Validity of estimating limb muscle volume by bioelectrical impedance

The present study aimed to investigate the validity of estimating muscle volume by bioelectrical impedance analysis. Bioelectrical impedance and series cross-sectional images of the forearm, upper arm, lower leg, and thigh on the right side were determined in 22 healthy young adult men using a specially designed bioelectrical impedance acquisition system and magnetic resonance imaging (MRI) method, respectively. The impedance index (L(2)/Z) for every segment, calculated as the ratio of segment length squared to the impedance, was significantly correlated to the muscle volume measured by MRI, with r = 0.902-0.976 (P < 0.05). In these relationships, the SE of estimation was 38.4 cm(3) for the forearm, 40.9 cm(3) for the upper arm, 107.2 cm(3) for the lower leg, and 362.3 cm(3) for the thigh. Moreover, isometric torque developed in elbow flexion or extension and knee flexion or extension was significantly correlated to the L(2)/Z values of the upper arm and thigh, respectively, with correlation coefficients of 0.770-0.937 (P < 0.05), which differed insignificantly from those (0.799-0.958; P < 0.05) in the corresponding relationships with the muscle volume measured by MRI of elbow flexors or extensors and knee flexors or extensors. Thus the present study indicates that bioelectrical impedance analysis may be useful to predict the muscle volume and to investigate possible relations between muscle size and strength capability in a limited segment of the upper and lower limbs.