Exercise or overloading: effect on skeletal muscle grafts of rats.

The effects of increased usage on regenerated muscle grafts was studied in rats. Soleus muscles were grafted orthotopically, either without neuromuscular anastomoses (standard grafts), or with their original nerves undamaged (nerve-intact grafts). The rats were either run on a treadmill or their soleus grafts were overloaded by extirpation of approximately 50% of the gastrocnemius muscles. Twitch and tetanic contractions, glycogen concentration, and histological features of the grafts were evaluated 60 days after grafting. The results showed that exercise enhanced glycogen levels in nerve-intact grafts as in normal muscle. Overloading had no effect on glycogen. The nonexercised standard grafts had the lowest values for the mechanical parameters studied. However, this was apparently due to the smaller degree of innervation rather than from the lack of exercise. Within the population of nerve-intact grafts, neither exercise nor overloading significantly improved the twitch and tetanic tensions. It is concluded that exercise, but not overloading, is likely to have positive effects on muscle graft metabolism.