Muscle activities in the region of neck, shoulder and back during isometric horizontal jaw exercises in various postures

Abstract

Eleven healthy participants were made to perform isometric horizontal jaw movements with maximum voluntary efforts in various postures. Surface EMGs from the laterocervical, nucha, shoulder and back regions were bilaterally picked up, and simultaneously recorded with jaw force. The results obtained were as follows: 1. Electromyographic power value in these regions depended on the directions of the jaw exercises (posteriorly pull greater than posterolaterally pull greater than anteriorly push not equal to anterolaterally push, P less than 0.0001). 2. The directional effects mentioned above were significantly obvious in the inferior laterocervical (Electrode No. 2) and back Electrode No. 5) regions (P less than 0.0001). 3. The postural effects on the power value were varied with the directions of the jaw exercises (P not equal to 0.03); i.e., the highest value during jaw pull was observed in an upright position, while that during jaw push was found in a supine position. 4. From above results, it would be considered that occlusal habits with sustained isometric jaw retrusion might have higher probability to provoke the discomfortableness in the neck, shoulder and back regions than those with protrusion, and that the habits with the retrusion might be more injurious in a supine than in an upright position, while those with the protrusion more injurious in an upright position.