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Title: Optimising the use of GPS technology to quantify biomechanical load in elite level soccer
Author: Demopoulos, Pantelis
ISNI:       0000 0004 5990 6990
Awarding Body: Edge Hill University
Current Institution: Edge Hill University
Date of Award: 2016
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Application of GPS technology in elite level soccer is a growing area of research. This thesis comprises an examination of current practice in elite youth level soccer, and a critical examination of the potential applications in the PlayerLoadTM measure to quantify the biomechanical demands of match play. The thesis comprises four experimental studies that consider the development of monitoring biomechanical intensity in training and/or competitive matches. The first experimental study provides a critical examination of the biomechanical specificity of training drills relative to competitive match play. This study utilised the performance metrics as collated on a daily basis by the football club. Specifically, in relation to tri-axial accelerometry the measurement of PlayerLoad was restricted to total accumulated loading. Additional parameters related to distance and velocity parameters were also examined. ‘Small-Sided Games’ generated similar values to 90-min matches for PlayerLoad (standardised for duration) and total distance covered. However, these drills failed to provide a valid demand in terms of high-intensity running, which was most valid in ‘Movement Pattern’ drills. Drills described as ‘Possession’ and ‘Game-Related’ failed to match the mechanical demands of match play. The implications of these findings relate directly to the micro-design of the training week, and the monitoring of player performance. The correlation between PlayerLoad and distance covered was stronger in small-sided games (r=0.92) than in regulation 11 vs 11 match play (r=0.37), highlighting mechanical issues in the calculation of PlayerLoad. The smaller pitch size is likely to promote a greater frequency of speed and or directional change, and as such the summation principle applied to generate a “total” or 3- dimensional loading value is limited. 6 In the second experimental study the analysis of tri-axial accelerometry was extended to provide a uni-axial consideration of PlayerLoad. Biomechanically, this is analogous to analysing each force vector rather than the development of a “total” kinetic parameter based on a summation principle. This uni-axial analysis of mechanical loading was first applied to the influence of playing age via a comparison of the U16, U18 and U21 squads within the same club. The U16s performed the greatest total distance, primarily in the lower speed zones. Correlation between PlayerLoad and total distance ranged from r=0.26-0.56, for the three age groups, with evidence of higher coefficients in the U16 group. The U18s exhibited the greatest PlayerLoad, evident in each movement plane. Uni-axial analysis highlighted a higher contribution from medio-lateral loading in the U18s, indicative of greater lateral movement. This finding might also relate to the higher injury incidence observed in this U18 age group. The practical applications of this study relate to the transition of players through the academy structure and into senior football. The unique movement patterns identified by a uni-axial analysis of PlayerLoad highlights potential in the greater analysis of movement. This uni-axial analysis was extended in the third experimental study to further examine issues in the movement profile with a consideration of the influence of playing position on mechanical loading. Whilst not generalisable beyond this team and playing strategy, attackers covered the greatest (total and high speed) distance, whilst midfielders exhibited the greatest load across all movement planes. Correlation between PlayerLoad and total distance was position specific, forwards and midfielders recorded values of r=0.74 and r=0.16 respectively. Playing position categorising defenders, midfielders and attackers failed to identify the impact of positional width on the biomechanical demands of match play. The traditional grouping of playing units might therefore be considered in terms of individualising training programmes. The distinction between distance covered and PlayerLoad is consistent throughout the first three experimental studies, with a low correlation in part explained by the calculation used to 7 quantify PlayerLoad. In the final experimental study the PlayerLoad calculation is critically examined beyond the uni-axial nature of acceleration. Having previously examined the summation principle, the failure of the PlayerLoad calculation to consider magnitude of acceleration is examined. The instantaneous change in acceleration is not influenced by the magnitude of acceleration, and in the final study a novel iLoad parameter is introduced which is analogous to the iEMG parameter utilised widely in electromyography. This parameter considers the integral of the acceleration-time curve. Further, the sign principle is critically examined, with the PlayerLoad calculation negating all negative values and thus making all movements forward, to the right, and upward. By considering both positive and negative values the tri-axial accelerometer has the capacity to differentiate between medial and lateral movement for example, with clear implications for the monitoring of performance and injury risk. This novel biomechanical analysis was applied to an examination of fatigue during match play, which has implications for both performance and injury. Over 15min segments of match play, fatigue did not influence the anterio-posterior or medio-lateral loading but there was a significant decrease in vertical load. There was also evidence of movement asymmetry in each plane, favouring movements forward and to the left. Correlation between iLoad and total distance was r=0.19. In conclusion, the thesis evaluated PlayerLoad and critically discussed the mechanical specificity of training activities. Furthermore, use of uni-axial load highlighted differences in positional demands and the influence of age group on GPS variables. Critical evaluation of PlayerLoad calculation aimed to highlight the deficiency of tri-axial acceleration of the formula. Thus, iLoad further developed calculation to refine movement quality data to examine fatigue. By adopting principles analogous to kinetic analyses in force platform and electromyography, additional analysis parameters may be defined which provide greater depth 8 of information in movement quality. The implications in movement asymmetry also have implications for the monitoring of injury risk.
Supervisor: Greig, Matt Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: RC1200 Sports Medicine