The purpose of this study was to determine the effect of endurance training prior to occurrence of muscle atrophy on the mass, myofibrillar protein content and fiber crossectional area of atrophied hindlimb muscles of rats. Adult female Wistar rats were trained prior to occurrence of muscle atrophy induced by hindlimb suspension. Training began on the lst day for 10min/day at 15m/min on a 0% grade, training exercise increased daily in time and intensity so that by the 4th week rats were running 60min/day, at 34m/min on a 13.5% grade. Wet weight and relative weight of soleus, plantaris and gastrocnemius muscle decreased significantly after seven days of hindlimb suspension. Wet weight and relative weight of soleus tended to increase and that of plantaris and gastrocnemius tended to decrease in the exercise group as compared to the control group. Myofibrillar protein content of soleus and gastrocnemius tended to in crease and that of plantaris tended to decrease in the endurance trained group as compared to the control group. Fiber crossectional area of Type I, II fiber in soleus and plantaris muscle tended to increase in the exercise group as compared to the control group. Wet weight and relative weight of soleus, plantaris and gastrocnemius decreased significantly, myofibrillar protein content of soleus, plantaris and gastrocnemius increased in hindlimb suspended rats following endurance training as compared to the control group. There was no change in fiber type percentage and crossectional area of type I and II fiber in soleus muscle and that of type I and II fiber in plantaris muscle decreased in the hindlimb suspended rats following endurance training as compared to the control group. Wet weight and relative weight of soleus and plantaris tended to increase, that of gastrocnemius increased significantly, myofibrillar protein content of soleus and plantaris muscle increased significantly and that of gastrocnemius tended to increase in the hindlimb suspended rats following endurance training as compared to sedentary rats following endurance training. Crossectional area of type I fiber of soleus muscle tended to increase, that of type I fiber of plantaris muscle increased significantly and that of type II fiber tended to increase in hindlimb suspended rats following endurance training as compared to sedentary rats following endurance training. The results suggest that endurance training prior to occurrence of muscle atrophy can attenuate the decrease of mass, myofibrillar protein content and fiber crossectional area induced by hindlimb suspension.

The purpose of this study was to determine the effect of regular exercise during dexamethasone injection in the body weight, weight of hind-limb muscles, myofibrillar protein content and glutamine synthetase activity. 180-200g female Wistar were divided into four groups: control, exercise, dexamethasone injection(dexa), and exercise during dexamethasone injection(D+E) group. The dexa group received daily subcutaneous injection of dexamethasone at a dose of 4mg/kg body weight for 7days. The exercise group ran on a treadmill for 60min/day(20minutes every 4 hours) at 10m/min and a 10degrees grade. The control group received daily subcutaneous injection of normal saline at a dose of 4mg/kg body weight for 7 days. The D+E group ran on a treadmill for 60min/day(20minutes every 4 hours) at 10m/min and a 10degrees grade during dexamethasone injection. Body weight of the control group increased significantly from days of experiment, that of the dexa group decreased significantly from day 4 of the dexa group decrease significantly from day 4 of the experiment resulting in a 82.4% decrease compared to the first day of the experiment. Body weight of the D+E group decrease significantly from day 5 of experiment resulting in a 81.77% decrease compared to the first day of the experiment. Body weights, muscle weight and myofibrillar protein content of the plantaris and gastrocnemius decrease significantly and muscle weight of the sleys tended to decrease with dexamethasone injection. Glutamine synthetase activity of the hind-limb muscles increase significantly with the dexamethasone injection. The relative weight of the soleus was comparable to the control group and that of plantaris decrease significantly and that of gastrocnemius tended to decrease compared to that of the control in the dexa group. Body weight and muscle weight of the plantaris and gastronemius of the exercise group were comparable to the control group, and the muscle weight of soleus showed a tendency to increase. The relative weight of the soleus increased significantly and that of the plantaris and gastrocnemius were comparable to the control in the exercise group. Myofibrillar protein content of the soleus and plantaris increased significantly and there was no change of GS activity of the hind-limb muscles compared to the control in the exercise group. Body weight of the D+E group was comparable to the dexa group, muscle weight of the hind-limb muscles increased significantly. Myofibrillar protein content of the soleus and plantaris increase significantly and that of the gastrocnemius tendency to increase compared to the dexa group. Body weight and muscle weight of the plantaris and gastrocnemius of the D+E group did not recover to that of the control group. Muscle weight of the soleus recovered to that of the control group. The relative weight and myofibrillar protein content of the hind-limb muscles recovered to that of the control group. From these results, it is suggested that regular exercise during dexamethasone injection might attenuate the muscle atrophy of the hind-limb muscles.