Injury and biomechanical perspectives on the rugby scrum: a review of the literature

Physiological and Biomechanical Monitoring in American Football Players: A Scoping Review

American football is the sport with the highest rates of concussion injuries. Biomedical engineering applications may support athletes in monitoring their injuries, evaluating the effectiveness of their equipment, and leading industrial research in this sport. This literature review aims to report on the applications of biomedical engineering research in American football, highlighting the main trends and gaps. The review followed the PRISMA guidelines and gathered a total of 1629 records from PubMed (n = 368), Web of Science (n = 665), and Scopus (n = 596). The records were analyzed, tabulated, and clustered in topics. In total, 112 studies were selected and divided by topic in the biomechanics of concussion (n = 55), biomechanics of footwear (n = 6), biomechanics of sport-related movements (n = 6), the aerodynamics of football and catch (n = 3), injury prediction (n = 8), heat monitoring of physiological parameters (n = 8), and monitoring of the training load (n = 25). The safety of players has fueled most of the research that has led to innovations in helmet and footwear design, as well as improvements in the understanding and prevention of injuries and heat monitoring. The other important motivator for research is the improvement of performance, which has led to the monitoring of training loads and catches, and studies on the aerodynamics of football. The main gaps found in the literature were regarding the monitoring of internal loads and the innovation of shoulder pads.

Body Composition Asymmetry in University Rugby Players: Influence of Sex, Position, and Injury

CONTEXT

Measures of side-to-side asymmetry in body composition may help identify players who are predisposed to lower limb injuries (LLI) or lower back pain (LBP). This study aimed to examine (1) side-to-side asymmetry in college rugby players according to sex and position and (2) whether side-to-side asymmetry is associated with LBP or LLI.

DESIGN

Cross-sectional study.

METHODS

Thirty-six rugby players (61% female) underwent a dual-energy X-ray absorptiometry assessment for total and regional (appendicular, truncal) outcomes of fat mass, lean mass, and bone mass. A subsample (n = 23) of players had a second dual-energy X-ray absorptiometry assessment 2 months postbaseline. Two-way analysis of variance was used to assess the effect of position (forward and backs) and sex on body composition asymmetry. Student paired t tests were used to assess side-to-side difference in body composition and compare baseline and follow-up measures. Logistic regression was used to assess possible associations between LLI, LBP, and the degree of side-to-side asymmetry in body composition.

RESULTS

Male players had greater asymmetry in arm bone mass compared with female players (P = .026), and trunk fat mass asymmetry was greater in forwards as compared with backs (P = .017). Forwards had significantly greater fat mass (P = .004) and percentage of fat (P = .048) on the right leg compared with the left. Backs had significantly greater bone mass in the right arm compared with the left (P = .015). From baseline to postseason, forwards had a significant increase in side-to-side asymmetry in arm lean mass (P = .006) and a significant decrease in side-to-side asymmetry in leg fat mass (P = .032). In backs, side-to-side asymmetry at baseline compared with postseason was significantly different (P = .011) for trunk fat mass. There were no significant associations between body composition asymmetry, LLI, or LBP by sex or position.

CONCLUSION

Our results revealed the presence of side-to-side asymmetries in body composition in university rugby players between sex and position. The amount of asymmetry, however, was not associated with LBP and LLI.

The association between contact sport exposure and cervical sensorimotor dysfunction: a scoping review of implications for future musculoskeletal injury risk

BACKGROUND

While morphological changes to the cervical spine have been observed for over 40 years in response to contact sport participation, little is known about the secondary effects of the cervical impairment on future musculoskeletal injury and disability.

OBJECTIVES AND DESIGN

A scoping review was performed to discuss the relationship between contact sport participation and morphological changes to the cervical spine. Moreover, the correlation between morphological changes in the musculoskeletal structures of the cervical spine and resultant deficits in cervical sensorimotor and neuromotor function are discussed. Lastly, how alterations in cervical sensorimotor function may affect overall risk of musculoskeletal injury is discussed.

METHODS

The scientific literature was searched in PubMed, Sport Discus, and Web of Science pertaining to contact-sport athletes and/or cervical pathology and the cervicocephalic network. The Asksey and O'Malley's framework and PRISMA for Scoping Reviews were used to conduct and report the following review. Included articles were grouped into three categories: (1) Morphological changes to the cervical spine in contact sport athletes. (2) The role of the neuromotor pathways of the cervical spine in maintenance of postural tone and coordination of the extremities. (3) The correlation between altered cervical sensorimotor function and a resultant increase in musculoskeletal injury risk.

RESULTS

Our search identified 566 documents, of which 405 underwent full-text screening, resulting in 54 eligible studies for the review. Widespread cervical sensorimotor dysfunction was observed in contact sport athletes. Independently, cervical sensorimotor function was demonstrated to play a critical role in postural control and limb coordination. However, limited research exists exploring the interaction between contact sport participation and altered cervical sensorimotor function, as well as an associated increase in musculoskeletal injury risk.

CONCLUSIONS

Limited evidence exists linking cervical injury and/or observed deficits in cervical sensorimotor and neuromotor function to musculoskeletal injury risk. Longitudinal studies combining imaging measures (e.g., MRI, DEXA), cervical functional test, and prospective injury risk are needed to further explore the correlation between resultant cervical sensorimotor deficits following contact sport impacts and future musculoskeletal injury risk.

Managing the Wellbeing of Elite Rugby Union Players from an Occupational Safety and Health Perspective

The intense, physical contact nature of rugby union often encourages the normalization of risk-taking behaviour resulting in a relatively high acceptance of risk. This study aims to explore safety culture in rugby union from an OSH perspective, with the purpose of assisting coaches and management in their decision-making processes to improve players' health, welfare, and long-term well-being. In terms of data collection, this study involved semi-structured interviews with senior support staff (n = 15) in elite rugby union. Interview transcripts underwent inductive analysis prior to an abductive analysis that was guided by an established occupational-safety-and-health (OSH) framework. Rugby union players' safety can be considered from two dimensions: management's commitment to safety (i.e., safety prioritization, safety empowerment, and safety justice), players' involvement in safety (i.e., safety prioritization, and trust in other players' safety competence, and players' safety concern for the opposition players). Within the themes identified, players' attitude towards their opponents' safety which has been rarely considered as a factor for injury prevention is also discussed in this study. If sport support staff (i.e., managers/coaches/medical) can become more involved in players' performance-orientated training using OSH management processes to aid in their decision-making, their exists the capacity to benefit players' safe return to play after injury rehabilitation. Meanwhile, directing the development of appropriate behavioural educational interventions to raise safety-awareness amongst players can improve their long-term health and well-being and provide them with the necessary safety and health information to support their own decision-making processes. As a multidisciplinary design, this study contributes new multidisciplinary insights that have the potential to advance managerial practices utilizing an OSH perspective, including decision-making supporting risk alleviation for safety and long-term health and wellbeing initiatives in competitive team sports.

The playing position significantly influences return to sports and recurrences after an arthroscopic Bankart repair in competitive rugby players

BACKGROUND

The purpose of our study was to investigate the influence of the different rugby playing positions on return to sports, functional outcomes, and recurrences after an arthroscopic Bankart repair.

METHODS

A total of 88 rugby players were treated for anterior shoulder instability in our institution between 2010 and 2018. Functional outcomes, return to sports, recurrences, complications, and revisions rates were evaluated according to the playing position.

RESULTS

Overall, 73.8% of the patients returned to rugby and 60% returned at the same level as before the injury. The tight forwards and outside backs experienced a significant decrease in their competitive level after surgery, and showed the lowest functional outcomes. The tight forwards and outside backs showed a statistically significant increase in recurrence and revision rates, and an OR for recurrence of 12.8 and 9.6, respectively.

DISCUSSION

The playing position significantly influenced return to sports and recurrences after an arthroscopic Bankart repair in competitive rugby players. Specifically, the tight forwards and outside backs have returned to a lower level than they had before surgery, showed the lowest functional outcomes, and a significant increase in recurrences and revisions rates than the other groups.

The incidence and transmission of SARS-CoV-2 infection in south African professional rugby players - AWARE II

Objectives

To describe the incidence and transmission of SARS-CoV-2 infections in South African professional rugby union players in different phases of return-to-competition during a pandemic.

Design

Prospective cohort study.

Methods

Players reported their history of SARS-CoV-2 infection before/during a national competition, using an online questionnaire (physician verified). Three periods of return to training/competition after a nation-wide complete lockdown during a pandemic were studied: 1) non-contact training, 2) contact training, 3) competition. The total period was 184 days (20/07/2020–20/01/2021) including 45 matches. Outcomes were: 1) incidence of SARS-CoV-2 infection (I: per 1000 player days; 95%CI) in each period (calculated using a Poisson distribution), 2) player symptoms, 3) median days to return-to-training following SARS-CoV-2 infection, 4) method of transmission, and 5) percentage matches cancelled due to SARS-CoV-2 infections.

Results

185 players had 42 physician verified positive SARS-CoV-2 infections (I = 1.23; 95%CI: 0.86–1.61). Incidences during the three periods were: non-contact training = 0, contact training (I = 1.04; 0.36–1.71; mostly forwards), and competition (I = 1.54; 1.00–2.10). 83 % of the infected players were symptomatic and 52 % of the 42 positive players had systemic symptoms. Median return-to-training was 14 days. 22 (52 %) SARS-CoV-2 infections were rugby-related: 13 off-field (31 %), 9 on-field (21 %). 11 % of matches were cancelled due to SARS-CoV-2 infections.

Conclusions

As contact in rugby was introduced back into the game following lockdowns there was an increasing incidence of SARS-CoV-2 infection. On-field rugby activities were responsible for 21 % of SARS-CoV-2 infections and 11 % of matches had to be cancelled, indicating the need for risk mitigation strategies.

Influence of Axial Load and a 45-Degree Flexion Head Position on Cervical Spinal Stiffness in Healthy Young Adults

Background: Neck pain is a major cause of disability worldwide. Poor neck posture such as using a smartphone or work-related additional cervical axial load, such headgear of aviators, can cause neck pain. This study aimed at investigating the role of head posture or additional axial load on spinal stiffness, a proxy measure to assess cervical motor control. Methods: The posterior-to-anterior cervical spinal stiffness of 49 young healthy male military employees [mean (SD) age 20 ± 1 years] was measured in two head positions: neutral and 45-degree flexed head position and two loading conditions: with and without additional 3 kg axial load. Each test condition comprised three trials. Measurements were taken at three cervical locations, i.e., spinous processes C2 and C7 and mid-cervical (MC). Results: Cervical spinal stiffness measurements showed good reliability in all test conditions. There was a significant three-way interaction between location × head position × load [F(2, 576) = 9.305, p < 0.001]. Significant two-way interactions were found between measurement locations × loading [F(2, 576) = 15.688, p < 0.001] and measurement locations × head position [F(2, 576) = 9.263, p < 0.001]. There was no significant interaction between loading × head position [F(1, 576) = 0.692, p = 0.406]. Post hoc analysis showed reduction of stiffness in all three measurement locations in flexion position. There was a decrease in stiffness in C2 with loading, increase in stiffness in C7 and no change in MC. Discussion: A flexed head posture leading to decreased stiffness of the cervical spine might contribute to neck pain, especially if the posture is prolonged and static, such as is the case with smartphone users. Regarding the additional load, stiffness decreased high cervical and increased low cervical. There was no change mid cervical. The lower spinal stiffness at the high cervical spine might be caused by capsular ligament laxity due to the buckling effect. At the lower cervical spine, the buckling effect seems to be less dominant, because the proximity to the ribs and sternum provide additional stiffness.

Effects of increasing axial load on cervical motor control

To investigate the effects of increasing axial load on cervical motor control. Surrogates of cervical motor control were active cervical range of motion (C-ROM) and joint position error (JPE) assessed in flexion, extension, lateroflexion and rotation directions in 49 healthy young men (mean age: 20.2 years). All measurements were executed with 0-, 1-, 2-, and 3-kg axial loads. Linear mixed models were used to assess the effects of axial loading and cervical movement-direction on C-ROM and JPE. Post-hoc analysis was performed to compare load levels. Axial loading (p = 0.045) and movement direction (p < 0.001) showed significant main effects on C-ROM as well as an interaction (p < 0.001). C-ROM significantly changed with 3-kg axial load by decreaseing extension (− 13.6%) and increasing lateroflexion (+ 9.9%). No significant main effect was observed of axial loading on JPE (p = 0.139). Cervical motor control is influenced by axial loading, which results in decreased C-ROM in extension and increased C-ROM lateroflexion direction.

The effect of compressive loading rate on annulus fibrosus strength following endplate fracture

Intervertebral disc degeneration poses a considerable healthcare challenge, although the process is not well understood. Endplate fracture marks severe biomechanical compromise in a segment and may be correlated with degeneration of the disc. The purpose of this experiment was to investigate the relationship between endplate fracture velocity and damage to the annulus fibrosus. Following overnight-thawing, 27 frozen porcine cervical spines were dissected into motion segments (vertebra-disc-vertebra) and compressed until fracture at one of three loading rates (fast=15 mm/s, medium=1.5 mm/s, and slow=0.15 mm/s), or remained unfractured (control). Two annular samples were extracted and mechanically tested from each segment: 1) Bilayer samples underwent uniaxial tension to a stretch-ratio of 1.5; 2) Multilayer samples were delaminated with a 180° peel test configuration. All three rates of compression resulted in specimen fracture observed in the endplate and/or vertebra with varying degree of severity. Significant differences were detected in compressive strength and stiffness of motion segments when loaded at different rates of compression; interestingly these differences were not observed in the mechanical properties of the annulus fibrosus suggesting that at slow rates of loading, fracture of the endplate precedes destruction of the annulus fibrosus. In corroboration of these findings, gross and histological analysis reported no signs of annular disruption, strengthening assertions that annular damage did not occur.

What Cognitive Mechanism, When, Where, and Why? Exploring the Decision Making of University and Professional Rugby Union Players During Competitive Matches

Over the past 50 years decision making research in team invasion sport has been dominated by three research perspectives, information processing, ecological dynamics, and naturalistic decision making. Recently, attempts have been made to integrate perspectives, as conceptual similarities demonstrate the decision making process as an interaction between a players perception of game information and the individual and collective capability to act on it. Despite this, no common ground has been found regarding what connects perception and action during performance. The differences between perspectives rest on the role of stored mental representations, that may, or may not facilitate the retrieval of appropriate responses in time pressured competitive environments. Additionally, in team invasion sports like rugby union, the time available to players to perceive, access memory and act, alters rapidly between specific game situations. Therefore, the aim of this study was to examine theoretical differences and the mechanisms that underpin them, through the vehicle of rugby union. Sixteen semi-elite rugby union players took part in two post-game procedures to explore the following research objectives; (i) to consider how game situations influence players perception of information; (ii) to consider how game situations influence the application of cognitive mechanisms whilst making decisions; and (iii) to identify the influence of tactics and/or strategy on player decision making. Deductive content analysis and elementary units of meaning derived from self-confrontation elicitation interviews indicate that specific game situations such as; the lineout, scrum or open phases of play or the tackle situation in attack or defence all provide players with varying complexity of perceptual information, formed through game information and time available to make decisions. As time increased, players were more likely to engage with task-specific declarative knowledge-of the game, stored as mental representations. As time diminished, players tended to diagnose and update their knowledge-in the game in a rapid fashion. Occasionally, when players described having no time, they verbalised reacting on instinct through a direct connection between perception and action. From these findings, clear practical implications and directions for future research and dissemination are discussed.

Identifying Contextual Influences on Training Load: An Example in Professional Rugby Union

ABSTRACT

Dalton-Barron, NE, McLaren, SJ, Black, CJ, Gray, M, Jones, B, and Roe, G. Identifying contextual influences on training load: an example in professional rugby union. J Strength Cond Res 35(2): 503-511, 2021-We aimed to investigate the contextual factors influencing training load (TL), as determined by session rating of perceived exertion (sRPE-TL), accumulated within a match-to-match microcycle in rugby union players. Session rating of perceived exertion-TL data were collected daily from 35 professional rugby union players from the same team in the English Championship over the course of an in-season period. Players were split by positional groups (backs and forwards) and sRPE-TL data were categorized as: field-based on-feet sRPE-TL (sRPEField-TL), gym-based sRPE-TL (sRPEGym-TL), and the total summation of both (sRPETotal-TL). Three 2-level linear mixed models were built for each dependent variable in each positional group, with magnitude-based inferences applied. Long between-match recovery cycles (≥7 days) resulted in very likely to almost certainly small to moderate increases in sRPE-TL for all modalities and positions (fixed effect [mean range] = 28.5%-42.0%), apart from sRPEField-TL for forwards. For backs, there was a very likely small decrease in sRPEField-TL as the season progressed (-16.7% per trimester). Losing the last league match was associated with very likely and almost certainly small decreases in sRPETotal-TL and sRPEGym-TL for backs (-20.7% and -36.4%, respectively). Losing the last match in any competition resulted in a very likely small increase in sRPEField-TL (21.2%) and a possibly small decrease sRPEGym-TL (-18.5%) for backs-with a likely smaller sRPEGym-TL for forwards (-33.4%). The strength of the upcoming opposition had no effect on sRPE-TL. Our findings highlight some of the multifactorial contextual factors that must be considered when planning and evaluating training microcycles.

Force production during the sustained phase of Rugby scrums: a systematic literature review

Background

Since World Rugby changed the laws regarding scrums in the 2013–2014 season, the sustained push phase of the scrum has increased in tactical importance. Therefore, the purpose of this systematic literature review was to examine the biomechanical demands during the sustained push phase of individual, unit, and full pack scrummaging.

Methods

Pubmed, EBSCO (specifically and simultaneously searching Academic Search Premier, CINAHL, and SPORTDiscus), and Google Scholar were searched for any research that presented force production in a live or simulated rugby scrum. Study quality was appraised using the National Institute of Health’s Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. Recorded scrum forces, positioning of players including joint angles, and testing procedures were extracted and narratively synthesized.

Results

Twenty six studies were included in the review. 50% of included studies were rated good, 31% fair, and 19% poor. Major limitations included not reporting any effect size, statistical power, or reliability. Reported group mean values for average sustained forces against a machine generally ranged from 1000 to 2000 N in individual scrums and 4000–8000 N for full packs of male rugby players older than high school age. Individuals seem to optimize their force generation when their shoulders are set against scrum machine pads at approximately 40% of body height, with feet parallel, and with knee and hip angles around 120°. A 10% difference in pack force seems to be necessary for one pack to drive another back in the scrum, but little data exist to quantify differences in force production between winning and losing packs during live scrums. Data collection within studies was not standardized, making comparisons difficult. There is a lack of data in live scrums, and the current research indicates that machine scrums may not replicate many of the demands of live scrums. There is a lack of data for female rugby players.

Conclusions

This review indicates an optimal individual body position for players to strive to achieve during scrummaging, consisting of a low body height (40% of stature) and large extended hip and knee angles (120° each).

The influence of hip mobility and quadriceps fatigue on sagittal spinal posture and muscle activation in rugby scrum performance

Rugby Union scrumming puts the spine under a high degree of loading. The aim of the current study was to determine how sagittal hip range of motion and quadriceps fatigue influence force output, spinal posture, and activation of the trunk and quadriceps muscles in rugby scrumming. Measures of sagittal hip flexion/extension range of motion were collected from 16 male varsity and club first XV level participants. Sagittal spine motion (electromagnetic motion capture), trunk and quadriceps activation (electromyography), and applied horizontal compressive force (force plate) were measured during individual machine scrumming. Participants performed a 5-trial scrum block involving 5 s of contact with 1-2 min recovery between each trial. They then performed a fatiguing protocol (wall sit to failure) and immediately returned to the scrum machine to perform another five trials. Though there was no significant influence of fatigue on the horizontal compressive force applied during contact (P = .83), there was a 52% increase in cervical flexion (P < .001), as well as decreased (18-23% lower) abdominal and erector spinae muscle activation (P < .05). Furthermore, quadriceps activation decreased (12-25% lower) over the course of the initial scrum block but increased (13-15% higher) in the post fatigue block (P < .05). Although athletes were able to maintain force output following the fatiguing wall sit task, there is the potential that they may be at an increased risk of spinal injury due to the combination of increased flexion and high-applied compressive force; a combination which has been shown to increase the likelihood of intervertebral disc herniation.

Effect of the PreBind Engagement Process on Scrum Timing and Stability in the 2013-16 Six Nations

This study examined whether changes in scrum engagement laws from the "crouch-touch-set" in 2013 to the "PreBind" engagement from 2014 onward have led to changes in scrum characteristics, specifically timing, in international rugby union. Duration and outcomes were identified for all scrums occurring in the 2013-16 Six Nations (N = 60 games) using video analysis. Scrum duration increased after the introduction of the PreBind engagement from 59 s in 2013 to 69 s in 2016 (P = .024, effect size = 0.93). A significant increase in mean contact duration per scrum occurred when prebinding was adopted (P < .05), moving from 7.5 s under the crouch-touch-set process to 8.5, 10.0, and 10.8 s with PreBind in 2014, 2015, and 2016 (effect size = 0.71, 2.05, and 3.0, respectively). The number of scrum resets and collapsed scrums, along with early engagement and pulling down infringements, was lower under the PreBind process. Overall, the PreBind engagement resulted in longer scrums with significant increases observed in overall and contact durations, with improved stability-related characteristics. The longer contact time is a consequence of increased stability with a shift from high-energy impact to a sustained push phase with a lower force that is a benefit to player welfare.

‘In a blink of an eye your life can change’: experiences of players sustaining a rugby-related acute spinal cord injury

Background

Though rare, rugby union carries a risk for serious injuries such as acute spinal cord injuries (ASCI), which may result in permanent disability. Various studies have investigated injury mechanisms, prevention programmes and immediate medical management of these injuries. However, relatively scant attention has been placed on the player’s experience of such an injury and the importance of context.

Aim

The aim of this study was to explore the injury experience and its related context, as perceived by the catastrophically injured player.

Methods

A qualitative approach was followed to explore the immediate, postevent injury experience. Semi-structured interviews were conducted with 48 (n=48) players who had sustained a rugby-related ASCI.

Results

Four themes were derived from the data. Participants described the context around the injury incident, which may be valuable to help understand the mechanism of injury and potentially minimise risk. Participants also described certain contributing factors to their injury, which included descriptions of foul play and aggression, unaccustomed playing positions, pressure to perform and unpreparedness. The physical experience included signs and symptoms of ASCI that is important to recognise by first aiders, fellow teammates, coaches and referees. Lastly, participants described the emotional experience which has implications for all ASCI first responders.

Significance

All rugby stakeholders, including players, first responders, coaches and referees, may gain valuable information from the experiences of players who have sustained these injuries. This information is also relevant for rugby safety initiatives in shaping education and awareness interventions.

Inconsistent anticipatory postural adjustments (APAs) in rugby players: a source of injuries?

Background

We are developing since 2010 with Thales and the Fédération Française de Rugby (FFR) M-Rex, a new kind of rugby scrum simulator. The study questioned whether it could improve safety and protect players from injury by using it as a tool for training/coaching the packs.

Aim

To explore the anticipatory postural adjustments (APAs) during the engagement of the ruck, because these predictive neck and back muscles contractions protect the spinal cord at the time of impacts, which is crucial to prevent injuries.

Methods

We quantified the kinematics and the EMG activities in high-level front row players during their initial engagement, when scrummaging with M-Rex. All studies were performed with one player interacting with the robot, at first, and then with the three players acting together.

Results

For most of the tested high-level players, the APA latencies were highly variable from trial to trial even though the engagement resulted in similar impacts. At time, the onset of the electromyography activity in the neck and back muscles showed latencies inferior to 50 ms or even close to zero prior to the impact, which rendered muscle contractions inefficient as APAs. We were also unable to identify clear muscular synergies underlying the APAs because of their great variability on a trial-to-trial basis. Finally, the APAs were not related to the amplitude of the ensuing impact and were asymmetric in most trials. All these characteristics held true, whether the player was playing alone or with two other frontline players.

Conclusion

Our result suggest that APAs should be systematically tested in high-level rugby players as well as in any high-level sport men at risk of neck and back injuries. Because APAs can be efficiently trained, our study paves the way to design individual position-specific injury prevention programme.

The influence of foot position on scrum kinetics during machine scrummaging

The purpose of this study was to investigate the effect of variations in the alignment of the feet on scrum kinetics during machine scrummaging. Twenty nine rugby forwards from amateur-level teams completed maximal scrum efforts against an instrumented scrum machine, with the feet in parallel and non-parallel positions. Three-dimensional forces, the moment about the vertical axis and sagittal plane joint angles were measured during the sustained pushing phase. There was a decrease in the magnitude of the resultant force and compression force in both of the non-parallel conditions compared to parallel and larger compression forces were associated with more extended hip and knee angles. Scrummaging with the left foot forward resulted in the lateral force being directed more towards the left and the turning moment becoming more clockwise. These directional changes were reversed when scrummaging with the right foot forward. Scrummaging with the right foot positioned ahead of the left may serve to counteract the natural clockwise wheel of the live scrum and could be used to achieve an anti-clockwise rotation of the scrum for tactical reasons. However, this would be associated with lower resultant forces and a greater lateral shear force component directed towards the right.

Lower extremity muscle function of front row rugby union scrummaging

A rugby scrum's front row must act uniformly to transfer maximal horizontal force and improve performance. This study investigated the muscle activation patterns of lower extremity muscles in front row forwards during live and machine scrums at professional and amateur levels. Electromyography was collected bilaterally on vastus lateralis, rectus femoris and gastrocnemius muscles of 75 male rugby prop players during live and machine scrums. ANOVAs compared muscle reaction time, rate of change in muscle amplitude and muscle amplitude between groups and conditions. Cross-correlation analysis explored muscle synchronicity. There were significantly greater rates of change in each muscle amplitude in professional players than amateur players. Additionally, there was significantly quicker muscle reaction time in all muscles, and greater amplitude in vastus lateralis and gastrocnemius, during the live scrum vs. machine condition. The professional props produced more synchronised muscle activation than amateur players and all players produced more synchronised muscle activation against the scrum machine vs. live scrummage. The results indicate a higher skill proficiency and muscle synchronicity in professional players. While scrum machine training is ideally suited for functional muscle strengthening during practice, to truly simulate the requirements of the scrum, training should incorporate the live situation as much as possible.

Can Neck Strength be Measured Using a Single Maximal Contraction in a Simulated Contact Position?

Salmon, DM, Handcock, PJ, Sullivan, SJ, Rehrer, NJ, and Niven, BE. Can neck strength be measured using a single maximal contraction in a simulated contact position? J Strength Cond Res 32(8): 2166-2173, 2018-Neck strengthening has been postulated to potentially reduce the incidence and severity of concussions and neck injuries in collision-based sports. A quick and reliable method to assess neck strength would permit identification of those at risk and tracking of progress after injury. The purpose of this study was to determine if neck strength could be reliably assessed in a simulated contact posture using a single maximal contraction. During a single session, 30 healthy male university students performed 3 maximal voluntary contractions of the neck musculature in each of the following directions: extension (Ext), flexion (Flx), left lateral flexion (LtFlx), and right lateral flexion (RtFlx). To evaluate the reliability of these measures, intraclass correlation coefficients (ICCs) were calculated. The findings revealed a significant effect for direction (p < 0.01), where Ext (234.8 N) tested stronger than Flx (141.0 N), LtFlx (134.5 N), and RtFlx (123.0 N). In addition, Flx tested stronger than RtFlx (p = 0.03). No other differences were observed between LtFlx and RtFlx. When the combined mean values of the trials (1: 151.6 N, 2: 160.0 N, 3: 163.5 N) and the interaction contrast were compared, these were not significant (p = 0.08-1.0), indicating no changes in peak force occurred over the 3 trials. The ICC values for Ext, RtFlx, and LtFlx were all "excellent" (0.91-0.94), whereas Flx demonstrated "good" reliability (0.86). In a simulated contact posture, a reliable measure of peak force was obtained using a single maximal contraction. This may have practical applications for the quick and reliable assessment of contact sport athletes in a position that has functional relevance to their sports.

Impact of the national prevention policy and scrum law changes on the incidence of rugby-related catastrophic cervical spine injuries in French Rugby Union

BACKGROUND AND AIMS

Catastrophic cervical spine injuries are rare in rugby union but require close monitoring. The aim of this study was to analyse the incidence of severe cervical spine injuries and determine the impact of a national prevention programme and new scrum rules implemented by the French Rugby Union.

METHODS

A prospective study was performed between 2006 and 2013 including all players affiliated to the French Rugby Union. All cervical spine injuries resulting in death, tetraplegia or a permanent neurological deficit were included. Prevention programmes were implemented from 2007 to 2013 and a change in scrum rules in 2010. To measure the impact of rule changes, results between 2006-2010 and 2010-2013 were compared using a Poisson regression.

RESULTS

Altogether, 31 injuries were observed and the mean annual incidence was 1.6 per 100 000 players. There were significantly more injuries in senior players compared to junior players (3.5 vs 0.6 per 100 000 players; CI 95% (2.1 to 4.9) vs (0.1 to 1.0)). Incidence decreased from 1.8 in 2006 to 1.0 per 100 000 players in 2013 (p<0.0001). After 2010, there were significantly fewer injuries during scrums (p=0.02). In contrast, there were significantly more injuries in backs during 2010-2013 compared to 2006-2010 (p=0.003).

CONCLUSIONS

The incidence of catastrophic cervical spine injuries has declined in French Rugby Union. The implementation of specific prevention programmes and scrum law changes has notably resulted in a decrease in scrum injuries in forwards. This prospective study should be continued to monitor the future progression of injuries and adapt prevention programmes accordingly.

An investigation into axial impacts of the cervical spine using digital image correlation

BACKGROUND CONTEXT

High-energy impacts are commonly encountered during sports such as rugby union. Although catastrophic injuries resulting from such impacts are rare, the consequences can be devastating for all those involved. A greater level of understanding of cervical spine injury mechanisms is required, with the ultimate aim of minimizing such injuries.

PURPOSE

The present study aimed to provide a greater understanding of cervical spine injury mechanisms, by subjecting porcine spinal specimens to impact conditions based on those measured in vivo. The impacts were investigated using high-speed digital image correlation (DIC), a method not previously adopted for spinal impact research.

STUDY DESIGN

This was an in vitro biomechanical study.

METHODS

Eight porcine specimens were impacted using a custom-made rig. The cranial and caudal axial loads were measured at 1 MHz. Video data were captured with two cameras at 4 kHz, providing measurements of the three-dimensional deformation and surface strain field of the specimens using DIC.

RESULTS

The injuries induced on the specimens were similar to those observed clinically. The mean±standard deviation peak caudal load was 6.0±2.1 kN, which occurred 5.6±1.1 ms after impact. Damage observable with the video data occurred in six specimens, 5.4±1.1 ms after impact, and the peak surface strain at fracture initiation was 4.6±0.5%.

CONCLUSIONS

This study has provided an unprecedented insight into the injury mechanisms of the cervical spine during impact loading. The posture represents a key factor in injury initiation, with lordosis of the spine increasing the likelihood of injury.