Development and validation of a novel movement screen to predict lower extremity injury in male youth soccer players

 Lower extremity non-contact injuries are common in male youth soccer players. Altered neuromuscular control defined as muscle strength, power or activation patterns that lead to increased joint loads has been suggested as a mechanism that underpins the occurrence of these injuries during rapid deceleration tasks. However, data pertaining to neuromuscular risk factors and screening in male youth soccer players is sparse. The purpose of this thesis was to investigate the validity of a novel movement screen to predict injury risk in elite male youth soccer players. Study 1 examined the test re-test reliability of a range of field-based neuromuscular control tests reporting acceptable values for measures of single leg dynamic balance, landing force, maximal hop distance and tuck jump knee kinematics; however, other commonly used assessments were more variable. The effects of chronological age on the measures deemed reliable in study 1 were then analysed in study 2. A number of between group differences were evident but this pattern was variable across the different constructs of neuromuscular control, thus an age-specific training emphasis may be required at different stages of a young player‟s development. Also, the normative data included for a range of chronological age groups in this study may be useful for practitioners, from which fluctuations in performances can be identified. The results of study 3 showed acceptable within subject variation on the majority of the tests measured at three time points across a soccer season. However, percentage change scores in neuromuscular control were more variable and differences between test sessions were often considerably lower than the random variation, thus observed changes may not be meaningful. However, single leg countermovement jump forces increased considerably throughout the season indicating that a „real‟ change occurred and this may be associated with greater injury risk. Seasonal variation in injury occurrence was also identified in study 4, but a major finding was a three-fold 4 increase in player incidence rate since the introduction of an early soccer specialisation model in the United Kingdom. This indicates that elite male youth players are now at a greater risk of injury. The final study examined the ability of a novel movement screen to predict noncontact lower extremity injury risk in male youth soccer players. A combination of anthropometric and neuromuscular risk factors were shown as predictors, but there was variability across the different chronological age groups. Single leg countermovement jump landing force asymmetry was the most frequently reported risk factor and univariate analysis also identified a number of significant predictors in respective chronological age groups. The results of this study provide an evidenced-based diagnostic assessment tool from which “at risk” players could be identified; the injury prevention asymmetry soccer screen (i-PASS). However, greater weightings of specific assessments may be required at different stages of a child‟s development due to variability across age groups. This thesis has made an original and significant contribution to the existing paediatric injury risk screening literature for soccer players. Furthermore, these findings can easily be applied by practitioners to more accurately screen their players and develop targeted prevention strategies to reduce injury risk.