Quantitative analysis of laryngeal EMG in normal subjects.

A method for quantitative analysis of the electromyographic interference pattern called "turns/amplitude analysis" was carried out with recordings from the cricothyroid and thyroarytenoid muscles of 12 normal subjects, 6 males and 6 females. The purpose was to investigate how the two muscles vary contraction force in relation to variations in pitch and voice intensity. Sustained phonations with systematic variation of pitch and intensity were analysed. The contraction force, in terms of turns and amplitude, increased with increasing pitch in both the cricothyroid and thyroarytenoid. More variability in contraction activity as a function of intensity was noted in the cricothyroid than in the thyroarytenoid. The increase in turns and amplitude in the thyroarytenoid with increasing pitch was highly significant, while little effect was seen of intensity variation. No great differences between males and females were noted.