Elastic kirigami patch for electromyographic analysis of the palm muscle during baseball pitching

Abstract: Surface electromyography (sEMG) is widely used to analyze human movements, including athletic performance. For baseball pitchers, a very precise movement is required to pitch the ball into the strike zone. The palm muscles appear to play a key role in this movement, and a real-time recording of sEMG from the palm muscle is useful in the analysis of motion during baseball pitching. However, the currently available devices with rigid and bulky electrodes (including connective wires) impede natural movements of the wearer and recording of sEMG from the palm muscles during vigorous action. Here, we describe a skin-contact patch consisting of kirigami-based stretchable wirings and conductive polymer nanosheet-based ultraconformable bioelectrodes, which address the challenge of mechanical mismatch between human skin and electrical devices. The key strategy is a kirigami-inspired wiring design and a mechanical gradient structure from nanosheet-based flexible bioelectrodes to a bulk wearable device. This approach would buffer the mechanical stress applied to the skin-contact bioelectrodes during an arm swing movement. With this patch, we precisely measure sEMG at the abductor pollicis brevis muscle (APBM) in a baseball player during ball pitching. We observe differences in the activity of the APBM between different types of pitches—fastball and curveball. This sEMG measurement system will enable the analysis of motion in unexplored muscle areas, such as on the palm and the sole, leading to a deeper understanding of muscular activity during performance in a wide range of sports and other movements.