In light of previous research highlighting the prevalence of asymmetries in soccer players and possible links to injury risks, there is a crucial gap in the biomechanical understanding of complex relationships between lower extremity and trunk asymmetries in elite soccer players. The purpose of this study was to investigate the level, relationships, and differences among twelve different parameters of strength, morphological, and neuromuscular asymmetries in elite soccer players. Methods: Elite male soccer players (n = 25, age 21.7 ± 3.9 years) were tested in the following tests: bilateral fluid distribution, hip flexor range of motion, postural stability, isokinetic strength of knee extensors and flexors, isometric lateral trunk rotation strength, eccentric strength of knee flexors, isometric bilateral strength of hip adductors, and vertical ground reaction force in counter-movement jump-free arms, counter-movement jump, squat jump, and drop jump tests. One-way ANOVA, Pearson's coefficient (r), and partial eta squared (η p 2) were used for data analysis. Results: Significant differences in asymmetries were found in elite soccer players (F11,299 = 11.01, p < .01). The magnitude of asymmetry over 10% was in postural stability and drop jump parameters. The lowest magnitudes of asymmetries were in the fluid distribution of the lower limbs and the vertical ground reaction force during the take-off phase in squat jumps. The highest asymmetries between the dominant and non-dominant sides were found in postural stability and drop jump. A total of eleven significant correlations (p < 0.05, r = 0.41-0.63, R2 = 0.17-0.40) were detected between the analyzed asymmetries in elite soccer players. The lateral trunk rotation asymmetries were significantly correlated to vertical ground reaction force asymmetries and knee extensors. Conclusion: Long-term exposure in elite soccer leads to unilateral biomechanical loading that induces abnormal strength and morphological adaptations in favor of the dominant side while linking lower limb and trunk strength asymmetries. By unraveling these complex relationships, we strive to contribute novel methods that could inform targeted training regimens and injury prevention strategies in the elite soccer community. The data should encourage future researchers and coaches to monitor and develop trunk strength linked to lower body kinematics.

• Keywords
• football, injury prevention, isokinetic, isometric, performance, power, strength,
• Publication type
• Journal Article MeSH

BACKGROUND: Foot morphology is associated with altered loading of the ankle-foot complex in adolescent footballers, predisposing to pain and injury. However, usual singular plane clinical assessments do not accurately capture the 3D nature of foot morphology. A new approach is 3D laser scanning, with statistical shape model techniques creating individual-to-group comparison. However, no research exists on the adolescent, football-playing foot. Furthermore, a link between 3D foot morphology, and usual clinical and performance measures would be beneficial for practical implementation. METHODS: Four hundred forty-seven 3D foot scans from 224 elite male footballers (U12-U19) in bilateral stance were collected and further processed with statistical shape model techniques. Weighted shape parameters for individual principal components (Modes) were extracted for each foot. Centre of pressure displacement expressed as total travelled way in millimetres was calculated for bilateral and unilateral postural stability measures. Clinical assessments (Clarke's Angle, Resting Calcaneal Stance Position) were calculated on the 3D foot scans. Differences in weighted shape parameters, postural stability measures, and clinical assessments between age groups were determined by ANOVA. Correlations determined the relationship of Modes and clinical assessments to postural stability measures. Linear regression established if clinical assessments predicted the mode describing foot arch variation. RESULTS: Age groups significantly differed for Mode 1 (foot length), Mode 2 (foot arch), and Mode 5 (tibial rotation relative to the foot) (p < 0.05). Resting Calcaneal Stance Position (r = .663) and Clarke's Angle (r = -.445) were low-to-moderately correlated to Mode 2 (both p < 0.001), and linear regression found they were both significant predictors of Mode 2, though only moderately (R2 = .522). There were low correlations of foot morphology to the postural stability tests. CONCLUSION: This is the first study to describe the 3D foot morphology of male football-playing adolescents, and discover the differences between age groups. This will improve understanding and assessment of foot morphology in male adolescents because 2D techniques, as discovered in this study, do not strongly correlate to, nor predict, the 3D foot arch. Foot morphology was only lowly correlated to postural stability, thus a multifaceted program would be required for improvements.

• Keywords
• Adolescents, Foot morphology, Football, Postural stability, Principal component analysis, Three-dimensional shape,
• MeSH
• Lower Extremity * MeSH
• Ankle Joint MeSH
• Humans MeSH
• Linear Models MeSH
• Adolescent MeSH
• Calcaneus * MeSH
• Tibia MeSH
• Check Tag
• Humans MeSH
• Adolescent MeSH
• Male MeSH
• Publication type
• Journal Article MeSH