Abstract
Aim: The aim of the present study was to determine the validity of position, distance traveled and instantaneous speed of team sport players as measured by a commercially available local positioning system (LPS) during indoor use. In addition, the study investigated how the placement of the field of play relative to the anchor nodes and walls of the building affected the validity of the system.Method: The LPS (Catapult ClearSky T6, Catapult Sports, Australia) and the reference system [Qualisys Oqus, Qualisys AB, Sweden, (infra-red camera system)] were installed around the field of play to capture the athletes' motion. Athletes completed five tasks, all designed to imitate team-sports movements. The same protocol was completed in two sessions, one with an assumed optimal geometrical setup of the LPS (optimal condition), and once with a sub-optimal geometrical setup of the LPS (sub-optimal condition). Raw two-dimensional position data were extracted from both the LPS and the reference system for accuracy assessment. Position, distance and speed were compared.Results: The mean difference between the LPS and reference system for all position estimations was 0.21 ± 0.13 m (n = 30,166) in the optimal setup, and 1.79 ± 7.61 m (n = 22,799) in the sub-optimal setup. The average difference in distance was below 2% for all tasks in the optimal condition, while it was below 30% in the sub-optimal condition. Instantaneous speed showed the largest differences between the LPS and reference system of all variables, both in the optimal (≥35%) and sub-optimal condition (≥74%). The differences between the LPS and reference system in instantaneous speed were speed dependent, showing increased differences with increasing speed.Discussion: Measures of position, distance, and average speed from the LPS show low errors, and can be used confidently in time-motion analyses for indoor team sports. The calculation of instantaneous speed from LPS raw data is not valid. To enhance instantaneous speed calculation the application of appropriate filtering techniques to enhance the validity of such data should be investigated. For all measures, the placement of anchor nodes and the field of play relative to the walls of the building influence LPS output to a large degree.
Highlights
Analyses of physical demands can improve the understanding of physical performance and injury risk in sports
Most local positioning systems (LPSs) used in team sports are radiofrequency based (Muthukrishnan, 2009; Frencken et al, 2010; Ogris et al, 2012; Sathyan et al, 2012; Leser et al, 2014; Rhodes et al, 2014; Stevens et al, 2014), in which radio-frequency signals are used to measure the distance between several base stations at known locations distributed around the field of play, and mobile nodes worn by the athletes (Muthukrishnan, 2009; Hedley et al, 2010)
The LPS overestimated the distance compared to the reference system for both the optimal and sub-optimal condition
Summary
Analyses of physical demands can improve the understanding of physical performance and injury risk in sports. High intensity events are reported using variables such as number of sprints, number of accelerations, or distances covered above a predefined speed threshold (Bangsbo et al, 2006; Michalsik et al, 2013; Luteberget and Spencer, 2017). The main drawback of GNSS is its restriction to outdoor facilities; indoor sports cannot use GNSS for tracking of players in competition and training In indoor sports such as team handball, video-based analysis has been the main method used to analyze position-related variables (Sibila et al, 2004; Chelly et al, 2011; Michalsik et al, 2012, 2013; Póvoas et al, 2012, 2014; Karpan et al, 2015). Most LPSs used in team sports are radiofrequency based (Muthukrishnan, 2009; Frencken et al, 2010; Ogris et al, 2012; Sathyan et al, 2012; Leser et al, 2014; Rhodes et al, 2014; Stevens et al, 2014), in which radio-frequency signals are used to measure the distance between several base stations (anchor nodes) at known locations distributed around the field of play, and mobile nodes worn by the athletes (Muthukrishnan, 2009; Hedley et al, 2010)
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