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Mark B.A. De Ste Croix, Neil Armstrong, and Joanne R. Welsman

The purpose of this study was to examine the reliability of repeated isokinetic knee extension and flexion in young children and to examine sex differences in 30 untrained subjects (16 boys and 14 girls) aged 12.2 ± 0.3 years. Total work and the percentage decline in average torque and work were recorded during 50 repetitions. Intra-class correlation coefficients indicated a strong positive correlation between test 1 and 2 for all parameters ranging from 0.36–0.95. Coefficient of variation data ranged from ± 0% to ± 5.4%. Repeatability coefficients and limits of agreement indicated that the extensors were more reliable than the flexors for both torque and work. There were no significant sex differences in any of the parameters measured. This study suggests that repeated isokinetic muscle actions of the knee, as a function of muscle endurance, can be reliably assessed in young people.

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Amândio M.C. Santos, Joanne R. Welsman, Mark B.A. De Ste Croix, and Neil Armstrong

Age- and sex-related differences in optimal peak power (PPopt) and associated measures determined using a force-velocity (F-V) cycling test were examined in pre teenage, teenage and adult males and females. Absolute PPopt increased significantly with age in both males and females. With body mass controlled for using allometric scaling significant age related increases remained, an effect masked in the females when PPopt was expressed as W • kg−1. Sex differences in PPopt were minimal in the preteens but males demonstrated higher PPopt than females in both teenage and adult groups. These patterns of change with age and sex broadly reflect those obtained for Wingate Anaerobic Test determined PP but the use of a single non-optimized braking force underestimates the magnitude of any differences observed.

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Jamie Salter, Mark B.A. De Ste Croix, Jonathan D. Hughes, Matthew Weston, and Christopher Towlson

Purpose: Overuse injury risk increases during periods of accelerated growth, which can subsequently impact development in academy soccer, suggesting a need to quantify training exposure. Nonprescriptive development scheme legislation could lead to inconsistent approaches to monitoring maturity and training load. Therefore, this study aimed to communicate current practices of UK soccer academies toward biological maturity and training load. Methods: Forty-nine respondents completed an online survey representing support staff from male Premier League academies (n = 38) and female Regional Talent Clubs (n = 11). The survey included 16 questions covering maturity and training-load monitoring. Questions were multiple-choice or unipolar scaled (agreement 0–100) with a magnitude-based decision approach used for interpretation. Results: Injury prevention was deemed highest importance for maturity (83.0 [5.3], mean [SD]) and training-load monitoring (80.0 [2.8]). There were large differences in methods adopted for maturity estimation and moderate differences for training-load monitoring between academies. Predictions of maturity were deemed comparatively low in importance for bio-banded (biological classification) training (61.0 [3.3]) and low for bio-banded competition (56.0 [1.8]) across academies. Few respondents reported maturity (42%) and training load (16%) to parent/guardians, and only 9% of medical staff were routinely provided this data. Conclusions: Although consistencies between academies exist, disparities in monitoring approaches are likely reflective of environment-specific resource and logistical constraints. Designating consistent and qualified responsibility to staff will help promote fidelity, feedback, and transparency to advise stakeholders of maturity–load relationships. Practitioners should consider biological categorization to manage load prescription to promote maturity-appropriate dose–responses and to help reduce the risk of noncontact injury.

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Amândio M.C. Santos, Neil Armstrong, Mark B. A. De Ste Croix, Peter Sharpe, and Joanne R. Welsman

These studies used multilevel modelling to examine optimised peak power (PPopt) from a force velocity test over the age range 12–14 years. In the first study, body mass, stature, triceps and subscapular skinfold thicknesses of boys and girls, aged 12.3 ± 0.3 y at the onset of the study, were measured on four occasions at 6 monthly intervals. The analysis was founded on 146 PPopt determinations (79 from boys and 67 from girls). Body mass and stature were significant explanatory variables with sum of two skinfolds exerting an additional effect. No gender differences were evident but PPopt increased with age. In the second study, thigh muscle volume (TMV) was estimated using magnetic resonance imaging at test occasions two and four. The analysis, founded on a subsample of 67 PPopt determinations (39 from boys and 28 from girls), demonstrated TMV to be a significant additional explanatory variable alongside body mass and stature with neither age nor gender making a significant contribution to PPopt. Together the studies demonstrate the influence of body size and TMV on young people’s PPopt.

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Paul J. Read, Jon L. Oliver, Gregory D. Myer, Mark B.A. De Ste Croix, and Rhodri S. Lloyd

Purpose: Asymmetry is a risk factor for male youth soccer players. There is a paucity of data confirming the presence of asymmetry using practically viable screening tasks in players at different stages of maturation. Methods: A cross-sectional sample (N = 347) of elite male youth soccer players who were either pre-, circa-, or post-peak height velocity (PHV) completed the following assessments: single-leg Y-Balance anterior reach, single-leg hop for distance, single-leg 75% hop and stick, and single-leg countermovement jumps. Results: Single-leg countermovement jumps landing force asymmetry was higher in both circa- and post-PHV groups (P < .001; d = 0.41–0.43). Single-leg 75% hop and stick landing force asymmetries were also highest in circa-PHV players, but between-group comparisons were not statistically significant and effect sizes were small. Single-leg hop for distance and single-leg Y-Balance anterior reach asymmetries reduced with maturation; however, no group differences were significant, with small to trivial effect sizes (d ≤ 0.25). Conclusion: Stage of maturation did not have a profound effect on asymmetry. Between-limb differences in functional performance seem to be established in early childhood; thus, targeted interventions to reduce this injury risk factor should commence in pre-PHV athletes and be maintained throughout childhood and adolescence to ensure asymmetry does not increase.