Enhanced Reaction Time Measurement System Based on 3D Accelerometer in Athletics

Reaction time (RT) is a key measure of neuromuscular and cognitive performance, but most existing methods rely on laboratory equipment or focus on localized actions such as finger taps or foot lifts, limiting their relevance for whole-body movements. In this work, we present a portable inertial measurement unit (IMU)-based system specifically designed to measure RT during sprint starts. The device integrates a triaxial accelerometer (ICM-20948, ±16 g) and an ESP32 microcontroller, which generates an auditory stimulus, acquires acceleration data at 1 kHz, and computes movement onset in real time. A fixed acceleration threshold, determined from calibration against a high-speed camera reference, was used to detect the first voluntary movement. Both desktop and smartphone applications were implemented to control the system, provide feedback, and store test data. Validation experiments showed good agreement with the high-speed camera used as a reference (R² = 0.9391), with a mean bias of -1.35 ms and 95% limits of agreement within ±25 ms. The proposed system combines high temporal resolution, portability, and straightforward deployment, enabling reliable assessment of whole-body RT in realistic sports and research environments.