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

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Spinal muscle activity in simulated rugby union

scrummaging is affected by different engagement conditions

Journal: Scandinavian Journal of Medicine and Science in Sports

Manuscript ID: SJMSS-O-809-14

Manuscript Type: Original Article

Date Submitted by the Author: 04-Nov-2014

Complete List of Authors: Cazzola, Dario; University of Bath, Department for Health

Stone, Benjamin; University of Bath, Department for Health Holsgrove, Tim; University of Bath, Department of Mechanical Engineering Trewartha, Grant; University of Bath, Department for Health Preatoni, Ezio; University of Bath, Department for Health

Keywords: Biomechanics, Injury Prevention, Sport Performance, Sport Impacts, Lumbar Spine

Scandinavian Journal of Medicine & Science in Sports - PROOF


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TITLE PAGE

Title

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

conditions

Running head (45 character limit)

Spinal muscle EMG in a simulated rugby scrum

Author list

Dario Cazzola(a,�,*), Benjamin Stone(a,*), Tim P. Holsgrove(b), Grant Trewartha(a), Ezio Preatoni(a)

Affiliations

(a) Sport, Health and Exercise Science, Department for Health, University of Bath, UK

(b) Centre for Orthopaedic Biomechanics, Department of Mechanical Engineering, University of Bath,

UK

(*) These authors equally contributed to the study

�� Corresponding author

Dario Cazzola

[email protected]

+44 (0)1225 385466

Sport, Health & Exercise Science, Department for Health, University of Bath

Applied Biomechanics Suite, 1.305

BA2 7AY - BATH (UK)

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SPINAL MUSCLE EMG IN A SIMULATED SCRUM

Keywords

Biomechanics, sports injury, sports performance, scrummaging technique, lumbar spine, cervical

spine

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ABSTRACT (200 WORDS MAX)

Biomechanical studies of rugby union scrummaging have focussed on kinetic and kinematic

analyses, whilst 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

practised in live situations to improve the specificity of their neuromuscular activation strategies in

relation to resisting external loads.

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INTRODUCTION

Rugby union scrummaging involves a dynamic engagement phase followed by a period of

sustained pushing (Milburn, 1990; Cazzola et al., 2014). Scrummaging places intense

biomechanical demands on players, particularly those playing in the front row (Quarrie & Wilson,

2000). Due to its physical nature, the scrum is associated with approximately 6 to 8% of all rugby

injuries (Brooks et al., 2005; Trewartha et al., 2014), 40% of catastrophic injuries (Quarrie et al.,

2002; Brown et al., 2013), and may lead to chronic degenerative spinal injuries (Castinel et al.,

2007; Delp et al., 2007; Hogan et al., 2010; Pinsault et al., 2010).

Machine and live scrummaging biomechanics have been described in terms of the forces generated

and motions observed (Cazzola et al., 2014; Preatoni et al., 2014). From these investigations, the

scrum has undergone a number of rule changes, most recently from a ‘crouch-touch-set’ (CTS, in

2012/2013) to a ‘crouch-bind-set’ (CBS, in 2013/2014) procedure, in an attempt to improve safety

by de-emphasising the initial impact of the scrum engagement (Cazzola et al., 2014; Preatoni et al.,

2014). The CBS technique resulted in a significant reduction, approximately a 20% effect, in the

biomechanical conditions (force, acceleration and impact speed) experienced by front row players in

live scrummaging (Cazzola et al., 2014). However, the external mechanical load acting on forwards

during a scrum is still considerable and the ways in which these loads transmit across the

anatomical structures as well as the possible threshold for injury are still to be understood and

described. Players’ neck and spinal strength is, therefore, crucial to absorb and control such

mechanical stresses. Rugby forwards have been shown to have a specific neck strength profile

(Olivier & Du Toit, 2008) that allows them to generate higher isometric force in extension, flexion

and rotation motions, compared with backs (Hamilton & Gatherer, 2014).

Currently, no study has investigated the effects of rule and technique changes on spinal muscle

activity. The analysis of neuromuscular activation patterns under different engagement conditions is

fundamental to elucidate the strategies employed by front row players as they prepare their bodies

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for the engagement and pushing actions. Such information may allow sports science and medicine

practitioners to provide optimal muscle conditioning and more specific rehabilitation programmes,

and may have a positive impact in terms of quicker and safer return to competition following injury.

In fact, cervical spine and neck injuries produce an excessively high number of early recurrent

injuries in elite Rugby Union, potentially due in part to unspecific and inappropriate rehabilitation

programmes (Williams S, unpublished observation). Analysis of muscle activation patterns during

scrummaging may also inform training practise, such as in the conditioning of novice front row

players with regard to preparation for live match scrummaging.

The aim of this study was to determine the activity of the bilateral upper trapezius,

sternocleidomastoid and erector spinae muscles under three scrummaging conditions; two machine

scrummaging conditions, the ‘crouch-bind-set’ and ‘crouch-touch-set’ and a single live scrummaging

condition were investigated. The first hypothesis was that spinal muscle activity is greater for the

CTS than the CBS scrummage due to the higher biomechanical conditions (forces, accelerations

and impact speed) experienced by front row players during the engagement in the CTS condition.

The second hypothesis was that spinal muscle activity would be greater for live scrummaging

compared with machine scrummaging due to a sustained push phase against a moveable target

that decreases scrum stability.

METHODS

Study design

In a repeated measures design, a group of rugby union front row forwards performed multiple trials

in three different simulated scrummage conditions (within-group factor) and throughout the phases

of scrummaging (within-group factor) to assess and compare spinal muscle activity (dependent

variable).

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Participants

Nine male rugby union players (age 20.3 ± 1.3 year, height 1.80 ± 0.10 m, weight 102.36 ± 15 kg),

of at least University 1st XV standard with a minimum of 3 years playing experience in the front row

and no history of spinal injuries in the 12 months prior to testing, participated in the study. All

participants provided written informed consent prior to participation and ethical approval was

obtained from the University of Bath Institutional Ethics Committee.

Data Collection

For electromyography (EMG) collection, six wireless electrodes (Delsys Trigno, Delsys Inc, USA),

sampling at 2000 Hz, were attached (Delsys adhesive interface) to: the sternocleidomastoid,

midway between the rostral and sternal attachments; upper trapezius, 1 cm superior to the scapula

spine midway between the medial origin of the scapula spine and the acromion; and, erector

spinae, 3.5 cm from the midline of the spine at the level of L4-5 (Sharp et al., 2014) (Figure 1).

Surface EMG signals were collected bilaterally on each participant (Delsys EMGworks 4.1.05,

Delsys Inc, USA). Prior to the mounting of electrodes, the skin surface was prepared by shaving,

lightly abrading and cleaning with alcohol wipes.

*** Figure 1 ***

Following a player led warm-up, each player performed two 4 s isometric maximal voluntary

contractions (MVC) of the upper trapezius, sternocleidomastoid and erector spinae, with a 1 minute

break between each measurement using the procedures defined in Table 1 (Vera-Garcia et al.,

2010; Morimoto et al., 2013).

Each participant then performed a number of sub-maximal scrummaging trials to become familiar

with the experimental and environmental conditions (indoor scrummaging on a rubber-based floor).

The three different engagement techniques: crouch-touch-set (CTS), crouch-bind-set (CBS) and live

2-versus-1 scrummaging (Live) (Table 2) were used. The machine scrummaging condition involved

a single participant engaging with a static scrum machine (Dictator, Rhino Rugby, Rooksbridge, UK)

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using the CTS and CBS variants followed by a sustained push (Preatoni et al., 2012). The live

condition involved a single participant passively engaging, for safety reasons, with two other

participants prior to the sustained push (Figure 2). Each participant then completed at least four

successful trials in each of the three scrum conditions, which were presented in a blocked random

order, up to a maximum of 24 trials in one session. Recovery intervals of ≥1 minute between

consecutive trials and ≥7 minutes between sets were included to avoid fatigue.

*** Figure 2 ***

A 13-camera (12 cameras Oqus 400, 1 Oqus 210c) motion capture system (Qualysis, Sweden)

capturing at 250 Hz was used to collect players’ kinematics and to determine the time of actual

engagement. A single marker was rigidly attached to the posterior aspect of each of the two central

scrum machine pusher-arm pads to detect movement on initial contact. A bespoke control and

acquisition system (cRIO-9024, National Instruments, Austin, Texas, USA) was programmed

(Labview 2010, National Instruments, Austin, Texas, USA) to synchronously trigger the acquisition

hardware (Delsys EMG, Qualysis) and playback pre-recorded cues given by the referee (Preatoni et

al., 2013). The cues, “crouch-touch-set” and “crouch-bind-set”, were delivered with consistent timing

(Table 2) for all the scrummaging conditions. Muscle activity was measured for 10 s from 1 s prior to

the “crouch” call.

Data Processing

Raw electromyograms were filtered by applying a bi-directional second-order Butterworth low pass

and high pass filter between 20-200 Hz. The data were then rectified and smoothed using a moving

average over 50 ms windows (Visual 3D v5, C-Motion Inc, USA). EMG signals were normalised to

the MVCs, which were calculated between 0.2-1.2 s after the initiation of maximum isometric

muscle contraction, with an average MVC value being calculated over two trials. Average muscle

activity (average rectified EMG amplitude) during scrum trials was calculated over three phases of

each scrum: the pre-engagement, the engagement and the sustained push phases.

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For the machine scrummaging conditions (CBS and CTS), the pre-engagement phase was defined

as the interval between the “set” cue and the instant of first contact between participant and pusher

arm. As in Preatoni et al. (Preatoni et al., 2014), and considering the fast loading rate in the shock-

absorption phase (Figure 3), the engagement phase was defined as the time the participant first

contacted the pusher arms until 1 s after the initial contact, the sustained push phase extended from

the end of engagement for 1 s (Figure 3). First contact between participant and pusher arms was

determined from the horizontal displacement of the markers on the scrum machine pusher arm

using the Qualysis analysis software (QTM 2.9). During live scrummaging, players were bound

together at the “set” call, which was an invitation for them to start pushing. Therefore, in the Live

scrummage, the sustained push phase was defined as the interval between 1 s and 2 s after the

“set” cue.

*** Figure 3 ***

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Statistics

Separate one-way repeated measure analysis of variance (ANOVA) (with scrummage conditions as

the within-group factor) and Bonferroni post-hoc analysis were applied (SPSS software, IBM Corp,

USA) to determine if there were any differences (p < 0.05) in muscle activation across scrummage

conditions during the sustained push phase (CBS vs CTS vs Live). A paired t-test was performed to

determine the differences in muscle activation in the pre-engagement phase (CBS vs CTS), and the

engagement phase (CBS vs CTS), as Live engagement included only the sustained push phase

(Figure 2). Further one way repeated measure ANOVAs (with scrum phases as the within-group

factor) were used to test possible changes in muscle activation across the different phases of the

scrum for the CTS and CBS machine trials, followed by Bonferroni post-hoc comparisons (p < 0.05).

Sphericity of the data was assessed using the Greenhouse-Geisser Epsilon, if the data was

aspherical a correction was applied to the calculated p value. Pairwise effect sizes calculated using

Cohen’s d statistic (d) (1998) were also considered (Appendix).

RESULTS

The time of contact (tENG) was highly repeatable across all participants (0.55 ± 0.08 s). Also, the

time of onset of movement had very low variability (0.04 s), and its average value was 0.03 s. This

provided the analysis with a consistent scrum phases duration (e.g. time interval between scrum

phases) across all the subjects.

Comparing Conditions

Left and right muscles in all the analysed muscle groups exhibited very similar level of activation

across the subsequent phases of scrummaging. Therefore, EMG data from left and right side were

pooled.

In the pre-engagement phase, all the measured muscles in both machine conditions were activated

in excess of 25% MVC (Figure 4). The activity of the sternocleidomastoid and upper trapezius was

significantly higher (p < 0.01) in the CBS condition than the CTS condition. The activity of the

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erector spinae was higher, although not significantly (p > 0.05) in the CTS condition during pre-

engagement than the CBS condition though a large effect size (d > 0.8) was observed.

During the engagement phase all the measured muscles were more active in the CBS than CTS

condition. The activity of the upper trapezius and sternocleidomastoid were significantly higher (p <

0.05 – paired t-test), showing an average increase of 20% ± 12% and 22% ± 20% respectively

(Figure 4) and large effect size (d > 1). The activity of the ES was also higher during the CBS

condition (effect size > 0.8), although not significantly.

During the sustained push phase the activity of the muscles across all three conditions (CBS, CTS

and Live) could be compared (Figure 5). The activity of the erector spinae was significantly higher

during the sustained push phase of live scrummaging than in either of the CBS or CTS conditions (p

< 0.01), with the erector spinae activity approximately 56% ± 26% lower (CBS vs Live) and 62% ±

18% lower (CTS vs Live) and large effect size (d > 0.8). The activity of the upper trapezius tended to

be lower in the CTS than the CBS and Live conditions (d > 1.1), whereas the activity of the

sternocleidomastoid was similar across conditions.

*** Figure 4 and 5 ***

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Comparing Across Phases 1

The activity of the sternocleidomastoid and erector spinae showed a decreasing trend 2

moving from pre-engagement through engagement to the sustained push in both the CBS 3

and CTS conditions (Figure 4). The activity of the sternocleidomastoid was significantly 4

higher during the pre-engagement and engagement phase than sustained push in CBS (p < 5

0.05), and in CTS pre-engagement tended to be higher than sustained push (p = 0.059) 6

showing a large effect size (d > 1.1). The activity of the erector spinae during both CBS and 7

CTS conditions was significantly higher during both the pre-engagement phase (p < 0.05) 8

and engagement phase (p < 0.05) when compared with the sustained push (Figure 4). There 9

was a significant pattern of decreasing activation from i) pre-engagement to engagement and 10

from ii) engagement to sustained push that was also reflected in large effect sizes (d > 1.7). 11

The activity of the upper trapezius in the CBS and CTS conditions peaked, but was not 12

significantly greater, during the engagement phase (Figure 4). No significant differences 13

were calculated, though large effect sizes (d > 1.2) were found for the upper trapezius 14

between the engagement phase and sustained push in both CBS and CTS conditions. Also 15

medium effect sizes (d > 0.5) were found for the upper trapezius between the pre-16

engagement phase and engagemnt in both CBS and CTS conditions 17

DISCUSSION 18

The aim of this study was to gain more insight into the activity of sternocleidomastoid, upper 19

trapezius and erector spinae muscles during machine (CBS and CTS) and live scrummaging. 20

Compared with the machine conditions, the live condition resulted in significantly higher 21

activation of erector spinae during the sustained push phase. In contrast with the initial 22

hypothesis, the activity of sternocleidomastoid, upper trapezius and erector spinae tended to 23

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be greater during the CBS condition than the CTS condition throughout the three phases of 24

the scrum. 25

Spinal muscle activity in both machine scrummaging conditions was characterised by a 26

considerable pre-activation of all 6 muscles (>25% MVC) prior to engagement. This pre-27

activation can functionally lead to an increase in cervical and lumbar spine stiffness 28

(Riemann & Lephart, 2002), which may better prepare the player’s spinal structures for the 29

high biomechanical loads placed upon the spine during engagement. A high level of muscle 30

pre-activation may potentially mitigate the effect of loads on spinal posture (Krajcarski et al., 31

1999; Choi, 2003) and help maintain optimal neutral spine position (Brooks & Kemp, 2011). 32

However, it must be observed that the stabilisation of the spine due to high-level of muscles 33

activation and agonist/antagonist co-contraction (Cheng et al., 2008) may not be enough to 34

limit cervical spine hyperflexion or buckling mechanisms (Dennison et al., 2012; Kuster et al., 35

2012) during high-dynamic impulsive impacts with misaligned geometry. In fact, in case of a 36

catastrophic injury the forces and moments acting on the cervical spine are presumably 37

much higher than the forces that can be generated by spinal muscle activation, and further 38

analyses are needed to elucidate the actual contribution that muscles activations can make 39

in certain high-risk loading conditions. 40

The activity of erector spinae has been measured in a similar machine scrummaging study 41

(Sharp et al., 2014), although the engagement condition was not clearly described and the 42

pre-engagement phase was defined as the 200 ms window prior to engagement, differing 43

from the current study. Sharp et al. (2014) reported a pre-activation of 65% of MVC in the 44

erector spinae, which is comparable with our findings of 68% and 75% erector spinae pre-45

activation in CBS and CTS conditions. Sharp et al. (2014) interpreted erector spinae pre-46

activation as necessary to maintain an efficient scrummaging position and to overcome 47

gravity forces causing a bending moment and a rotation of the trunk about the pelvis. Our 48

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results support this explanation, as the slight reduction in erector spinae activity in the CBS 49

condition when compared to the CTS condition, in the pre-engagement phase, can be 50

attributed to the pre-binding reducing the moment acting on the trunk joints due to torso 51

weight being partially supported. 52

The engagement phase of a scrum is characterised by a peak in both compression and 53

vertical force, approximately 0.1 s after first contact (Figure 3), followed by a lower plateau in 54

forces traces approximately 0.5 s after engagement (Preatoni et al., 2013; Cazzola et al., 55

2014; Preatoni et al., 2014). These changes in force generate the need for a high spinal 56

stiffness and therefore demand compensatory spinal muscle activation. (Cholewicki et al., 57

2000) identified that as the external load placed upon the spine increased, the stiffness of the 58

spine also increased, and most interestingly, this was caused by an increase in spinal 59

muscle activation. Therefore, we propose that the EMG signal of the participant’s spinal 60

musculature can take as an input parameter and respond to the time course of the external 61

load exerted on players’ shoulders. The spinal muscles are maximally activated in response 62

to the peak in external load and then decrease 0.5 s after engagement as the external load 63

reduces (Figure 3). This stabilisation in activation is observed in all six (e.g. left and right) 64

muscles during the sustained push phase irrespective of condition. 65

We have previously observed a reduction in external loading on players when scrums use 66

the CBS condition when compared with the CTS condition (Cazzola et al., 2014). If these 67

reductions in mechanical loading during the engagement were transferred to the modified 68

scrum condition used in the present study, it can be hypothesised that the spinal muscles 69

would be more active during CTS than CBS condition, as the spine is exposed to greater 70

mechanical stresses. However, the activity of the spinal muscles was comparable between 71

the conditions and the activity of the cervical spine muscles (sternocleidomastoid and upper 72

trapezius) was found, in the engagement phase, to be significantly greater in the CBS 73

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condition. These differences may be attributed to the differences in binding between the 74

conditions, as the upper trapezius is responsible for the maintenance of position of the 75

cervical spine and also the upper arm (Herrington & Horsley, 2009). In the CBS condition the 76

players establish a secure pre-bind prior to engagement, while in the CTS condition the 77

players have to bind during the engagement. Additionally, during the CBS conditions, players 78

set-up closer to the scrum machine (Preatoni et al., 2014), and this posture may effect spinal 79

muscle activation, where greater upper trapezius and sternocleidomastoid activation 80

increase cervical spine stiffness and may better maintain cervical spine posture during the 81

engagement. This indicates that a pre-bind procedure makes the upper spine more prepared 82

for the scrum engagement. 83

The activation of the erector spinae was significantly higher (p < 0.05) throughout the 84

sustained push phase of the live scrummaging condition than either of the machine 85

scrummaging conditions. Live scrummaging is an unstable dynamic condition when 86

compared with machine scrummaging, therefore the forces applied to the opposition players 87

are not equally matched in direction or magnitude, as they are during a scrum against the 88

machine. These eccentric forces theoretically generate moments at trunk level, causing 89

lumbar flexion, extension or rotation, and placing the participant in a compromised lumbar 90

spinal posture. Thus the participant needs to maintain optimal lumbar spinal posture via the 91

activation of the stabilising lumbar muscles (represented by the activation of the erector 92

spinae in this study). These findings demonstrate that although machine and live 93

scrummaging show comparable kinematic and kinetic characteristics, machine scrummaging 94

does not accurately replicate live scrummaging in terms of muscle activation strategies 95

required to maintain the sustained phase. Thus, it can be suggested that front row players 96

should be required to train in live situations and not only against scrum machines. These 97

findings suggest that although scrum machines are a useful training aid, a relative increase 98

in live scrummaging practise may be beneficial for all front row players from the perspective 99

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of training appropriate and specific neuromuscular activation patterns. This may be 100

particularly important under current rugby practice since the duration of the sustained phase 101

has markedly increased under the CBS engagement procedure. 102

In the current study each participant scrummaged individually in three conditions, this is a 103

constrained environment. The results observed in such modified conditions cannot be 104

extrapolated directly into a full scrummage scenario. During a complete scrummage eight 105

players interact and bind to one another generating the forces and movements of the 106

scrummage (Preatoni et al., 2014). Sharp et al. (2014) reported a peak compression force of 107

3.1 kN in single participant machine scrummaging, whereas this study recorded an average 108

maximum compression of about 2.8 kN. These magnitudes are about 25% less than the 109

ones found by Preatoni et al. (2014), who measured a peak compression force of 11.7 kN, a 110

vertical force of 1.5 kN and a lateral force 1.3 kN distributed across the three front row 111

players in a full scrummage of academy level. The reduction in compression forces and the 112

absence of extra-loading from multi-player interactions may result in a decrease in muscle 113

activation for 1-person scrummaging, suggesting that the results of the current study may 114

underestimate the spinal muscle activity observed throughout a full scrummage. Additionally, 115

front row and second row players have loads applied from front to back, which may cause 116

other types of loading patterns around the spine. 117

The current study was undertaken in an indoor lab with an individual scrummaging against a 118

machine or two other participants. The study was one of the first of its kind to measure 119

muscle activity in an impact event similar to match intensity, and is a fundamental first step 120

towards understanding the muscle activations in a full scrummage scenario. A limitation of 121

the current study was that muscle activity in the live condition was only measured during the 122

sustained push phase. Future research should build on the foundations of the current study, 123

with the objectives of improving its ecological validity through trials on natural turf and in a 124

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more complete scrummaging scenario (a full front row or a complete pack) either against a 125

scrum machine or in live conditions. The use of bilateral measurement of muscle activity is 126

advised, as a more complete scrummage is unlikely to match the symmetry of the current 127

binding conditions. 128

In conclusion, the activation of selected spinal muscles is greater in the CBS condition than 129

the CTS condition, particularly in the pre-engagement phase. This indicates that the muscles 130

of the cervical spine, in the CBS condition, are better prepared for the forces experienced 131

during the scrum engagement than in the CTS condition as cervical spine stiffness is greater. 132

Furthermore, this research provides evidence that the erector spinae is significantly more 133

active during live scrummaging than machine scrummaging. This reinforces the requirement 134

for individuals to practise and learn scrummage techniques in a live situation, rather than 135

purely against a machine, as machine scrummaging does not replicate the demands of a live 136

contest. 137

138

PERSPECTIVES 139

The findings of this study may have an impact in sports medicine, especially in the injury 140

prevention and injury biomechanics areas. Firstly, the evidence of spinal muscles pre-141

activation highlights the presence of a specific trunk stiffening strategy aiming to prepare the 142

body for the impact, and therefore its contribution needs to be considered during any real-143

world injury mechanisms analysis in contact sports. Also, the description of the activation 144

patterns of the trunk muscles may provide new insights for the optimisation of specific 145

training and rehabilitation programmes with a specific view to injury prevention. Finally, this 146

study can provide further evidence on which to inform discussions relating to the scrum laws 147

of rugby union when seeking to improve player welfare. In fact, the resulting information adds 148

the measure of spinal muscles activation to the analysis of the movements and forces 149

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involved during different scrum engagements (Preatoni et al., 2013; Cazzola et al., 2014; 150

Preatoni et al., 2014), providing a better understanding of the biomechanical load 151

experienced by rugby forwards. 152

153

ACKNOWLEDGMENTS 154

The authors would like to thank Dr Polly McGuigan, Dr Richie Gill, Dr Sabina Gheduzzi, Dr 155

Keith Stokes, and Dr Tony Miles for their involvement in the wider programme of reseach 156

and their comments on this manuscript. Also we would like to thank all rugby forward players 157

that took part to the study. 158

COMPETING INTERESTS 159

None of the authors has competing financial, professional or personal interests that might 160

have influenced the performance or presentation of the work described in this manuscript. 161

162

FUNDING 163

This project is funded by the Rugby Football Union (RFU) Injured Players Foundation. 164

165

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SPINAL MUSCLE EMG IN SIMULATED SCRUM

FIGURES

Figure 1. Electrode and marker set-up. Electrodes positions are highlighted with black circles. Sternocleidomastoid

(SCM) is shown on the left-hand side of the figure whilst upper trapezius (UT) and erector spinae (ES) on the right-hand

side.

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Figure 2. Images of ‘key instances’ in the CBS (left), CTS (central) and live (right) scrummaging conditions. A= crouch

position; B= ‘bind’ call; C= sustained push phase. Phases A and B are not reported during live scrummaging as muscle

activity was only measured during the sustained push due to the passive engagement.

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Figure 3. Exemplary compression force and normalised trapezius EMG signal from a CTS scrummaging trial. The three

phases (Pre-Engagement, Engagement, and Sustained Push) considered in the study are highlighted in the graph.

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Figure 4. Normalised values (% Maximal Voluntary Contraction) of muscles activation (mean and standard deviation) of

sternocleidomastoid (SCM), upper trapezius (TRAP) and erector spinae (ES) during CBS (Crouch-Bind-Set) and CTS

(Crouch-Touch-Set) engagements. Muscles activation during CBS and CTS engagements are shown throughout the three

scrum phases: pre-engagement, engagement and sustained push. Live engagement is not included because in that

condition EMG measures were carried out only during sustained push phase. The dashed and dotted lines show the

muscles activation trend in respectively CTS and CBS, and are representative of the differences (ANOVA) between i) pre-

engagement and sustained push and ii)engagement and sustained push. ‡ = significant difference between CBS and CTS

(p<0.05 – paired t-test); ¥=significant difference between both i) pre-engagement and sustained push, and ii) engagement

and sustained push in CBS (p<0.05 - ANOVA);§= significant difference between both i) pre-engagement and sustained

push, and ii) engagement and sustained push in CTS (p<0.05 - ANOVA).

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Figure 5. Normalised muscle activation (mean and standard deviation) of sternocleidomastoid (SCM), upper trapezius

(TRAP) and erector spinae (ES) during CBS, CTS and Live engagements throughout the sustained push phase. * =

significant difference between CBS and Live (p < 0.01 - ANOVA), † = significant difference between CTS and Live (p <

0.01 - ANOVA).

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TABLES

Table 1. Positions and resistances used to measure MVC for the sternocleidomastoid, upper trapezius and erector

spinae.

Condition Description

Sternocleidomastoid

(SCM)

Participant stands with trunk and hips flexed so that the trunk is parallel to the floor with

the neck in a neutral position with the forehead placed on the scrum machine pad. The

participant attempts to flex the neck against the fixed pad.

Upper trapezius

(UT)

Participant lies in a prone position with both arms abducted at the shoulder (~45°) and

externally rotated with the elbow flexed. The participant attempts to abduct the arms

against manual resistance applied to the elbow.

Erector spinae

(ES)

Participant lies in a prone position with the torso on the table and the legs projected

horizontally over the end of the table. The participant attempts to extend the lower trunk

and hip against manual resistance applied to the posterior thigh.

Table .2. Scrummage conditions.

Condition Description

CTS (2012-2013) A single participant engaged with a scrum machine following the engagement cues

'crouch-touch-set'. On 'Crouch' (t = 0 s) the participant moved into their normal crouch

posture. On 'Touch' (t = 1.7 s) the participant moved their right arm to touch the pad and

then withdrew the arm to assume the crouch posture. On 'Set' (t = 4 s) the participant

dynamically engaged with the scrum machine and then started a sustained push for

approximately 3 s.

CBS (2013-Present) A single participant engaged with a scrum machine following the engagement cues

'crouch-bind-set'. On 'Crouch' (t = 0 s) the participant moved into their normal crouch

posture. On ‘Bind’ (t°=°1.7°s) the participant moved their right and left arm to bind onto the

scrum machine pusher arms. On 'Set' (t = 4 s) the participant dynamically engaged with

the scrum machine and then started a sustained push for approximately 3 s.

Live A single participant scrummaged against two other participants when cued by the call 'Set'

(t°=°4°s). Prior to the cue the participant passively engaged with the two opposing

participants binding with both arms on to the opposing participants' backs. The two

opposing participants bound together, as would a loose head prop and a hooker in a

complete front row. The opposing participants were asked to place their unbound hand on

the ground to provide additional stability and to hold the test participant in a relatively

static position. On 'Set' the participant maximally pushed against the two opposing

participants for approximately 3 s.

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Appendix

Table I. Pairwise effect sizes calculated between CBS, CTS and Live conditions in pre-engagement

(Pre-Eng), engagement (Eng) and sustained push (Sus-Push) scrum phases.

Muscles

Condition Phase SCM TRAP ES

CBS Pre-Eng - Eng 0.38 0.51 1.70

Eng – Sus-Push 2.70 1.46 11.46

Pre-Eng – Sus-Push 1.54 0.01 4.89

CTS Pre-Eng - Eng 0.57 0.69 4.11

Eng – Sus-Push 2.50 1.38 9.78

Pre-Eng – Sus-Push 1.15 0.01 2.81

Note: Pairwise effect sizes were calculated using Cohen’s (d) values. |d|>0.8 large effects;

|d|>0.5moderate effects; |d|>0.2 small effects.

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Table I. Pairwise effect sizes calculated between CBS, CTS and Live conditions in pre-engagement (Pre-Eng),

engagement (Eng) and sustained push (Sus-Push) scrum phases.

Muscles

Phase Condition SCM TRAP ES

Pre-Eng CBS vs CTS 1.26 1.46 0.87

Eng CBS vs CTS 2.97 1.17 0.91

Sus Push CBS vs CTS 0.57 1.86 1.74

Sus Push CBS vs Live 0.26 0.88 0.88

Sus Push CTS vs Live 1.80 0.87 0.87

Note: Pairwise effect sizes were calculated using Cohen’s (d) values. |d|>0.8 large effects;

|d|>0.5moderate effects; |d|>0.2 small effects.

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