Fiber type composition of epaxial muscles is geared toward facilitating rapid spinal extension in the leaper Galago senegalensis

Am J Phys Anthropol. 2018 May;166(1):95-106. doi: 10.1002/ajpa.23405. Epub 2018 Jan 10.


Objectives: We hypothesized that the vertical leaper Galago senegalensis will have epaxial extensor muscles with a fast fiber phenotype to facilitate rapid spinal extension during leaping in comparison to the slow-moving quadruped Nycticebus coucang. To test this, we determined the percentage of fiber cross-sectional area (%CSA) devoted to Type 2 fibers in epaxial muscles of G. senegalensis compared to those of N. coucang.

Materials and methods: Immunohistochemistry was used to identify Type 1, Type 2, and hybrid fibers in iliocostalis, longissimus, and multifidus muscles of G. senegalensis (n = 3) and N. coucang (n = 3). Serial muscle sections were used to estimate and compare proportions, cross-sectional areas (CSAs), and %CSAs of Type 1, Type 2, and hybrid fibers between species.

Results: Epaxial muscles of G. senegalensis were comprised predominantly of Type 2 fibers with large CSAs (%CSA range ≈ 83-94%; range of mean CSA = 1,218-1,586 μm2 ). N. coucang epaxial muscles were comprised predominantly Type 1 fibers with large CSAs (%CSA range ≈ 69-77%; range of mean CSA = 983-1,220 μm2 ).

Discussion: The predominance of Type 2 fibers in G. senegalensis epaxial muscles facilitates rapid muscle excursion and spinal extension during leaping, and is consistent with their relatively long muscle fibers. The predominance of Type 1 fibers in N. coucang epaxial muscles may aid in maintaining stable postures during bridging and cantilevering behaviors characteristic of slow-climbing. These histochemical characteristics highlight the major divergent locomotor repertoires of G. senegalensis and N. coucang.

Keywords: Galago senegalensis; Nycticebus coucang; histochemistry; spinal extensor muscle.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anthropology, Physical
  • Female
  • Galago / physiology*
  • Lorisidae / physiology
  • Male
  • Muscle Fibers, Skeletal / chemistry
  • Muscle Fibers, Skeletal / physiology*
  • Muscle, Skeletal / anatomy & histology
  • Muscle, Skeletal / physiology*