Masticatory muscle EMGs and their self-control under stress loading in a vertical space

我们知道，在视觉能力和姿态控制之间存在着一种反馈回路。然而，咀嚼肌收缩对姿势控制的影响尚不清楚。我们使用虚拟空间中的三维运动图像来观察GF在不同下颌骨位置下的变化。牙齿接触体位包括轻度咬合（LC）和下颌休息体位（RP）。招募5名男性志愿者，平均年龄22.4岁，无颞下颌疾病（TMD）病史。研究对象包括明治大学的学生。用活动电极记录咬肌、胫前肌和腓肠肌两侧肌电图。受试者被要求站在虚拟空间的GF传感器板上。在3d“过山车”动画（持续80秒）的显示过程中记录肌电信号和GF。每个受试者轮流使用LC和RP。实验前，所有被试在视觉肌电反馈下保持10%的最大自主收缩作为控制LC。然后他们被要求在LC实验开始时保持这个姿势。在RP过程中不需要牙齿接触。从与显示相关的最显著姿势变化发生的时间点开始分析综合肌电图值。通过分析GF面积来确定机体平衡与LC之间的关系。除R-GM外，LC组综合肌电信号均显著高于RP组。与RP相比，LC组GF面积明显减小，说明机体平衡控制良好。由于在轻度握紧状态下，胫骨前肌和腓肠肌在调节身体平衡时比在下颌休息位置时明显被激活，因此牙齿接触可能有助于姿势调节系统。

It is known that there is a feedback-loop between the faculty of sight and posture control against gravity fluctuation (GF). However, the effect of masticatory muscle contraction on posture control is not well understood. We used 3-D motion pictures in a virtual space with GF, to examine changes in GF with different mandibular positions. Tooth contact positions included light clenching (LC) and mandibular rest position (RP).Five male volunteer subjects (mean age of 22.4 years old) with no history of temporomandibular disorders (TMD) were recruited. Subjects included students at Meikai University. Electromyograms (EMGs) from both sides of the masseter, tibialis anterior (TA) and gastrocnemius muscles (GM) were recorded with an active electrode unit. Subjects were asked to stand on a GF sensor board in the virtual space. EMGs and GF were recorded during the display of a 3-D "roller coaster" animation (80sec duration). Alternation of LC and RP was performed by each subject. Prior to the experiments, all the subjects were trained to maintain 10% of maximum voluntary contraction as controlled LC under visual EMG feedback. They were then asked to maintain this position at the beginning of the LC experiment. No tooth contact was required during the RP session. Integrated EMG values were analyzed fromthe time point when the most significant postural change associated with the display occurred. The area of GF was also analyzed to determine the relationship between body balance and LC.Except for R-GM, integrated EMG showed a significant increase under LC when compared with RP. The area of GF decreased significantly under LC when compared with RP which indicated well controlled body balance. Since tibialis anterior and gastrocnemius muscles were activated significantly more in regulating body balance under light clenching conditions than in the mandibular rest position, tooth contact could contribute to the postural regulation system.