The relation between interangle span and in vivo resultant force in the perioral musculature.

The variable nature of the perioral system as a force generator is due, in large part, to differences in the spatial arrangement and degree of muscle representation in this region. This fact requires careful consideration when attempting to compare select properties of force dynamics among individual subjects in health and disease. The objective of the present study was to determine the relation between an indirect measure of muscle length (interangle span) and in vivo resultant force in the perioral region of normal adult subjects. Perioral force associated with the maximum voluntary contraction (MVC) was found to increase systematically with increases in the span between the load sensitive cantilevers positioned between the corners of the mouth. The active force component of the MVC was significantly greater for male than female subjects, whereas passive forces were equal. Active force is discussed in relation to rest positions of the oral opening and the assessment of the force operating range for speech and other oromotor behaviors in health and disease.