Automated LED tracking to measure instantaneous velocities in swimming

Josje Van Houwelingen,Ad P C Holten,Ernst Jan Grift,Herman J H Clercx,Jerry Westerweel,Jerry Westerweel,Raf M Antwerpen

doi:10.1007/s12283-018-0288-8

Josje Van Houwelingen, Ad P C Holten + Show 5 more

Open Access

https://doi.org/10.1007/s12283-018-0288-8

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Abstract

In this paper a video-based method to automatically track instantaneous velocities of a swimmer is presented. Single cameras were used to follow a marker (LED) attached to the body. The method is inspired by particle tracking techniques, traditionally used in the field of fluid dynamics, to measure local velocities of a fluid flow. During the validation experiment, a white LED was attached to the hip of a swimmer together with a speedometer. A swimmer performed four different stroke types. The velocity profiles using LED tracking were captured and showed less noise than the speedometer measurements. Only at times when the marker disappeared above the water surface due to body role in front crawl and backstroke swimming did the LED tracking fail to capture the athlete’s motion. The algorithm was tested in a 2D case with a single LED to illustrate the proof of principle, but should be suitable for implementation in a 3D analysis or multiple LED analysis.

Highlights

The need for measuring the intra-cyclic velocity variations (IVVs) and velocity profiles in an experiment including many swimming trials [1] forms the framework of this study
The settings of the LED tracking algorithm were kept constant throughout the analysis of different recordings
The LED was tracked automatically, only the starting position was selected manually. Note that this can be automated, but this was not implemented in this study

Summary

Introduction

The need for measuring the intra-cyclic velocity variations (IVVs) and velocity profiles in an experiment including many swimming trials [1] forms the framework of this study. The most widely used method to access the instantaneous velocity of a swimmer is a speedometer, known as a tachometer [2,3,4,5,6,7]. A thin, non-stretching cable is attached to the waist of a swimmer. The rotation speed within the instrument is measured when pulling the cable while swimming. The use of a speedometer is straightforward, the method just offers 1D information and limits the swimmer’s motion. Other techniques have been developed as well

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