Effects of head and neck inclination on bilateral sternocleidomastoid EMG activity in healthy subjects and in patients with myogenic cranio-cervical-mandibular dysfunction

This study was conducted in order to determine the effect of head and neck position on bilateral electromyographic (EMG) activity of the sternocleidom astoid muscles. The study was performed on 16 patients with myogenic cranio -cervical-mandibular dysfunction (CMD) and 16 healthy subjects. EMG recordi ngs at rest and during swallowing of saliva and maximal voluntary clenching were performed by placing surface electrodes on the right and left sternoc leidomastoid muscles. EMG activity was recorded in the left lateral decubit us position, in a darkened room and with the individual's eyes closed, unde r the following experimental conditions: 1. Head, neck, and body horizontal ly aligned; 2. Head and neck upwardly inclined with respect to the body, si mulating the effect of a thick pillow, 3. Head and neck downwardly inclined with respect to the body, simulating the effect of a thin pillow. Variatio n of head and neck positions was determined by measuring the distance from the angle of neck and shoulder and the apex of the shoulder (SND = shoulder - neck distance) of each individual. Then, head and neck were forward or d ownwardly inclined with respect to the body at one-third of SND. A signific antly higher contralateral EMG activity and a more asymmetric EMG activity were observed in the CMD group than in the healthy subjects (Kruskal-Wallis Test). These results suggest a different behavior of bilateral sternocleid omastoid EMG activity in CMD patients than in healthy subjects depending on the positioning of the head and neck.