Design and Fabrication of Fiber Bragg Grating-Based Flexible Insole for Monitoring Execution of Classical Dance Exercises

Accurate monitoring of classical dance movements, such as the demi plié and grand plié, is crucial for understanding postural dynamics and preventing injuries. In this work, the execution of the above-mentioned ballet exercises performed by one professional ballet dancer and nine amateurs is analyzed. The monitoring system consists in a 3D-printed wearable insole based on an optical fiber with eight fiber Bragg grating (FBG) sensors, used to detect pressure changes and displacements of the center of pressure (COP). In addition, standardized dimensionless indices [asymmetry index and time in boundary (TIB)] are introduced and used for the evaluation of both asymmetries and a quantitative understanding of postural stability and muscle control during performance. The results prove that the FBG insole can detect pressure variations with high sensitivity (0.5–0.8 pm/kPa), showing significant differences between demi plié and grand plié in terms of maximum pressure ( $28.1~\text {kPa} \times \text {m}^{{2}}/\text {kg}$ for demi plié and $46.3~\text {kPa} \times \text {m}^{{2}}/\text {kg}$ for grand plié) and COP stability. The FBG-based insole tailored for ballet dance activity and allowed comparison of the performance of the amateurs with the one of the professional dancer, and to identify potential errors during the execution of the exercises (e.g., heel lifting). The implemented methods and the obtained results allow to evaluate improvement solutions for training, readjust preparation, and, in the future, identify possible injury sources.