ON THE MYOFIBROUS ORGANIZATION OF HUMAN ILIOPSOAS MUSCLE (PSOAS MAJOR MUSCLE AND ILIACUS MUSCLE)

The myofibrous organizations of psoas major muscle and iliacus muscle in man were investigated and those functional characteristics were compared with other human muscles. 11 pairs of psoas major muscle (6 males, 5 females) and 6 iliacus muscles (3 males, 3 females) were examined by Haematoxylin-Eosin staining method. And the muscles from one cadaver (female, 45 years) were investigated by Sudan Black B staining method and compared with former. Results: I. Views obtained from Sudan Black B staining method. 1) As for the ratios of three muscle fiber types, the white muscle fiber (41.3 %) was the highest in psoas major muscle, while in iliacus muscle, the white (38.3 %) was almost equal to the intermediate muscle fibers (40.5 %) . The ratio of red muscle fibers was the lowest in both muscles. 2) The average thickness of each fiber type was large in the order of the red, the intermediate and the white muscle fibers. The red muscle fibers were about three times as large as the white. 3) As for the density of muscle fibers, those of the red and the intermediate muscle fibers were the highest in psoas major and iliacus muscle respectively. II. Views obtained from Haematoxylin-Eosin staining method. 1) The cross-sectional area of psoas major muscle were superior in males to females, but in iliacus muscle there was no difference between both sexes. While in each muscle, there was no difference in males, but in females, iliacus muscle tended to be superior to the other. 2) The number of muscle fibers in 1 mm₂ in psoas major muscle was superior to iliacus muscle, and had no differences caused by sex. In iliacus muscle, it tended to be superior in females to males. 3) The total numbers of muscle fibers in each muscle were equal to that of biceps brachii muscle. In males, those were more in psoas major muscle than iliacus muscle, while in females, iliacus muscle was more. 4) The thickness of the muscle fibers was superior in iliacus muscle to psoas major muscle, and the latter was equal to biceps brachii muscle. From the distribution pattern of the thickness of muscle fibers, it was considered that the muscle fibers of psoas major muscle had an obvious tendency to atrophy in comparison with iliacus muscle. 5) The density of muscle fibers was about 80 % in both muscles. In psoas major muscle, it was superior in males to females and tended to become low with aging in both sexes. 6) As above mentioned, both muscles were suggested to work to maintain the winding position of hip joint and to have a muscle capacity which was almost equal to biceps brachii muscle. When walking, iliacus muscle was also suggested to work to rotate femur, and that was supposed to be more remarkable in females.