The measurement and analysis of the physical performance of soccer players
Creators: name: Flanagan, Troy
Publisher: name: RMIT University
Year: 2024

description: The purpose of this thesis was to identify a solution to the problem previously identified by sport scientists and coaches working with elite professional soccer teams: it is difficult to measure and analyse the physical performance of soccer players during match play (Bangsbo &amp; Mohr, 2005; Burgess et al., 2006; Krustrup et al., 2006). This thesis comprised of chapters that sequentially identified the problem, examined how to analyse the on-field physical performance, determined how to comprehensively measure the on-field movements, successfully validated a possible solution and trialled a new locomotion tracking prototype.<br><br>The review of literature in Chapter 1 primarily focused on reviewing the data and the measurement techniques that have been employed by investigators to quantify the physical performance of soccer players. This review facilitated the identification of the problem and revealed the inadequacy of current measurement techniques to quantify the physical performance of soccer players. There has been very little data published by investigators on soccer player performance beyond describing only general movements made by players during a match. Short term, ballistic and sport specific movements have rarely been measured due to the technical limitations of the measurement techniques adopted by investigators. Consequently, the problem that current technology was either too invasive or was not sensitive enough to remotely track all types of movements made by players was identified and translated into a clear problem definition.<br><br>The requirements for solving this problem were detailed in Chapters 2 and 3. Chapter 2 focused on identifying the requirements for interpreting the on-field performance of soccer players. More specifically, this section identified what information was needed to effectively analyse and interpret the physical performance of soccer players. This information was used to describe the required measures and how these different variables can be used to evaluate if a player's performance was successful. Chapter 3 examined the requirements for comprehensively measuring the movements of a soccer player during a match. The critical measurements that must be made by a new tracking system were identified. The design requirements were prioritised and a hardware technology solution was selected from a range of possible options.<br><br>From the analysis in Chapter 3, it was identified that no technology solution was readily available to coaches and sport scientists that met the design requirements and could also measure the entire range of complex and sport specific movements made by players in any playing environment. Chapter 4, therefore, focused on determining the reliability and validity of magnetic and inertial motion tracking technology; its ability to detect ballistic and subtle sports specific actions; and its ability to be modified to meet the design requirements for elite sport so that it can operate in a professional soccer match environment. For initial proof of concept, a somewhat invasive magnetic and inertial motion tracking system, Shadowbox™ (Shadowbox, Park City, USA), previously designed for tracking skis and snowboards, was used in a series of validity studies. When attached to the ankle, the Shadowbox™ tracking system was proven to have high validity against a criterion method, the Vicon MX™ motion tracking system (Vicon Motion systems Ltd, Oxford, UK), during a series of soccer specific actions (R2=0.93 for kicking a ball, R2=0.92 for one-touch pass of a ball, R2=0.95 for slide tackle) and also against the Optojump™ gait analysis system (Microgate, Bolzano, Italy) during walking (R2=0.99) and running (R2=0.99) experiments. Validating the technology using these movements was important, since the majority of movements made by soccer players are either soccer specific actions or movement (gait) around the field (Bangsbo, 1995). In addition, the problem of examining the data collected by magnetic and inertial motion tracking technology to distinguish different movements was also addressed. Two similar movements, jumping and heading the ball, were selected to determine if there were infact differences between the ankle biomechanics of the two actions. The magnetic and inertial motion tracking technology was able to detect the biomechanical differences between the two actions when the sensor was attached to the ankle. Despite the actions being performed in random order over two trials, the trajectory, displacement and speed of the ankle was reproducible and differentiated the actions. Curve fitting equations for the average 3D trajectory of the ankle during jumping and heading were developed. These can be used to detect jumps or headers from random movement data during a match. This experiment validated the magnetic and inertial navigation motion analysis system's ability to detect and discriminate between different soccer specific actions from movement data.<br><br>Since this motion tracking technology solution was proven to be a valid and reliable solution for motion tracking of soccer players, a new miniature and inertial navigation (MAIN) motion tracking system was developed to meet more of the design requirements, compared to the larger, unusable commercially available sensors and those previously used by other investigators to measure sports biomechanics (Brodie et al., 2008). The MAIN motion tracking system was 80% smaller and had 86% less mass compared to the Shadowbox™ system. It was miniaturised to a point where is was significantly less invasive than any other system and was small enough to potentially be built into a shoe or shin pad in future applications. In addition to size, other high priority design requirements were also met, including high sensor precision, operates independently from a computer, extended battery life, structurally robust to handle impact and an on-board memory capacity to last an entire match. Results from the experiments on the MAIN motion tracking system showed it to have high precision with an average typical error of measurement (TEM) of 0.88% error between steps during a walking trial. These results proved that modifying the magnetic and inertial sensors to meet the identified design requirements for operation in the professional soccer match environment did not significantly impact the precision of the technology. In summary, this thesis systematically identified and solved a series of challenging problems. This thesis was the first of its kind to prove that the magnetic and inertial navigation motion tracking technology: (1) can perform valid measures of soccer specific movements, including one-touch pass of a ball, slide tackle, kicking (drive) a ball, jumping and heading a ball, (2) can perform valid measures of gait, including walking and running, (3) can discriminate kinematic differences between short-term, ballistic soccer specific actions including jumping and heading a ball, (4) can be modified to meet the unique design requirements for operation in the elite soccer match environment without compromising the sensor precision and (5) is the first viable solution of its kind suitable for measuring the physical performance of soccer players. <br><br>