Classification of muscle fiber types based on succinic dehydrogenase and myofibrillar ATPase reactions in normal and randomly reinnervated rat skeletal muscles.

In the normal and randomly reinnervated plantaris muscle of rat staining for succinic dehydrogenase (SDH) activity differentiates three fiber types (A, B and C), staining for myofibrillar adenosine triphosphatase (ATPase) differentiates three fiber types (alpha, beta and alpha beta). Here we present our finding type A corresponds to alpha beta fibers, B to beta or alpha beta, C to alpha or alpha beta. In normal soleus muscle both classifications were found to be compatible and B fibers correspond to beta and C to alpha fibers. An exception is the small percent of alpha beta fibers which correspond to B type. In randomly reinnervated soleus muscle changes in ATPase activity are not followed by changes in SDH staining and B fibers correspond to alpha, beta or alpha beta types.