On the total number of muscle fibers in venter of human anterior tibialis muscle

Abstract

Using peripheral quantitative computed tomography, (pQCT XCT540, Norland Stratec Co.Ltd.), we quantitatively investigated the age changes of cross-sectional shape of left distal radius (4% of forearm length) inChimpanzees and Japanese Macaques. We devised the Roughness index to quantify the contour shape, that is, standard deviation of radius (from center of gravity of contour). We also analyzed the age change of body weight and other bone parameters (Total Area of the cross-section, Cortical Area and Cortical Density). The results obtaind are as follows: 1) There are three types in patterns of age change. First is the patterns of body weight, Total Area of the cross-section and Cortical Area, which are composed of rapid increase growth and flat adult phases. Second is that of Cortical Density, composed of rapid increase and slow increase phase. Third is that of the Roughness index, increasing linealy with age without significant change of pace. 2) The noticeable differences between the two species are observed in growth span, Cortical Density in adulthood and the intercept of the regression of Roughness Index against age which relates to the fact that the shapes of cross-section is square in Chimpanzees and triangle in Japanese Macaques. 3) The increase in Roughness index and Cortical Density in adulthood indicates remodeling process continues after growth, i.e.,redistribution of bone materials among Cortical parts. By the remodeling, the strengh of bone may be increaced in a specific direction (medio-laterally). The difference of the cross-sectional shapes in the two species appears to reflect the difference in th direction of the secondary mechanical stress in distal forearm.