The tetrapolar bioelectrical impedance (BI) method has been proposed as a convenient, valid approach for estimating the body composition of normal healthy adults. However, the validity of the BI method has not yet been confirmed for Japanese junior high school boys and girls. The purpose of this study was to develop convenient and useful equations for predicting the body composition in junior high school boys and girls by the BI method. The subjects were 297 healthy boys and girls, aged 12.15 years, all of whom were Japanese. Impedance was measured using a tetrapolar bioelectrical impedance plethysmograph (800 pA, 50 kHz SIF-891) manufactured by Selco. Multiple regression analysis was used to derive prediction equations for Db that were specifically applicable to boys and girls. The effective prediction equations for Db were as follows : 1) Db=1.1860-0.1282 (Wt·Z) /Ht2, and 2) Db=1.1402-0.0706 (Wt·Z) /Ht2-0.0007· (abdomen) for boys. 1) Db=1.1337-0.0778 (Wt·Z) /Ht2, and 2) Db=1.1124-0.0498 (Wt·Z) /Ht2-0.0006· (subscapular) for girls, where Db=body density (g/ml), Wt=weight (kg), Z =impedance (ohms), Ht=height (cm) . Db estimated by each respective equation was highly correlated with body density measured by underwater weighing (UW-Db) : 1) r=0.881, SEE=0.00868/ml, 2) r=0.902, SEE=0.00788/nil for boys and 1) r= 0.741, SEE=0.0101 g/ml, 2) r=0.775, SEE =0.0095g/ml for girls. Furthermore, in a cross-validation analysis of prediction equations for Db, another sample consisting of 40 boys and 66 girls was used. Db estimated from each respective equation was correlated highly with UW-Db : 1) r=0.856, 2) r=0.887 for boys and 1) r=0.837, 2) r=0.860 for girls. There were no significant differences between the mean Db obtained by the BI method and that by the criterion method. We suggest that the prediction equations proposed in this study are useful for valid assessment of body composition of Japanese junior high school boys and girls aged 12 through 15 years.
