Physical properties of the human trunk as determined by computed tomography.

The purpose of this study was to determine the center of mass of the trunk in living subjects by using computed tomography (CT), thus providing more accurate data to aid scientists in their effort to describe human motion quantitatively. This advanced x-ray was used to analyze the trunk segment of four subjects, two men and two women, ranging in age from 46 to 68 years. Scans were taken at 1 cm intervals, from the level of the superior surface of the pubic symphysis to the suprasternal notch. Data were processed by an on-line computer, with the object represented on photographic film as a gradient image of gray levels. The intensity of the gray scale in each cross-sectional scan corresponded to a particular density of human body tissue. The computer program was capable of interpreting this information, thereby providing values for the center of mass, tissue density, segmental mass, and volume. The study's conclusions are based on data obtained from living subjects which may be representative of the general adult population. We found that the mean center of mass of the trunk segment was 49.35% of the total length as measured from the line joining the greater trochanters across the superior surface of the pubic symphysis to the suprasternal notch. Furthermore, the segmental mass of the trunk segment was found to be 52.58% of total body weight. These data differ from trunk cadaveric studies already published.