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 al ea 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.