A multidisciplinary investigation into "playing-up" in academy football according to age phase.

In an attempt to facilitate more appropriate levels of challenge, a common practice in academy football is to play-up talented youth players with chronologically older peers. However, the context of playing-up in academy football is yet to be empirically explored. Thus, the purpose of this study was to examine the multidimensional factors that differentiated players who play-up from those who do not. Ninety-eight participants from a single football academy were examined within their age phase: Foundation Development Phase (FDP; under-9 to under-11; n = 40) and Youth Development Phase (YDP; under-12 to under-16; n = 58). Drawing upon the FA Four Corner Model, 27 factors relating to Technical/Tactical, Physical, Psychological, and Social development were assessed. Following MANOVA analysis within both the FDP and YDP, significant differences were observed for Technical/Tactical and Social sub-components (P < 0.05). Further differences were observed for Physical and Psychological sub-components (P < 0.05) within the YDP. In sum, Technical/Tactical and Social characteristics appeared to differentiate those who play-up compared to those who do not within the FDP. In the YDP however, there were measures representing all sub-components from the FA Four Corner Model. Subsequently, it is suggested coaches and practitioners consider these holistic factors when playing-up youth football players within relevant age-phases.

The Efficacy of Lower-Limb Screening Tests in Predicting PlayerLoad Within a Professional Soccer Academy.

CONTEXT: Training exposure has been associated with injury epidemiology in elite youth soccer, where lower-limb musculoskeletal screening is commonly used to highlight injury risk. However, there has been little consideration of the relationship between lower-limb screening and the loading response to soccer activities. OBJECTIVE: To quantify the efficacy of using screening tests to predict the loading elicited in soccer-specific activities and to develop a hierarchical ordering of musculoskeletal screening tests to identify test redundancy and inform practice. DESIGN: Correlational. SETTING: Professional soccer club academy. PARTICIPANTS: A total of 21 elite male soccer players aged 15.7 (0.9) years. INTERVENTION: Players completed a battery of 5 screening tests (knee to wall, hip internal rotation, adductor squeeze, single-leg hop, and anterior reach) and a 25-minute standardized soccer session with a Global Positioning System unit placed at C7 to collect multiplanar PlayerLoad data. MAIN OUTCOME MEASURES: Baseline data on each screening test, along with uniaxial PlayerLoad in the mediolateral, anteroposterior, and vertical planes. RESULTS: Stepwise hierarchical modeling of the screening tests revealed that dominant leg knee-to-wall distance was the most prevalent and powerful predictor of multiplanar PlayerLoad, accounting for up to 42% of variation in uniaxial loading. The adductor squeeze test was the least powerful predictor of PlayerLoad. Of note, one player who incurred a knee injury within 3 weeks of testing had shown a 20% reduction in knee-to-wall distance compared with peers, and elicited 23% greater PlayerLoad, supporting the hierarchical model. CONCLUSIONS: There was some evidence of redundancy in the screening battery, with implications for clinical choice. Hierarchical ordering and a concurrent case study highlight dominant leg knee-to-wall distance as the primary predictor of multiaxial loading in soccer. This has implications for the design and interpretation of screening data in elite youth soccer.

Association between ACTN3 R577x and the physical performance of Chinese 13 to 15-year-old elite and sub-elite football players at different positions.

The purpose of this study was to investigate the prevalence of ACTN3 polymorphisms in Chinese elite and sub-elite football players aged 13-15 years at different positions. Specifically we explored whether ACTN3 genotypes were linked with athletic performance of elite and sub-elite players at different positions. The RR genotype frequency of elite defenders (p = 0.018) and midfielders (p = 0.008) was significantly higher than that of sub-elite XX genotype in elite players. Furthermore, the R allele frequency of elite defenders (p = 0.003) and midfielders (p = 0.008) was significantly higher than that of sub-elite players. In all subjects, RR players performed faster and exhibited more explosive power than RX or XX players. RR, RX and XX elite players' 20 m/30 m sprint, 5 × 25-m repeated sprint ability (5 × 25 m RSA), and standing long jump were stronger than sub-elite players, but there was no significant different in aerobic endurance between elite and sub-elite players at different positions. In conclusion, there were significant differences in ACTN3 genotypes and alleles between elite and sub-elite players at different positions, and the RR genotype was significantly associated with power-related athletic performance in Chinese youth football players.

Marker location and knee joint constraint affect the reporting of overhead squat kinematics in elite youth football players.

Motion capture systems are used in the analysis and interpretation of athlete movement patterns for a variety of reasons, but data integrity remains critical regardless. The extent to which marker location or constraining degrees of freedom (DOF) in the biomechanical model impacts on this integrity lacks consensus. Ten elite academy footballers performed bilateral overhead squats using a marker-based motion capture system. Kinematic data were calculated using four different marker sets with 3DOF and 6DOF configurations for the three joint rotations of the right knee. Root mean squared error differences between marker sets ranged in the sagittal plane between 1.02 and 4.19 degrees to larger values in the frontal (1.30-6.39 degrees) and transverse planes (1.33 and 7.97 degrees). The cross-correlation function of the knee kinematic time series for all eight marker-sets ranged from excellent for sagittal plane motion (>0.99) but reduced for both coronal and transverse planes (<0.9). Two-way ANOVA repeated measures calculated at peak knee flexion revealed significant differences between marker sets for frontal and transverse planes (p < 0.05). Pairwise comparisons showed significant differences between some marker sets. Marker location and constraining DOF while measuring relatively large ranges of motion in this population are important considerations for data integrity.