The aim of this experiment was to observe the phenotypic changes of intermediate filaments in skeletal muscle fibers during the degeneration and regeneration of the physical injury.

The gastrocnemius muscles of rats were physically damaged by needles and serial cryosections of the damaged muscles were prepared at 2, 4, 6, 9, 15, 21 and 35 days after injury. The cryosections were immunolabelled with desmin, vimentin and histochemically reacted with NADH-TR (nicotinamide adenine dinucleotide tetrazolium reductase).

Myotubes, asvisualized by desmin and vimentin, appeared at 9 days after injury. The regenerative myofibers were similar to normal muscles 35 days after injury. Degeneration and regeneration occurred simultaneously and positive reactions for desmin disappeared earlier than those of vimentin.

Both desmin and vimentin are strong staining tools for the evaluation of myopathy. The phenotypic patterns of intermediate filaments showed various degrees of regeneration in the early stages after physical injury.