Biomechanics of Rugby Union Scrummaging

Summary

In the game of rugby union, the scrum epitomises the physical nature of the game. It is both a powerful offensive skill, affording a base for attacking play, and a defensive skill in denying the opposition clean possession. However, the scrum has also been implicated in a large proportion of serious spinal injuries in rugby union. The majority of injuries are found to occur at engagement where the forces experienced by front-row players (more than two-thirds of a tonne shared across the front-row) can exceed the structural limits of the cervical spine. These large forces are a consequence of the speed of engagement and the weight (and number) of players involved in the scrum. This highlights not only the need for physical preparation of all forwards but particularly player restraint at engagement, and justifies the ‘crouch-pause-engage’ sequence recently introduced to ‘depower’ the scrum. As the hooker is the player exposed to the greatest loads throughout the scrum and subsequently most at risk, he should determine the timing of engagement of the 2 front-rows.

Stability of the scrum is an indication of front-row players’ ability to utilise their strength to transmit the force to their opponents as well as the push of second-row and back-row players behind them in the scrum. This appears to be independent of the size of players. Equally, it reflects the risk of chronic degeneration of the musculoskeletal system through repeated exposure to these large stresses. However, not only are older and more experienced players better able to generate and transmit these forces, they are also able to maintain the integrity of the scrum.

A large proportion of individual players’ efforts to generate force is lost in their coordinated effort in a normal scrum. It is assumed these forces are dissipated through players re-orientating their bodies in the scrum situation as well as to less efficient shear forces and to the elastic and compressive tissues in the body. It again reinforces the importance of physical preparation for all forwards to better withstand the large forces involved in scrummaging.

Despite negative publicity surrounding the risk of serious spinal injury in rugby union, limited research has been conducted to examine either the mechanisms of injury or techniques implicated in causing injury. Biomechanical information can provide systematic bases for modifying existing techniques and assessing the physical capacities necessary to efficiently and safely play in the scrum. This will both improve performance of game skills and minimise the potential for injury.