In the present study, the age-related changes of the capillary system were investigated in the diaphragm and rectus abdominis muscles of 1, 8, and 18-month-old rats. The activation patterns of these muscles differ in the sense that the diaphragm is regularly mobilized many times at each minute during the entire life of the animal, while the rectus abdominis, although mobilized during breathing, is much less and more irregularly activated. The muscular fibers were pre-incubated in pH 4.35 and stained by the Padykula and Herman method to study of ATP-ase myofibrillary activity, enabling the separation of the fibers into 3 groups: slow oxidative (I); glycolitic fast oxidative (IIA) and fast oxidative (IIB) and the identification of the capillary around the fibers in the same section. The capillary/fiber relationship and the capillary density were obtained. The analysis of the capillary/fiber relationship and of the area between the 2 muscular groups showed us different patterns of capillary development, in aging, of diaphragm muscle's non-fatigable fibers (I and IIA) in comparison to rectus abdominis. These age-related changes of the diaphragm and rectus abdominis muscles could be related to continuous diaphragm contraction and could be a natural model of permanent exercise and muscle aging.
Aging; Diaphragm; Exercise
