Biomechanical determinants of injury risk and performance during change of direction : implications for screening and intervention

Changing direction is a key action linked to successful performance in multidirectional sports, but also an action associated with non-contact anterior cruciate ligament (ACL) injuries. Despite the importance of directional changes for sports performance and its association with ACL injury risk, biomechanical studies generally investigate performance and injury risk determinants independently. Preliminary evidence indicates that the mechanics and techniques associated with faster change of direction (COD) performance are at odds with safer (i.e., reduced knee joint loads) COD, known as the “performanceinjury conflict”. Therefore, understanding the mechanics and techniques, screening tools, and training interventions that can reduce the relative risk of injury during COD actions, while improving performance, are of great interest to practitioners working with multidirectional athletes. The primary aims of the thesis are three-fold: 1) to identify the biomechanical determinants of performance and injury risk during cutting, in order to better understand the potential “performanceinjury conflict”; 2) to validate a qualitative screening tool against three-dimensional (3D) motion analysis for evaluating cutting movement quality and identifying athletes who display high peak knee abduction moments (KAM); and 3) to understand the biomechanical effects of a COD technique modification intervention, with the aim of reducing knee joint loads while maintaining or enhancing cutting performance. Initially, Study 1 (Chapter 4) aimed to examine the effect of trial size on the within- and between-session reliability measures and outcome values for cutting biomechanics. Cutting joint angle, ground reaction force (GRF), and knee flexion moment (KFM) variables demonstrated high reliability, while knee internal rotation moments (KIRMs), KAMs and angles demonstrated high variability and bias between sessions. Increasing trial size had a negligible effect on reliability measures and outcome values; thus, trial sizes of three to five appear adequate to capture reliable cutting biomechanical data, with no apparent requirement for greater trial sizes. Study 2 (Chapter 5) aimed to investigate the biomechanical determinants of cutting performance and injury risk (knee joint loads). The primary findings were that techniques and mechanics associated with faster cutting performance (i.e., faster velocities over the COD, greater final foot contact [FFC] braking forces over shorter ground contact times (GCT), greater FFC KFMs, smaller hip and knee flexion angles and range of motion (ROM), wider lateral foot plant distances, and greater internally rotated foot postures) are in direct conflict with safer cutting mechanics (i.e., reduced knee joint loading), and support the concept of a “performance-injury conflict”. xiv Study 3 (Chapter 6) aimed to validate a qualitative screening tool for identifying “high-risk” cutting mechanics and peak KAMs, against 3D motion analysis. The screening tool, titled the “Cutting Movement Assessment Score” (CMAS), was a 9-item tool, based on a literature review and findings from Study 2 containing the “high-risk” postures and mechanics. A strong relationship was observed between CMAS and peak KAMs, and trials and participants who displayed greater CMASs typically displayed “higher-risk” postures and greater multiplanar knee joint loads. Finally, studies 4 and 5 (Chapters 7 & 8) aimed to examine the effects of a COD technique modification intervention on cutting performance and injury risk biomechanics. Study 4 served as a feasibility study which was performed in an applied setting. The primary findings were that 6-weeks COD technique modification training with externally directed verbal coaching cues improved cutting performance and movement quality (i.e., reduced CMASs) in male youth soccer players. Study 5 expanded on the feasibility study by comprehensively monitoring the biomechanical changes (3D motion and GRF analysis) in response to COD technique modification. The primary findings were that 6-weeks COD technique modification training with externally directed verbal coaching cues resulted in significant and meaningful improvements in cutting performance. When examining group means, no statistically significant or meaningful changes in multiplanar knee joint loads were observed; however, there was considerable individual variation in response to the training intervention, with athletes considered “higher-risk” responding positively to the intervention. Overall, these studies in combination help to provide further insight into the “performanceinjury conflict” that is present during cutting, and overall assist in the development of more effective COD speed and ACL injury mitigation training programmes. The findings from the thesis provide practitioners with: 1) a greater insight into the coaching of faster and safer COD; 2) a field-based qualitative screening tool for evaluating cutting movement quality; and 3) training interventions that can be easily implemented in the field with minimal equipment to improve COD performance and potentially reduce knee joint loading.

Level dc:type.qualificationlevel

Doctoral (Level 8)

Year dc:date.issued

2020

Author dc:creator

• Dos'Santos, T

Language dc:language

en

Identifier

oai:salford-repository.worktribe.com:1361339

OAI identifier oai:identifier

oai:salford-repository.worktribe.com:1361339