RESUMEN
A study was conducted to investigate the influence of a series of quick stretches during tetanic stimulation of skeletal muscle fibers in growing mice.<BR>Mice were anesthetized with pentobarbital sodium. The distal tendon of the extensor digitorum longus muscle was attached to a servomotor. The effects on the muscles of a series of isometric contractions (ISO), a series of quick stretches during contractions (ST), and a sham operation for 1 h were assessed in terms of changes in tetanic tension, serum creatine kinase and lactate dehydrogenase activities, and the histological appearance of the muscle.<BR>The data indicated the following ; 1) Serum enzyme activities were not altered in any of the experiments. 2) ST resulted in a decrease in tetanic tension compared with ISO values in mice of all ages. The rate of decrease in tetanic tension for 1 h ST was higher in muscles of young mice than in those of mature mice. 3) Muscle histology demonstrated numerous areas of localized sarcomere widening immediately after the series of ST.<BR>These observations suggest that muscle stretching during contraction causes greater injury to developing skeletal muscles.