What is the role of EMG in motor unit recruitment study?

Updated: Oct 16, 2019
  • Author: Friedhelm Sandbrink, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Answer

The needle EMG examination cannot assess anatomic size or degree of tension of a motor unit. In an EMG study, the term "size" of a motor unit usually refers to the amplitude of the motor unit action potential (MUAP). The size principle is also true to a limited extent for the EMG study. In rather general terms, the later recruited type II fibers, especially the FF type, have larger diameter muscle fibers generating higher potentials than the smaller, slow twitch type I units. Because of the small uptake area of standard EMG needle electrodes, however, the size of consecutively recruited MUAPs during an EMG study varies considerably. [5]


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