Abstract
When freestanding individuals raise an arm as rapidly as possible, anticipatory muscle activities are evoked in the ipsilateral biceps femoris muscle (BFi) prior to the initiation of electromyographic activity of the deltoid muscle. This finding indicates that anticipatory activities of BFi are preprogramed in the brain, and reflect the function of positive postural adjustment rather than reorganization by postural reflexes.
The purpose of the present study was to investigate whether or not the above-mentioned anticipatory postural muscle activity, i.e. postural synergy, in sternocleidomastoid muscle could appear during ballistic voluntary jaw movements. Informed consent was obtained from a group of 10 healthy male subjects (24-27 yr) without functional disturbances of the jaw and with natural dentitions. Each subject was asked to perform the maximum clenching, the unilateral food-biting, and the maximum jaw opening as rapidly as possible.
As a result, postural synergy was observed during only the ballistic voluntary jaw opening.
