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

众所周知，在视觉和姿态控制能力之间存在着一个反馈回路。然而，咀嚼肌收缩对姿势控制的影响还不清楚。我们使用三维运动图片在虚拟空间与GF，检查GF的变化与不同的下颌骨位置。选择5名无颞下颌关节紊乱病（TMD）病史的男性志愿者，平均年龄22.4岁，分别采用轻咬位（LC）和下颌静止位（RP）。研究对象包括明海大学的学生。用主动电极记录双侧咬肌、胫骨前肌（TA）和腓肠肌（GM）的肌电图。受试者被要求站在虚拟空间中的GF传感器板上。在显示3D“过山车”动画（持续80秒）期间记录EMG和GF。由每名受试者交替进行LC和RP。实验前，所有受试者在视觉肌电反馈下进行训练，以保持最大自主收缩的10%作为控制LC。然后要求他们在LC实验开始时保持这个位置。RP会话期间不需要牙齿接触。综合EMG值从与显示器相关的最显著姿势变化发生的时间点开始分析。除R-GM外，整体肌电图在LC下均较RP下显著增加。与RP相比，LC下GF面积显着减少，表明身体平衡控制良好。由于胫骨前肌和腓肠肌的激活显着更多的调节身体平衡轻咬紧条件下比在下颌休息的位置，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.