Influence of brief daily tendon vibration on rat soleus muscle in non-weight-bearing situation

The purpose of this study was to investigate whether tendon vibration could prevent soleus muscle atrophy during hindlimb unloading (HU). Mechanical vibrations with a constant low amplitude (0.3 mm) were applied (192 s/day) with constant frequency (120 Hz) to the Achilles tendon of the unloaded muscle during the 14-day HU period. Significant reductions in muscle mass (−41%), fiber size, maximal twitch (−54%), and tetanic tensions (−73%) as well as changes in fiber type and electrophoretic profiles and twitch-time parameters (−31% in the contraction time and −30% in the half relaxation time) were found after 14 days of HU when compared with the control soleus. Tendon vibration applied during HU significantly attenuated, but did not prevent, 1 ) the loss of muscle mass (17 vs. 41%); 2 ) the decrease in the fiber cross-sectional area of type IIA (−28 vs. −50%) and type IIC (−29 vs. −56%) fibers; and 3 ) the decrease in maximal twitch (−3 vs. −54%) and maximal tetanic tensions (−29 vs. −73%) and the half relaxation time (1 vs. −30%). Changes in the contraction time and in histological and electrophoretical parameters associated with HU were not counteracted. These findings suggest that tendon vibration can be used as a paradigm to counteract the atrophic process observed after HU.