Validation of a wearable low-cost EMG prototype device to support knee extension exercises

As the demand for home-based musculoskeletal (MSK) rehabilitation grows, developing a wearable, cost-effective, and efficient device to monitor kinematics and muscle activity during exercises has become increasingly important. Traditional surface electromyography (sEMG) systems are expensive, complex, and require expert application, making them unsuitable for home use. This study introduces a wearable low-cost prototype device to address these challenges. The device consists of an sEMG sensor and two inertial measurement units to estimate joint kinematics. This study validated the feasibility of measuring joint angles under various conditions by comparing measurements obtained from the device to the OptiTrack motion capture system. Additionally, the relationships between joint angles and muscle activation, as well as limb dominance and muscle activation, were explored to validate its feasibility for measuring muscle activation. Following ethical approval, fifteen healthy participants performed knee extensor maximum voluntary isometric contractions at different knee joint angles as well as dynamic knee extensions under varying loads. The results demonstrated that the overall root mean square error between the OptiTrack motion capture system across both static and dynamic tests ranged from 7.2° to 16.8°. The device showed excellent repeatability in measuring knee joint angles during the static test and acceptable repeatability during the dynamic test. The observed decrease in quadriceps muscle activation with increasing knee angle, and higher muscle activation in the non-dominant leg during dynamic tests, as well as greater force in the dominant leg during static tests, align with previous literature.Clinical Relevance- This study validates the feasibility of the wearable low-cost sEMG device for measuring joint angles and muscle activation. The device could be used as a basic biofeedback tool and also integrated with AI-enabled games, with the potential to be used as a valuable tool to optimise home-based MSK rehabilitation by enhancing patient engagement and personalising exercises.