Influence of Passive Stretching on Inhibition of Disuse Atrophy and Hemodynamics of Rat Soleus Muscle

The purpose of this study was to determine the influence of passive stretching on inhibition of disuse atrophy and hemodynamics among longitudinal regions of the rat soleus muscle. Disuse muscle atrophy was induced by hindlimb suspension for two weeks. Muscle blood flow was evaluated using thallium-201 (²⁰¹Tl) which is a radiotracer that has been reported to be useful to assess blood perfusion in skeletal muscle. Thirty-nine male Wistar rats were divided randomly into 5 groups: control (C: n = 10), a group with hindlimb suspension (HS: n = 7), a group with hindlimb suspension and stretching (ST: n = 7), a group receiving only a single session of stretching after the hindlimb suspension period that was killed just after stretching (HSB: n = 7), and a group receiving only a single session of stretching hindlimb suspension and stretching period that was killed just after stretching (STB: n = 8). From the results of the cross-sectional area (CSA) and the capillary-to-fiber ratio (C/F), muscle atrophy and inhibition of atrophy were shown more in proximal than in distal regions of experimental groups. These results suggest that the alterations of the C/F and CSA were different among muscle regions in experimental groups. These differences may depend on the level of stretching. Moreover, alteration of blood flow resulting from alteration of the mechanical environment had little influence on muscle atrophy or inhibition of atrophy.