Fig. 3. Effect of physical exercise (PhyEx) and testosterone (T) on skeletal muscle fiber composition. (A) Representative images of periodic acid–Schiff (PAS) staining of vastus medialis cross-sections from untreated rabbits (RD) and rabbits fed a regular diet (RD) and treated with testosterone (RD+T) and/or physical exercise (RD+PhyEx, RD+T+PhyEx). Scale bar 50 µm. Based on PAS staining intensity, indicative of glycogen content, fibers are classified as light-, medium- or dark-stained, ranging from oxidative to glycolytic. T and PhyEx treatments do not affect the overall fiber composition, maintaining the ratio between oxidative (light) and glycolytic (medium/dark) fibers, as quantified by counting ten fields from muscle sections of at least three animals for each experimental group (B). (C) An increased fiber diameter was detected in PAS-stained muscle cross-sections from PhyEx and T-treated groups, as analyzed using Image J 1.51f software (National Institutes of Health). ^ap<0.001 vs. RD; ^bp<0.001 vs. RD+PhyEx.