A VIDEO-BASED SYSTEM FOR THE ESTIMATION OF THE INERTIAL PROPERTIES OFBODY SEGMENTS

A system for the estimation of the inertial properties of human body s egments using advanced video technology and computer image processing was developed. The system is based on the photogrammetric technique, w here three-dimensional information is determined from two separate two -dimensional video images. The inertial properties are calculated usin g an image-processing algorithm which provides volumetric information, coupled with a database of anatomical densities provided in the liter ature. In order to determine the accuracy of the system and its limita tions, the system estimates of the inertial properties of solid bodies were compared to theoretically calculated values. The application of the system to kinesiological studies is illustrated by measuring the i nertial properties of the shank of three subjects, and comparing the r esults to data generated using regression equations provided in the li terature. Human factors, such as segment boundaries identification and color thresholds selection, were found to introduce the largest error s. A proper selection of the optical setting can reduce the errors to levels of 5% or better. On the average, the system overestimated the i nertial properties of solid objects by 2.51% for mass, 1.21% for cente r of mass, 4.53% for transverse moments of inertia and 3.65% for longi tudinal moment of inertia. The video-based estimates of the mass and c enter of mass of the shank were comparable to values obtained from ant hropometric-based regression equations. The predictions of the transve rse moment of inertia of the shank varied considerably among the metho ds. The findings suggest that a video-based system represents a promis ing technique for estimating inertial properties of human body segment s for individual subjects. Further studies of the inertial properties of cadaver body segments and the comparison to MRI-generated values ar e required to test the system estimates further.