Asymmetries within elite youth soccer players: an investigation into the impact of soccer-specific loading

This PhD thesis aimed to investigate how the training environment in youth soccer can influence the development of interlimb asymmetries and propose a holistic approach to reduce these asymmetries. The literature review provides a comprehensive review of the physical and technical demands of youth soccer and how they contribute to asymmetrical loading and adaptation between limbs. The high frequency of unilateral actions places uneven stress on each limb, potentially leading to performance deficits or increased injury risk if players are not adequately prepared to handle the load on their weaker side. Although current methods for reducing asymmetries have shown effectiveness, their implementation may be challenging owing to financial and time constraints. Moreover, these methods may only provide short-term solutions, as consistent loading discrepancies within soccer make asymmetries likely to reoccur. Therefore, it may be more appropriate to focus on reducing inter-limb loading discrepancies within the training environment for young soccer players. To assess the current perceptions and practical interventions regarding asymmetry in soccer from technical and physical standpoints, Study 1 explores the viewpoints of coaches, practitioners, and players. Survey responses revealed that although there is agreement on the importance of limb symmetry from a technical standpoint, coaches do not adequately emphasise training the non-dominant limb. Players often rely on their dominant limb for actions such as shooting and passing, indicating that current coaching methods are insufficient for promoting skill symmetry. On the other hand, practitioners reported a significant emphasis on reducing physical asymmetries during gym sessions by consistently prescribing unilateral exercises. However, the high prevalence of physical asymmetries among youth soccer players suggests that these gym programs alone are insufficient to achieve limb symmetry. The persistence of imbalances highlights the need for a more balanced distribution of load between limbs throughout the training week, as the current integrated training methods from coaches and practitioners are inadequate to resolve asymmetry in youth soccer players. Study 2 involves match analysis to quantify high-intensity unilateral actions, such as change of directions (CODs) and single-leg decelerations (SLDs), as well as the total sum of CODs and SLDs (TOT), performed by elite academy players during soccer matches. On average, 292 ± 34.1 unilateral actions were performed per match. When considering the direction of asymmetry (dominant vs. non-dominant limb), the frequency of CODs was significantly greater for the dominant limb than for the non-dominant limb. Furthermore, the analysis revealed large differences in the frequency of utilisation between limbs when direction was not considered. This indicates that although the difference in actions performed between the dominant and non-dominant limbs is only identified for COD frequency, players display significant asymmetries in the actions performed throughout a soccer match at the individual level. Study 3 focuses on the reliability of common tests used to assess physical asymmetries in elite male youth soccer players (U12-U16) across different maturation groups. Tests such as the isometric mid-thigh pull (IMTP), countermovement jump (CMJ), single-leg countermovement jump (SLCMJ), and single-leg drop jump (SLDJ) were analysed. The results showed good reliability for the propulsive and braking phase metrics in jumping tests (CMJ and SLCMJ), whereas the metrics in the landing and transition phases were less reliable, particularly in the pre-peak height velocity (PHV) group. PHV is defined as the maximal rate of growth during the adolescent growth spurt (Read et al., 2016). The reactive strength index of the SLDJ also exhibited poor reliability. The IMTP peak force was reliable; however, time-specific forces were less reliable across groups, with reliability varying among maturation groups. In Study 4, a body weight warm-up program aimed at reducing asymmetry in elite youth soccer players is examined. Participants were assigned to a control group, bilateral warm-up group, or unilateral warm-up group. The warm-up was performed twice a week for six weeks, and players were tested before and after the intervention using the SLCMJ, bilateral CMJ, and IMTP. The results showed no significant reduction in asymmetry for any group or test, suggesting that alternative training methods may be needed to address asymmetry in youth soccer players. In summary, despite the recognised importance of symmetry, youth soccer players develop substantial asymmetry between limbs because of consistent asymmetric loading. Match analysis confirmed a high number of unilateral actions performed during games, with significant differences between limbs at the individual level. The warm-up protocol proposed in this study failed to reduce the asymmetry values for the reliable metrics identified in Study 3. This indicates that a longitudinal approach with a more even distribution of loading between limbs may be necessary as limb asymmetries are established over consistent loading over a longer period. Additionally, external resistance loads may be required, along with an even distribution of loading, to assist in reducing limb asymmetry in youth soccer players.

Citation

Grant, L. (2023) Asymmetries within elite youth soccer players: an investigation into the impact of soccer-specific loading. University of Wolverhampton.

Publisher

University of Wolverhampton

URI

http://hdl.handle.net/2436/625504

Type

Thesis or dissertation

Language

en

Description

A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy.

Rights

Attribution-NonCommercial-NoDerivatives 4.0 International

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Theses and Dissertations