Consideration of Tetanic Contraction Properties of Different Skeletal Muscle Fibers Using Displacement MMG

Abstract

Mechanomyogram (MMG) which measures the slight vibration of muscle contraction can evaluate the mechanical function of the muscle. There are few reports describing the surface displacement (displacement-MMGs) along the cross-section direction during tetanus. Using the laser displacement sensor, we recorded the displacement-MMGs of the human Rectus Femoris (type Ⅱ superiority) and Abductor Pollicis Brevis (type I superiority) during tetanus with a 30-s continuous electrostimulation at the frequency ranging from 0.2 to 50 [Hz], and discussed the contraction properties of these mixed fiber-type skeletal muscles. Three male and one female subjects (21- to 25-year-old) without medical histories of muscular disease joined the experiment repeatedly. The results showed that incomplete tetanus in the mixed fiber-type skeletal muscles were induced by two steps, and the displacement-MMG amplitude was affected by the component ratio of the area of muscle fiber. Furthermore, according to contraction and relaxation time of muscle force in type I, II twitches, the frequency regions of the first phase of incomplete tetanus and the second almost corresponded with those of type I and type II, respectively.