System Identification of Mechanomyogram at Various Levels of Motor Unit Recruitment

Abstract

: The mechanomyogram from a single motor unit and the induced mechanomyogram at various levels of recruitment were measured with an acceleration sensor. The transfer functions between motor unit action potential (or electrical stimulation) and the mechanomyogram were identified using the singular value decomposition method. The purpose of this study is to clarify how the model order of the transfer function depends on the recruitment level. The second-to tenth-order transfer functions were calculated, and the difference between the observed and the estimated mechanomyograms using the transfer function, the fitness, was calculated. The relationship between the model order and the fitness was tested using the Holm-Bonferroni multiple comparison. At low levels (single motor unit, 20, and 40%) of recruitment, there were significant differences between the fourth-and higher-order models, but there were no significant differences between the fifth-and higher-order models. In contrast, at high levels (60, 80, and 100%) of recruitment, the fourth-order model did not show significant differences between the fifth-or higher-order models. As a result, the fifthand fourth-order models were appropriate at low and high recruitment levels, respectively. The differences in the order might be caused by interactions between active and resting motor units.

System Identification of Evoked Mechanomyogram to Clarify Lower Limb Muscle Stiffness in Treadmill Walking

“…We proposed a method to estimate muscle stiffness during rest by identifying the evoked MMG as an impulse response [7]. This method has been applied to the analysis of muscle stiffness depending on recruitment [8], stimulation frequency [9], and isometric contraction level [10]. These studies investigated muscle stiffness in isometric contraction to suppress a motion artifact.…”