Abstract
The myofibrous composition of the tibialis anterior and vastus intermedius muscles in 8-week-old Wistar strain rats was studied after a 3-week program of treadmill running to evaluate the effects of physical exercise and the effects of different exercise intensity. The animals were classified into three groups: Group I ran 30 minutes three times a week, Group II ran 30 minutes six times a week and the control. The tibialis anterior and vastus Intermedius muscles were removed at the age of 8 weeks, and cross-section areas were measured and classified into three muscle fiber types: red, white and intermediate in the section stained by succinic dehydrogenase or Sudan black B. The size of the muscle fibers and the ratio of the three muscle fiber types in a cross-section were measured and calculated to assess the muscle composition. The ratio of muscle fiber types in the loaded groups was not different from the control in either the tibialis anterior or the vastus Intermedius. The size of muscle fibers, however, increased in Groups I and II. In the tibialis anterior, the ratio of hypertrophy was particularly high in the white muscle fibers; in the vastus intermedius, it was very high in the red muscle fibers.
