Hébert-Losier, KimRichards, JimClissold, TraceyWard, SarahButcher, Anna J.2025-10-052025-10-052025https://hdl.handle.net/10289/17688Background: Anterior cruciate ligament (ACL) injuries account for 45% of internal knee injuries and are burdensome to society due to prolonged recovery times, substantial costs of care, functional movement impairments, and an increased risk of early-onset posttraumatic osteoarthritis. Non-contact ACL injury occurrence rates are increasing in young athletes; however, post-pubertal females are more susceptible to non-contact ACL injuries than their male counterparts or pre-pubertal individuals. Considerable growth and development occur during pubertal maturation, including to the musculoskeletal and neuromuscular systems, which contribute to changes in movement patterns during dynamic manoeuvres. These changes in movement patterns may be linked to non-contact ACL injuries, however, there remain gaps in our understanding of the potential changes in biomechanics associated with ACL injury risk across maturational phases and between sexes. It is possible that the greater non-contact ACL injury risk in post-pubertal females is linked with their biomechanical movement patterns during dynamic tasks. Using injury risk screening tasks that reflect sport and ACL injury risk manoeuvres could assist in informing preventative strategies. Aim: The main aim of this PhD thesis was to investigate the effect of sex and maturation on biomechanics associated with risk of ACL injury in a series of dynamic tasks suitable for clinical use. Methods: This thesis comprises two parts: first, a systematic literature review and pilot study; and second, the main experimental study. The systematic review identified studies examining ACL-related biomechanics during defined maturational phases in dynamic tasks. The pilot study tested 26 court and field sport athletes using 2D video analysis completing a maximal and normalised land-cut task and informed the methods for the main experimental study. For the main experimental study, test-retest reliability and cross-sectional experiments were conducted that involved four different single-leg drop-landing tasks: single-leg drop-land, single-leg drop-land and cut, single-leg rotating drop and hop, and single-leg drop and vertical hop. The reliability portion establishes the test-retest reliability of the biomechanical measures collected using 3D motion capture and force plates from 15 young individuals, whereas the cross-sectional portion compared the biomechanical and performance metrics of the four investigated single-leg tasks between males and females across three specific maturation stages from 69 individuals. Results: The systematic review included 18 studies examining 400 males, 1377 females, and 315 participants of undefined sex across various maturation stages. The methodological quality of most studies (n = 16) was considered good, and satisfactory for two. The most reported variables were knee abduction angle, knee abduction moment, knee flexion angle, and vertical ground reaction force (GRF). Knee abduction angles and moments and knee flexion angles were greater in late- and post-pubertal females than males and pre-pubertal females during both landing and cutting tasks. When normalised for body mass, ground reaction forces were generally greater in males compared to females overall and for less mature participants for both sexes. Overall quality of evidence was low or medium across the four biomechanical measures and findings were inconsistent between studies. Leap distances in the pilot study of the single-leg drop-land and cut task were significantly larger under a maximal than normalised to 150% of leg length condition (p < 0.001, ηp2 ≥ 0.417), with the maximal mean being 154.5 ± 24.7 cm (175.1 ± 18.6% leg length) and the normalised mean being 140.7 ± 19.7 cm (159.0 ± 5.8% of leg length). Regarding the reliability portion of the experimental study, all tasks demonstrated adequate [intraclass correlation coefficient (ICC) values > 0.50] levels of reliability for kinematic angles and moments aside from the metrics of peak extension moment, moment ranges, anterior/posterior GRF, and medial/lateral GRF; however, large coefficient of variation values were commonly observed, likely due to the small magnitude of measures. In the cross-sectional experiment, few significant differences were found between males and females within the ages of 7 and 20 years when not accounting for maturation stage, including at the knee. Most of the observed significant differences were found between maturation stages. In general, the pre-pubertal participants demonstrated higher relative vertical GRFs, more extended knee positions, and greater variability in coronal and transverse plane knee angles and moments. Post-pubertal males also occasionally exhibited some mechanics typically associated with increased risk of ACL injury. Discussion: The significant difference in single-leg drop-land and cut landing distances found in the pilot study between normalised and maximalised conditions imply that methods matter, whereby the normalised task may be better suited for heterogenous samples, but maximal for homogenous samples or pre-post study designs. Regarding the experimental study, it is possible that the movement pattern changes observed in the males were associated with improved performance or movement competence and not directly associated with an increased ACL injury risk. Additionally, although the results suggest that pre-pubertal participants exhibit biomechanics associated with ACL injury risk, it is relatively rare that ACL injuries occur in this population. A lack of exposure to more challenging sport and ACL injury specific manoeuvres, like the tasks used in the current research, likely contribute to their biomechanics differing from the more mature groups. Few differences in biomechanics were identified to indicate a decreased ACL injury risk with maturation, particularly in females. Hence, this lack of change combined with more frequent exposure to potentially injurious situations and greater sporting demand could contribute to the increased ACL injury occurrence in the late- to post-pubertal female population reported in the literature. Conclusion: Overall, the lack of significant biomechanical differences found between sexes suggests there is no need to make screening tools or training interventions sex specific. As biomechanical factors associated with greater ACL injury risk were observed in the pre-pubertal groups, implementing screening and injury prevention in younger athletes (starting pre-puberty) could assist in development of safer landing strategies, proprioception, and neuromuscular control that significantly reduces the risk of ACL injuries as they mature.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.ACLPubertyMaturationSexInjury preventionBiomechanics3D motion captureThesis