[Changes in the ultrastructure of muscle fibers of the diaphragm in response to physical loading (morphometric...

Red and white fibers have been investigated in the diaphragm of white rats, normal and under effect of physical loadings, various in intensity and duration. Relative volume and amount of lipid inclusions and mitochondria and their profiles and amount of glycogen granules have been estimated per one unit of the fiber section area. In unadapted animals acute physical loadings result in exhaustion of the reserves in the areas with a high volumetric density of mitochondria. These changes are mostly pronounced in the red fibers. Under a prolonged effect of the physical loadings of the training regimen, muscle fibers of both types have similar ultrastructural changes, demonstrating certain increase in their oxidative potential.