Surface electromyographic evaluation of the asymptomatic human masseter muscle with turns and amplitude analysis

Electromyographic turns, or reversals of direction, per second (TS) and mea n amplitude per turn (AT) are variables that have been widely used to assis t and support an electrodiagnosis in neuromuscular disorders. The purpose o f this study was to explore the feasibility of utilizing the TS and AT in c onjunction with surface electrodes as a method for assessing masticatory mu scle function. Ten normal subjects were instructed to exert brief isometric contractions at various levels, and the TS and AT were calculated from the surface electromyographic signals of the masseter muscle, Our results show ed that the AT increased with contraction at all contraction levels, demons trating a linear relationship while the TS showed a nonlinear increase char acterized by an initial steep rise followed by a plateau, which was simulat ed with a third polynomial function. It is considered that the TS and AT ma y provide valuable physiological information about the underlying mechanism s of recruitment and the firing of motor units.