B10 A Contemporary analysis of tackle height: Implications for head injury risk and tackler technique in Rugby Union

Abstract

Rugby tackles pose significant head injury risks, raising concerns for players' well-being. Despite advocating for lower tackle heights for safety, limited research exists explaining how tackle height influences head characteristics and tackler technique. This study aimed to investigate the effects of two tackle heights, aligned with recent law changes in the community game, on head and joint kinematics for both tackler and the ball carrier. To strengthen ecological validity, innovative techniques were employed, including markerless motion capture and Inertial Measurement Units (IMUs), for tracking of the tackler's joint kinematics and head accelerations until ground contact, addressing a key limitation in previous research. Ethical approval was granted by Cardiff Metropolitan University. Ten male participants (mean ± SD age: 22 ± 3 years, stature: 184 ± 10 cm, mean mass: 94 ± 15 kg) alternated between tackler and ball carrier roles, executing upper and lower body tackles. Theia3D markerless motion capture software (Theia3Dv2022.1.0.2309, Theia Markerless, Inc., Kingston, ON, Canada) and Vicon IMeasureU Blue Trident dual-G IMUs measured tackle height's impact on head and joint kinematics. Discrete joint angles at key events and continuous joint angles normalised from 0% at Step 1 to 100% at Contact were exported. Peak head accelerations and continuous normalised head acceleration data were exported. Statistical analyses included a paired t-test for discrete joint angle data and the Wilcoxon Rank Sum Test for peak linear and angular accelerations. Cohen’s d and effect sizes were calculated for respective analyses. One-dimensional statistical parametric mapping (SPM) and one-dimensional statistical non-parametric mapping (SnPM) facilitated statistical differences across continuous variables of interest. Significant increases (P < 0.05) were noted in ball carriers' inertial head kinematics in the upper body tackle, while no such distinctions were observed for tacklers. The low tackle condition consistently exhibited substantial reductions in bilateral hip flexion, particularly during contact (Effect size; lead: −1.866; rear: −1.977). Lumbopelvic flexion significantly decreased in each event for the low tackle condition, with the largest effect size during contact (−3.91). These findings underscore the heightened inertial loading with higher tackles, indicating an elevated risk of head injury, despite current tackle height regulations. The adjustments made by the tackler in response to varying tackle heights are not evident in knee flexion. Increased knee flexion during the preparatory phase could alleviate the necessity for such a flexed lumbopelvic angle. This study, utilising innovative techniques, highlights the potential for more ecologically valid approaches to biomechanical research in rugby tackling.