EMG Characterization of Embouchure Muscle Activity: Reliability and Application to Embouchure Dystonia

Abstract

The purpose of the study was to develop a method to quantitatively and qualitatively describe the activity of selected muscles of the embouchure in French horn players using surface electromyography (EMG). Also, the reliability of several dependent variables that may be useful in future studies of embouchure dystonia (ED) was assessed. Five volunteers, including four normal French hornists (two male, two female) and one performer with ED performed two standardized tasks on two different occasions. The first task consisted of playing four iterations of two notes, one that elicited tremor in the ED subject and one that did not. This was followed by a 60-sec fatigue trial on the nontremor note. The levator labii and depressor anguli oris muscles were instrumented with miniature surface electrodes, and a microphone within a mute allowed audio signals from the horn to be simultaneously recorded. The presence of tremor was uniquely identified in the ED subject using EMG, and continuous wavelet transformation scalogram comparisons indicated temporal differences in signal power (μV2/Hz) as well as in the dominant frequency range. Within-trial reliability for amplitude, mean and median frequency, zero crossings, and power was excellent (r ≥ 0.977) for both muscles on the first performance task. Between-session reliability ranged from fair to good (r = 0.677–0.898) on these same variables. Numerous other variables associated with the fatigue task also showed good to high reliability (r = 0.90–0.99) between testing sessions. The findings suggest that the simple testing protocol presented may be of use in future studies of ED.