The Evaluation of Instep Soccer Kick Technique and Performance Through an Analysis of Movement Variability
Creators: name: Bennett, Timothy
Publisher: name: Leeds Beckett University
Year: 2022
Subjects: Uncategorized

description: Instep kick research has shown that skilled soccer players display natural variations in their technique from trial-to-trial (Egan et al., 2007; Lees &amp; Barton, 2005; Lees &amp; Rahnama, 2013). This inherent movement variability (MV) has been described as a demonstration of ‘motor equivalence’, which has been defined as the ability to achieve an invariant end using variable means (Abbs &amp; Cole, 1987). This movement strategy would benefit a soccer player by facilitating a consistent (stable) performance outcome whilst utilising a flexible range of solutions to adapt to different constraints. ‘Motor equivalence’ is closely associated with the concept of synergies, which can be identified and quantified using a motor control tool called the ‘uncontrolled manifold’ (UCM). The theoretical appeal of the UCM as an analysis tool has also been identified, but not implemented in recent sports biomechanics studies (Carson et al., 2014a; Carson et al., 2014b). Therefore, the UCM method was used as vehicle for evaluating MV structure and ‘motor equivalence’ within a sport-specific task, and to determine whether the UCM method could provide a better understanding of instep soccer kick technique and performance in comparison to a traditional biomechanics approach. Twelve male university soccer players (age 20.8 ± 2.7 years, height 1.80 ± 0.03 m and mass 79.6 ± 6.2 kg) who were right foot dominant participated in this project and were instructed to perform a maximal instep kick at a 1m2 target at a distance of 11m. Three-dimensional kinematic data was recorded from a motion analysis system using a 15-segment whole-body model to compute kinematic variables for the traditional biomechanical analysis. For the UCM analysis, trial-to-trial variations of seven joint angles of the kicking leg, and principal components of the whole-body, were analysed across the normalised whole movement trajectory to investigate the MV structure of eight hypothesised performance variables. The dependent measures were UCM variability measures and strength of synergy. The main findings from the research project were: Selected technique, performance and task variables produced values consistent with instep kicking literature. There was no clear differences between hit and missed kicks across all biomechanical variables. The UCM analysis across all participants revealed that eight hypothesised performance variables produced synergies, across all time periods of the instep kick. This finding provided empirical evidence to support the demonstration of ‘motor equivalence’ in instep soccer kicking technique. Clear differences were noted between hit and missed kicks base on the UCM analysis. Missed kicks were characterised as producing lower strength of synergies, higher ranges of solutions, higher total variability and less stability across all performance variables for all time periods of the instep kick. A case study analysis showed clear differences between hit and missed kicks and highlighted unique differences in comparison to the group UCM analysis. A comparison between UCM variables and instep kick task variables did not reveal any clear relationship between these different outcomes, which were attributed to the kicking task constraints used for this project. This current project provided an original contribution to contemporary understanding of a complex technique through an evaluation of instep soccer kicking and MV structure.