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July 17, 1967

Diagnostic Electromyography

JAMA. 1967;201(3):208. doi:10.1001/jama.1967.03130030078027

To the Editor:—  In the paper entitled "Diagnostic Electromyography" (199:727, 1967), I wish to call attention to a few confusing and controversial features.The statement that normal muscle at rest presents no electrical potentials should be qualified. There is a normal variety of spontaneous discharges which are frequently encountered when the electrode is inserted within the zone of innervation of a muscle. The potentials are identifiable and in their several forms are referred to as end-plate activity.The features of the electrical potential observed on the cathode-ray oscilloscope screen are a function of the size and number of subunits of a given motor unit which are detected within the restricted area of recording. Since more than one subunit may be involved, the waveform may be altered so that a quadriphasic potential is not to be considered abnormal. It is invalid to say that a normal potential "will have no