Abstract
The myofibrous organization of psoas major muscle in man was investigated by mean of the Sudan Black B staining method. The psoas major muscle was obtained from 10 patho-anatomical cadavers (4 males, 6 females) which was from 23 to 87 years old (average 65.4 years) . The cross-sectional area of the muscle, the number of muscle fibers in 1mm2, total number of muscle fibers in the cross section and each percentage, mean size and density of three fiber types were measured. Results : 1) The average of the crosssectional area, the number of muscle fibers in 1mm2, and the total number was 581mm2, 830 and 507, 579, respectively. The total number was superior in males to females and it tended to decrease with aging. 2) The average percentage of the 3-muscle fiber type was 62.8% in the white muscle fiber, 21.2% in the intermediate muscle fiber and 16.0% in the red muscle fiber. The composition was equal as that of gluteus maximus muscle in monkeys. 3) The average thickness of the 3-muscle fiber type was large in the order of the red muscle fiber, intermediate muscle fiber and white muscle fiber. The thickness of the white muscle fibers in the psoas major muscle was smallest in the prior reports. 4) On the distribution of the thickness of the muscle fibers, the compensatory hypertrophy according to the decrease of the number of muscle fibers was considered. But the muscle fibers had the tendency of the atrophy, ultimately. 5) The average density of the muscle fiber was 91.6%, and tended to become more rough with aging in both sexes.
