Electron microscopical characterization of muscle fiber types of the rat diaphragm using a cluster analysis.

Muscle fibers of one rat diaphragm were selected for sterological investigation of some ultrastructural parameters. Histograms and scattergrams did not exhibit consistently the existence of several subgroups of muscle fibers. A cluster analysis was performed to reveal groupings. 2 populations were defined using a stepwise discriminant analysis. The most important parameters for the discrimination of the 2 groups proved to be the volume density of mitochondria and the width of the Z line, all other parameters determined were of minor importance. It was tried to apply numerical taxonomic procedures to the problem of the ultrastructural characterization of skeletal muscle fibers. Thus difficulties arising from subjective determinations of several types of muscle fibers could be avoided.