An Initial Assessment of Head Acceleration Events in Rugby League using Instrumented Mouthguards and Qualitative Video Analysis

There is a growing concern that the long-term effects potentially associated with contact sport are not only caused by concussions, but by the accumulation of subconcussive impacts. It is therefore important to understand the head acceleration event (HAE) exposure sustained by contact sports individuals. In this thesis, a combination of qualitative video analysis and biomechanical instrumented mouthguard data is used to quantify and characterise HAE sustained by professional male rugby league players during competitive matches. Peak linear acceleration (PLA), peak angular acceleration (PAA) and peak change in angular velocity (ΔPAV) were collected using custom-fit instrumented mouthguards with an 8 g or 800 rad/s2 resultant data acquisition threshold. A total of 725 HAE were collected from 31 player matches throughout 10 male players. Multiple HAE often occurred in the same tackle phase and 47.6% of HAE occurred after the initial contact between a tackler and the ball-carrier. Indirect HAE accounted for around half of HAE from carries (50.4%) and a quarter of HAE from tackles (23.8%), they also led to significantly greater ΔPAV than direct HAE (p < 0.001, ES = 0.69, interpretation = moderate). Each kinematic was also skewed to lower values, therefore applying a data acquisition threshold of 10 g led to an exposure rate of around half (13.8 ± 6.9 HAE per player, per match) than the exposure rate reported using an 8 g or 800 rad/s2 threshold (28.0 ± 10.6 HAE per player, per match). The results and methodology from this study demonstrate the efficacy of a combination of biomechanical data with qualitative video analysis in quantifying and characterising HAE exposure in rugby league and will form the basis for a future league wide instrumented mouthguard study. Abbreviations Abbreviation Phrase ATD Anthropometric Test Dummy BAM Brain Angle Metric BIC Brain Injury Criteria BRIC Kinematic Brain Injury Criterion BrIC Brain Injury Criterion CG Centre of Gravity CIR Concussion Interchange Rule CISG Concussion in Sports Group CP Combined Probability CSDM Cumulative Strain Damage Measure cSP Cortical Silent Period CTE Chronic Traumatic Encephalopathy DTI Diffuse Tensor Imaging ES Effect Size ESL European Super League FE Finite Element fMRI Functional Magnetic Resonance Imaging GRTP Graduated Return to Play GSI Gadd's Severity Index HAE Head Acceleration Event HIA Head Injury Assessment HIC Head Injury Criterion HIP Head Impact Power ImPACT Immediate Post Concussion Assessment and Cognitive Testing KLC Kleiven's Linear Combination LICI Long Interval Intracortical Inhibition LOC Loss of Consciousness MPS Maximum Principle Strain MRS Magnetic Resonance Spectroscopy NFL National Football League NRL National Rugby League of Australia PAA Peak Angular Acceleration PAV Peak Angular Velocity PCS Principle Component Score PLA Peak Linear Acceleration PRHIC Power Rotation Head Injury Criterion PTC Post Tackle Contact RIC Rotational Injury Criterion ROI Region of Interest SCAT-5 Sports Concussion Assessment Tool 5 ΔPAV Peak Change in Angular Velocity