Isometric training of rats — Effects upon fast and slow muscle and modification by an anabolic hormone (Nandrolone Decanoate)

Summary

Some effects of isometric exercise were studied in fast rectus femoris muscle and slow soleus muscle of the male rat. Isometric twitch contraction time did not change in both muscles, however, maximum tetanic tension increased in the fast muscle. Changes in the enzyme activity pattern of energy supplying metabolism of the rectus femoris muscle consisted in an increase of creatine kinase and citrate synthetase and a decrease of mitochondrial glycerolphosphate dehydrogenase. Treatment with Nandrolone Decanoate caused much smaller changes in male than observed in the preceding study on female rats. There was a higher performance of the trained animals under the influence of the hormone, but no changes could be found in the activities of the investigated enzymes. Combination of training with hormone treatment led to no further increase of maximal tetanic tension of the rectus femoris. Training and hormone treatment together caused an increase in glycogen phosphorylase and prevented partially the decrease in mitochondrial glycerolphosphate dehydrogenase observed under training alone. Some of the changes seen in the rectus femoris muscle after training were comparable to those in the female rats. Neither training nor hormone treatment induced changes in the male soleus muscle, except for the increase of soluble protein in sedentary hormone treated animals.