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There is limited information regarding the normal function of the medial pterygoid (MP) muscle, a major jaw muscle. The aims of our study were to develop a methodology to record from the MP during standardized isometric jaw closing tasks, to determine the range of tasks over which activity can be recorded in the MP, and to determine whether there is evidence for functional heterogeneity within the MP muscle by comparing electromyographic (EMG) features in different regions of the MP. Fifteen healthy participants were included in the study. The EMG activity of the right MP was recorded with intramuscular electrodes during the performance of isometric jaw closing tasks onto a force transducer as well as isometric contralateral (i.e. to the left side), protrusive (straightforward) and ipsilateral (i.e. to the right side) jaw tasks using another force transducer in the same participants. The isometric tasks were ramp tasks (at a fast rate and at a slow rate) and step level tasks (at 2 force levels). A computed tomography (CT) scan was performed for all participants and the presence of MP activity, thresholds of single motor units, and root means square (RMS) activity were assessed in the tasks. The MP was active in all jaw closing tasks in all participants, but in the horizontal tasks, the MP was mostly active in the protrusive and contralateral tasks (85% of participants), while it was activated in 57% of the participants in the ipsilateral tasks. The mean force threshold value for the fast jaw closing ramp task was significantly (P |
