Compensatory hypertrophy of skeletal muscle was induced by tenotomy in nine strains of inbred mouse male rats at the same developmental stage were divided into control and experimental group. The tendon of the gastrocnemius muscle of the right leg was transected 2 mm proximal to the upper margin of the retinaculum. The tenotomized animals behaved normally without visible disability. The plantaris and soleus muscles of the treated and the contractile limb were removed for examination 7 days after the operation, weighed using a Metler electronic balance. The mean weight of these muscles was compared between the control and tenotomized limbs.
　As parameters of hypertrophy, the absolute increment of muscle weight, absolute increment of muscle weight per unit body weight and percentage of increase in the weight of hypertrophied muscle were calculated to demonstrate the level of skeletal muscle hypertrophy, the different strains of inbred mice. It was found that the mean values of plantaris and soleus in the top ranking three strains were significantly increased in comparison with those of the three lowest-ranking strains. The rate of increase in the weight of the plantaris muscle in C 57 BL/ 10 Cr mice was the lowest at 25.5%. However, the rate of increase in the weight of the plantaris muscle of NZW/N mice was highest at 98.4%.
　The highest mean value for NZW/N was four times the lowest mean value for C 57 BL/ 10 Cr, and the rate of increase in plantaris muscle weight was significantly different between these two strains. Comparison of the absolute increase of muscle weight and absolute increase of muscle weight per unit body weight among the nine strains revealed a similar tendency to the rate of muscle weight gain. The variance of these values in the nine strains was greater than that of the values within the same strain. Therefore, in inbred mouse strains, these results strongly suggest that genetic factors influence the process of work-induced hypertrophy of skeletal muscle after tenotomy. Comparison of the increase in weight of the soleus as slow muscle and the plantaris as fast muscle indicated the dominance of fast muscle in the process of hypertrophy.

DESCENTE SPORTS SCIENCE Vol.13/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE