Effects on recovery of soleus and extensor digitorum longus muscles of prolonged wheel running during a period of repeated nerve damage.

The right sciatic nerve in NMRI mice was frozen under anaesthesia 13 times at three-week intervals for a total period of 8.5 months. During this period, but not afterwards, one sub-group of these mice had access to running wheels in which the animals ran several kilometres per night, thereby actively or passively training reinnervated or denervated leg muscles, as well as the intact contralateral muscles. A number of distinct effects persisted for as long as 14-18 weeks after the termination of this "endurance training". In reinnervated soleus muscle, tetanic force was significantly higher (37%) in the trained muscles as was muscle weight (36%); in general, negative effects of the nerve damage persisted. In the reinnervated extensor digitorum longus, tetanic force and muscle weight were significantly smaller in the trained animals (by 11 and 16%, respectively) which are considered typical effects of endurance training. The resistance of the soleus neuromuscular junction to block by both curare and Mg2+ was depressed on the damaged side but this property was not influenced by the training; in extensor digitorum longus the pattern was similar. It is concluded that training during the period of repeated cycles of denervation-reinnervation produced significant effects which impressively outlasted the training period. The possible nature of these effects is discussed.