Validity of bioelectrical impedance equations for estimating fat-free mass in young athletes

This study examined the validity of bioelectrical impedance (BIA) equations for estimating fat-free mass (FFM) in 117 Caucasian athletes (M age +/- SD = 11 +/- 2 yrs) who volunteered to undergo underwater weighing (UWW) and BIA assessment. Eleven BIA equations and a machine-generated value (BIAM) were cross-validated. Cross-validation analyses included examination of constant error (CE), standard error of estimate (SEE), r, and total error (TE). The results indicated that the equation of Guo most accurately estimated FFM due to a nonsignificant CE (p > 0.004) (0.12 kg), the lowest SEE (1.99 kg), and the lowest TE (2.09 kg). Two equations developed by Houtkooper and BIAM resulted in TE values of less than or equal to 2.69 kg and should be considered acceptable alternatives to the equation of Guo.