Variability of GPS Units for Measuring Distance in Team Sport Movements

Abstract

Purpose: To examine the difference in distance measured by two global positioning system (GPS) units of the same model worn by the same player while performing movements common to team sports. Methods: Twenty elite Australian football players completed two trials of the straight line movement (10, 20, 40 m) at four speeds (walk, jog, stride, sprint), two trials of the changes of direction (COD) courses of two different frequencies (gradual and tight), and five trials of a team sport running simulation circuit. To assess inter-unit variability for total and high intensity running (HIR) distance measured in matches, data from eight field players were collected in three Australian Hockey League (AHL) matches during the 2009 season. Each subject wore two GPS devices (MinimaxX v2.5, Catapult, Australia) that collected position data at 5 Hz for each movement and match trial. The percentage difference ±90% confidence interval (CI) was used to determine differences between units. Results: Differences (±90% CI) between the units ranged from 9.9 ± 4.7% to 11.9 ± 19.5% for straight line running movements and from 9.5 ± 7.2% to 10.7 ± 7.9% in the COD courses. Similar results were exhibited in the team sport circuit (11.1 ± 4.2%). Total distance (10.3 ± 6.2%) and HIR distance (10.3 ± 15.6) measured during the match play displayed similar variability. Conclusion: It is recommended that players wear the same GPS unit for each exercise session to reduce measurement error. The level of between-unit measurement error should be considered when comparing results from players wearing different GPS units.

What are talent scouts actually identifying? Investigating the physical and technical skill match activity profiles of drafted and non-drafted U18 Australian footballers

“…Acknowledging the limitations associated with microtechnology, 9,23 and given data availability, this study could only utilise four physical criterion variables. Additionally, given the depth of notational analytics undertaken during the National U18 AFL Championships, only six technical skill criterion variables could be accurately utilised.…”

“…Previous work has suggested that these variables appear to be the most clinimetrically robust when compared to other GPS metrics. 9 A specific selection of individual technical skill criterion variables for each game were retrieved from a commercial statistical provider (Champion Data © , Melbourne, Australia). Data from this provider has previously been shown to provide a reliable means for quantifying players technical skill match activity profile for AF.…”

“…7,8 As such, some of the more common metrics reported relating to GPS include total or absolute distance (m), relative distance (m.min -1 ) and high intensity running (distance (m) > 15 km.hr -1 ). 9 In addition to quantifying the physical match activity profiles of players, commercial statistical providers; namely Champion Data © (Champion Data © , Melbourne, Australia), provide AFL teams with in-depth reports surrounding the technical skill activity profiles of players ingame play. These statistics; inclusive of but not de-limited to the total number of skill involvements (total possessions), the number of inside 50's (attacking passages of play) and the number rebound 50's (attacking passage of play from defence) are useful for both coaching and research purposes.…”

Wearable Training-Monitoring Technology: Applications, Challenges, and Opportunities

“…1 Higher sampling frequencies and improvements in technology have been found to improve reliability in a similar way to validity. 44,51 The intraunit reliability of velocity and distance at any given velocity is difficult to accurately determine as it requires participants to perform multiple trials at the exact same speed. Interunit reliability is also difficult as it is unclear how wearing multiple devices may affect GPS signal quality and accelerometer results may vary when placed in different locations.…”

“…While interunit reliability appears to have improved it is recommended that the same device be used on a given athlete when monitoring training load to minimize intraunit variability. 51 The validation of the accelerometers measure of Player Load is problematic as it represents an arbitrary unit, however its reliability has been assessed under laboratory and field conditions. 37 When using a hydraulic universal testing machine to oscillate devices at specified acceleration ranges, devices showed strong interunit and intraunit reliability (CV of <1.10%) for Player Load.…”