Download The role of core stability in sustaining high speed running hamstring

Revalidatiewetenschappen en Kinesitherapie
Academiejaar 2014-2015
The role of core stability in sustaining high speed
running hamstring injuries in male soccer players
Masterproef voorgelegd tot het behalen van de graad van
Master of Science in de Revalidatiewetenschappen en Kinesitherapie
Bonte Jelle
De Brabander Joachim
Promotor: Prof. Dr. D. Van Tiggelen
Copromotor: Schuermans Joke
Word of thanks
We would like to thank the people who helped directly or indirectly with the achievement of this
article. First of all, we want to thank the soccer players who participated in this study. They all had to
make several hours of their time free to come to the testing location and do at least 12 maximal
accelerations. We definitely want to express our gratitude to our copromotor, Joke Schuermans, to
give straight and immediately feedback. We could always contact her for questions and she always
stayed calm when something went wrong. She supported us during the long hours of analyzing data
in a way that motivated us to go on. I think we can both say for sure that every copromotor should
work like Joke Schuermans did with us. We also want to thank Tanneke Palmans for the technical
support. We experienced many technical problems during the process of this study, but Mme
Palmans came up with a solution. We knocked her door several times and sometimes at very busy
moments, but she always made some time free to help us with our not always so intelligent
questions. Furthermore a great thanks to our family for the warming support during the at times
stressful year of testing, analyzing and writing. We could for example always use a car when
necessary and enjoy the waffles they made during the testing period. I, Joachim De Brabander, would
also like to thank someone special. Lauren was always ready to listen and motivate me during the
hard work. She even made time for me when she was on an exchange program in Madagascar, to
keep me go on and finish this project. This support is not always so self-evident and that is why I
really appreciate the things she has done for me. Last but not least, we (Jelle Bonte and Joachim De
Brabander) would like to thank each other. We were good friends before these 2 years of thesis but
now we are even closer friends. We both went on Erasmus and had a difficult time during our first
weeks back in Ghent. But we helped each other through these difficult moments while we had to
work at our thesis. We were a complementary team by knowing each other’s strong and weak
points. We literally spent weeks together in the chamber of data processing. But we motivated each
other by playing music at the right moment or knowing when to have to stop playing music, by
buying lunch for each other, by shout out our frustrations together … I, Jelle Bonte, could not have
wished a better friend/colleague to bring this thesis to a good end.
Table of contents
Figures and tables list…………………………………………………………………………………………………………………………5
List of used abbreviations………………………………………………………………………………………………………………..…6
Abstract ................................................................................................................................................... 7
Introduction............................................................................................................................................. 9
Materials and Methods: ........................................................................................................................ 11
Participants........................................................................................................................................ 11
Testing procedure ............................................................................................................................. 11
Data analysis ...................................................................................................................................... 13
Statistical analysis.............................................................................................................................. 14
Results ................................................................................................................................................... 15
Anthropometrics and injury characteristics ...................................................................................... 15
EMG-Data .......................................................................................................................................... 15
3D-kinematic data ............................................................................................................................. 16
Discussion .............................................................................................................................................. 19
Conclusion ............................................................................................................................................. 22
References ............................................................................................................................................. 22
Abstract in lekentaal…………………………………………………………………………………………………………………………27
Appendix………………………………………………………………………………………………………………………………………….28
Figures and tables list
Figure 1: Electrodes of internal and external oblique muscles…………………………………………………………12
Figure 2: Electrodes of the lumbar erector spinae……………………………………………………………………………12
Figure 3: Participant ready for sprint trials with 44 passive sensors and elastic cohesive bandage….13
Figure 4: Pelvis-thorax dynamics………………………………………………………………………………………………………17
Figure 5: Anterior tilting in the thorax in the injury group compared to the control group………………17
Figure 6: Hip joint angle at heelstrike……………………………………………………………………………………………….18
Figure 7: Greater hip ROM towards extension in control group compared to injury group……………..18
Figure 8: Knee joint angle at heelstrike…………………………………………………………………………………………….19
Table 1: Anthropometrics of both groups…………………….……………………………………………………………….….15
Table 2: Significant difference of lumbar erector spinae activity in front swing phase……………………..16
Table 3: Correlations between hamstring - and core muscle activity………………………………………………..17
List of used abbreviations
ant
anterior
BF
Biceps Femoris
CSA
Cross sectional area
DTS
Direct Transmission System
ECG
ElectroCardioGram
EMG
ElectroMyoGram
GM
Gluteus Maximus
HSI
Hamstring Strain Injury
IBM
International Business Machines
IR
InfraRed
JB
Jelle Bonte
JDB
Joachim De Brabander
JS
Joke Schuermans
LES
Lumbar Erector Spinae
LLTmodel
Lower Limb Trunk-model
MRI
Magnetic Resonance Imaging
MTU
Motor Tensile Unite
MVC
Maximal Volonturay Contraction
post
posterior
ROM
Range of Motion
rs
spearman correlation
Sig.
significance
SM
SemiMambranosus muscle
SPSS
Statistical Package for the Social Sciences
ST
SemiTendinosus muscle
The role of core stability in sustaining high speed running
hamstring injuries in male soccer players
Abstract
Background Core stability and lumbo-pelvic control exercises have a considerable share in primary
and secondary prevention of hamstring injuries nowadays. Former research has suggested that
lumbo-pelvic muscle activity would have an important influence on the amount of hamstring stretch
and - loading. However, the exact role of the core and pelvic muscles in the occurrence and
sustaining hamstring strain injuries (HSI) in a population of soccer players has not clearly been
investigated yet.
Objectives To assess the quality and the quantity of lumbo-pelvic muscle functioning during a
maximal acceleration effort in male soccer players and to verify whether these muscle activation
patterns differ based on the presence or the absence of a hamstring injury history.
Study design Cross-sectional study
Methods 12 soccer players with a recent hamstring injury history (within 2 years) and 12 matched
controls performed several sprints, in which the maximal acceleration phase was used for analysis.
Lower limb and trunk 3D kinematics and EMG data from the lumbo-pelvic stabilizers and the
hamstring muscles were gathered within this phase. Prior to sprinting, MVC’s of each muscle were
measured. In the post hoc EMG and kinematic data analysis main focus oriented towards the results
in terminal swing phase, which appears to be the most susceptible phase for HSI in the running cycle.
Results The lumbar erector spinae muscle at both sides were significantly less active in the injured
group (96% of MVC) compared to the control group (192% of MVC)(p=0.030) during the front swing
phase of the involved leg. Injury history was able to predict over 20% (R2=0.203) of the variability
within the observed outcome on lumbar erector spinae muscle activity during front swing. (p=0.030).
At heel strike, the injury group demonstrated a significantly higher anterior thorax tilting (p=0.044)
and a tendency towards greater hip and knee flexion in comparison to the control group.
Conclusion The lumbar erector spinae could play a major role in the pathophysiology (and reoccurrence) of HSI due to its function to control the forward flexion of the trunk and to maintain an
adequate vertebral position. The part of other core stability muscles in the mechanism of HSI was not
cleared out. Lumbo-pelvic (and lower limb) running kinematics most probably determine the soccer
player’s hamstring injury risk, however large scale prospective studies are required to confirm (and
identify the exact nature of) this hypothesis.
Keywords: hamstring strain / core stability / sprint / football / EMG
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Achtergrond Core stability en lumbo-pelvische controle oefeningen hebben momenteel een
aanzienlijk aandeel in primaire en secundaire preventie van hamstringblessures. De literatuur
suggereert dat activiteit van de lumbo-pelvische spieren een belangrijke invloed zou hebben op rek
en belasting van de hamstrings. Maar de exacte rol van de stabiliserende romp –en bekkenspieren bij
het ontstaan en de recurrentie van een hamstringverrekking bij voetbalspelers is nog niet specifiek
onderzocht geweest.
Doelstellingen De kwaliteit en kwantiteit van lumbo-pelvische activiteit tijdens een maximale
versnelling onderzoeken bij voetbalspelers en hierbij verifiëren of de activeringspatronen van deze
spieren een belangrijk verschil vertonen bij aan- of afwezigheid van een eerder opgelopen
hamstringblessure.
Onderzoeksdesign Cross-sectionele studie
Methode 12 voetbalspelers die de voorbije 2 jaar een hamstringblessure opgelopen hebben en 12
spelers functionerend als controlegroep, hebben verscheidene sprints uitgevoerd, waarbij de fase
van maximale versnelling werd geanalyseerd. Zowel 3D kinematica van het onderste lidmaat en
romp als EMG gegevens van de lumbo-pelvische stabilisatoren en de hamstrings werden gemeten in
deze fase. Voor het sprinten, werden maximale willekeurige contracties (MWC’s) afgenomen. Bij
verwerking van de EMG en de kinematica gegevens lag de focus op de resultaten in de terminale
zwaaifase, die in de literatuur beschreven wordt als de meest provocatieve fase voor een
hamstringblessure.
Resultaten De lumbale erector spinae vertoonde beiderzijds significant minder activiteit in de
geblesseerde groep (96% van MWC) dan in de controlegroep (192% van MWC)(p=0.030) tijdens de
voorwaartse zwaaifase van het aangedane lidmaat. In deze fase kan een eerder opgelopen
hamstringblessure 20% (R2=0.203) van de variabiliteit in lumbale erector spinae activiteit voorspellen
(p=0.030). Bij hielcontact vertoonde de voorheen geblesseerde groep een significant hogere
voorwaartse verplaatsing van de romp en een tendens naar grotere heup - en knieflexie in
vergelijking met de controlegroep.
Conclusie De lumbale erector spinae zou op basis van deze resultaten een belangrijke rol toebedeeld
kunnen worden in het ontstaan en recurrentie van hamstringblessures als gevolg van zijn functie in
het controleren van voorwaartse rompflexie en in het behoud van een adequate positie van de
wervelkolom. Het aandeel van de andere stabiliserende bekken-en rompspieren in het mechanisme
van hamstringblessures kon aan de hand van deze studie niet verder verduidelijkt worden.
Waarschijnlijk bepaalt de lumbo-pelvische kinematica, net zoals de kinematica van het onderste
lidmaat, het risico op een hamstringblessure tijdens het sprinten bij voetbalspelers. Maar er is nood
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aan grootschalige prospectieve studies om deze hypothese te staven en het exacte mechanisme
ervan te achterhalen.
Introduction
Hamstring injuries are one of the most common injuries in sports that include running and sprinting
such as soccer. Ekstrand et al. (2015)6 found an injury incidence of 8.0 injuries per 1000 h of exposure
in soccer. 12% of these injuries were hamstring injuries. Hamstring strain injuries (HSI) are the single
most predominant sports injuries, that also have the highest tendency to reoccur. J. Ekstrand (2011)5
reported a recurrence rate of 16%. In an attempt to decrease this high (re)injury incidence,
researchers have been investigating the risk factors (loss of eccentric hamstring strength 14,19, reduced H:Q ratio 3,28, -asymmetrical power of the hamstrings 7,16, -reduced flexibility 10,27, -previous
hamstring injury 8,15,25, previous knee injury 25, Aboriginal race 25, motor control 3, fatigue 9,23 and age
8,10,15,25
) -and the underlying injury mechanisms. Soccer players tend to injure their posterior thigh
region the most during explosive running and kicking activities. In terms of this injury mechanism,
previous research has demonstrated that the hamstrings are most vulnerable for strain injuries in the
terminal swing phase of the running cycle. Previous research has already demonstrated that
predominantly the lateral hamstring, the long head of the biceps femoris (BF), seems to be subject of
strain or rupture, whereas the medial hamstrings, semitendinosus (ST) and semimembranosus (SM),
are less frequently injured.
Researchers took into account the influence of running kinematics and hamstring function during
sprinting, to explain why the hamstring are most susceptible for strain injuries during specifically the
terminal swing phase of the running cycle. The hamstrings reach their maximum length during the
terminal swing phase24, where they also demonstrate maximal activity4. The hamstrings also have to
work eccentrically during the front swing phase, with a rapid conversion to efficient concentric
contraction in the early stance phase, for adequate propulsion29. The eccentric work and the high
amounts of muscle stretch during the terminal swing phase, are two major factors that most
probably contribute to the susceptibility for strain injuries seen in the hamstrings.
The lateral Biceps BF (and in particularly the long head) is more susceptible to strain injuries than the
medial hamstring muscles. Former research has been trying to explain this location specific injury
occurrence by investigating the exact muscle mechanics and loading characteristics of the 3 biarticular hamstring bellies in sprinting.
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From these findings we conclude that the hamstring muscles are most susceptible to contractioninduced damage (cf. explosive running and kicking related muscle injuries) when they are activated
and lengthened simultaneously. An active MTU stretch of 5% can already be sufficient to cause
damage to the muscle2. The hamstring muscles show the largest stretch at the point where they have
to work eccentrically. This point corresponds with the terminal swing phase, as illustrated above.
Based on the exact nature of this (eccentric) effort-related injury mechanism, protecting the
hamstring muscle against strain injury would require providing the muscle complex with (1) maximal
explosive strength capacity and (2) sufficient stretching tolerance, whilst protecting the muscletendon unit against excessive stretch and strain loading throughout the running cycle. The amount of
tensile stretch/stress placed upon the muscle unit is dependent on several factors. There might be an
important influence of the lumbo-pelvic muscles in the stretch on the hamstring muscles4, next to
fatigue12,22 and increasing speed18. But the exact role of the core and pelvic muscles in the occurrence
and sustaining HSI in a population of soccer players has not clearly been investigated yet.
However, there are some findings that may indicate that a rehabilitation program including core
stability has better outcomes in terms of HSI re-injury 21 and that injuries of the lower extremity
could be predicted by taking into account the endurance capacity of the core muscles26 and the size
of the lumbar erector spinae (LES) muscle11.
The hamstring muscles are phasic mobilizing muscles with a primary dynamic function in locomotion.
(concentric effort during stance - and backswing phases, eccentric effort during front swing phase)
Due to their anatomy and topography however, the hamstring muscles can also contribute to pelvic
control and stability through isometric and bilateral activity. Because of their morphology, this
stabilizing function is only a side issue and certainly no key feature within their primary task. That is
why, to our opinion, a lack of core stability and lumbo-pelvic control during sprinting, could increase
the biomechanical demands placed on the hamstring muscles, which could result in overload.
We assume that the function of core stability might play a major role in the occurrence of HSI. Up
until now, prospective studies have only been focusing on analytical core muscles functioning,
without assessing the core muscle integrity during functional and dynamic sports activities. However,
more information about the function of the core muscles during sprinting is necessary to determine
the exact role of the core muscles in the occurrence of HSI in soccer. That is why the main objective
of this study is to assess the quality and the quantity of lumbo-pelvic muscle functioning during a
maximal acceleration effort in a population at risk (male soccer players) and to verify whether these
muscle activation patterns differ based on the presence or the absence of a hamstring injury history.
10
In this cross-sectional study, we will specifically focus on the activity of the lumbo-pelvic (“core
stability”) muscles and the 3D movement of the core and pelvis in the terminal swing phase of
sprinting (cf. injury mechanism). By comparing the exact electromyographic activation features of the
stabilizing muscles and the kinematic data of the core and pelvis regions between a group with a
history of HSI and a healthy matched control group, we hope to gain some understanding in the
exact role of “core stability” in the predominant hamstring injury mechanism.
Materials and Methods
Participants
From February to May 2014, 24 players from several Belgian soccer clubs were recruited via
physiotherapists, osteopaths and trainers. All recruited players met the inclusion criteria: male
players participating in Belgian soccer competition, aged between the limits of 18 and 35, member of
a soccer club, and for the injury group, reporting having sustained a significant hamstring injury
somewhere within the 2 last seasons, preventing the athlete to participate in training or match play
for at least one entire week. Participants were excluded if they reported an important knee or hip
injury in their medical history, which could have influenced their running pattern and biased our
results. Ultimately, all 24 soccer players were included, of which 12 players with a recent hamstring
injury history and 12 matched controls. All participants did not have any complaints or restriction to
play at the moment of testing. Written informed consent statements were obtained after
participants had read the volunteer information papers.
Testing procedure
The entire testing was performed during the first two weeks of July as well as the last week of August
2015 and took place in “Topsporthal Vlaanderen”(Ghent, Belgium). Prior to testing, each participant
was thoroughly informed about the content and the purpose of the testing procedure and was asked
to sign Informed Consent and to complete a questionnaire (injury history, foot dominance,
competition level, field position, possible current injuries …). After taking care of the administration,
the participants were instructed to perform a standardized 10 min warming up session, during which
they were instructed to run along the central running track at a comfortable pace, while sporadically
doing several explosive accelerations towards maximal sprinting velocity. Next, subject preparation
was commenced. We gathered 3D kinematics of the lower limb and trunk as well as EMG data from
11
the lumbo-pelvic stabilizers and the hamstring muscles. For the kinematic analysis, Qualisys
hardware devices (8 IR Oquus cameras and 44 passive markers) and homonymous software package
were attributed (Qualisys Motion Capture Systems, Qualysis AB, Gothenburg, Sweden). For the EMG
testing procedure, the wireless 16 channel Noraxon DTS (Direct Transmission System) was used
(Velamed GmbH, Köln, Germany).
When the participant finished his warming up session, the researchers began with the electrode
placement for the Maximal Voluntary Contraction capacity (MVC) procedure. After skin preparation
(shaving, scrubbing and cleaning), a total number of 32 Ag/AgCl pre-gelled electrodes were placed on
the muscles of the lower limb and trunk: internal and external obliques, LES, gluteus maximus (GM),
ST, SM and BF (figure 1 and 2). The SENIAM guidelines were used for standardized electrode
placement (Surface Electromyography for the Non-Invasive Assessment of Muscles). An elastic
cohesive bandage was attached around the participant’s trunk to stabilize the electrodes and the DTS
amplifiers. After electrodes and amplifiers were carefully put in place, MVC was determined for each
of the above mentioned muscles, which allowed us to normalize the activity signal evoked during
dynamic sprinting task during data analysis. Each MVC was held for 5 seconds. External resistance
was systematically provided by the same qualified assessor (JDB). Every muscle was tested three
times, with a little break of 15 seconds in between repetitions.
Figure 1: electrodes of internal
and external oblique muscles
Figure 2: electrodes of the
lumbal erector spinae
After completing the MVC assessment, the 44 passive sensors of the Qualisys system were placed on
the trunk and lower limb of the participant (figure 3 and appendix). For this kinematic testing
procedure and the post-hoc analysis, the LLT model was used. (Jos Van Renterghem, John Moores
University, Liverpool, UK). Before the sprint trials, one static trial and four ‘functional joint’ trials
were captured (functional hip- and knee-joint trials for the left and right legs). This static
measurement as well as the ‘functional joint’ measurements, which were needed to accurately
12
determine the rotational axis of the knee- and hip joints in each individual, are required for the
assembly of a virtual model, to which the kinematic data during full sprint could be scaled during
data analysis. After capturing the static and functional joint trials, 3D kinematic analysis and EMGrecording of the hamstring and lumbo-pelvic muscles were performed in between meter 15 and 20
of a 35 meter sprinting track, which is an optimal distance to reach maximal acceleration without
risking injuries. There were no kinetic measurements. The sprint trial had to be maximal and was only
accepted if a full stride was measured by the Optogait system (Microgate, Italy) which was necessary
for processing. Because no kinetic data were measured, the use of the Optogait system was essential
for stance- and swing phase differentiation. Finally, 6 clean left and right strides were captured
within the Qualisys, Noraxon DTS and Optogait software packages. The entire testing procedure was
performed by the same researchers (JS, JB, JDB) which minimized the risk of inter-tester bias. This
study was approved by the Ethics Committee of the Ghent University Hospital (number of approval:
EC/2013/118).
Figure 3: participant ready for
sprint trials with 44 passive sensors
and elastic cohesive bandage
Data analysis
The EMG data were processed using the MR3.6 software (Noraxon). The MVC-signals were corrected
for ECG interference, rectified and smoothed within a 20ms window. The EMG signals, captured
during the sprints, were corrected for ECG signal, high-pass filter at 20Hz, rectified and smoothed
within the same 20ms window. For each stride, we focused on the bilateral internal and external
oblique, the bilateral LES and the contralateral GM, ST and BF. For the left stride (left toe off to left
heelstrike) for example, we assessed the entire core as well as the GM and hamstring muscles of the
right leg.
13
The 3D data of the sprint trials and static trials were processed by using the Qualisys and Visual 3D
(C-Motion, Germantown, USA) software packages. All markers were identified and the sprint trials
were cropped to 1 stride within the Qualisys Track Manager interface. These trials were transferred
to C3D files for segment and joint angle calculation during swing and stance in Visual 3D (C-Motion).
We specifically focused on lower limb and trunk kinematics (with primary attention to pelvis
kinematics) in transversal, frontal and sagittal planes during terminal swing and initial stance phases
of the sprinting cycle.
Statistical analysis
When creating the general database of all kinematic and EMG data during sprinting, we replaced ‘left
and right side’ kinematics and muscle activation patterns with 3D and EMG characteristics of the
‘involved and non-involved body-sides’. In this way, we could combine all injured sides at once
without having to take into account if a right or left stride was recorded. Determination of which side
was involved or noninvolved in the control group, was randomly done by assessing the percentage of
dominant side injuries in the injury group (63%) and including the same amount of dominant
(respectively non-dominant legs) in the control group, for in-between-group comparison. First of all,
descriptive statistics were attributed to assess the distribution of the data (normality testing) and
getting a general overview of means and standard deviations of the anthropometric data and the
kinematic and EMG-related outcome variables.
For the EMG-data analysis, only the MVC corrected signals were used. Statistical analysis of the EMGdata was focused on the muscle activation patterns during specifically the front swing phase of the
involved side. To check for in-between-group differences in front-swing related muscle activity, the
independent students t-test or the Mann-Whitney U test was used. Afterwards, possible linear or
logistic associations between injury history and running related muscle activity was evaluated.
Possible correlations between the activity features of the hamstring muscles and those of the core
and pelvis muscles were also assessed, using the Spearman and Pearson correlation coefficients. The
same procedure was performed for the statistical analysis of the kinematic data. An independent
samples student t-test was used to examine possible in-between-group differences in joint angles
(knee, hip, pelvis and thorax) at the moment of touch down (primary ground contact) or in Joint
Range of Motion throughout the entire stride. Data analysis was done with the SPSS V.22 Statistical
Software package (IBM Corp. New York, USA), and the level of significance was set at α=0.05.
14
Results
Anthropometrics and injury characteristics
Anthropometrics of both groups can be found in table 1. There were no significant differences found
between the 2 groups .
CONTROL
INJURY
weight
77,4 +-6,1
74,5+-7,1
height
1,84+-0,1
1,81+-0,1
BMI
22,9+-1,4
22,8+-1,7
age
23,0+-3,9
25,0+-3,5
Table 1: Anthropometrics of both groups
(mean +- standard deviation)
EMG-Data
The LES at the side of the previously injured hamstring, was significant less active in the injured group
(96% of MVC) than in the control group (192% of MVC)(p=0.030) during the front swing phase of the
involved leg (Table 2). Nonparametric testing revealed that the LES at the noninvolved side is also
significantly less active during this frontswing phase (with the homonymous leg being in backswing
phase at that moment). There were no significant differences for the amount of abdominal muscle
activity, GM activity or hamstring muscle activity during this frontswing phase, nor did we find inbetween-group differences in muscle activity during stance- or backswing phases.
Regression analysis revealed that injury history was able to predict over 20% (R2=0.203) of the
variability within the observed outcome on LES activity during front swing. (p=0.030)
Contralateral LES activity (corresponding the non-injured side or non-involved side) was significantly
correlated with ST (p=0.033, rs= 0.673) and BF muscle activity in the injury group ( p=0.043,
rs=0.618), but not in the control group. Finally, GM activity in the involved side was significant
correlated with BF activity, but not with ST activity, in both groups. Other less important correlations
between hamstring- and core muscle activity can be found in table 3.
15
Levene's Test
for Equality of
Variances
t-test for Equality of Means
95% Confidence Interval
Sig.
F
MU_I_FS_
Equal
NONINVOLVED
variances
STRIDE_MVC
assumed
,292
Sig.
,596
t
2,361
df
(2-
Mean
Std. Error
tailed)
Difference
Difference
of the Difference
Lower
Upper
17
,030
,96001857
,40654111
,10229180 1,81774533
2,280 13,148
,040
,96001857
,42111744
,05129150 1,86874563
Equal
variances
not
assumed
Table 2: Significant difference of Lumbal erector spinae activity in front swing phase
(significant values are highlighted in blue).
control group:
independent
biceps femoris (front swing)
semitendinosus (front swing)
Injured group:
biceps femoris (front swing)
semitendinosus
Muscle
gluteus maximus
semitendinosus
Internal Oblique
injured side
biceps femoris
Correlation coefficient
0.881
0.810
0.905
p-value
0.004
0.015
0.002
0.810
0.015
iliocostales thoracicus
injured side
Lumbar erector
spinae noninjured
side
external oblique noninjured side
Internal oblique
injured side
gluteus maximus
Lumbar erector
spinae non-injured
side
external oblique noninjured side
interne oblique
injured side
-0.627
0.039
0.618
0.043
0.827
0.002
0.782
0.004
0.827
0.673
0.002
0.033
0.636
0.048
0.661
0.038
Table 3: correlations between hamstring - and core muscle activity
16
3D-kinematic data
The injury group presented significantly less pelvis-thorax dynamics in the sagittal plane throughout
the front swing in sprinting, with an average Range of Motion of 8.5° versus 11.3° in the control
group. (figure 4)(p=0.018) Furthermore, the amount of anterior tilting in the thorax (in reference to
the pelvis position) at the moment of heelstrike of the involved leg, was significantly greater in the
injury group compared to the control group (mean difference of 6.3°, p=0.044) (Figure 5).
Figure 4: Pelvis-thorax dynamics (red =injured group; grey = control group)
Figure 5: anterior tilting in the thorax in the injury group
compared to the control group (p=0.044)
17
These findings indicate a more rigid thorax-pelvis coordination pattern/interplay tilt pattern during
the front swing phase, resulting in a more pronounced flexion in the lumbo-pelvic joints at the
moment of heel strike in the formerly injury group, compared to the control group. In terms of the
hip and knee joint angles, the injury group presented the tendency towards greater flexion range of
motion in the hip joint (-48.35643577) than the control group (-43.54561406) at heel strike (Figure 6
and 7). At knee joint level, the control group presented a tendency towards larger extension joint
angle than the injury group at heel strike (Figure 8).
Figure 6: Hip joint angle at heelstrike
Figure 7: greater hip ROM towards extension in control group
compared to injury group. (red =injured group; grey = control group)
18
Figure 8: Knee joint angle at heelstrike
Discussion
As stated in the introduction it is commonly known that the pathophysiology of HSI exists of a high
eccentric hamstring muscle loading while being stretched simultaneously. In this study, several
interesting kinematic and EMG characteristics were found that could be associated with a history of
hamstring injuries and highlight the importance of adequate running kinematics and corresponding
muscle activity in hamstring injury risk reduction.
First of all, a significantly smaller pelvic forward-backward rotation ROM was found in the injury
group. Taking into account that the front swing phase in sprinting induces a backward rotation of the
pelvis because of the considerable amount of hip flexion in this phase, the establishment of
significantly more pronounced anterior rotation of the pelvis in the injury group during this phase,
indicates the existence of a maladaptive movement strategy, inducing even higher levels of muscle
tendon stretch on the already heavy loaded hamstring complex. Next to this increased anterior
rotation of the pelvis compared to the control group, the tendency towards a higher hip flexion ROM
during the terminal swing phase of sprinting in the injury group, might also induce elevated muscle
stretch and excessive loading on the already weakened hamstring unit, possibly increasing the risk of
re-injury. The kinematic findings in the injury group, possibly evoking greater stretch on the
19
hamstrings muscles could be explained by multiple causes. First, we also found that the LES muscles
are significantly less active in terminal swing phase of sprinting in the injury group, compared to the
control group. A lack of eccentric activity of the LES muscles could lead to the more forward flexed
trunk position during sprinting, also seen in the injury group. Secondly, the iliopsoas muscle could
play a major role in these altered running kinematics after hamstring injury. Chumanov et al (2007)4
showed that an excessively active iliopsoas muscle during the double float phase of running, can
significantly increase hamstring muscle-tendon stretch. This muscle induces hip flexion and a small
amount of knee extension of the opposite leg (myofascial chains), which both increases hamstring
stretch. This iliopsoas tightness or hyperactivity could also explain the greater hip flexion in the injury
group. However, not only an excessively active or tight Iliopsoas can cause increased hamstring
loading, also active weak or fatigued iliopsoas muscle can cause increased pelvic tilting and
decreased lumbo-pelvic control 22.
If we consider the LES as a stabilizing muscle of the spine, the function of the LES is not only
controlling the forward flexion of the trunk with an eccentric contraction, but also keeping the spine
in a correct and stable position while moving. We found that the LES is less active during the terminal
swing phase in the injury group. If we take into account that a hyperactive or tight iliopsoas muscle,
as mentioned in the study of Chumanov et al. (2007)4, acts on the spine during airborne phase, in
which the lumbo-pelvic complex is fairly unstable, it seems very plausible that the iliopsoas can cause
excessive forward tilted position of the pelvis as well as a more forward flexed position of the trunk,
as it has to compensate for LES deficiency.
We also found a tendency of greater knee flexion at heel strike in the injury group. This can be seen
as a compensation strategy for the greater anterior tilt of the pelvis and the tendency of greater hip
flexion at the moment of heel strike in the injury group. This strategy could be sufficient for the
medial hamstring muscles but the lateral hamstring muscles can still experience a stretch since the
BF has a smaller knee flexion moment arm compared to the medial hamstrings1. As a consequence of
this potential compensation strategy, the BF experiences an earlier stretch than the medial
hamstrings during sprinting. This would explain the results of Higashira et al.(2010)12, who found that
the lateral hamstring muscles are active earlier than the medial hamstrings and Schache et al.
(2013)18 who found that too early activation of the BF during forward swing would be one of the
mechanisms of lateral HSI. In this aspect, Schuermans et al.(2014)20 found that there is more
symmetrical activity between the lateral and medial hamstring muscles after injury, what indicates a
change in neuromuscular control between the hamstring bellies. This causes a less efficient
contraction, decrease in pH and an earlier fatigue. The authors mention that the ST would be less
20
resistant to a pH changes, which would oblige the BF to compensate for the lack of endurance of the
ST. The BF itself would be less resistant to stretch and high negative work during the terminal swing.
If the hamstring muscles have to compensate for a greater anterior pelvis tilting with simultaneously
altering knee kinematics, the eccentric load on the hamstrings increases and starts earlier
throughout the swing phase. This possibly causes excessive muscle loading and earlier onset of
fatigue, which might imply a greater risk of HSI. Besides, LES deficiency during sprinting not only
increases muscle stretch, but forces the hamstrings to collaborate in the maintenance of lumbopelvic stability in running, for which it is not morphologically nor metabolically suited. This could
possibly explain why the smaller pelvis range of motion is less in the injury group, as mentioned
above. In this way, the hamstrings could restrict pelvic ROM because in an attempt to adequately
stabilizing the lumbo-pelvic region, next to their phasic propulsion function around the hip and knee
joints. This could be another explanation of the compensation at knee level.
For all other core muscles, we could not find any significant differences in EMG activity for other core
muscles, based on injury history. Although, Chumanov and colleagues (2007)4 showed that the
internal oblique muscles have an important role in decreasing the stretch of the BF muscle, we could
not find any differences in activity of the obliques between both groups.
Limitations and recommendations for future research
There are a number of limitations that should be considered while interpreting the results of this
study. First of all, due to a small sample size, the power of this study may be too low to make some
generalized conclusions for all soccer players. Secondly, the consecutive sprints were performed with
only a short resting period in between. Increased fatigue could influence the sprinting mechanics and
mean EMG activity of the measured muscles. Morin et al (2012)13 only mention a decrease in
maximum strength, but no changes in running patterns/mechanics in high intensity sprint fatigue,
which places this possible limitation into perspective. On the other hand, soccer players also
experience fatigue during competition or training on the soccer field, so presence of fatigue might
make this sprinting analysis even more specific and sensitive to possible injury related adaptations.
Furthermore, taking in account the major role of the iliopsoas muscle in our discussion, the
significant results of this study could be better interpreted if we also disposed of the EMG activity of
the iliopsoas and the quadriceps muscle during the sprinting trials. Besides, to our opinion, the role
of the diaphragm in core stabilization and spinous alignment has to be investigated more thoroughly.
Next, determining muscle force from EMG data is not a straightforward process, particularly for
21
sprinting. It is influenced by muscle length, muscle fatigue, contraction type, contraction velocity and
the amount of contribution provided by synergistic muscles 17. In contrary to muscle functional MRI,
we could not measure solitary the pars profundus of the multifidus muscle due to crosstalk. This is
why we preferred to use the LES as term instead of multifidus lumbalis in this article. The effect of
crosstalk is minimalized by standardizing the placement of electrodes in both groups and by
comparing the results of both groups. Finally, there has to be the consideration if a straight, clean
sprinting trial is representative for a soccer related hamstring injury. Soccer players have to change
directions all the time and ball manipulation during sprinting could lead to substantially different
trunk mechanics than those investigated in this study.
Conclusion
From this discussion we can conclude that the LES possibly plays a major role in the pathophysiology
(and re-occurrence) of HSI due to its function to control the forward flexion of the trunk and to
maintain an adequate vertebral position. We found that the LES, is significantly less active during the
terminal swing phase of the running cycle in the formerly injured group. These results correspond
with Hides et al.(2011)11, who showed that smaller cross sectional area’s (CSA) of the multifidus
lumbalis muscle at L5 levels and a smaller CSA and disfunction of the multifidus lumbalis at L3 and L4
levels can predict injuries of the groin, hip or thigh. This could mean that multifidus lumbalis
inactivity and/or disfunction is directly correlated with HSI. This study revealed that injury history was
able to predict over 20% (R2=0.203) of the variability within the observed outcome on LES muscle
activity during front swing (p=0.030). The role of the other core stability muscles, such as internal and
external obliques, GM and diaphragm in the mechanism of HSI during sprinting was not cleared out.
Further research is necessary to identify the role of the stabilizing core muscles (both separately and
in functional cocontraction) in prevention of sprinting related hamstring injuries in soccer players.
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Abstract in lekentaal
Achtergrond Buikspieren, spieren rond het bekken en spieren ter hoogte van de lage rug worden
gezien als belangrijke stabilisatoren van romp, bekken en zelfs het onderste lidmaat. Hun functie is
daarom van kapitaal belang voor veilig dagdagelijks en sportief bewegen. Daarenboven zouden deze
spieren een invloed hebben op de hoeveelheid rek die de achterste dijspieren (hamstrings) te
verduren krijgen tijdens het sprinten. Hoe meer rek op de spier, hoe groter de kans op blessure.
Dergelijke hamstring blessure is de meest voorkomende sportblessure bij voetballers. De exacte rol
van deze stabiliserende spieren in het blessuremechanisme van de hamstrings is nog niet echt
aangetoond in de literatuur.
Doelstellingen De activiteit van de stabiliserende spieren onderzoeken bij voetballers tijdens het
uitvoeren van een maximale loopversnelling en hierbij nagaan of de activiteit van de stabiliserende
spieren verschillend is naargelang aan-of afwezigheid van een eerder opgelopen hamstringblessure .
Methode 12 voetbalspelers met een recent hamstring blessure verleden en 12 gezonde controles
(spelers met zelfde lichaamsbouw en actief op hetzelfde competitieniveau), voerden verscheidene
maximale versnellingen uit. Tijdens het sprinten hebben we enerzijds driedimensionale bewegingen
van de benen en de romp, en anderzijds de spieractiviteit van de hamstrings en de stabiliserende
spieren gemeten. Bij de verwerking van de resultaten lag de focus op driedimensionale informatie en
de spieractiviteit tijdens de voorste zwaaifase van de loopcyclus, aangezien de hamstrings in deze
fase de meeste rek moeten tolereren en hier zodoende ook het meest kwetsbaar zijn.
Resultaten Een van de belangrijkste diepe stabiliserende spieren die achteraan tegen de
wervelkolom ligt (lumbale erector spinae), wordt duidelijk minder geactiveerd bij de voorheen
geblesseerde personen dan bij de controlegroep bij de fase van het volledig naar voor gezwaaide
been. Wanneer het naar voor gezwaaide been grondcontact maakt met de hiel, dan vertoont de
voorheen geblesseerde groep een duidelijk hogere voorwaartse buiging van de romp (wat meer rek
op de hamstrings teweegbrengt) en wordt de heup en knie meer geplooid dan bij de controlegroep.
Conclusie Het feit dat bovenstaande diepe stabiliserende spier minder actief is als je al een
hamstringblessure hebt gehad, zou erop kunnen wijzen dat ze een belangrijke rol speelt in het
ontstaan en het opnieuw oplopen van een hamstringblessure. Door te weinig activiteit kan deze spier
de voorwaartse buiging van de romp niet voldoende controleren, waardoor de hamstring meer op
rek komt en dus meer risico loopt op blessure. Bovendien heeft deze spier door zijn diepe ligging
tegen de wervelkolom een zeer belangrijk aandeel in het behouden van een adequate positie van de
wervelkolom tijdens het sprinten. Het aandeel van de andere stabiliserende buik-, rug- en
bekkenspieren in het mechanisme van de hamstringblessures kon aan de hand van deze studie niet
verduidelijkt worden. Looptechniek en degelijke controle van lage rug en bekken tijdens sprinten, zijn
hoogst waarschijnlijk essentieel in het voorkomen van hamstringblessures binnen de voetbalsport.
Toekomstig, grootschalig onderzoek is noodzakelijk om deze hypothese te staven.
Sleutelwoorden: hamstring strain/ core stability/ sprint/ soccer/ EMG
Appendix
LLT-model
Trunk segment (4+2)
Marker name
C7
STERNUM
XIP_PROC
T8
ACROM_L
ACROM_R
Description
C7
Sternum
Xiphoid Process
T8
Acromion Left
Acromion Right
Lower body (30+8)
ASIS_L
PSIS_L
ILCREST_L
GTROC_L
ASIS_R
PSIS_R
ILCREST_R
GTROC_R
UL_PR_ANT_L
UL_PR_POST_L
UL_DI_ANT_L
UL_DI_POST_L
KNEE_MED_L
KNEE_LAT_L
LL_PR_ANT_L
LL_PR_POST_L
LL_DI_ANT_L
LL_DI_POST_L
MAL_MED_L
MAL_LAT_L
HEEL_L
MTH1_L
MTH5_L
UL_PR_ANT_R
UL_PR_POST_R
UL_DI_ANT_R
UL_DI_POST_R
KNEE_MED_R
KNEE_LAT_R
Anterior Sacral Iliac Crest Left
Posterior Sacral Iliac Crest Left
Iliac Crest Left
Greater Trochanter Left
Anterior Sacral Iliac Crest Right
Posterior Sacral Iliac Crest Right
Iliac Crest Right
Greater Trochanter Right
Upper Leg Proximal Anterior Left
Upper Leg Proximal Posterior Left
Upper Leg Distal Anterior Left
Upper Leg Distal Posterior Left
Knee Medial Epicondyle Left
Knee Lateral Epicondyle Left
Lower Leg Proximal Anterior Left
Lower Leg Proximal Posterior Left
Lower Leg Distal Anterior Left
Lower Leg Distal Posterior Left
Maleolus Medial Left
Maleolus Lateral Left
Heel Left
Metatarsal Head 1 Left
Metatarsal Head 5 Left
Upper Leg Proximal Anterior Right
Upper Leg Proximal Posterior Right
Upper Leg Distal Anterior Right
Upper Leg Distal Posterior Right
Knee Medial Epicondyle Right
Knee Lateral Epicondyle Right
LL_PR_ANT_R
LL_PR_POST_R
LL_DI_ANT_R
LL_DI_POST_R
MAL_MED_R
MAL_LAT_R
HEEL_R
MTH1_R
MTH5_R
Lower Leg Proximal Anterior Right
Lower Leg Proximal Posterior Right
Lower Leg Distal Anterior Right
Lower Leg Distal Posterior Right
Maleolus Medial Right
Maleolus Lateral Right
Heel Right
Metatarsal Head 1 Right
Metatarsal Head 5 Right
Bold markers were removed after the static trials.