Humans control the stiffness of joints depending on type of the target task. This implies that profiles of the stiffness includes fruitful information about skillfulness of the human performing. The purpose of this research is to analyze motions by estimating the stiffness and equilibrium points of joints based on sEMG measurements and musculoskeletal model. In this paper, the proficiency evaluation method is proposed based on the calculation of the stiffness ellipse and the trajectory of the equilibrium points of joints.