[Electron microscope study of skeletal muscle fibers during physical exercise in high-altitude hypoxia].

Experiments on rats exposed to intense exercise and high-altitude hypoxia have shown the reduction in physical efficiency and in the training effect of muscle loads as compared to the same characteristics examined under the conditions of plain. Electron microscopy of rat skeletal muscle fibers has discovered significant changes in their ultrastructure. Morphometric analysis of the same changes has shown a reduction in the relative volume of mitochondria, an increase in the relative volume of sarcoplasmic reticulum an abrupt fall of the glycogen reserves in the early stages of experiment with a further tendency towards the normalization of this characteristic. The changes described were followed by focal destructive-degenerative abnormalities in the energy and in the contractile-myofibrillar apparatuses.