Programming of antagonist muscle stiffness during masticatory muscle unloading in man.

The activity of the masseter and digastric muscles was monitored carrying out a controlled, isometric biting task. In 7 out of 10 subjects, the level of activity in the digastric muscle, during the phase of isometric biting, was greater when the subjects expected the resistance between their teeth to yield suddenly than when they were confident that the resistance would not yield. It is therefore concluded that the co-activation of the digastric muscle which occurs during forceful isometric bites can be modified in accordance with the subject's expectation of the outcome of the bite.