A Stretchable Low Hysteresis Capacitive Sensor for Dynamic Muscle Monitoring in Sports and Rehabilitation

In fields such as sports and rehabilitation, monitoring muscle function is essential for preventing injury, optimizing performance, and ensuring the recovery of damaged muscles. However, current muscle monitoring techniques often rely on rigid or bulky sensors that are not well-suited for dynamic tissue deformation. This mechanical mismatch can lead to inaccurate readings or discomfort during use. Therefore, developing a soft, stretchable, and durable sensor is key to enhancing muscle monitoring applications.<br/>In this study, we present a novel stretchable capacitive sensor designed specifically for muscle force gauging. The sensor employs a sandwich structure consisting of stretchable elastomeric barriers (SEBs) as the middle layer and stretchable silver (Ag) paste as the conductive elements on either side. The stretchable capacitive sensor utilizes a sandwich structure to balance mechanical flexibility with reliable electrical performance. At the core of this structure is the SEB layer, which serves as a dielectric medium. This middle layer provides mechanical decoupling, allowing the sensor to stretch and deform along with the muscle tissue while maintaining stable capacitance. On either side of the SEB, a stretchable Ag paste is used to form the conductive layers. These layers are crucial for capturing changes in capacitance due to muscle deformation, enabling the sensor to function as a muscle force gauge.<br/>To validate the performance of the stretchable capacitive sensor, we conducted a series of in vitro tests. When subjected to strain, the sensor demonstrated consistent changes in capacitance, reflecting muscle contraction and relaxation. The sensor maintained its functionality under various levels of mechanical deformation, including 100% strain, without compromising its ability to track dynamic muscle movements. One of the key performance characteristics was the low hysteresis of the sensor during repeated cycles of stretching and relaxation. Low hysteresis is crucial for ensuring that the sensor’s output to improve the precision of muscle monitoring. The next phase of this work will involve testing the sensor in vivo, particularly in a muscle stimulation model. The stretchable capacitive sensor will be placed on target muscles, and voltage stimulation will be applied to induce muscle contractions. By capturing the resulting deformation, the sensor will provide real-time monitoring of muscle force. This information is critical for tracking muscle fatigue, which can help prevent injuries in athletes by identifying early signs of overexertion.<br/>Future developments for this stretchable capacitive sensor will focus on integrating wireless communication modules for remote monitoring. Wireless data transmission will allow users to freely move while receiving real-time feedback on muscle state. Additionally, biocompatibility testing, and long-term stability studies will be critical to ensure that the sensor can be safely used in prolonged clinical applications or during high-intensity athletic training, injury prevention and rehabilitation