As muscle and strength decline with age, the risks of falling down and becoming disabled increase for the elderly. However, rehabilitation for patients through long-term treatments and assessments in medical institutions take a long time. It reduces the elderly people's quality of life and causes a burden on their living and financial on their family. Therefore, the goal of this study is to design the wearable sEMG device based on wireless sensing technology for muscle rehabilitation. We aim to help the elderly train their lower limbs at home and simultaneously collect physiological signals though training for remote medical diagnosis. In this study, the design direction is established through focus group interviews. The rehabilitation actions were observed, and the position of muscle movement was measured to establish design parameters and procedures. The designed wearable device was evaluated through a pilot study and semi-structured interview to understand its usability and feasibility. Finally, experts evaluated the usability of the device. From the results, it was found that rehabilitation at home using the designed wearable sEMG device was accepted by most of the elderly respondents. They think that it is very convenient to receive medical feedback at home. Furthermore, medical staff can also use the physiological data to understand the patient's condition and provide diagnosis and treatment. We hope that the product can be widely used to receive signals of the rehabilitation of elderly's lower limb muscles at home in the future. Further discussions on the design implications of the development process can be a reference for future related product development.