[Morphologic and morphometric characteristics of rat skeletal muscles following prolonged static loading]

Musculus gastrocnemius and m. soleus in Wistar rats have been studied at a prolonged static loading. The static loading does not produce any changes in the animals' body mass and in m. gastrocnemius, while the mass of m. soleus statistically differs after the experiment. There are some changes in relative amount of muscle fibres: in m. gastrocnemius the number of white muscle fibres increases, and the number of red muscle fibres decreases, in m. soleus the number of intermediate muscle fibres increases. In m. gastrocnemius of the test animals the transversal section areas of white and intermediate muscle fibres statistically decrease, and in m. soleus the transversal section areas of both muscle fibre types increase. Examination of semi-thin and celloidin sections demonstrate fibre-targets, fibres with centrally situated nuclei, partly splitting fibres and fibres of small diameter, their number reaching 4.3% of the whole number of fibres. Possible mechanisms for muscle fibre formation are discussed.