Myofiber Type Distribution in the Cranial Portion of M. biceps femoris of Japanese Black Young Steers

抄録

Histochemical properties of M. biceps femoris were examined in Japanese Black young steers (11 months of age). The cranial portion of M. biceps femoris was dissected out from M. gluteobiceps after measuring its weight and was divided into 3 parts of equal length, namely the proximal, middle and distal. At the center of each part, the muscles were collected from the 5 subparts of equal depth from the superficial to the profound. Using the histochemical reactions for myosin ATPase and reduced nicotinamide adenine dinucleotide dehydrogenase, myofibers were categorized into Type I, Type II A and Type II B⁴⁾. Different distributions of myofiber types among the parts were also recognized in these young steers showing the same tendency as in the fattened adult in our previous study⁷⁾. However, Type II A myofibers occurred at higher percentage in the young than in the adult in every parts and Type I and Type II B showed the reverse tendency except for Type II B in the proximal part. These results indicated that the biceps muscle underwent a change in the myofiber type composition with transformation of Type II A to Type I and Type II B from 11 to 29 months of age.