[Ultrastructural changes in the skeletal muscles after physical exertion in rats of various ages].

The white rats of the age 1, 3 and 12 months ran in the treadmill at a speed 45 m/min for 20, 40, 60 and 90 days. There is not any linear dependence of muscular transformations and the intensity of physical loading. Changes of the material components of muscular fibers are of undulated character, depending on the age, increase in quantity of myofibrils is always accompanied with a decrease in the quantity of mitochondria. When the total share of myofibrils and mitochondria increases, the quantity of other ultrastructural elements of the muscular fibers and hyaloplasm decreases.