Estimating segment inertial properties: comparison of magnetic resonance imaging with existing methods.

To explore magnetic resonance imaging (MRI) as the basis of a technique for estimating body segment inertial properties directly on subjects, MRI-based estimates were compared with those generated with more traditional methods. The sensitivity of mass, center of mass location, and moment of inertia estimates to the estimation methods and the distribution of muscle, bone, and fat tissues in the lower leg were also evaluated. A series of transverse plane images spaced 2.5 cm apart on the right lower leg of 12 adult males were taken, using MRI. Cross-sectional area data determined from the images served as the basis of the inertial calculations. MRI-based estimates for mass, center of mass location, and moment of inertia about a transverse axis through the center of mass all fell within the range of values obtained with other methods. While the center of mass position was similar for all estimation methods, MRI-based estimates of lower leg mass and moment of inertia showed considerable variability among methods. In addition, MRI mass and moment of inertia values were higher than those from most of the other prediction methods. It is suggested that the higher MRI-based estimates for these descriptors may be reasonable when age and structural differences between young adult runners and cadaver specimens for the comparison studies are considered. These results provide further support for MRI as a means of generating valid inertial property estimates.