[Electron microscopic study of signs of skeletal muscle fiber hyperplasia in athletes].

Biopsies of skeletal muscles obtained from volunteers, young (19--20 years of age) skilled sportsmen have been studied electron microscopically. Sarcolemmic invaginations, deeply intruding into sarcoplasm of the muscle fibres, have been found; they result in muscle microbud formations. Small, round, spindle-like or having irregular from muscle fibres have been found with longitudinally situated myofibrils in them, as well as narrow long young fibres, their contractile apparatus being incompletely formed, with great number of mitochondria, glycogen granules and polysomes. A suggestion is made that under a systematic physical training the human mature skeletal muscle undergoes hyperplasia of the muscle fibres. New muscle fibres might be formed from myosatellites, from segregating myosatellites and microbuds and also, possibly, by splitting the fibres already existing.