A video-based system for the estimation of the inertial properties of body segments

Abstract

A system for the estimation of the intertial properties of human body segments using advanced video technology and computer image processing was developed. The system is based on the photogrammetric technique, where three-dimensional information is determined from two separate two-dimensional video images. The inertial properties are calculated using an image-processing algorithm which provides volumetric information, coupled with a database of anatomical densities provided in the literature. In order to determine the accuracy of the system and its limitations, 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 inertial properties of the shank of three subjects, and comparing the results to data generated using regression equations provided in the literature. Human factors, such as segment boundaries identification and color thresholds selection, were found to introduce the largest errors. A proper selection of the optical setting can reduce the errors to levels of 5% or better. On the average, the system overestimated the inertial properties of solid objects by 2.51% for mass, 1.21% for center of mass, 4.53% for transverse moments of inertia and 3.65% for longitudinal moment of inertia. The video-based estimates of the mass and center of mass of the shank were comparable to values obtained from anthropometric-based regression equations. The predictions of the transverse moment of inertia of the shank varied considerably among the methods. The findings suggest that a video-based system represents a promising technique for estimating inertial properties of human body segments for individual subjects. Further studies of the inertial properties of cadaver body segments and the comparison to MRI-generated values are required to test the system estimates further.