Figure 4

Joint angle of ankle and hip at motion tracking frequency f in Eq. (5) with regard to 0.15Â [Hz] and 1.5Â [Hz]. Where, energy consumption penalization parameter \(\gamma\) in Eq. (6) is 20. The motion amplitude A of target point in Eq. (5) is 0.1 [m]. Ankle and hip stiffness remains 25Â [Nm/rad] and 125Â [Nm/rad]. \(t_0\) and \(t_1\) are the timesteps corresponding to the maximum angles of the ankle and hip in the current motion cycle.