BODY POSITION EFFECTS ON EMG ACTIVITY OF STERNOCLEIDOMASTOID AND MASSETER MUSCLES IN HEALTHY-SUBJECTS

This study was conducted in order to determine the effects of body pos ition on integrated electromyographic (IEMG) activity of stemocleidoma stoid and masseter muscles in 20 healthy subjects. EMG recordings at r est and during swallowing of saliva and maximal voluntary clenching we re performed by placing surface electrodes on the stemocleidomastoid a nd masseter muscles (contralateral to the habitual side of sleeping of each subject), in the following body positions: standing, seated, sup ine, and lateral decubitus position. Significant higher EMG activities were recorded in the stemocleidomastoid muscle in the lateral decubit us position, whereas significant lower EMG activities were recorded in the masseter muscle in the supine position, This finding supports the idea that there may exist a differential modulation of the motor neur on pools of the sternocleidomastoid and masseter muscles of peripheral and/or central origin. Significant differences in the EMG pattern as well as in the levels of EMG activities upon variations in body positi ons were observed between healthy subjects and patients with myogenic craniomandibular dysfunction reported by Palazzi, et al.(J Craniomandi b Pract 1996, 14(3):200-209).