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

Dos'Santos, T


T Dos'Santos



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 “performance
injury 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 “performance
injury 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”.

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 “performance
injury 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.


Dos'Santos, T. Biomechanical determinants of injury risk and performance during change of direction : implications for screening and intervention. (Thesis). University of Salford

Thesis Type Thesis
Deposit Date Apr 8, 2020
Publicly Available Date Apr 8, 2020
Award Date Jan 1, 2020


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