Modeling of muscle vibration during a twitch

In this study, the vibrating bar theory is used for modeling the muscle vibration, or vibromyographic (VMG) signal under functional electrical stimulation (FES). The simplified movement equation is derived, with the assumption that the muscle is a bar as a fibrous cable and undergoes transverse vibration only. The numerical simulation is performed with the parameters given either from published literature or by rough estimation. The simulation result is compared with that of experiment to test physiological validity of the model. It is found that the the vibrating bar model can well describe the feature of VMG signal elicited by FES. Finally, the relationship between the peak frequencies of the simulated VMG signals and the mechanical and physiological parameters of muscle, such as muscle tension and muscle stiffness, is discussed. It can be concluded that both muscle tension and stiffness affect the frequency of VMG signal and that the peak frequency is sensitive to the resting bending stiffness, E_b0, when E_b0 is in the range from 1.0×10⁴ N/m² to 1.0×10⁶ N/m². Therefore VMG signal analysis may be used as a potential tool for predicting muscle fatigue