Frequency of bifurcated muscle fibers in hypertrophic rat soleus muscle.

The total number of bifurcated and nonbifurcated fibers were counted in rat soleus muscles induced to hypertrophy by surgical ablation of the gastrocnemius and plantaris muscles. Sham-operated and normal soleus muscles served as controls. Every muscle fiber within the entire muscle was individually examined and counted with the aid of a dissecting microscope following a 10-12 hour nitric acid digestion of the connective tissue. The results show that the total number of muscle fibers in the hypertrophic soleus did not differ significantly from the control. The frequency of bifurcated fibers observed in the control muscles was significantly greater than has been previously reported, and their frequency in the hypertrophic muscles, although slightly increased, was not significantly different from control values. These data confirm that fiber hypertrophy is not accompanied by hyperplasia, and they further suggest that bifurcated fibers probably play an insignificant role during muscle adaptation to hypertrophy due to their very low frequency.