An investigation to establish how the evolution of rugby influences the risk of spinal injury during scrummaging

The rugby scrum results in a large number of injuries to the players of the front row, particularly the hooker. Front row players have been known to suffer from acute and chronic injuries of the cervical spine as well as low back pain. The principal goal of this research was to develop a method to measure spinal biomechanics of the hooker’s role during rugby scrummaging and use this method to address the question of whether recent changes in rugby affect the risk on hooker spinal injury. In recent years, a number of changes have occurred in rugby which may have an effect in injury risk, however, little is currently known about the effect of these changes. This was accomplished through three experimental stages. Firstly, a review of kinematic measurement techniques was undertaken in order to determine the most feasible measurement technique. Inertial sensors were chosen and validated for orientation output against high precision digital encoders with high levels of concordance for each axis of each sensor (>0.95). In addition to this, a method of using electromyography to predict muscle force production was investigated. Determined force and recorded force were found to be insignificantly different (p>0.05) across the 12 participants investigated. Having proved this to be a feasible method, it was put into practise in-field. Inertial sensor technology was combined with a laboratory tested force-EMG correlation to assess spinal biomechanics during live, contested, training scrums for an initial sample of 9 rugby union hookers. No significant differences (p>0.05) were observed for peak kinematic variables or EMG data. The second study assessed whether a change in playing surface affects hooker spinal kinematics by evaluating key variables such as peak range of motion and angular velocity as there has been a recent shift towards the use of artificial surfaces. Twenty-two participants took part in this study with 11 participants in each group. The groups were not significantly different (p>0.05) in terms of anthropometric and background information. The results of this study indicated that key kinematic variables did not differ significantly (p>0.05) between playing surfaces. There was, however, a large effect (d>0.8) for certain peak angular velocity measurements of the thoracic region. THESIS SUMMARY iii The final study investigated how different engagement techniques affected hooker spinal biomechanics since a recent law change was introduced governing the scrum. These techniques included machine scrummaging and live scrummaging of two different engagement sequences. Twenty-nine participants took part in the live-vs-live comparison with 14 of those taking part in all three experimental conditions. The results of this final study indicate significant biomechanical differences (p<0.05) between machine and live scrummaging indicating that machine scrummaging is a much more constrained environment. Live scrummaging of the two different sequences did not yield any significant differences (p>0.05) for both kinematic and muscle activity/determined force data indicating that the sequences do not affect hooker spinal biomechanics. These results suggest that the recent changes in rugby do not significantly affect the risk of spinal injury of the rugby union hooker.