Movement patterns of rugby union players performing scrummaging against a scrum machine: the effect of playing level and engagement condition

Introduction
The scrum is an important element of rugby union from a performance perspective but has also attracted attention from an injury potential perspective. Little is known about the characteristics of expert technique or the effect of modifying the method of scrum engagement on players’ technique. Therefore, our aim was to analyse the movement patterns of rugby union forwards performing scrums against a scrum training machine, taking into account playing level and engagement condition.
Methods
Thirty-four forward packs (n=272 participants), ranging in playing level from Under 18 age group to Senior International teams, performed repeated scrum trials against an instrumented scrum machine (contact forces measured in three directions at 500 Hz) under five different engagement conditions, designed in part to modify the biomechanical loading experienced by players. Player’s whole-body (CM motion), segment (trunk alignment) and joint (ankle-knee-hip) motions were reconstructed in the transverse and sagittal planes via video analysis (Vicon Motus v9.0) at 50 Hz.
Results
Engagement speeds ranged from 2.3 m/s (U18) to 3.0 m/s (Elite Club) between playing levels in the ‘Base’ engagement condition, and from 1.8 m/s (‘FoldIn’) to 2.9 m/s (‘Base’) between engagement conditions for the International level. ‘FoldIn’ engagement significantly reduced the maximum value of a combined kinetic/kinematic measure (trunk angle deviation multiplied by peak force) by approximately 50% compared with all other engagement conditions. Assessing player’s joint actions in the sagittal plane uncovered few significant differences between playing levels due to within-group variability, but moderate effects were observed for professional players to have more flexed knee and hip joints at movement onset and to more closely maintain a horizontal trunk position throughout all phases of the scrum.
Discussion
Previous research has not found strong associations between player technique (joint angles) and performance (force production) during the sustained phase of scrummaging (Quarrie & Wilson, 2000; Wu et al., 2007). Our study confirmed that there were not obvious differences between playing levels in sagittal plane motions through all stages of the scrum including the engagement phase, although this was partly due to within-group variability. Modifying the engagement condition to introduce a ‘FoldIn’ engagement meant the same kinematics (body alignment) were executed in the presence of reduced forces, and therefore the injury potential was considered to be reduced.
References
Quarrie K, Wilson B. (2000). J Sports Sci, 18, 237-246.
Wu, W, Chang, J, Wu, J, Guo, L (2007). J Strength Cond Res, 21, 251-258.
Acknowledgement
Funded by the International Rugby Board