Musculoskeletal Joint Angle Estimation based on Isokinetic Motor Coordination

Motion estimation plays an important role in motor coordination exploration and optimal control of human-machine interaction. Muscular strength training, such as isokinetic exercise, aims to improve one’s muscular strength and endurance with adjustable resistance at a constant speed. To explore motion estimation and muscle coordination, this paper proposes a sEMG based musculoskeletal model to estimate joint angle trajectory of elbow isokinetic exercise to build the relationship between surface-Electromyography (sEMG) and its related joint movement. A set of motion protocol is designed to evaluate the model, including isokinetic movements under 100% and 50% joint torque levels (TL), and isotonic exercise. sEMG sensors and isokinetic dynamometer are employed in which muscle activations are calculated from sEMG signals as the input of musculoskeletal model. The experiment of three motion protocols is conducted by seven healthy subjects. The synergy patterns indicate the muscle coordination consistency with $\text{R}^{2} {>}$ 0.92. The estimated joint angle trajectory confirms that the musculoskeletal model predicts the isokinetic movement and isotonic movement accurately with $\text{R}^{2} {>}$ 0.90 and the normalized root mean squared deviation NRMSD < 0.18. The research outcome in different levels of muscle forces paves the way for tailoring isokinetic exercise in clinical therapy such as stroke rehabilitation.