Front-Crawl Instantaneous Velocity Estimation Using a Wearable Inertial Measurement Unit

TLDR

Monitoring performance is crucial for elite sports, yet velocity measurement in swimming remains immature due to the complexities of measuring in water. This study aims to estimate front‑crawl velocity using a single inertial measurement unit (IMU). Thirty swimmers wore a sacrum‑mounted IMU while performing four ascending 25‑m front‑crawl trials, with a tethered speedometer as reference, and the authors applied biomechanical constraints and a change‑detection framework to achieve drift‑free integration of forward acceleration for velocity estimation. The IMU estimates differed by only 0.6 ± 5.4 cm s⁻¹ in mean cycle velocity and 11.3 cm s⁻¹ RMS in instantaneous velocity from the reference, demonstrating a practical, drift‑free tool that delivers timely feedback to coaches without complex setups.

Abstract

Monitoring the performance is a crucial task for elite sports during both training and competition. Velocity is the key parameter of performance in swimming, but swimming performance evaluation remains immature due to the complexities of measurements in water. The purpose of this study is to use a single inertial measurement unit (IMU) to estimate front crawl velocity. Thirty swimmers, equipped with an IMU on the sacrum, each performed four different velocity trials of 25 m in ascending order. A tethered speedometer was used as the velocity measurement reference. Deployment of biomechanical constraints of front crawl locomotion and change detection framework on acceleration signal paved the way for a drift-free integration of forward acceleration using IMU to estimate the swimmers velocity. A difference of 0.6 ± 5.4 cm · s(-1) on mean cycle velocity and an RMS difference of 11.3 cm · s(-1) in instantaneous velocity estimation were observed between IMU and the reference. The most important contribution of the study is a new practical tool for objective evaluation of swimming performance. A single body-worn IMU provides timely feedback for coaches and sport scientists without any complicated setup or restraining the swimmer's natural technique.