EMG amplitude patterns in rat soleus and medial gastrocnemius following seven days of hindlimb suspension

Recently, the authors showed that hindlimb suspension (HS) in the rat, i.e. ´unloading´ the hindlimbs by tail suspension, results in a dramatic decrease, at least initially, in the daily amount of neuromuscular activity in the major plantarflexors of the ankle. By seven days postsuspension, however, the total integral of the electromyographical signal (EMG) recording using intramuscular electrodes over a 24-hour period was similar to presuspension values in both the soleus (sol) and the medial gastrocnemius (MG) muscles. The authors analyze these activation records and show that the interrelationship of the EMG amplitude patterns (i.e. the recruitment patterns) between these two synergists for plantar flexion are significantly altered. The data demonstrate that there is an alteration in the normal recruitment pattern of these two synergists under unloaded conditions. The data further suggest that the observed changes in activation patterns may be related to the magnitude of the mechanical and metabolic adaptations in the sol and MG following suspension.<>