The Current Use of GPS, Its Potential, and Limitations in Soccer
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The Current Use of GPS, Its Potential, and Limitations in Soccer Liam Hennessy, PhD1,2 and Ian Jeffreys, PhD, FNSCA, CSCS*D, RSCC*D3 1Setanta College, Thurles, Co Tipperary, Ireland; 2Department of Sport and Exercise, University of South Wales, Pontypridd, Wales; and 3Department of Sport and Exercise, University of South Wales, Pontypridd, Wales Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (http://journals.lww.com/nsca-scj). ABSTRACT multitude of fitness components GLOBAL POSITIONING SYSTEM needed to perform at a high level. DEFINED IN SOCCER, GLOBAL POSITION- Added to this are the logistical chal- GPS is a satellite-based navigation sys- ING SYSTEM (GPS) MONITORING lenges of developing these capacities tem and is made up of over 30 orbiting OF PLAYER WORKLOADS IS NOW in conjunction with the extensive tech- satellites. The system was originally EXTENSIVELY USED ACROSS ALL put into orbit by the U.S. Department nical and tactical training a player will LEVELS OF THE SPORT. TO MAKE of Defense for military use in the early need to undertake, on a daily basis. BETTER USE OF THIS TECHNOL- 1970s. Later, in the 1980s, it was made This challenge is further exacerbated OGY IT IS IMPORTANT TO APPRE- available for civilian use. The orbiting by the increasing length of playing sea- CIATE HOW IT WORKS. FURTHER, satellites transmit unique signals that sons and an increasing density of fix- WHEN THE LIMITATIONS OF GPS allow GPS devices to locate the satel- tures within these seasons (42). USE ARE APPRECIATED AND THE lites precise location. Essentially, the RATIONALE OF USE IS AGREED Partly in response to these develop- GPS receiver calculates the distance AND ARTICULATED, THEN THE ments, there has been an increased to each satellite by the amount of time POTENTIAL OF GPS MONITORING focus on the overall monitoring of it takes to receive a transmitted signal CAN BE EFFECTIVELY REALISED player workloads in an attempt to with the result that the user’s location TO BETTER MANAGE PLAYERS understand the stress placed on the can then be precisely determined. PERFORMANCE, WORKLOAD AND player during training and match play, Once the receiver links with a number of orbiting satellites, a GPS receiver WELFARE. (SEE VIDEO, SUPPLE- with the goal of maximizing perfor- can provide a reasonably exact position MENTARY DIGITAL CONTENT, mance and minimizing the risk of and speed of the receiver device. There NUMBER 1, WHICH SUMMARIZES injury (30,70). To facilitate this, there are 2 main communication systems GPS USE, LIMITATIONS, AND has been a great increase in the use associated with GPS technology. The POTENTIAL IN SOCCER, HTTP:// of global positioning system (GPS) direct satellite to receiver device sys- LINKS.LWW.COM/SCJ/A238). technology (31). However, although this technology is now used by many tem of communication described clubs at both amateur and professional above is known as nondifferential, INTRODUCTION levels, it is important to appreciate the whereas the use of ground-based cor- ith over 265 million partici- limitations of this technology. Further- rection techniques to enhance the pants, soccer is the most more, it is important to understand quality of location data gathered using Wpopular sport in the world how the technology works and how GPS receivers is known as a differential across both sexes and all age groups related metrics are derived. Finally, it system (44,45). The important point to (25). The sport provides one of the is equally important to appreciate the KEY WORDS: greatest challenges to the strength potential of GPS and related technol- technology; global positioning and conditioning coach with the ogy in supporting the goals to improve system; monitoring; potential; limita- player performance and ultimately, to Address correspondence to Dr. Liam Hen- tions; soccer nessy. [email protected]. ensure better player welfare. Copyright Ó National Strength and Conditioning Association Strength and Conditioning Journal | www.nsca-scj.com 83 The Current Use of GPS note is that although the nondifferen- currently derived from integrated GPS cumulative concept, be they physical tial system can provide useful data, and MEMS technology (Table 1). or otherwise. The quantification and there will always be a degree of error There is no doubt that GPS technology use of these workload data within which the practitioner needs to be has facilitated a greater understanding a broader concept of workload is a desir- aware of (44). Some of this can come of the physical activity demands of dif- able goal for all involved in sport but it is for the sampling frequency of the ferent team formations and positional also a challenge for the support staff of device and others from factors that profiling during match play, as well as a team of players. affect the signal, as the signal from training, and when integrated with the satellites can be influenced by the internal responses such as heart rate RELIABILITY AND VALIDITY atmosphere and obstructions such as (HR) monitoring, a more holistic tall buildings (45). Differential GPS workload evaluation may be attained As with all measuring devices in sport, can help to reduce this error. Differen- (1,14,53,61,63,68). it is important to assess both reliability tial GPS uses stationary receivers and validity of GPS and related devices. placed at known locations on the EARLY WORKLOAD MONITORING GPS devices are classified by the rate at IN SPORT ground. These fixed-position receivers which they sample per second. In the are then used to facilitate better com- Foster et al. (26,27) established the val- early years of GPS use in sports, the munication with orbiting satellites (45). idity of using “rating of perceived exer- devices used a sampling rate of 1 Hz tion” or RPE as a tool to monitor or 1 sample per second (3,43). When EVOLUTION OF GLOBAL physical workload. Both team and indi- such devices were assessed for reliability POSITIONING SYSTEM vidual sports have since used this and validity, studies reported that these TECHNOLOGY method to establish exercise workload devices were somewhat unreliable and One of the first studies using GPS tech- (34). Studies also reported the use of not valid especially for short high- nology was published by Ishii et al. (38). session RPE and duration as a valid intensity sprint runs (18,39,41,43,46). This group used mobile GPS units to instrument for tracking workload Jennings et al. (39), for example, used track referees during match play in both within anaerobic sports and within GPS devices sampling at 1 and 5 Hz rugby union and soccer. The study a resistance training exercise environ- and concluded that GPS systems may compared video tracking, manual ment (49,62,66). In parallel with this be limited for the assessment of short recording, and GPS tracking of the ref- growth and interest in sport-related high-speed straight-line running and ef- eree and found that there was little dif- workload monitoring, methods were forts involving change of direction. The ference among all 3 methods for total investigated that could provide objec- authors did note that an increased sam- distance covered in the match. Since the tive data on workload. An important ple rate improved validity and reliability original study of Ishii et al. (38), GPS factor that assisted in this development of GPS devices. Other authors sup- technology has become more sophisti- was when GPS selective availability ported this finding when assessing 1- cated in the metrics it can provide and was removed in 1999, making it avail- and 5-Hz GPS devices (18,41). has been integrated with other micro- able for use within a sporting environ- Johnston et al. (41) reported that GPS electromechanical sensors (MEMS) ment (45). Subsequently, RPE and error was found to increase along with such as accelerometers and gyroscopes. session duration workload quantifica- the velocity of movement and noted that This has been facilitated by team sport tion were supplemented with GPS- more caution should be exercised when governing bodies that now allow play- derived workload metrics and these analyzing movement demands .20 ers to use GPS tracking devices during measures became increasingly popular km$h21. Coutts and Duffield (18) re- match play (24,57). Recently, the world (3,34,35,39). ported an acceptable level of accuracy governing body for soccer (FIFA) With a view to establish a broader and reliability for total distance during amended their rules to allow the use definition of what workload means in high-intensity, intermittent exercise but of GPS technology in competitive a sporting environment, Quarrie et al. not for higher intensity activities. Subse- match play (26). This has created the (57) defined “load” within a team sport quently, the use of 10-Hz devices became opportunity for the quantification of perspective as “the total stressors and more common in team sport and Varley several physical workload metrics asso- demands applied to the players.” This et al. (69) reported that devices using ciated with elite competitive soccer included sport-related and non–sport- such higher sampling rates were 2–3 match play (Table 1). related stress inputs. Furthermore, the times more accurate than the 5-Hz de- The integration of MEMS technology authors noted that the relevance of load vices. The same authors then concluded now allows for the quantification of to athlete performance, well-being, and that newer GPS devices may provide an metrics related to body impact, adding injury risk should be considered from an acceptable tool for the measurement of to the concept of workload monitoring acute and cumulative perspective.