Rugby union is a popular contact sport where high impact collisions frequently occur. High rates of concussion have been reported in the sport. Concern exists surrounding these rates, and regarding the overall brain health of those playing the game as repeated sub-concussive collisions may compromise rugby players’ neurological integrity. In response to this, wearable sensors are being increasingly used to measure the number and size of the head acceleration events experienced in sport, including rugby. Presently little objective data exist in this research space regarding adolescent rugby players. More research is justified in this population as adolescents make up the majority of those playing the game (76% in Aotearoa New Zealand). Moreover, adolescents may be at higher risk of concussion than adults, and the adolescent brain is still developing and may generally be more susceptible to injury. This thesis attempts to quantify head impact exposure of male adolescent players, and to gain an understanding of the effect of repeated head impact exposure on neurological integrity.

Forty-one participants, aged 14-16, were recruited from two male under-16 rugby teams playing in the Ellesmere Rugby Sub-union: one team in the 2022 season, one team in the 2023 season. Thirty-nine participants underwent pre- and post-season MRI scanning, including T1-weighted structural imaging and high angular resolution diffusion imaging. Participants also completed pre- and post-season neuro-cognitive and conscious motor control assessments. Participants were fitted with HitIQ Nexus A9 instrumented mouthguards to record head acceleration events experienced during the season. All training sessions and games were video recorded to verify mouthguard data. Video verification and analysis of mouthguard data took place using Catapult Focus software. Post-season processing of MRI scans focused on within-subject analysis of pre- to post-season changes in white matter as measured by diffusion tensor imaging. Linear mixed models were used to investigate correlations between neurological changes and cumulative head impact loading recorded by the mouthguards.

The results of the study quantified head acceleration events (HAEs) among male adolescent rugby players over a season. Although data were collected over two seasons, we report findings on one season per player. Head acceleration events (HAEs) were more frequent and intense in games than trainings, with playing position and acceleration type (linear vs. rotational) closely correlated. Most recorded HAEs were low in magnitude (< 15.5 g), with high magnitude events occurring 6.8% of the time. Five concussions were recorded in the study. Results from pre- and post-season MRI scans indicated a non-significant relationship between HAE exposure in one season of rugby and changes in white matter microstructure, including for those players exposed to a higher level of impact magnitude. Results from post-concussion MRI scans similarly found non-significant changes in white matter microstructure compared to baseline scans.

Conclusions that can be drawn from the results include that collision incidence variability was influenced by contact disposition, while relative magnitude variability was influenced by impact mechanism, match action, and player technique. Headgear use decreased linear acceleration in direct HAEs. Major risk factors for concussion included high speed, poor anticipation, uncontrolled falling, and head-to-ground impact. Proper technique, especially in the tackle situation, and good anticipation reduced risk of high magnitude events. Pre- to post-season changes in neuro-cognitive assessments were non-significant, including for the concussion cohort. Results from structural and diffusion-based MRI scans suggest exposure to one season of rugby for healthy adolescent male players does not directly result in neurological compromise.