Abstract
As a basis of making clear the effects of therapeutic exercise in neuromuscular diseases, the histochemical study was performed to elucidate the adaptive transformation of normal rat muscle fiber types after endurance training.
16 young male Wistar rats (4 weeks old) and 24 adult male Wistar rats (12 week old) were trained by free running in their own wheeling drums. After 4 and 8 weeks of training, the soleus and extensor digitorum longus (EDL) muscles were studied. 42 rats in the sedentary and the control groups were put in their own narrow cage for same period. Using histochemical staining for myofibrillar ATPase after preincubation at pH 9.4, pH 4.6 and pH 4.3, four major types of muscle fiber could be identified.
The muscle was continuously adjusted to growth of rats. Between 4 and 12 weeks the proportion of type 1 fiber of soleus muscle increased, and type 2A, 2B and 2C fiber decreased. Thus, it seems reasonable to assume that progressing transformation processes of “2A→2C→1” and “2B→2C→1” had occurred during growth. The proportion of Type 2A and 2C fiber of EDL decreased between 4 and 8 weeks, while the proportion of Type 2B fiber increased. It seems similarly reasonable to assume that transformation processes of “2A→2B” and “2C→2B” had occurred.
Changes in proportion of each fiber types to training have been observed only in young rats. After 8 weeks running, soleus muscles of young rats contained a lower percentage of type 1 and a higher percentage of type 2C fibers than the sedentary rats. EDL muscles contained a higher percentage type 2A and a lower percentage type 2B fiber. These results show that free running gives forces to transformation process of soleus muscle fiber “1→2C” and to transformation process of EDL muscle fiber in the direction of “2B→2A”. However, the facts that there have been no effects on transformation in the adult rats mean that changeableness of transformation varies with age.
