The use of GPS technology to quantify the game demands of elite youth soccer: implications for training design.

The transition from academy to the professional level is one of the pivotal key stages in the development of elite professional soccer players and our understanding of this process is incomplete (Mills et al. 2012). A comprehensive detailed assessment of elite youth players match performance is limited and a clear gap in the literature exists which has consequences for the development programs of academy players (Harley et al. 2010). Global positioning systems (GPS) have been developed for use within a sports context to measure distance and velocity, however the methods employed for determining accurate capture conditions has not been examined and rely solely on historical criteria established before its use in dynamic sports such as soccer. The studies contained in this thesis are designed to further examine how an increase understanding of the match demands of youth soccer through the use of GPS technology to allow the development of highly tailored training programs to maximise the development of youth players. The aim of the first study (Chapter 4) was to compare data collected using 5Hz GPS (MinimaxX, Catapult) and the ProZone? (PZ) match analysis system and to establish satellite and Horizontal Dilution of Precision (HDOP) threshold limits to allow direct comparison between the two data sets. Ten elite outfield youth team players were monitored with PZ and GPS during a match and the data grouped into 10 minute capture periods and categorised into players who averaged a mean satellite lock of more than 5.5, 5, 4.5, and 4 over the ten minute period and a mean an HDOP of less than 1.8, 2, 3 and 4. The distance covered in each of the predetermined PZ speed categories were compared. The data showed significant differences (p <0.05) in all of the capture categories with the exception of the less than 1.8 HDOP group (p > 0.05) with small to large effect sizes. These data therefore suggested that for the accurate assessment of high velocity running (>4m/s) using GPS a HDOP threshold of 1.8 be used. Using the valid GPS capture conditions obtained in study 1, the aim of the second study (Chapter 5) was to quantify match play according to outfield playing position in elite youth soccer at a scholarship (U18) level and compare to First team players. Eleven Under 18 games were analysed using GPS. Total distance covered and the maximal sprinting speeds were comparable with first team players in addition to the type of sprint performed (leading or explosive). The very high intensity running distance was less than that of first team players (range 532 to 804m vs 632 to 1196m) with the youth performing less sprints (range 9 to 12 vs 23 to 44) and with each sprint over a longer distance (50% over 10m vs under 10m) . The data highlights that the acceleration profiles of youth players need to receive the greatest attention at Under 18 level for there to be successful progression to the elite level. By highlighting the discrepancy in the number of sprints and the distance covered by elite youth players the purpose of study three (Chapter 6) was to adapt the Draper and Lancaster test (ADL) to soccer specific distances and determine its reliability and ability to discriminate between different levels of players. The reliability of the total time of the ADL proved to be highly reproducible (TE = 0.17, ICC = 0.99, CV =0.7) along with the three sub-component tests (LE7m TE = 0.38, ICC = 0.93, CV = 1.6, 505 TE = 0.28, ICC = 0.96, CV = 1.3, and EX7m TE = 0.21, ICC = 0.98, CV =1.2). In assessing the validity of the ADL test the national players showed that they were significantly quicker in the ADL (mean diff = 0.41, t = 5.32, p <0.005, CI = 0.25, 0.57, d = 1.4) the EX7m (mean diff = 0.19, t = 6.72, p <0.005 , CI = 0.14, 0.25, d = 1.76) and 505 (mean diff = 0.14, t = 3.27, p <0.005, CI = 0.05, 0.22, d = 0.86) sub component tests compared to the club level players but not in the 7mLE (mean diff = 0.05, t = 1.79, p = 0.08, CI = 0.01, 0.11, d = 0.47). The data demonstrate that the ADL test was reliable in test retest situations and a valid predictor of level of sport participation because it discriminated between players of lesser ability (club) and higher ability (national) and can be used in a football setting to assess the main fitness components (explosive speed, leading speed and agility) which have been highlighted as important in the elite game. Extending on this work, the aim of study 4 (Chapter 6) was to investigate the application of the A505 field test for the assessment of functional asymmetries of the lower limb. Measurement of the fastest time for each side was recorded along with the peak torque of the hamstrings and quadriceps measured on an isokinetic dynamometer. The data showed that there were significant differences recorded in three of the four categories of the dominant side movements, concentric extension (Mean difference = 44.18, t = 5.70, p