Rugby union is well recognised as New Zealand’s unofficial national game. As such it is one of the most popular sports in New Zealand. Unfortunately, concussion, a form of traumatic brain injury (TBI), is an inherent risk of participating in contact, combat or collision sports. Children exposed to TBIs can face long-term developmental, health and quality of life difficulties extending into adulthood. Even a single TBI may disrupt the neurological mechanisms underlying ongoing development. Despite the acknowledged high incident rates of TBI, important gaps in the research remain evident, especially for junior rugby players. In the past few years, there has been increased attention on possible concussion mitigation through using protective headgear, with World Rugby introducing new testing standards for headgear as a medical device. This allows innovative headgear designs to be tested for medical benefits such as potential concussion mitigation. However, the methods used in this standard to simulate rugby head impacts lack rigorous scientific backing, and the standard does not define the measurable medical benefit it aims to assess. Using a head impact simulation method that lacks any real-world validation limits the conclusions regarding headgear effectiveness during gameplay and hinders the progress of headgear development. The lack of data surrounding head impact kinematics in rugby union, data-driven head impact simulation methods, and biomechanical analyses of the link between brain injury metrics and head impacts in rugby does not facilitate an increase in player safety.

This thesis presents several streams of novel work, covering the analysis of the impact mitigation of rugby headgear during laboratory testing, a comparison between these current testing methods and youth rugby head impacts, the relationship between head impact kinematics, gameplay scenarios, and brain strain, and finally, puts forward a set of recommendations for more accurate head impact reconstruction in the laboratory and areas of the game to look to reduce the severity of head impact exposure.

Under a laboratory drop testing regime that covered 5 impact locations over 3 impact surface angles at 4 different heights, all rugby headgear significantly lowered the peak linear and rotational accelerations. Headgear that incorporates low-density, closed-cell foams (also described as traditional headgear) and has received World Rugby approval did not reduce peak linear acceleration or HIC to the same extent as the new generation headgear that used denser open-cell foams. The results of this study show that the headgear tested can lower the peak linear acceleration by up to 50%, and the peak rotational acceleration by up to 60%. The results lacked the same clarity when looking at the peak rotational velocities and brain strain metrics. Headgear constructed with lightweight, closed-cell foam only lowered the peak rotational velocity and regional brain strain reduction in isolated cases. In contrast, the newer generation headgear, which employed higher-density, viscoelastic, open-cell foam, consistently demonstrated significant reductions in peak rotational velocity and regional brain strain. However, drop testing onto the MEP pad impact surface may not adequately reflect the impact conditions specific to rugby gameplay. This underscores the need for a well-validated impact test methodology tailored to rugby-specific head impacts.

Analysing the difference in impact kinematics between common drop test methods, we found that the impact surface stiffness greatly affected the peak linear accelerations and the duration of the linear acceleration peak. The inclusion of the neck significantly affected the rotational kinematics in both duration and kinematic profile. Peak linear accelerations showed the highest variation between drop test conditions with steel impacts creating the highest linear accelerations, and 45° MEP impacts creating the lowest. Peak rotational accelerations showed less variance than linear accelerations between drop-test conditions while peak rotational velocities did not vary between drop test conditions. Angled impacts produced the highest rotational velocities for a given linear acceleration, and steel impacts produced the lowest.

When comparing these drop-test conditions to those measured in the field, peak linear and rotational kinematics were significantly higher than the field head impacts while the durations of the acceleration peaks were significantly lower on average. Peak linear and rotational accelerations diverged vastly from those on the field as the change in linear velocity increased. Peak rotational velocities showed lower divergence with increasing linear velocity but were still significantly higher during drop tests. Drop testing with a neck onto an angled impact surface produced peak linear acceleration durations similar to head impacts to bony areas of the body and the ball. Drop testing without a neck failed to recreate the appropriate duration of the peak linear and rotational kinematics. Drop tests with the neck resulted in a much closer approximation of the durations of the on-field rotational kinematic peaks. Those onto the angled impact surface simulated most male and female head impact conditions.