Fig. 7

Estimated joint stiffness as a function of joint angle for 10 human subjects. Each subject is represented by a different colored line while the large circular marker represents the estimation for the parameter value at the first iterations of the Kalman filter. a Stiffness of the ankle joint \(k_{1}\) with respect to the measured ankle joint angle. b Stiffness of the ankle joint \(k_{1}\) with respect to the measured hip joint angle. c Stiffness of the hip joint \(k_{2}\) with respect to the measured ankle joint angle. d Stiffness of the ankle joint \(k_{2}\) with respect to the measured hip joint angle