Effects of high-frequency (500-1,000 Hz), indirect stimulation on slow and fast muscle relevant to orthotic applications.
The effects of indirect stimulation at 500-1,000 Hz on force production by the cat's slow-fibered soleus and mixed-fiber medial gastrocnemius (MG) muscles were compared for their relevance to the use of such "high-frequency" stimulation to modulate spasticity or the induced contraction of a centrally paralyzed muscle. Severe loss in force was seen in both muscles, and slow (S) motor units (MUs) within the MG showed about the same susceptibility as fast (FF) units. Both muscles and isolated fast and slow MUs within the MG exhibited an initial spike of tension and throughout stimulation a low level of residual tension. Despite the minimal output of work, a contribution to fatigue could be detected in the poststimulation period, as well as a delayed facilitative effect. Possible mechanisms are discussed.
Eldred
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Department of Anatomy and Cell Biology, University of California at Los Angeles, Los Angeles, California, U.S.A.; Brain Research Institute, University of California at Los Angeles, Los Angeles, California, U.S.A.
Solomonow
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