[Morphometric and cytochemical parameters of skeletal muscle during long-term physical exertion]

Daily swimming for 40 days increased weight of the fast (gastrocnemius) and slow (soleus) muscles in white rats and altered the size of plane section and the relative amount of different fibers in the muscles. The slow muscle developed an anaerobic spectrum of lactatdehydrogenase isoenzymes characteristic of an intact fast muscle, whereas the fast muscle intensified its specific "muscular" spectrum of isoenzymes. By the 40th day the parameters under study tended to normalize.