A Laboratory Protocol for Shoulder-Head and Head-Ground Dummy Head Accelerations During Player High-Speed Rugby Tackles

Abstract

BACKGROUND: The purpose of this study was to demonstrate the effectiveness of a novel laboratory testing protocol for dummy head biomechanics of the shoulder-head and subsequent head-ground impacts during rugby tackles. Currently, no research in tackles utilizes a real player as the tackler and considers the second impact when the opponent's head hits the ground. METHODS: A dummy was instrumented with an inertial measurement unit (IMU; 1,200 Hz) behind the right ear. Eleven rugby players with a shoulder placed IMU executed right shoulder high tackles to the left side of the dummy's head at two closing velocities (high-speed 15-17 km/hr and very-high-speed 21-23 km/hr) for three dummy head conditions (no headgear, club-level headgear, professional-level headgear). Peak resultant linear and rotational accelerations were calculated for the first impact event (shoulder-head) for the player's shoulder IMU and for the two impact events (shoulder-head, head-ground) for the dummy head IMU. RESULTS: Whilst the player experienced low linear accelerations (fast-speed = 10 g, very-fast-speed = 13 g) through their shoulder during the tackle impact (shoulder-head collision), the linear accelerations were six times higher (63 g; p = 0.003) for the dummy head for the high-speed approach and seven times higher (88 g; p = 0.003) for the very-high-speed approach. The second head-ground impact was generally lower for the linear accelerations (p < 0.004) but unchanged for the rotational accelerations (fast-speed = 4,589-4,955 rad/s2, very-fast-speed = 6,948-7,123 rad/s2) for the dummy head. Resultant rotational acceleration significantly increased for the dummy head-ground impact when club-level headgear was worn for the very-high-speed approach (8,434 rad/s2, p = 0.045). No other significant differences were observed between the no headgear and headgear tests. CONCLUSIONS: This study demonstrates the effectiveness of a protocol measuring linear and rotational accelerations of a dummy's head during high-speed rugby tackles where a real player's shoulder hit the dummy's head and the dummy's head hit the floor. Trialing the protocol showed high impact accelerations experienced when receiving a tackle did not reduce with headgear. The experimental methodology and tools developed provide the basis for more complete testing of head biomechanics in tackles.