Sex-Related Differences in Mechanomyography of Stepwise Loading during Elbow Flexion

Abstract

The purpose of this study was to clarify sex differences in mechanomyographic （MMG） amplitude and frequency using a condenser microphone type MMG sensor during isometric muscle loading by comparing them with conventional electromyography （EMG）. Isometric elbow flexion exercises were performed with a gradual increase in the load from 10％ to 80％ maximum voluntary contraction （MVC）. Root Mean Square (RMS) values for EMG amplitude were load and BMI dependent but did not differ among sexes. The median EMG power frequency was almost constant regardless of load and tended to be of higher frequency in men. RMS values for MMG were load dependent and higher for in every load range in men. The median MMG power frequency was also load dependent but did not appear to differ among sexes. Based on EMG, women are considered to have a larger amount of slow-twitch muscle fibers and men are considered to have a larger amount of fast-twitch muscle fibers. This supports the belief that the amount and percentage of recruitment of these fibers characterizes EMG data. Furthermore, MMG amplitude is a good indicator of load.; however, the propagation characteristics of mechanical vibration may lead to steady differences among sexes independent of contraction strength.