The Adaptation of Myoglobin with Age and Training and its Relationship to the Three Fiber Types of Skeletal Muscle in Miniature Pig
Format of Original
European Journal of Applied Physiology and Occupational Physiology
Muscle biopsies were performed on 6 endurance and 6 sprint trained and 5 control miniature pigs after 3 and 7 months of training. The biopsied muscle was fixed, sectioned and stained for myoglobin. The darkest staining fibers were called dark fibers, the lightest staining were called light fibers and those of intermediate intensity were called moderate fibers. The distribution of the three fiber types, identified by myoglobin staining, did not change following either an endurance or sprint running regimen despite physiologically measured training effects. Myoglobin increased substantially with maturation as reflected by a significant increase in the number of dark myoglobin fibers in the biceps femoris at 11 compared to 7 months of age. It was suggested that the large increase in myoglobin content due to normal maturation may have obscured the differences among groups due to training. With enzyme histochemical analysis, dark myoglobin fibers were found to be slow red or fast intermediate fibers, but never fast white fibers. This relationship between myoglobin and the oxidative fibers (slow red and fast intermediate) supports the concept that myoglobin stores oxygen and aids its diffusion into muscle fibers in need of a constant oxygen supply.