Age-related Changes in Skeletal Muscle Fiber Types of Rats after Long Period Aerobic Exercise

Objective: Aerobic exercise is known to play a key role in the skeletal muscle fiber-type determination. To investigate the effectiveness of age-related changes on skeletal muscle fiber types of rats after aerobic swimming exercise, we designed this experiment. Methods: Seventy two female rats were divided into age groups of 4, 8 and 12 weeks. For fiber typing, cross sections of quadriceps femoris muscles were stained for ATPase activity at various PHs. Results: (1)After 12 weeks aerobic training, the percentage of slow switch fibers( I %) of 4W group,8W group and 12W group were increased 19.9%(P<0.01),15.3%(P<0.01) and 7.4%(P>0.05)as compared with corresponding control group.(2)After 12 weeks aerobic training, the percentage of fast switch fibers( II %) of 4W group,8W group and 12W group were declined 19.6%(P<0.01),14.4%(P<0.05) and 8.2%(P>0.05)as compared with corresponding control group. Conclusions: (1) It demonstrated that Aerobic training can make type II change into type I effectively, but it would be more difficult in the adult rats. (2)It appears that the degree of type II change into type I will be more obviously if the rats are younger. (3)Aerobic training can upgrade the activity of aerobic metabolizing enzyme in skeletal muscle selectively.