A multimodal investigation of in vivo muscle behavior: System design and data analysis

The study is aimed to investigate in vivo behaviors of the rectus femoris muscle during isometric contraction by integrating simultaneously recorded electromyography (EMG), mechanomyography (MMG), and ultrasonography (US). We developed an experimental platform for simultaneous acquisition of EMG, MMG, US, as well as the torque, during isometric muscle contraction. Features from multimodal signals and images were then automatically extracted and calibrated to present time-varying characteristics of muscle behaviors. We further applied local polynomial regression (LPR) to reveal nonlinear and transient relationships between multimodal muscle features and torque. The results suggested that the proposed multimodal signal acquisition and integration are capable of providing novel and complete information about in vivo muscle contraction. The proposed experimental platform is a potentially useful tool for muscle assessment in various clinical and practical applications.