EXERCISE TRAINING OF MODERATE INTENSITY DOES NOT ABATE THE EFFECTS OFDENERVATION ON MUSCLE MORPHOLOGY

Denervation elicits profound alterations in the morphometry of skeleta l muscle. These alterations include changes in fiber type composition as well as reductions in fiber size. There is evidence that the increa sed mechanical load placed upon muscle via rhythmic stretching attenua tes denervation induced alterations in muscle morphology. The purpose of the present study was to determine whether the mechanical stimuli a ssociated with exercise training, i.e. rhythmic stretching and mechani cal loading, would effectively moderate the changes in muscle morphome try observed following denervation. Unilateral denervation of the sole us muscle of eight male Sprague-Dawley rats was performed under asepti c conditions. The animals were then randomly assigned to two groups: s edentary controls and exercise trained. The exercise training protocol featured treadmill running five days per week for six weeks. At the c onclusion of the experimental period, animals from both groups were sa crificed and soleus muscles were histochemically analyzed for muscle m orphometry. Results demonstrated that denervation caused marked altera tions in fiber type profile and in fiber cross-sectional areas. Intere stingly, the degree of denervation induced atrophy appeared to be fibe r type specific. However, the data presented here indicate that in den ervated soleus muscles there were no significant differences in fiber type composition or fiber size between the sedentary and exercise trai ned groups. Hence, it appears that the mechanical stimuli provided by treadmill running of moderate intensity and duration are not sufficien tly potent to ameliorate muscle morphometric responses to denervation.