Development of an Embedded Magnetometer-Free IMU-Based Sensing System for Motion Analysis of Kendo Swings

In recent years, wearable sensing technologies have been widely used for motion analysis in sports; however, in kendo, motion evaluation still largely relies on subjective assessment, and quantitative approaches remain limited. This study proposes an embedded Inertial Measurement Unit (IMU) based sensing system for motion analysis of kendo swings. The system integrates a compact IMU and a microcontroller within the handle of a bamboo sword (shinai), enabling unobtrusive measurement without affecting usability. To achieve robust orientation estimation under highly dynamic conditions, an error-state Kalman filter (ESKF) is applied using only 6-axis IMU data, without relying on magnetometer measurements. This enables stable gravity compensation and reliable extraction of motion-related acceleration components. Experimental results showed that experienced practitioners exhibited significantly higher peak acceleration (p = 0.002) and smaller peak width (p = 0.022) than novices, indicating sharper and more efficient motion. No significant difference was observed in the secondary peak ratio. These results demonstrate that the proposed system can quantitatively capture kendo motion characteristics and distinguish practitioners of different proficiency, highlighting the effectiveness of magnetometer-free IMU-based motion analysis for highly dynamic movements.