A sEMG-Based Method for Estimating Upper Limb Joint Stiffness in the Sagittal Plane

As human-machine interaction advances across various fields, the perception of upper limb joint stiffness has become a research focus. However, traditional mechanical perturbation methods are limited to measuring stiffness in horizontal plane, while electromyography-based approaches oversimplify muscle contributions during contraction. In this paper, a surface electromyography (sEMG)-based estimation method is proposed to estimate joint stiffness. To obtain the muscle states in real-time, the contraction-aware muscle stiffness estimation method is presented based on the Hill-type muscle-tendon model. A musculoskeletal model of the upper limb in the sagittal plane is developed to derive the transformation matrix for mapping muscle stiffness to joint stiffness. A pilot experiment was conducted to verify the proposed method. The experimental results indicate the mechanism of muscle contraction through variations in joint stiffness. Furthermore, the estimated joint stiffness values show high consistency with the measured values using the perturbation method.