Relationship between ease of swallowing and deglutition-related muscle activity in various postures

The purpose of this study was to investigate the relationship between the ease of swallowing and the deglutition-related muscle activity in various body and head postures by surface electromyography (EMG). Bipolar surface electrodes were placed on the right suprahyoid and infrahyoid muscles of nine healthy adults (19-28 years) while swallowing jelly. Ten postures per subject were examined: five body angulations (0 degrees [supine], 30 degrees, 60 degrees, 90 degrees [upright] and 120 degrees from the horizontal) and two head positions (chin-up and chin-down). The duration and amplitude of suprahyoid and infrahyoid muscle activity were measured by an electromyograph, and the ease of swallowing was subjectively determined by using a rating scale (0 = difficult to swallow, 10 = easy to swallow). The group-average duration and amplitude of muscle activity and the group-average rating scales mostly showed insignificant changes with the body angulations independent of the head positions. Interestingly, the duration and amplitude of muscle activity during swallowing were negatively correlated with the rating scales, indicating that a shorter duration and smaller activity of muscle activity corresponds to easier swallowing. Consequently, the duration and amplitude of suprahyoid and infrahyoid muscle activity measured by surface EMG would be a useful indicator of the easy-to-swallow performance.