Adaptations of skeletal muscle grafts to chronic changes of physical activity

After grafting, many structural and functional characteristics of skeletal muscle change with time until reaching a stable value. For several characteristics, these stable values are less than those observed in control skeletal muscle. Characteristics such as mass and fiber cross-sectional area are influenced by chronic changes in physical activity. The extent of our understanding of the dimensions and mechanisms of activity-induced adaptations of grafts is limited and based solely on experiments with rats. Improvements in mass, protein content, oxidative capacity, and glycogen concentration have been documented with conditioning by running of sufficient intensity and duration. The growth and development of soleus muscle grafts are severely impaired when normal weight-bearing activity is removed. The mass and maximum tension development of grafts are increased with ablation of muscles that function synergistically to the grafts, but are diminished after chronic electrical stimulation. Chronic electrical stimulation does increase oxidative capacity, capillarity, and the resistance to fatigue. Much remains to be learned about the mechanisms by which activity-related adaptations occur in skeletal muscle grafts.