[Electromyographic study on the effects of head position to head and neck muscles].

The purpose of this study is to reveal the relationship between the head position, and the neck and head muscles. At 4 head positions, the activities of masseter, anterior temporal, anterior digastric, sternocleidomastoid and trapezius muscle of ten normal subjects standing straight were investigated electromyographically with surface electrodes during voluntary maximal clenching in centric occlusion. Head positions were right tilting, left tilting, up-right and natural head position. The results obtained were as follows; 1. During head tilting, the activities of anterior digastric and sternocleidomastoid muscle on the tilting side were increased, the activities of masseter and trapezius muscle on the opposite side of the tilting side were increased, the activity of the anterior temporal muscle did not vary from the activity during up-right head position. 2. During natural head position, only the activity of sternocleidomastoid muscle on the natural tilting side was increased.