Background The Rugby Union scrum has evolved into a highly dynamic activity, particularly during engagement. Although catastrophic spinal injuries in rugby are extremely rare, approximately 40% of these are associated with the scrum. Repeated scrum engagement may also contribute to premature chronic degeneration of the cervical spine in rugby players.

Objective To compare the biomechanical stresses experienced by rugby forward players during live contested scrummaging under different scrum engagement processes, taking into account different playing standards.

Design A cross-sectional design, where teams from five different playing levels performed live scrums under three engagement processes: 1) CTPE (Crouch-Touch-Pause-Engage, 2011–2012); 2) CTS (Crouch-Touch-Set, 2012–2013); and 3) PreBind (Crouch-Bind-Set, 2013–2014). Measures were made via body-worn sensors and video analysis.

Setting Outdoors, natural turf rugby pitches.

Participants 27 rugby teams (i.e. 54 forward packs, n=432 players) from five playing levels - International, Elite, Community, Women and University.

Risk factor assessment The three engagement processes. PreBind differs from CTS/CTPE with a legal bind that is taken at the “Bind” call and maintained through the “Set” action.

Main outcome measurements Biomechanical stresses (force, acceleration) and kinematics (engagement speed, joints angles) characterising the scrum motion.

Results The PreBind process reduced biomechanical stresses by 15–25% with respect to both CTPE and CTS during the engagement phase without reducing force during the sustained push phase. For front row players, peak cervical acceleration was reduced from 8.2 g (CTPE) and 7.9 g (CTS) to 6.8 g (PreBind), and peak compression forces decreased from 8.4 kN (CTPE) and 8.3 kN (CTS) to 6.3 kN (PreBind). Players' movements/postures did not differ significantly between engagement processes. The mixed design ANOVA did not evidence any significant interaction effect (engagement type-playing level) in any variable.

Conclusions The PreBind process reduced the mechanical stresses on front row players and may lead to safer conditions without affecting performance.