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Influence of nutrition and aging on the composition and function of rat skeletal muscle.

Previous studies suggest that nutrition and age affect the composition and function of skeletal muscle. We have investigated these effects in vitro using model muscle preparations obtained from SPF Fischer 344 rats of different ages. Five different dietary groups of rats were studied. In three of these groups food consumption was restricted to 60% of ad libitum intake for varying fractions of the life span. Two groups of rats were fed ad libitum, and in one of these, the protein content of the food was limited to 60% of that consumed by the control group. Composition and contractile function were measured in lateral omohyoideus and soleus muscles. The data revealed a striking absence of functional change in these muscles with age and diet. Only minor changes in composition were found. The results suggest that the fibers present in the muscles of aged rats are functionally intact and are unaffected by long-term dietary restriction. Thus, age-related deficiencies of motor function are probably related to other factors, such as those associated with neuromuscular transmission or propagation of nerve impulses.