Spinal muscle activity in simulated rugby union scrummaging is affected by different engagement conditions

Introduction
Previous kinetic and kinematics studies on machine(1) and live(2) scrummaging in Rugby Union indicated a reduction of the biomechanical load experienced by front row players when a ‘crouch-bind-set’ (CBS) engagement procedure was used instead of a ‘crouch-touch-set’ (CTS) one. These findings led to law amendments that were trialled during the 2013-14 competitive season. The reduction in biomechanical loading on front-row players may reduce stresses on the spinal structures, and ultimately decrease spinal injury incidence. The activation of neck and spinal muscles may have an effect on the stiffness of the cervical area and hence on the distribution of load, but the contribution of these muscles during the engagement phase has still to be thoroughly investigated. This study aimed to compare spinal muscles activation in three different scrummaging conditions.
Materials and Methods
Nine male front-row forwards were asked to perform individual scrum engagements. Three engagement conditions were analysed: CBS (players pre-bind before they engage) and CTS (players engage and bind simultaneously) against a scrum machine; and, “Live”, against one another in a two versus one live condition (passive engagement). Muscle activities of the sternocleidomastoid (SMC), upper trapezius (UT) and (ES) were measured over the pre-engagement, engagement and sustained push phases, with the latter being the only phase studied in the Live condition.
Results
Muscle activity tended to be higher in CBS than CTS, significantly (p < 0.05) for UT and SCM in the engagement phase (Figure 1 (a) and 1 (b)). The activity of ES was significantly higher (p < 0.05) in Live than either CBS or CTS during the sustained push phase (Figure 1 (c)).
Discussion
The increase in spinal muscle activation in CBS compared to CTS may be influenced by the differences in binding techniques between the conditions. Since the increase in UT and SCM activity increases upper truck stiffness, in CBS the higher activity of spinal muscles, combined with a decrease in spinal loading(2), may ultimately reduce spinal injuries when compared to the CTS condition.ES was significantly (p < 0.05) more activated in Live than in either of the machine conditions. In live conditions, front row players scrum against a dynamic and unstable target therefore they need extra activation for stabilising lumbar muscles to maintain optimal lumbar spinal posture, and decrease the risk of injuryConclusionThe increased activity of the UT and SCM in CBS indicates that a pre-bind procedure make the upper spine more prepared to accept external load. This may lead to a reduction in spinal injury rates. Machine scrummaging does not replicate the demands of a live contest. This emphasises the requirement of individuals to practise and learn scrummage techniques in a live situation, rather than against a machine.
References
(1) Preatoni et al. (2014). BJSM [Epub ahead of print] 10.1136/bjsports-2013-092938
(2) Cazzola et al. (2014). BJSM [Epub ahead of print] doi: 10.1136/bjsports-2013-092904