Effects of food consistency and subject's posture on the electromyographic activity in the genioglossus muscle in humans

To evaluate the functional role of the tongue, electromyographic (EMG) activity of the genioglossus (GG) muscle, an extrinsic tongue muscle, was recorded during voluntary jaw and tongue movements including swallowing. Ten healthy subjects were recruited and surface EMGs of the left suprahyoid (SHy) and GG muscles were recorded. First, subjects were asked to rest, hold the jaw maximally opened, extend the tongue in a forward direction and then retrude it. Subjects were asked to keep each position for five seconds and mean amplitudes of EMG activity were calculated for the mid-two seconds. Second, for the test food, 4ml of liquid, syrup or jelly of 0.5% and 1.0% agar powder were prepared and subjects were asked to swallow each randomly. They were also asked to change their neck position, i.e, neutral direction, flexor direction at 30 degrees or left rotation at 30 degrees, as requested by the experiment supervisor. The same tasks were repeated three times and the mean amplitude of duration, peak and the area of the EMG burst were compared. In respect to GG burst, there were two bursts in a single swallow-related activity; termed GG1 and GG2 bursts. Large activities were obtained for the GG and SHy muscles during tongue protruding, as predicted, which disappeared in the GG muscle when the tongue was retruded while a small activity remained in the SHy muscle. This may have suggested that the SHy muscle also contributed to the tongue movements. There was a trend that all values were larger during swallowing a thick than a thin food, although there was a significant difference among the foods only in the duration of the GG1 burst. The results showed that we successfully demonstrated that EMG activity of the GG muscle was an applicable measure of the functional role of the tongue. The results showed that we successfully demonstrated that EMG activity of the GG muscle was an applicable measure of the functional role of the tongue. The effects of food consistency and a subject's posture on tongue movements of healthy humans during swallowing were small in terms of the activity pattern of the GG muscle.