Dario Cazzola

Cervical spine trauma from sport or traffic collisions can have devastating consequences for individuals and a high societal cost. The precise mechanisms of such injuries are still unknown as investigation is hampered by the difficulty in experimentally replicating the conditions under which these injuries occur. We harness the benefits of computer simulation to report on the creation and validation of i) a generic musculoskeletal model (MASI) for the analyses of cervical spine loading in healthy subjects, and ii) a population-specific version of the model (Rugby Model), for investigating cervical spine injury mechanisms during rugby activities. The musculoskeletal models were created in OpenSim, and validated against in vivo data of a healthy subject and a rugby player performing neck and upper limb movements. The novel aspects of the Rugby Model comprise i) population-specific inertial properties and muscle parameters representing rugby forward players, and ii) a custom scapula-clavicular joint that allows the application of multiple external loads. We confirm the utility of the developed generic and population-specific models via verification steps and validation of kinematics, joint moments and neuromuscular activations during rugby scrummaging and neck functional movements, which achieve results comparable with in vivo and in vitro data. The Rugby Model was validated and used for the first time to provide insight into anatomical loading and cervical spine injury mechanisms related to rugby, whilst the MASI introduces a new computational tool to allow investigation of spinal injuries arising from other sporting activities, transport, and ergonomic applications. The models used in this study are freely available at simtk.org and allow to integrate in silico analyses with experimental approaches in injury prevention.

Tackling in Rugby Union is an open skill which can involve high-speed collisions and is the match event associated with the greatest proportion of injuries. This study aimed to analyse the biomechanics of rugby tackling under three conditions: from a stationary position, with dominant and non-dominant shoulder, and moving forward, with dominant shoulder. A specially devised contact simulator, a 50-kg punch bag instrumented with pressure sensors, was translated towards the tackler (n = 15) to evaluate the effect of laterality and tackling approach on the external loads absorbed by the tackler, on head and trunk motion, and on trunk muscle activities. Peak impact force was substantially higher in the stationary dominant (2.84 ± 0.74 kN) than in the stationary non-dominant condition (2.44 ± 0.64 kN), but lower than in the moving condition (3.40 ± 0.86 kN). Muscle activation started on average 300 ms before impact, with higher activation for impact-side trapezius and non-impact-side erector spinae and gluteus maximus muscles. Players’ technique for non-dominant-side tackles was less compliant with current coaching recommendations in terms of cervical motion  (more neck flexion and lateral bending in the stationary non-dominant condition) and players could benefit from specific coaching focus on non-dominant-side tackles.

ABSTRACT 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. 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. 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. Outdoors, natural turf rugby pitches. 27 rugby teams (i.e. 54 forward packs, n=432 players) from five playing levels - International, Elite, Community, Women and University. 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. Biomechanical stresses (force, acceleration) and kinematics (engagement speed, joints angles) characterising the scrum motion. 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. The PreBind process reduced the mechanical stresses on front row players and may lead to safer conditions without affecting performance.

This study aimed to investigate how competition standard and progression speed affect race walking technique. Fifteen experienced athletes divided into three groups (Elite, International and National) were studied while race walking on a treadmill at two different speeds (12.0 and 15.5 km/h). Basic gait parameters, the angular displacement of pelvis and lower limb, and the variability in continuous relative phase between six different joint couplings were analysed.
Most of the spatio-temporal, kinematic and coordination variability measures proved sensitive to the change in speed. Conversely, nonlinear dynamics measures highlighted differences between athletes of different competition standard when conventional analytical tools were not able to discriminate between different skill levels. Continuous relative phase variability was higher for National level athletes than International and Elite in two couplings (pelvis obliquity – hip flex/extension and pelvis rotation – ankle dorsi/plantarflexion) and gait phases (early stance for the first coupling, propulsive phase for the second) that are deemed fundamental for correct technique and performance.
Measures of coordination variability showed to be a key tool for the finer detection of skill- dependent factors in competitive race walking, and showed a good potential for being integrated in the assessment and monitoring of sports motor abilities.

Biomechanical studies of rugby union scrummaging have focused on kinetic and kinematic analyses, while muscle activation strategies employed by front-row players during scrummaging are still unknown. The aim of the current study was to investigate the activity of spinal muscles during machine and live scrums. Nine male front-row forwards scrummaged as individuals against a scrum machine under “crouch-touch-set” and “crouch-bind-set” conditions, and against a two-player opposition in a simulated live condition. Muscle activities of the sternocleidomastoid, upper trapezius, and erector spinae were measured over the pre-engagement, engagement, and sustained-push phases. The “crouch-bind-set” condition increased muscle activity of the upper trapezius and sternocleidomastoid before and during the engagement phase in machine scrummaging. During the sustained-push phase, live scrummaging generated higher activities of the erector spinae than either machine conditions. These results suggest that the pre-bind, prior to engagement, may effectively prepare the cervical spine by stiffening joints before the impact phase. Additionally, machine scrummaging does not replicate the muscular demands of live scrummaging for the erector spinae, and for this reason, we advise rugby union forwards to ensure scrummaging is practiced in live situations to improve the specificity of their neuromuscular activation strategies in relation to resisting external loads.


Spinal muscle activity in simulated rugby union scrummaging is affected by different engagement conditions. Available from: https://www.researchgate.net/publication/274081243_Spinal_muscle_activity_in_simulated_rugby_union_scrummaging_is_affected_by_different_engagement_conditions [accessed Mar 29, 2015].