Quantitative analysis of approximate shapes in a myofiber cross-section and their relationship with myofiber cross-sectional area.

[Purpose] Although the shapes observed in myofiber cross-sections have been subjectively identified as polygonal, precise methodologies to classify such shapes have not been elucidated previously. Therefore, we aimed to determine the approximate shapes found in myofiber cross-sections, and to elucidate their relationship with the myofiber cross-sectional area. [Materials and Methods] Soleus muscles of five 11-week-old male Wistar rats were collected as specimens. The muscle specimens were rapid-frozen in isopentane-cooled in dry ice and acetone-and sliced into 10-μm slices in a cryostat and stained with hematoxylin-eosin. The NIH ImageJ software was used to analyze the number of corners that were counted according to the proposed criteria and the myofiber cross-sectional areas of 500 myofibers. [Results] In assessments of the approximate shapes of myofiber cross-sections, the proportion of pentagons was 41%, which was the highest among polygons. A weak positive correlation was noted between the corner count and myofiber cross-sectional area, which indicated that polygons with more corners were associated with a larger myofiber cross-sectional area. [Conclusion] The myofiber cross-sections of the soleus muscle were considered to frequently show an approximately pentagonal shape. Moreover, a correlation was observed between the myofiber cross-section shape and myofiber cross-sectional area, suggesting that the area was also associated with the relevant functional features.