, Volume 348, Issue 3, pp 247-255

Human soleus muscle: A comparison of fiber composition and enzyme activities with other leg muscles

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The relationship between fiber composition and enzyme profiles as estimated from in vitro enzyme activities has been studied in human skeletal muscle. Samples from the soleus, gastrocnemius, and vastus lateralis muscles were obtained both by biopsying normal subjects and from patients during nonmuscular related general surgery. The samples were analyzed for fiber composition, phosphorylase (a+b), phosphofructokinase, and creatine phosphokinase activities. The fibers were assigned to two major types based on the histochemical display of alkaline stable myofibrillar adenosine triphosphatase staining. This staining is related to the activity of the enzyme and thus the contractility of the fibers. One fibre type lacks (Type I or slow twitch fiber) and the other one (Type II or fast twitch fiber) contains this enzyme. The soleus muscle contained predominantly slow twitch (Type I) fibers with the mean for all subjects being 80% (range 64 to 100%). In contrast the gastrocnemius and vastus lateralis muscles only contained 57% slow twitch fibers (range 34–82%). The activities of the glycolytic enzymes assayed, except hexokinase, were lower in predominantly slow twitch as compared with muscle with many fast twitch fibers and this was consistent with muscle histochemical staining patterns for alpha glycerophosphate dehydrogenase. Succinate dehydrogenase and creatine phosphokinase activities were not related to fiber distribution.