In lower-limb rehabilitation, there is a specific group of patients that can perform voluntary muscle contraction and visible limb movement provided that the weight of his/her leg is fully supported by a physical therapist. In addition, this therapist is necessary in guiding the patient to switch between hip-only and knee-only motions for training specific muscles effectively. These clinic needs have motivated us to devise a novel reconfigurable gravity-balanced mechanism for tackling with the clinical demands without the help from therapists. The proposed mechanism has two working configurations, each leading the patient to do either hip-only or knee-only exercise. Based on the principle of static balancing, two tensile springs are attached to the mechanism to eliminate the gravitational effect of the mechanism and its payload (i.e., the weight of the patient's leg) in both configurations. The gravity balancing design is verified by a numerical example and adams software simulation. A mechanical prototype of the design was built up and was tested on a healthy subject. By using electromyography (EMG), the myoelectric signals of two major muscles for the subject with/without wearing the device were measured and analyzed. The results show that the myoelectric voltages of the stimulated muscles in both hip-only and knee-only motion modes are reduced when the subject is wearing the device. In summary, the paper for the first time demonstrates the design philosophy and applications by integrating the reconfigurability and static balancing into mechanisms.

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