and Bioelectrical Impedance

Thirty Caucasian males (aged 19-32yr) participated in this study designed to investigate the reliability of multiple bioelectrical impedance analysis (BIA) and near-infrared spectroscopy (Futrex, FTX) measurements and the validity of BIA and FTX estimations of hydrostatically (UW) determined percent body fat ( % BF). Two BIA and two FTX instruments were used to make 6 measurements each of resistance (R) and optical density (OD) respectively over a 30 min period on two consecutive days. Repeated measures ANOVA indicated that FTX and BIA, using manufacturer's equations, significantly (p<0.01) under 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 FTX estimates of UW % BF across trials, days, and machines all exceeded 0.97. A significant random error term associated with FTX and a significant subject-by-day interaction associated with BIA was revealed using the generalizability model. Although FTX and BIA estimates of UW % BF were reliable, due to the significant underestimation of UW % BF and high SEE and TE, neither FTX nor BIA were considered valid estimates of hydrostatically determined % BF.

Key words

Percent body fat - near-infrared spectroscopy/in-teractance - electrical impedance