CYCLICAL PASSIVE STRETCH INFLUENCES THE MECHANICAL-PROPERTIES OF THE INACTIVE CAT SOLEUS

The effects of cyclical, passive manipulation (PM, 30 min day(-1), 5 d ays week(-1) for 6 months) mimicking the length excursions observed du ring stepping on the mechanical and associated biochemical properties of the inactive cat soleus muscle were determined in five cats. Inacti vity was produced via spinal cord isolation (SI), i.e. complete spinal cord transections at low thoracic and high sacral levels and bilatera l dorsal rhizotomy between the transection sites. Passive manipulation was administered to one leg of each SI cat. Compared with normal cont rols, SI resulted in similar to 70 % decrease in weight, an 80 % decre ase in maximum tetanic tension (P-0) and an similar to 100% increase i n maximum rate of shortening (V-max) and myosin adenosine triphosphata se (mATPase) activity of the soleus. The passive manipulation regime p artially ameliorated these effects. When compared with the control SI soleus, the SI-PM soleus weight and maximum tetanic tension were 12 an d 21 % higher, respectively, and the V-max and mATPase activity 21 and 12% (p > 0.05) lower, respectively. Thus, inactivity resulted in a sm aller and faster muscle, whereas passive manipulation for only 30 min a day tended to maintain these properties closer to normal control val ues. The results suggest a potential therapeutic effect of short bouts of cyclical, passive manipulation on otherwise inactive skeletal musc les.