System Identification of Evoked Mechanomyogram in an Isometric Contraction

The purpose of this study is to clarify the elasticity of the anterior tibial muscle from an evoked mechanomyogram (MMG) and dorsiflex torque in an isometric contraction. Electrical stimulation was applied to the common peroneal nerve in a resting state and an isometric contraction at various contraction levels (5, 10, 20, 30% of the maximum voluntary contraction). The MMG and dorsiflex torque were measured with an acceleration sensor and a strain gauge load cell, respectively. The superimposed MMG and torque were extracted, and their systems were identified using a singular value decomposition method. The natural frequency of the system was calculated from the poles of the transfer function. In conclusion, the transfer function of the superimposed MMG and dorsiflex torque matched well with a sixth- and a second-order model, respectively. The natural frequency increased as the contraction level increased. It was concluded that the muscle elasticity in an isometric contraction was revealed by the proposed method.