Recently, assisting human motion with a wearable robot is studied widely. These assisting systems are proposed from various points of view. Our study has proposed an assisting system that the torque, angle, and the viscoelasticity of the joint are variable because the human muscle has the characteristic of variable viscoelasticity. This system consists of antagonized muscle that the stiffness is variable and magneto-rheological fluid brake that the viscosity is variable. Therefore, the system

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... ables the wearable assistive device such as exoskeletons to be structurally soft and to provide the wearer with a high back-drivability. We have proposed the assisting method by changing the viscoelasticity of the device joint according to the viscoelasticity of wearer's muscle. But suitable viscoelasticity of the joint for the assistive motion is not well known. In this paper, an experiment is conducted to examine how the viscoelasticity of the joint affects to human motion when assisting. Also, based on the results from the experiments, we propose the control method for the joint viscoelasticity of the device that responds to the assistive motion and confirm the effects with the experiments.