A multimodal wearable sensing approach combining FBG insole and IMU data for workloads and performance monitoring in classic dance

Quantitative monitoring of biomechanical load in classic ballet remains a challenge due to the highly dynamic nature of the movements and the need for non-invasive tools. This study presents a multimodal sensor approach based on the integration of a smart insole with fiber Bragg gratings (FBG) and an inertial measurement unit (IMU) for the simultaneous monitoring of kinematic parameters. The insole, made of thermoplastic polyurethane (TPU) using 3D printing, houses eight FBG sensors for detecting plantar pressure, while the IMU, positioned on the shinbone, estimates the orientation of the body segment. The system is used in experimental tests on a professional dancer during the execution of demi and grand-plié, comparing correct and incorrect execution, where parameters like the vertical ground reaction force (vGRF), the angle of the shinbone and the knee joint forces are measured and estimated. The results indicate that incorrect execution leads to a significant increase in the vGRF, which rises from a peak of 1.22 • BW (i.e., body weight) to 2.45 • BW in the grand-plié. Using a data fusion strategy, tibiofemoral and patellofemoral knee compression forces were estimated, highlighting knee joint loads that double (up to ~19 • BW) in the presence of technical errors. The proposed system proves effective also in identifying instability through displacement of the Center of Pressure (CoP) and variations in contact time (CT), offering an objective tool for injury prevention and artistic performance optimization.