Glycogen depletion of type I and type II muscle fiber was studied during exercise with prednisolone treated rat skeletal muscles. Glycogen content in individual fibers were calculated as optical denity of Periodic Acid-Schiff (PAS) stain and structural changes were observed under electron microscope.

The experimental rats were divided into 6 group: In the control group, nothing but injection of distilled water was applied. First group was exercised only without prednisolone treatment. Second, third and fourth groups respectively had, 5, 10, 15 days of prednisolone treatment with exercise and the fifth group had 30 days of recovery after the completion of 15 days prednisolone treatment with exercise.

Glycogen depletion was observed in almost all type I fibers during the short term exercise, and in about 90% of Type II fibers with prolonged exercise. Glycogen restoration was observed more in type II fibers after 30 days rest than in Type I fibers.

In the ultrastructural observations for rats with 5 days exercise without prednisolone treatment the noticeable findings were the disappearance of A and I bands in the myofibrils of both soleus and gastrocnemius.

However, these bands appered to be gradually increased with the exercise of the muscles and prednisolone injection for 5, 10, 15 days (group 2, 3, 4).

In one of the groups exercised for 5 days (gruop I), the glycogen particles of the former, however, decreased successively reaching to the group 4 or 5. And those of the latter were markedly decreased in all groups (group 1∼5).

In both type I and type II fibers, most of mitochondria showed electron lucent area (hydrophilic degeneration) with the 30 days rest after the completion of 15 days treatment of prednisolone with exercise.

The sarcoplasmic reticulum showing marked dilatation of its cistern was not found in the type II fibers but it was found in many areas of myofibril of the I fibers.

From these results, it may suggest that exercise induce the glycogen depletion in prednisolone treated skeletal muscles as well as in normal skeletal muscles in both type I and type II fibers and it may give some organellar changes in the muscles fibers as mentioned above.

Keywords :Skeletal muscles, Histochemical, Ultrastructure, Exercise, Rat