Characterization of Rugby Headgear Padding Thickness and its Influence on Head Kinematics

Introduction: Rugby, a global sport with approximately 10 million athletes worldwide, faces challenges regarding concussion prevention, as concussions constitute 10-25% of all rugby-related injuries. Unlike other contact sports, where head protection is mandatory, rugby relies primarily on tackling rules to reduce concussion risk. Despite tackling rules implemented in rugby, 30% of head injuries are caused by illegal tackles. Head injuries in rugby often occur when a player strikes their head against another player or the player’s head impacts the ground. World Rugby, one of the governing bodies of rugby, developed standards for rugby headgear and mandated that their padding thickness, including any fabric on each side of the headgear shell, must not exceed 12 mm when uncompressed. This study investigated the relative impact performance of rugby headgear compared to bare-head response under various impact conditions. Additionally, this study aimed to relate headgear model performance to padding thickness at each impact condition.

Materials and

Methods: A pendulum impactor was used to simulate head impacts that rugby athletes would experience each season. The pendulum arm was 190.5 cm long and had a total mass of 37 kg with a moment of inertia of 72 kg∙m2. The impactor face consisted of CELL-FLEX® vinyl nitrile 740 foam and was 12.7 cm in diameter and 1.27 cm thick. The pendulum impacted a 50th percentile male NOCSAE headform modified with a custom adaptor plate to fit a Hybrid III 50th percentile neck. The NOCSAE headform was instrumented with three linear accelerometers and a triaxial angular rate sensor (ARS) placed at the headform center of gravity. Data was sampled at 20 KHz and was filtered using SAE J211 4-pole Butterworth low pass filter with a cutoff frequency of 1650 Hz for accelerometer data and 300 Hz for ARS data. Impact tests were conducted on two samples of 15 different headgear models and bare headform. Test conditions comprised four impact locations (front, frontboss, rear, and rearboss), three pendulum impact speeds (3.0, 3.6, and 4.0 m/s), and two trials per impact condition. The thickness of headgear padding was measured at each impact location using calipers on both headgear samples. A linear mixed model with headgear as a random effect to quantify the effects of location, speed, and padding thickness on PLA, PRA, and PRV, and least square mean differences were used for contrasts.

Results, Conclusions, and Discussions: The linear mixed effects model determined that pendulum impact speed (p < .001), impact location (p < .001), and padding thickness (p < .001) had strong effects on PLA and PRA. Across all headgears, for every mm of padding thickness added, PLA was reduced by 2.2 g, and PRA was reduced by 78 rad/s^2. Impact location and impact speed (p < .001) had a strong effect on PRV (p < .001); however, thickness (p = .640) did not. Overall, we found that headgear with more padding thickness resulted in greater reductions of PLA and PRA. However, the rugby headgear tested did not have sufficient padding to mitigate PRV experienced during impacts. The top 4 performing headgear (Adidas Force, Gamebreaker Scrum, Gamebreaker Pro, and Shock Doctor Showtime) saw similar reductions in PLA and PRA at low energy impacts as other headgears; however, they saw larger reductions at 3.6 and 4.0 m/s impacts as seen in Figure 1. The top-performing helmets' padding thickness ranged from 16.8-22.3 mm, about double all other headgear models tested, ranging from 6.5-12.0 mm, as seen in Figure 2 . While the top-performing headgears exceed the 12 mm standard by World Rugby, World Rugby does not state why headgear thickness cannot exceed 12 mm. Some rugby enthusiasts state that players wearing headgear could perform illegal tackles that will result in higher head injury rates. The study is limited because we did not measure padding stiffness or area at each impact location. The study suggests that future headgear design and regulations should consider the effect of having thicker headgear with appropriate stiffness to allow for higher attenuation of head kinematics at higher high-energy head impacts.

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