This proposal is designed to study the effect of cast immobilization on the cyto-architecture, biochemistry and physiologic characteristics of reinnervating rat mucle. Using these parameters, previous studies have demonstrated that reinnervation of the rat plantar-flexors following sciatic nerve crush takes place between 2 and 3 weeks post-crush. A vigorous prolonged exercise program, treadmill running at 35% grade once or twice daily for 1 hour at a speed of 26.8 m/min., was initiated just prior to (at 2 weeks post-crush) or after (at 3 weeks post-crush) reinnervation. The results have indicated that twice daily exercise for 4 weeks markedly enhances the protein synthesis and concentration of myofibrillar proteins. In addition, the muscles showed histological and physiologic evidence of faster muscle characteristics when they were analyzed at 5 weeks post-crush. Therefore, it can be concluded that exercise initiated just prior to or after reinnervation does not interfere with reinnervation. On the contrary, exercise enhanced the process of reinnervation. Now, the question arises whether inactivity imposed by cast immobilization during reinnervation may enhance or retard the recovery of regenerating motor units. The goal for 1977-78 will be to biochemically, histochemically, and physiologically evaluate the effects of cast immobilization on rat plantar-flexors. This work is clinically important because it will help define specific methods of managing peripheral nerve injuries. BIBLIOGRAPHIC REFERENCES: Herbison, G.J., Jaweed, M.M., Ditunno, J.F.: Cast immobilization: effect on cytoarchitecture of the adult rat soleus and plantaris muscles. Arch. Phys. Med. Rehab. 57:538, 1976. Jaweed, M.M., Herbison, G.J., Ditunno, J.F.: The influence of exercise upon protein synthesis in reinnervating rat gastrocnemius. Federation Proc. (Abst. #2163) 1977.