title: Composition of psoas major muscle fibers compared among humans, orangutans, and monkeys.
abstract: In primate species the m. psoas major, the only muscle simultaneously controlling the spinal column and lower extremity, is expected to reflect morpho-functional adaptation to diversified locomotor behavior. By using histochemical analysis with Sudan black B staining, composition of different types of muscle fibers in the psoas major was compared between 2 Japanese macaques, 2 hamadryas baboons, 2 anubis baboons, 2 orangutans, and 17 humans. The comparison has revealed unique features of this muscle in humans: 1) Type 1 or red fibers are thicker than Type 2 or white fibers in humans but vice versa in nonhumans; 2) among the species examined the number of the muscle fibers per unit cross-sectional area is largest, implying the fibers are thinnest, in humans; 3) frequency of Type 1 fibers is highest in humans, intermediate in monkeys, and lowest in the orangutan, whereas Type 2 fibers show an inverse trend among the species. These results suggest a correspondence in primates between the composition of the psoas major muscle fibers and difference in substrates inhabited as well as in their positional behaviors.
authors.affiliation: Department of Biomedical Anatomy and Physiology, Univeristy of Shizuoka, School of Nursing, Japan.
authors.forename: Tadanao
authors.initials: T
authors.lastname: Kimura
mesh_terms: D000818:Animals; D005260:Female; D006651:Histocytochemistry; D006801:Humans; D008251:Macaca / Q000033:anatomy & histology*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000145:classification* / Q000648:ultrastructure; D010215:Papio / Q000033:anatomy & histology*; D011148:Pongo pygmaeus / Q000033:anatomy & histology*; D016658:Psoas Muscles / Q000033:anatomy & histology*