title: Analysis and application of techniques to monitor training load in youth soccer players
Creators: name: Maughan, Patrick C.
Publisher: name: University of Glasgow
Year: 2023

description: Soccer is regarded as the world’s most popular sport, performance in which depends on a range of factors generally characterised as being technical, tactical, physical, or psychological. The lucrative nature of the sport has allowed clubs to invest in academies in the hope of developing future players. These academies are supported by a range of practitioners, alongside investment in further understanding talent identification and talent development. A key role of practitioners within clubs is monitoring the load undertaken by players, with the aim of supporting training prescription to optimise performance and reduce the risk of injury. This thesis develops around five projects, analysing commonly used objective and subjective measures of training load to establish their relationships, developing novel methods of analysing subjective load, and testing the implementation of these methods within the transition from academy to full-time professional soccer. The first data chapter aimed to describe and quantify relationships between subjective and external measures of training load in professional youth soccer players. Data from differential ratings of perceived exertion (dRPE) and seven measures of external load were collected from twenty youth professional soccer players over a 47-week season. Relationships were described via bivariate correlations and multivariate factor analysis methods. Results from these analyses suggested that there was a theoretical dispersion between measures which may be representative of volume, such as total distance covered, and measures which may be representative of intensity, such as sprint distance. Additionally, it was found that subjective measures of breathlessness and lower body muscle exertion provided limited additional insight over gestalt ratings of perceived exertion (sRPE) within the analysed population. The second data chapter investigated the influence of training theme or competition on previously described relationships. Subjective load data was collected via sRPE and seven external load measures. General characteristics of training sessions were categorised based on their proximity to match day, with match-play also included within the analyses. Similarly to the first data chapter, analysis presented two, or three, readily interpretably components. The first component was represented by measures of volume, whilst the second and third components were generally represented by measures of intensity. This supports the finding of study one, that the identification of multiple components indicate that load monitoring should comprise multiple variables. Whilst generally the findings of this study mirrored study one, there were minor differences which suggest that effective monitoring practices should account for the demands of different session types. The third data chapter assessed the relationship between subjective and external load measures whilst accounting for the impact of phase of season. Subjective load relationships were collected via RPE, whilst data were collected via microelectromechanical system (MEMS) devices to analyse seven external load variables. Data were collected across a 47-week season with phases categorised as being pre-season phase, or competitive phases. Interestingly, when performing principal component analysis and using an alternative method to determine component extraction, only one component was retained for the competitive phases, whilst two components were retained for the pre-season phase. However, if using previously utilised methods similar results would have been found as to the previous data chapters. These findings highlight the importance of clearly defined methodology within factor analysis. Additionally, these results highlight that factoring load based on measures of volume and intensity may be considered as worthwhile practice by practitioners. Given the collective results from the previous data chapters, the aim of the fourth data chapter was to investigate the structure of relationships between measures of training load and assess whether these can be modified through non-linear transformations. To control for the effects of session duration, sessions were categorised into short (≤ 60mins) or long (&gt; 60mins), based on the mean session duration for both training and match-play. All sRPE were analysed in their raw form and with the inclusion of session duration (sRPE-TL). Additionally, sRPE and sRPE-TL was modified through nonlinear transformations by raising to a series of exponentials to provide a metric termed “modified RPE” (sRPEmod). Similarly, to previous data chapters, following PCA two components were retained which provided theoretical representations of volume or intensity. Non-linear transformations had little effect on loading profiles for long sessions. For short sessions the loading became more equal between intensity and volume for sRPE-TL, and more aligned to intensity for sRPE. The study demonstrated that sRPE and sRPE-TL predominantly reflect measures of training volume, however, these measures can be modified to better reflect intensity for training sessions less than 60mins in duration. A key issue within soccer is optimising the transition of players going from academy to full-time professional soccer, therefor the aim of the fifth data chapter was to investigate the load experienced by players undergoing this transition. Additionally, the chapter aimed to determine whether subjective measures of load can provide useful insight into training volume, training intensity, or a combination of the two constructs in an applied setting. Data were collected from 4 academy players who had been identified as transitioning into full-time soccer. Data were then collected the following pre-season from the pre-determined transitioning players, and current development squad players. Subjective data were collected via sRPE and sRPEmod, whilst external load measures were collected via MEMS devices. Results showed that there were significant differences between academy and transition phases for players with regards to sRPEmod and weekly sRPE and sRPEmod. There were no significant differences identified between the academy and transition phase for daily sRPE or sRPE-TL. With regards to external measures of load, there were no significant differences between transition and development players in either sessional or weekly measures. These findings suggest that using a proposed modified subjective measure to identify differences in the load experienced by transition, academy, and development players, however the exact nature of these differences is unknown. The collective findings in this thesis highlight relationships between subjective and external measures of load within youth soccer players. The results highlight the lack of additional information provided by dRPE, questioning the use of this measure within this population. Additionally, the results highlight that it appears logical to factor load based on volume and intensity, and that these relationships appear to remain relatively consistent regardless of training theme or stage of season. This thesis also highlights complexities involved in modifying subjective measures of load to provide a greater representation of intensity to allow practitioners who may not have access to external load measures to greater account for this. Whilst the methods proposed showed the relationship between subjective and external measures could be modified, this was only for short duration sessions. Finally, when monitoring the transition of players from academy to full-time professional soccer it was shown that sRPEmod highlighted differences within players undergoing a transition, however the exact nature of this was unclear. These findings can be used to enhance the monitoring approaches of practitioners working within professional soccer. Additionally, these findings provide evidence that practitioners who are limited to subjective measures of load should consider alternative methods if monitoring training intensity is required. Further research is required to investigate modifying subjective measures of load to greater represent intensity. Additionally, further research is required to understand the load experienced by players undergoing a transition from academy to full-time professional environments.