Morphometric analyses on the muscles of exercise trained and untrained dogs.

Nine adult dogs were subjected to an endurance training program consisting of gradually increasing periods of treadmill exercise. Biopsies of vastus lateralis muscles taken prior to an on completion of the training program were used to study the alterations in the capillary network and muscle-fiber nuclei. Combined morphometric and stereological analyses showed that the total length of capillaries (LV) and their total surface area (SV) per unit volume of muscle was significantly increased during training. Changes in the properties of myonuclei following training were also studied. Highly significant increases in the number of nuclei per unit volume of muscle (NV) were found. The increase in the numerical density of muscle-fiber nuclei would seem to indicate that the new nuclei were formed in the muscle during prolonged training. The relative amounts and distribution of heterochromatin and euchromatin were measured in trained and untrained dogs using a simple point-counting and random-transect technique. Their content of the different types of chromatin (volume functions and chromatin patch sizes in micrographs) were found to be altered significantly as a result of the training. The findings were consistent with the view that the amount of euchromatin within nuclei varies according to the degree of cellular activity.