Exercise training of moderate intensity does not abate the effects of denervation on muscle morphology

Denervation elicits profound alterations in the morphometry of skeletal muscle. These alterations include changes in fiber type composition as well as reductions in fiber size. There is evidence that the increased mechanical load placed upon muscle via rhythmic stretching attenuates denervation induced alterations in muscle morphology. The purpose of the present study was to determine whether the mechanical stimuli associated with exercise training, i.e. rhythmic stretching and mechanical loading, would effectively moderate the changes in muscle morphometry observed following denervation. Unilateral denervation of the soleus muscle of eight male Sprague-Dawley rats was performed under aseptic conditions. The animals were then randomly assigned to two groups: sedentary controls and exercise trained. The exercise training protocol featured treadmill running five days per week for six weeks. At the conclusion of the experimental period, animals from both groups were sacrificed and soleus muscles were histochemically analyzed for muscle morphometry. Results demonstrated that denervation caused marked alterations in fiber type profile and in fiber cross-sectional areas. Interestingly, the degree of denervation induced atrophy appeared to be fiber type specific. However, the data presented here indicate that in denervated soleus muscles there were no significant differences in fiber type composition or fiber size between the sedentary and exercise trained groups. Hence, it appears that the mechanical stimuli provided by treadmill running of moderate intensity and duration are not sufficiently potent to ameliorate muscle morphometric responses to denervation.