Technical considerations for electromyographic research on the shoulder

This study compared 2 methods of indwelling bipolar electrode insertion. One method used a single needle for the insertion of both wire leads, and the second method used 2 needles for the independent insertion of both leads at a specified interdetection distance. Simultaneous electromyography recordings from the 2 different electrode configurations were made during the activation of nonfatigued supraspinatus and infraspinatus muscles from 10 healthy subjects. Subjects performed 6 different isometric contractions at 3 different levels of force (100%, 60%, and 30% effort). In this study, the bipolar electrode configuration using 2 hypodermic needles for placement of the 2 leads produced superior electromyography recordings than did the configuration using a single needle for the wire lead insertion. The separated bipolar electrodes produced a significantly higher amplitude electromyography signal with less intersubject variability and greater partial correlation with force. This study suggests an alternative method of bipolar wire electrode placement that results in improved signal characteristics and decreased variability of signal acquisition. A standardization of wire electromyography examination of the shoulder that improves signal characteristics and acquisition ultimately will lead to more accurate results with greater clinical use and validity.