Electromyographic Studies of Neuromuscular Disorders

Numerous electromyographic studies of neuromuscular disorders have been made since 1910. The usual technic employed consisted of placing pad electrodes on the skin over an affected muscle group and leading off the potential changes to a string galvanometer. The electromyograms obtained were useful for indicating gross changes of muscular activity, but little could be done with them by way of analysis of the individual waves. Some investigators measured the frequency and amplitude of each oscillation of the irregular electromyogram, whereas others separated the large and small waves into so-called "primary" and "secondary" waves, which were thought to be of different origin. During the last few years new methods of recording the small, transient potentials of the body have been developed. Oscillographs have been substituted for string galvanometers of low natural period, and amplification of minute potentials has been made possible. In addition, the work of Adrian and Bronk,¹Denny-Brown,