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CHALLENGING THE GOLDEN
STANDARD IN HAMSTRING INJURY
PREDICTION COMPARING THE VALIDITY OF ISOKINETIC AND FUNCTIONAL
STRENGTH ASSESSMENTS IN RECOGNIZING AND PREDICTING
HAMSTRING INJURY IN MALE SOCCER PLAYERS
Word count: 5,160
Esmoreit Groosman, Cedric Hubrechsen, Loewis Kinget Student numbers: 01403238, 01402443, 01407934
Supervisors: dr. Joke Schuermans, Prof. dr. Erik Witvrouw
A dissertation submitted to Ghent University in partial fulfilment of the requirements for the degree of
Master of Science in Rehabilitation Sciences and Physiotherapy: Rehabilitation Sciences and
Physiotherapy with Musculoskeletal Afflictions
Academic year: 2018 – 2019
Expression of Gratitude
After five good years, we finish our Master in Rehabilitation Sciences and
Physiotherapy with this master's thesis. Writing it was a difficult but fascinating task.
This would not have been possible without the help and support of a number of people,
we would like to thank them.
First of all, we would like to thank our supervisor, prof. dr. Erik Witvrouw, for providing
us with a topic that we were very interested in. We also want to thank our supervisor,
dr. Joke Schuermans, for her time and patience, for her help and feedback, for her
kindness and enthusiasm on the subject.
A big thank you to all the participants who participated in the study, for their time and
energy that they put in coming to Gent and performing the tests. Research is not
possible without them.
We also want to thank our friends for the necessary distraction, relaxation and support.
We want to thank our parents for letting us study, grow and invariably believe in us from
our first day at university.
Table of Contents
Expression of Gratitude.......................................................................................................... 3
Table of Contents................................................................................................................... 4
List of Tables and Figures ...................................................................................................... 5
List of Abbreviations ............................................................................................................... 6
1. Abstract .......................................................................................................................... 7
1.1 Abstract (ENG) ........................................................................................................ 7
1.2 Abstract (NL) ........................................................................................................... 8
2. Introduction ................................................................................................................... 10
3. Methods ........................................................................................................................ 12
3.1 Design ................................................................................................................... 12
3.2 Participants ............................................................................................................ 12
3.3 Procedure .............................................................................................................. 13
3.4 Follow-up of hamstrings strain ............................................................................... 14
3.5 Statistical analysis ................................................................................................. 14
4. Results .......................................................................................................................... 16
4.1 Incidence of hamstring injury ................................................................................. 16
4.2 Comparing injured and non-injured players ............................................................ 16
4.3 Correlation between IKD and RDL ......................................................................... 20
5. Discussion .................................................................................................................... 21
5.1 Detecting previous hamstring strain injury .............................................................. 21
5.2 Predicting future hamstring strain injury ................................................................. 21
5.3 Correlation between RDL and IKD ......................................................................... 22
5.4 The value of IKD .................................................................................................... 22
5.5 The value of RDL ................................................................................................... 23
5.6 Limitations ............................................................................................................. 23
5.7 Conclusion and implications for future research ..................................................... 24
6. References ................................................................................................................... 25
7. Lekenabstract ............................................................................................................... 28
8. Bewijs indiening ethisch comité..................................................................................... 29
9. Appendix ....................................................................................................................... 32
9.1 Appendix 1 ............................................................................................................. 32
9.2 Appendix 2 ............................................................................................................. 35
List of Tables and Figures
Table 1: Division of the participants: mean values of each group’s properties ...................... 12
Table 2: Mean values of isokinetic parameter relative peak torque (in N.m/kg.100) at different
angular velocities ................................................................................................................. 17
Table 3: Mean values of the isokinetic parameter average relative peak torque (in
N.m/kg.100) at different angular velocities ........................................................................... 18
Table 4: Mean values of the isokinetic parameter average power (in Watt) at different angular
velocities .............................................................................................................................. 18
Table 5: Ratios at different angular velocities and RDL values for each goup ...................... 19
Table 6: Significant mean differences between the hamstring injury history group and the
retrospective control group................................................................................................... 19
Table 7: Significant correlation coefficients between isokinetic hamstring strength measures
at different angular velocities and RDL values ..................................................................... 20
List of Abbreviations
HSI: Hamstring strain injuries
IKD: Isokinetic dynamometry and Isokinetic dynamometer
RDL: Romanian deadlift
DCR: Dynamic control ratio
PT: Peak torque
AvrPt: Average peak torque
AvrPower: Average Power
BW: Bodyweigth
Con Q: Concentric quadriceps
Con H: Concentric hamstrings
PT/BW : Relative peak torque
7
1. Abstract
1.1 Abstract (ENG)
Background: Hamstring strain injuries (HSI) are the number one most common injury
in professional male football players. To prevent these injuries from (re)occurring, it is
important to determine if there is a valid assessment tool available to predict future HSI
in players (at risk). To what extent hamstring strength assessment can be used as a
valid tool for hamstring injury risk evaluation and which strength testing modalities are
the most valid ones, has been a subject of discussion throughout the years.
Study design: A mixed cross-sectional and prospective cohort study.
Objectives: The purpose of this study was to investigate whether isokinetic
dynamometry (IKD) and/or a more functional strength test can detect previous
hamstring injury and identify players at risk. Furthermore, the correlation between the
isokinetic parameters and the outcome of the functional strength test were explored.
Methods: A total of 49 male football players were tested in the inter-season period of
the 2018-2019 football season. Knee flexion and extension torques were gathered
bilaterally at angular velocities of 60 (°/s) and 240 (°/s) concentrically for both
quadriceps and hamstrings followed by a protocol at velocities of 30 (°/s) and 120 (°/s)
concentrically and eccentrically for the hamstring muscles on a isokinetic
dynamometer. A maximal effort Romanian Deadlift (RDL) protocol was used as
functional strength test in which the number of repetitions to exertion was used as a
functional estimate of hamstring strength and endurance. Different groups of injured
players were compared to a control group, and injured legs were compared to non-
injured legs of the same group.
Results: Looking at eccentric isokinetic parameters of the hamstring muscles, there
were no significant differences found between any of the injured groups and the control
group. Multiple concentric isokinetic parameters, such as peak torque (PT) and power
at different velocities for the quadriceps and hamstrings, were significantly higher in the
group of football players with a hamstring injury history than in the control group.
Looking at the RDL as a parameter for injury detection or injury risk, no significant
association was found with injury history nor injury occurrence during follow-up. More
8
so, RDL performance showed no meaningful correlation with any of the isokinetic
parameters.
Conclusion: IKD and RDL testing did not reveal hamstring strength deficits in players
who have sustained a hamstring injury in the past seasons or during the follow-up
period. Thereby, strength testing alone is not enough to detect a previous HSI, or to
predict if a player is at risk for future injuries.
Key words: Isokinetic dynamometry, hamstring strain injury, Romanian Deadlift,
football.
1.2 Abstract (NL)
Achtergrond: Hamstringblessures zijn de meest voorkomende blessure bij
professionele mannelijke voetballers. Om te voorkomen dat deze blessures zich
(opnieuw) voordoen, is het belangrijk om te bepalen of er een geldig
beoordelingsinstrument beschikbaar is om toekomstige hamstringblessures te
voorspellen in spelers (met een verhoogd risico). In hoeverre de beoordeling van de
hamstringsterkte kan gebruikt worden als een valide instrument voor de evaluatie van
het risico op een hamstring letsel en welke testmethoden het meest valide zijn, is in de
loop der jaren onderwerp van discussie geweest.
Onderzoeksdesign: Een gemengd cross-sectionaal en prospectieve cohortstudie.
Doelstellingen: Het doel van deze studie was om te onderzoeken of isokinetische
dynamometrie (IKD) en/of een meer functionele krachttest eerdere hamstringblessures
kan detecteren en risicospelers kan identificeren. Verder werd de correlatie tussen de
isokinetische parameters en de uitkomst van de functionele krachttest onderzocht.
Methode: In totaal werden 49 mannelijke voetballers getest in het tussenseizoen van
het voetbalseizoen 2018-2019. Knieflexie- en extensie draaimomenten werden
bilateraal verzameld bij hoeksnelheden van 60 (°/s) en 240 (°/s) en 240 (°/s)
concentrisch voor zowel quadriceps als hamstrings, gevolgd door een protocol bij
snelheden van 30 (°/s) en 120 (°/s) concentrisch en excentrisch voor de
hamstringspieren op een isokinetische dynamometer. Een Romanian Deadlift (RDL)
protocol fungeerde als functionele krachttest, waarbij het aantal herhalingen tot
uitputting werd gebruikt als functionele inschatting van de kracht en het
uithoudingsvermogen van de hamstrings. Verschillende groepen van geblesseerde
9
spelers werden vergeleken met een controlegroep, en gekwetste benen werden
vergeleken met niet-gekwetste benen van dezelfde groep.
Resultaten: Als we kijken naar de excentrische isokinetische parameters van de
hamstringspieren, zijn er geen significante verschillen gevonden tussen de
geblesseerde groepen en de controlegroep. Meerdere concentrische isokinetische
parameters, zoals piek draaimoment en vermogen bij verschillende snelheden voor de
quadriceps en hamstrings, waren significant hoger bij de groep voetballers met een
geschiedenis van hamstringblessures dan bij de controlegroep. Kijkend naar de RDL
als een parameter voor letseldetectie of letselrisico, werd er geen significant verband
gevonden met een eventuele geschiedenis van een letsel of het optreden van letsel
tijdens de follow-up. Sterker nog, de RDL-prestaties toonden geen betekenisvolle
correlatie met een van de isokinetische parameters.
Conclusie: IKD- en RDL-testen hebben geen tekort aan kracht in de hamstrings aan
het licht gebracht bij spelers die een hamstringblessure hebben opgelopen, in de
afgelopen seizoenen of tijdens de opvolgingsperiode. Het testen van de sterkte alleen
is dus niet voldoende om een eerder hamstringletsel te herkennen of om te voorspellen
of een speler in de toekomst risico loopt op een blessure.
Trefwoorden: Isokinetische dynamometrie, hamstringblessure, Romanian Deadlift,
voetbal
10
2. Introduction
Football is a popular sport, played by a substantial portion of men and women
worldwide, regardless of age and level. Besides the obvious health benefits related to
sports participation, it is also associated with a decent injury risk.1 Hamstring strain
injuries (HSI) are the number one most common injury professional male football
players cope with.2 Not only has HSI a high incidence rate, but it also is associated with
significant recurrence rates.3 Therefore a valid assessment tool to prevent injuries and
detect players at risk is necessary, if this is possible taking into account the
multifactorial origin of hamstring injuries.4
The biceps femoris is the most commonly (53%) strained muscle of the hamstring
complex.3 The hamstring muscles must control the torque towards knee extension and
hip flexion eccentrically during running activities. Due to the maximized load on the
hamstrings in the elongated position, most of the strains occur during the late swing
phase in running.5
In the current literature many predisposal risk factors have been appointed. Age,
previous injury, ethnicity, strength imbalances, insufficient flexibility, fatigue,
inadequate warm-up, are all factors that have been proposed relating to HSI risk.6,7 Lee
et al. have proved that the following three factors were linked to increased risk of acute
hamstring strains: significant lower isokinetic hamstring strength, a Hecc/Qcon ratio
lower than 0.55 and a previous injury.8 The Dynamic Control Ratio (DCR), also known
as a functional or mixed ratio (Hecc/Qcon), is suggested to identify strength imbalances
by Wright et al.9
In this regard it is of essential importance to measure the eccentric strength accurately.
A now commonly used way to measure eccentric strength is by using an isokinetic
dynamometer (IKD), but this strength might not compare to the strength needed for
running and might therefore not give valid information for injury prediction. When we
measure strength on the IKD, we ask the person to hold a position against a greater
force. This is not the same movement as the late swing phase in running.16 Therefore
the IKD, which is considered the golden standard for strength measurement, can be
called into question.
The inconsistencies about HSI predictors found in the previous part of this dissertation
suggest that IKD might not be the best assessment tool for predicting HSI. The present
literature uses many assessment tools but none of them seem to be completely valid.
This might imply a ‘missing link’ in HSI risk identification, which hampers the predictive
11
value of the baseline screening protocols used to evaluate the athlete’s future injury
susceptibility nowadays. As multiple researchers have questioned the methodological
quality of eccentric strength testing using IKD, this missing link could potentially consist
of valid eccentric hamstring strength objectivation and as such, an actual reliable
measure of hamstring muscle function. Maximal eccentric hamstring strength potential
is generally evaluated using IKD, but it is unknown whether this muscle activation
actually accords to the same neuromuscular activation patterns needed during high
speed running activities (during which hamstring injuries mostly occur). More so, the
majority of hamstring strength testing is executed in a seated position, which is a non-
functional position and does not allow functional hamstring muscle activation as is the
case in high speed running.
In this study we want to investigate the value of isokinetic strength measurements in
HSI risk identification, by comparing eccentric hamstring performance investigated by
means of isokinetic strength assessment with eccentric hamstring performance during
an RDL task. The latter is a functional movement similar to the movement happening
on the field. Besides there is a maximized hamstrings activity relative to other functional
exercises.10 The authors wish to investigate to what extent isokinetic eccentric strength
correlates with functional eccentric performance objectified by a standardized RDL test
and to verify whether these measurements can predict if an athlete is at risk of future
injury. In other words, can we predict and detect injuries by only looking at a single
strength measurement? And if yes, is the functional strength measurement an
appropriate assessment tool?
We hypothesize that the functional strength measurement will present the best
association with hamstring injury history and occurrence, whereas isokinetic eccentric
results will be less sensitive for hamstring injury risk prediction. In addition we also
expect to find no correlation between the RDL and IKD values.
12
3. Methods
3.1 Design
A retrospective cross-sectional and prospective cohort study design was used in this
study.
3.2 Participants
As it is hard to convince a complete football team to participate in a study like this one,
the authors recruited individual football players by advertising on social media and by
word-of-mouth communication in the authors’ social circles. Ultimately, forty-nine male
football players competing at recreational level were willing to participate. They were
divided into different groups, based on the presence of HSI and the time of the injury.
Table 1: Division of the participants: mean values of each group’s properties
HSI last season
(SD)
HSI history
(SD)
HSI during
follow-up (SD)
Control group
(retrospective)
(SD)
Control group
(prospective)
(SD)
n 7 15 6 19 15
Age in years 24.0 (5.6) 22.3 (2.0) 21.2 (1.9) 21.3 (2.1) 21.4 (2.0)
Height in cm 181.0 (7.3) 180.0 (7.7) 179.7 (5.0) 179.5 (6.2) 179.5 (5.8)
Weight in kg 74.9 (5.5) 74.2 (7.2) 74.8 (9.0) 71.0 (8.4) 71.1 (8.1)
BMI in kg/m² 22.9 (2.5) 22.9 (1.8) 23.1 (2.4) 22.0 (1.8) 22.0 (1.7)
Experience in
years
16.6 (7.3) 14.7 (3.9) 15.0 (1.7) 14.4 (3.7) 15.1 (2.2)
Weekly sport
time in hours
5.1 (0.99) 5.2 (0.88) 5.6 (0.58) 5.4 (1.1) 5.2 (0.96)
Thirty-eight subjects (78%) reported that they were right-leg dominant with respect to
kicking and eleven (22%) were left-leg dominant. Participants completed an injury
history questionnaire (Appendix 1) regarding their general injury history and HSI in the
past. Footballers were eligible if they were over 18 years of age and competing on a
recreational level within the Belgian Football competition series. Participants were
excluded if they reported suffering from any injury or physical complaint at the time of
testing, preventing them to perform maximally during training and game play.
13
3.3 Procedure
All players were tested during the interseason period of the 2017-2018 and the 2018-
2019 football season (June, July and August 2018). The subjects were asked not to
train vigorously or participate in gameplay 48 hours prior to testing, to avoid fatigue
related bias. All participants were evaluated under the same conditions in a research
laboratory at the Ghent University Hospital (UZ Gent, Ghent, Belgium) and were
informed about the purpose of the study. They read and signed an informed consent
prior to testing. The study was approved by the Medical Ethics Committee of the
University of Ghent. Each participant underwent a standardized testing procedure,
consisting of a 10-minute warm up on a stationary bike, followed by a maximal
isokinetic strength evaluation and a standardized functional RDL testing procedure.
Isokinetic data collection was performed using a Biodex Isokinetic dynamometer
(BIODEX System 4, Biodex medical systems, NY, US). The subjects were positioned
sitting upright and secured using torso, thigh and shin stabilization straps. The axis of
rotation of the IKD was aligned with the axis of rotation of the subject’s knee. The shin
stabilization strap at the end of the lever arm was positioned 2 cm proximal to the lateral
malleolus. Subjects were asked to place their hands on the handles at either side of
the dynamometer. Concentric and eccentric knee flexion and extension torques were
systematically recorded within a standardized knee range of motion going from +/- 0°
up until 100° of knee flexion. Extension and flexion torques were gathered bilaterally,
the dominant leg being evaluated first. A comprehensive isokinetic testing protocol was
used, consisting of both concentric and eccentric measurements at different angular
velocities. Unilateral maximal voluntary torque for the hamstrings and quadriceps were
measured in the following order; 60 degrees/second (°/s) concentrically, 240°/s
concentrically for both quadriceps and hamstrings. This was followed by a protocol only
for the hamstrings at 30°/s and 120°/s concentrically and eccentrically. Between the
different velocities, subjects had 45 seconds rest. During the test a standardized
protocol with verbal instructions was used. An adequate familiarization with the IKD
was given by a few submaximal test repetitions at each velocity. In case of pain the
subjects could always terminate the test by pushing the release button.
After the isokinetic testing, a short cooling down of 5 minutes on the stationary bicycle
was foreseen, in order to allow the legs to recover dynamically before submitting the
participants to subsequent RDL testing. The reason why they had to perform a RDL is
because of the maximized hamstring activity in the RDL relative to leg curl and the
good morning exercise.10 It also corresponds with the movement happening on the
field. The RDL testing protocol was initiated with a standardized explanation on how to
14
perform an RDL, providing the athletes with both verbal and visual instructions. They
were instructed to lower the bar just underneath the patella with extended arms, which
accords with circa 80° of hip flexion, keeping both knees flexed approximately 20°
throughout the entire RDL procedure. They were asked to do this while maintaining a
neutral position of the spine. Participants were instructed to perform these deadlifts at
a standardized pace, using the guidance of a metronome. Each deadlift needed to be
performed within a 3-second time window, in which the eccentric downward phase had
to be covered within the first 2 seconds, whereas the concentric upward phase needed
to be performed in only 1 second. In this way, angular velocity was estimated to be
approximately 40°/s for the eccentric phase, and 80°/s for the concentric phase, which
is in line with the isokinetic testing speed (resp. 30°/s eccentrically and 60°/s
concentrically). RDL testing performance was objectified by counting how many times
the deadlift was executed correctly (constant speed, no compensations).
For the data analysis, the value corresponding to the following calculation was used:
Value = number of correctly executed repetitions, multiplied by the weight lifted (olympic
barbell + weights), divided by body weight.
3.4 Follow-up of hamstrings strain
After strength testing, participants were monitored prospectively on injury occurrence
throughout the first part of the 2018-2019 football season (from September until
December 2018). This was done by sending out questionnaires (Appendix 2) on a
weekly basis, via which they were asked to report whether they were experiencing any
pain or discomfort in the lower limbs as a result of football exposure (training or
gameplay). In case of a major injury concerning the hamstrings more information was
asked. They were asked to report how long the injury lasted, how long they were absent
from the game and training and how the injury was treated.
3.5 Statistical analysis
Parameters obtained by isokinetic testing were Peak Torque (PT), average Peak
Torque (avrPT) and average Power (avrPower). For the hamstring muscles these
parameters were measured both concentrically at 30°/s, 60°/s, 120°/s and 240°/s, and
eccentrically at 30°/s and 120°/s. Quadriceps muscles were only measured
concentrically at 60°/s and 240°/s. The bodyweight (BW) reported in the questionnaire
was used to calculate relative PT and avrPT (PT/BW and avrPT/BW). Ratios (H:Q and
DCR) were calculated with the measured parameters.
15
Participants were divided into groups depending on the type and time of injury. The first
group consisted of players who had sustained a hamstring injury in the season just
before testing (2017-2018) but were recovered and fit to play at the time of testing. A
second group was made up out of players with a history of hamstring injuries, before
the season of 2017-2018. If players had a history of hamstring injuries and injured
themselves again in the previous season, they were put in the first group. This choice
was made because a more recent injury was assumed to have more impact on the
strength testing than an older one. Players who got injured on their hamstring muscles
during our follow-up period (from September to December 2018) where classified in a
third group.
Because we had to start analysing the results before the end of the follow-up period,
there are two control groups. The first control group consists out of all the players who
did not sustain an injury that could influence the hamstring function. These injuries
include a direct hamstring injury, injuries at the knee or hip joint, or low-back pain. This
first control group was used to analyse the data of the players injured in previous
seasons. After the follow-up period a second control group was created. This was
necessary because some players of the first control group injured themselves during
the follow-up period. Their injuries included hamstring related injuries, but also other
injuries that caused an absence longer than one month. A player might be susceptible
for a hamstring injury, but not get injured because of little exposure time.
The Independent-Samples T Test was used to compare the means of the injured legs
of the injured groups and the control groups. The Paired-Samples T Test was used to
compare injured and non-injured legs in the different injured groups and dominant and
non-dominant leg in the control groups. Correlation between the RDL values and the
isokinetic parameters for the concentric and eccentric hamstring strength was
investigated using the Pearson test.
16
4. Results
4.1 Incidence of hamstring injury
Seven of the forty-nine players (17.5%) had recently, being last season prior to testing,
injured their hamstring muscle. One of those seven players injured his dominant leg,
while three injured their non-dominant leg. Another three players sustained an HSI on
both of their legs. When asked if they had injured their hamstring muscles before, three
players answered yes. The injuries occurred at the same leg.
Looking at history of HSI, i.e. injuries that occurred more than one season ago, fifteen
players (31.6%) indicated to have injured their hamstring muscles in the past. Nine of
those injuries occurred at the dominant leg, three at the non-dominant leg, and another
three at both legs.
During the follow-up period six players (12.5%) sustained an HSI. Four injuries were
on the dominant leg, two on the non-dominant leg. Two of the players who got injured
during the follow-up period had already sustained an HSI in the past. One player
sustained it during the previous season, the other one the season before that.
Combining these figures shows that 46.9% of the study population has suffered from a
hamstring injury at least once in their career.
4.2 Comparing injured and non-injured players
Mean values obtained by IKD are shown in tables 2, 3 and 4. Table 5 shows the
calculated ratios and RDL values for the different groups. All groups of injured players
were compared to a control group. Players with a recent hamstring injury and players
with a history of hamstring injury were compared to a control group who had never
suffered from an HSI. This control group is named ‘control group (retrospective)’
because it is used to detect a previous injury.
The isokinetic parameters of players with a recent HSI, sustained during the 2017-2018
season, showed no significant difference (p>0.05) to this control group. Furthermore,
neither the functional test, nor the RDL, nor any of the ratios show a significant
difference (p>0.05) when these groups are compared.
However, differences are found when the group of players with a history of hamstring
injuries is compared with that same control group. Concentric quadriceps (con Q) and
17
hamstring (con H) relative peak torque (PT/BW), measured at 60°/s, is significantly
higher in the injured group (p=0.003 and p=0.043, respectively).
For the same angular velocity, the average PT/BW is also higher in the injured group
when quadriceps (p=0.027) and hamstrings (p=0.016) are measured concentrically. At
the same angular velocity of 60°/s, the concentric avrPower of the quadriceps and
hamstring muscles of the hamstring injury history group is significantly higher (Q:
p=0.033, H: p=0.008) than the values measured in the retrospective control group.
AvrPT/BW of the hamstring muscles concentrically measured at 240°/s is also higher
in the injured group (p=0.021). Moreover, the avrPower of Q and H measured at this
speed shows higher values for the players with a history of hamstring injury (p=0.018,
p=0.001). Comparing the hamstring injury history group with the retrospective control
group gives no significant differences in RDL values or any of the ratios (p>0.05).
At last, a group containing the players that got a hamstring injury during the follow-up
period was compared to a control group with players who never have had an HSI
(control prospective). This comparison showed no differences in isokinetic parameters
for Q or H, concentric or eccentric, at any measured angular velocity (p>0.05). Ratios
and RDL values are not significantly different either between both groups (p>0.05).
Overall, none of the eccentric isokinetic hamstring parameters were significantly
different between any of the injured groups and control groups. The same goes for the
ratios and RDL values (p>0.05).
Table 2: Mean values of isokinetic parameter relative peak torque (in N.m/kg.100) at different angular velocities
Hamstring
injury last
season (SD)
Hamstring
injury history
(SD)
Hamstring
injury during
follow-up (SD)
Control group
(retrospective)
(SD)
Control group
(prospective) (SD)
Q con 60
H con 60
248.7 (62.9)
121.8 (31.2)
296.7 (26.6)*
150.5 (24.6)*
265.2 (42.9)
130.1 (39.6)
259.7 (37.6)
131.3 (27.5)
263.7 (39.1)
139.5 (27.7)
Q con 240
H con 240
148.9 (31.0)
93.8 (30.5)
165.0 (16.8)
104.8 (14.0)
155.8 (28.2)
88.1 (27.9)
158.2 (23.4)
95.0 (18.7)
154.6 (22.5)
98.3 (17.3)
H con 30
H ecc 30
172.4 (47.2)
193.4 (50.0)
191.1 (47.9)
223.0 (50.0)
202.6 (38.3)
226.7 (51.7)
190.9 (63.2)
221.8 (53.4)
191.1 (56.6)
224.9 (51.0)
H con 120
H ecc 120
199.7 (62.8)
202.3 (63.7)
207.2 (47.0)
226.0 (44.3)
194.4 (50.9)
211.7 (48.5)
199.3 (49.3)
214.6 (50.7)
202.5 (42.3)
216.0 (45.3)
18
Q: quadriceps muscle, H: hamstring muscle, con: concentric, ecc: eccentric, SD: standard
deviation
Significant values are indicated with *.
Table 3: Mean values of the isokinetic parameter average relative peak torque (in N.m/kg.100) at different angular velocities
Hamstring injury
last season (SD)
Hamstring injury
history (SD)
Hamstring injury
during follow-up
(SD)
Control group
(retrospective)
(SD)
Control group
(prospective)
(SD)
Q con 60
H con 60
215.3 (52.4)
109.4 (28.0)
267.5 (34.1)*
141.3 (23.7)*
228.2 (44.3)
110.5 (26.3)
235.1 (44.9)
120.3 (24.3)
238.9 (44.4)
128.2 (24.7)
Q con 240
H con 240
138.6 (36.1)
84.3 (28.3)
150.2 (14.1)
95.7 (12.2)*
137.2 (26.8)
77.2 (27.4)
139.0 (18.3)
83.8 (15.8)
135.4 (18.2)
86.9 (14.9)
H con 30
H ecc 30
153.3 (44.7)
167.7 (49.4)
173.2 (46.9)
199.1 (52.8)
176.0 (43.3)
193.6 (64.8)
164.9 (63.2)
190.8 (41.0)
164.5 (54.3)
197.7 (49.7)
H con 120
H ecc 120
176.1 (60.8)
163.8 (57.9)
178.0 (41.4)
198.3 (46.2)
178.9 (54.7)
186.8 (59.4)
166.8 (46.6)
180.5 (47.3)
169.2 (41.2)
182.7 (43.2)
Q: quadriceps muscle, H: hamstring muscle, con: concentric, ecc: eccentric, SD: standard
deviation
Significant values are indicated with *.
Table 4: Mean values of the isokinetic parameter average power (in Watt) at different angular velocities
Hamstring injury
last season (SD)
Hamstring injury
history (SD)
Hamstring injury
during follow-up
(SD)
Control group
(retrospective)
(SD)
Control group
(prospective)
(SD)
Q con 60
H con 60
110.1 (28.6)
63.7 (22.2)
138.4 (23.0)*
84.7 (19.0)*
125.5 (21.0)
66.3 (22.0)
118.1 (28.6)
67.4 (16.8)
121.2 (30.6)
73.8 (19.2)
Q con 240
H con 240
254.1 (77.8)
134.7 (52.1)
275.7 (30.8)*
167.6 (28.2)*
250.8 (72.4)
135.2 (66.1)
241.3 (45.8)
130.9 (28.8)
135.4 (18.2)
140.0 (34.4)
H con 30
H ecc 30
31.3 (10.4)
47.4 (13.4)
37.2 (11.8)
57.5 (15.5)
34.7 (11.6)
59.5 (21.3)
29.4 (11.8)
50.8 (13.3)
30.7 (12.7)
54.0 (16.1)
H con 120
H ecc 120
74.3 (34.7)
151.1 (62.2)
81.2 (24.8)
191.9 (56.0)
79.5 (32.0)
175.9 (61.3)
70.3 (24.2)
163.3 (49.7)
71.7 (26.0)
171.3 (54.5)
Q: quadriceps muscle, H: hamstring muscle, con: concentric, ecc: eccentric, SD: standard
deviation
Significant values are indicated with *.
19
Table 5: Ratios at different angular velocities and RDL values for each goup
Hamstring
injury last
season (SD)
Hamstring
injury history
(SD)
Hamstring
injury during
follow-up (SD)
Control group
(retrospective)
(SD)
Control group
(prospective)
(SD)
H:Q 60
H:Q 240
0.50 (0.098)
0.63 (0.15)
0.51 (0.070)
0.64 (0.10)
0.49 (0.13)
0.56 (0.15)
0.51 (0.078)
0.61 (0.12)
0.53 (0.070)
0.64 (0.12)
DCR 30/60
DCR 30/240
DCR 120/60
DCR 120/240
0.78 (0.098)
1.31 (0.28)
0.81 (0.15)
1.36 (0.37)
0.75 (0.13)
1.36 (0.31)
0.76 (0.12)
1.38 (0.29)
0.86 (0.20)
1.47 (0.32)
0.81 (0.19)
1.36 (0.23
0.86 (0.18)
1.41 (0.31)
0.83 (0.17)
1.37 (0.30)
0.86 (0.19)
1.47 (0.34)
0.82 (0.16)
1.42 (0.32)
RDL 20.6 (5.28) 17.4 (8.80) 22.1 (11.2) 17.4 (9.52) 16.2 (7.21)
H:Q stands for the conventional concentric hamstring:concentric quadriceps ratio
DCR: Dynamic Control Ratio, eccentric hamstring:concentric quadriceps
RDL: Romanian Deadlift
Significant values are indicated with *.
Table 6: Significant mean differences between the hamstring injury history group and the retrospective
control group
mean difference (SD) significance = p
PT/BW Q con 60 H con 60
36.94 (11.48) 19.12 (9.08)
0.003 0.043
avrPT/BW Q con 60 H con 60 H con 240
32.42 (13.99) 21.04 (8.31) 11.96 (4.95)
0.027 0.016 0.021
avrPower Q con 60 H con 60 Q con 240 H con 240
20.24 (9.08) 17.32 (6.15) 34.49 (13.81) 36.77 (9.86)
0.033 0.008 0.018 0.001
Q: quadriceps, H: hamstring, con: concentric, PT: peak torque, BW: bodyweight, avrPT: average
peak torque, avrPower: average power
20
4.3 Correlation between IKD and RDL
Concentric and eccentric hamstring strength parameters, obtained by IKD, were
compared to the RDL values. Because the RDL is a bilateral exercise, isokinetic
measures from both dominant and non-dominant leg were used in the comparison.
The Pearson correlation test showed significant (p<0.05) coefficients between these
two strength measurements, but all were below 0.37. This is shown in table 7.
Table 7: Significant correlation coefficients between isokinetic hamstring strength measures at different angular velocities and RDL values
Pearson correlation coefficient
significance = p
PT/BW con 30 ndom con 120 ndom ecc 30 ndom ecc 120 dom ecc 120 ndom
0.312 0.308 0.282 0.348 0.359
0.029 0.032 0.049 0.014 0.011
avrPT/BW con 30 ndom con 120 ndom ecc 30 ndom ecc 120 dom ecc 120 ndom
0.307 0.368 0.296 0.330 0.307
0.032 0.009 0.039 0.021 0.032
avrPower ecc 120 dom
0.334
0.019
PT: peak torque, BW: bodyweight, avr: average, con: concentric, ecc: eccentric, dom: dominant leg, ndom:
non-dominant leg
21
5. Discussion
This study wanted to investigate the value of strength testing in HSI risk evaluation in a sample
of male football players, by using both IKD at different speeds and a more functional RDL task.
The first hypothesis was that a functional strength measurement would be more valuable in
detecting previous hamstring injury and predicting injury than IKD. This could not be confirmed
by the empirical study.
Secondly, it was hypothesized that the values of the RDL test would not correlate with the
isokinetic hamstring strength measures. The study supports this second hypothesis.
5.1 Detecting previous hamstring strain injury
Significant results were achieved only in the analysis of the players with a history of hamstring
injury (>1y). With this group, the concentric quadriceps and hamstring strength parameters
obtained by IKD were higher than those of the control group. This was also established in the
study of Bennell et al.11, suggesting that hamstring strengthening throughout rehabilitation
could be indeed effective. It should however be noted that only the concentric parameters were
higher, not the eccentric ones. This could suggest that rehabilitation programs should focus
more on eccentric rather than concentric strength training for lowering the risk of future HSI.12
However, the higher concentric parameters could not be found with the players who got injured
last season, which could mean that the higher parameters were rather a coincidence. This
should be further explored.
All of these findings show that it is not possible to accurately identify players with a previous
HSI out of a group, based solely on strength testing.
5.2 Predicting future hamstring strain injury
Higher concentric quadriceps strength could lead to an increased risk of HSI, if the hamstring
muscles are not capable to counteract the movement of the lower limb created by concentric
quadriceps activation. To evaluate this, the DCR was used. In the DCR we compare the
eccentric hamstring strength to the concentric quadriceps strength. This is based on the idea
that the hamstring muscles are contracting eccentrically to control the late swing phase during
running.13
22
Yet, our results showed no significantly higher concentric quadriceps strength, nor a lower
DCR for the group of players who sustained an HSI during the follow-up period. This leads to
believe that concentric quadriceps strength is not a useful parameter to consider when trying
to predict HSI. This is in line with the findings of Bakken et al. who have found a difference in
concentric quadriceps strength of injured and non-injured groups, but the difference is too small
to clinically distinguish both groups.14
Our results did not show lower eccentric hamstring strength in players who sustained an HSI
during the observation period. A study by van Dyck et al. identified lower eccentric hamstring
strength, adjusted for BW, as a risk factor for HSI, but only with a weak association.15 They
however note that their findings have little clinical value.
Research by Van Hooren et al. on the other hand, suggests that the hamstring muscles are
only contracting isometrically while other, elastic structures are lengthened passively.16 This
implies that the conditions under which the hamstring muscles must function during running
activities does not correlate with the conditions under which they are tested during strength
measurements. Therefore, this leads to inconsistencies in the literature.13,16 These
inconsistencies were pointed out in the previous part of this dissertation.
5.3 Correlation between RDL and IKD
Results showed no correlation between the concentric or eccentric isokinetic hamstring
strength parameters and RDL values: the coefficients for the significant parameters were lower
than 0.37. This is in line with what was expected and hence confirms the hypothesis that the
IKD and the RDL exercise both ask a different type of activity from the hamstring muscles.
5.4 The value of IKD
IKD might not be valuable in the prediction and evaluation of risk concerning HSI, but this does
not mean this strength test is to be abandoned. The test is an objective way to establish
strength deficits, and thereby identify players who might need specific training. Strength
training has actually shown to reduce the incidence of lower limb injury.17 Another valuable
advantage of IKD is that it can measure the effect of a training programme.
On the other hand, there are several reasons to question the value of IKD as a predictor. First,
measuring muscle strength alone is not enough to establish an injury risk profile because of
the multifactorial cause of injury. A player can be predisposed for injury because of an internal
risk factor, such as muscle strength, and become susceptible for injury because of an external
risk factor, bad weather for example. Still, to actually sustain an injury an inciting event has to
23
take place, such as an increase in gameplay.18 All of these factors should be taken into account
when establishing a risk profile.
Another reason why IKD did not qualify as valid predictor for HSI in this study, might be
explained by the fact that IKD was used only to measure the peak torque and not the strength
at a certain angle. However, hamstring injuries are most likely to occur in 20°/30° of knee
flexion.19 Further research should investigate this.
5.5 The value of RDL
If the function of the hamstring muscles during running, controlling the motion of the leg
eccentrically or isometrically, differs from what is tested during IKD, a different strength test
might be needed to evaluate the strength deficiencies associated with HSI.12,16 The RDL
seemed a promising alternative.
While IKD is an open kinetic chain exercise performed in a seated position, the RDL is a closed
kinetic chain exercise that incorporates core strength and shows a high hamstring EMG
activation.10,20 In this study, the RDL test was also used to evaluate the strength endurance of
the hamstring muscles. HSI are more common at the end of the game when fatigue sets in,
implying that strength endurance could be an important parameter in the injury mechanism.21
However, the RDL test did not allow us to distinguish injured players from healthy subjects, as
the differences were not significant.
5.6 Limitations
Although being the first to evaluate the value of a functional strength testing protocol using
isokinetic strength testing, the golden standard reference, in function of HSI history and
occurrence in a sample of male football players, this study is not without limitations.
The first limitation is the participant recruitment. Because of the selection process, that was
not completely random, it is plausible that players with a previous injury and thus higher risk
for reinjury showed more interest to participate in the study. This possible bias would not have
been present if we would have been able to test complete football teams. Moreover, the
limitations due to the selection process could also explain the high HSI incidence rate of 49.6%
in our study. However, the participants’ average age was rather low, given that most of them
were friends of acquaintances of the three authors. The proven risk factor of higher age
therefore was not present within the group of participants.22,23
24
Secondly, it is possible that the RDL performance value was influenced by some of the
participants’ unfamiliarity with the exercise. The RDL has a specific movement pattern and
must be performed correctly to activate the hamstring muscles and thus be a valid test.
Another consideration here is the time lag between testing and injury. Several intervening
factors may have altered a player’s strength profile during the three-month follow-up. This
would have been a less important factor if the study had tested complete teams, of which the
players get more or less the same training schedule.
A last important limitation concerns the fact that this study did not control for football exposure
during the follow-up period. The incidence of injuries is strongly related to the number of games
played, as a player is seven times more likely to be injured during a game than during a training
session.24 As a result, the players who have played more games have been exposed to a
greater risk of getting injured. The number of games played was not considered in the follow-
up.
5.7 Conclusion and implications for future research
In this study we established that it is not possible to detect players with a previous HSI or
players that will sustain an HSI by solely testing their muscle strength.
Although we could not confirm that an RDL test is able to detect or predict HSI, we are
convinced that a functional strength test is more suitable for measuring hamstring strength
than IKD. Further research should investigate which functional strength test resembles the
hamstring function during high speed running the most. This functional strength test should
then be implemented in a larger test battery, looking at internal and external risk factors, as
well as possible exposure to inciting events. Only when all of this is taken into account, we
might be able to establish an athlete’s injury risk profile.
25
6. References
1) Krustrup, P., Nielsen, J. J., Krustrup, B. R., Christensen, J. F., Pedersen, H., Randers, M.
B., ... & Bangsbo, J. (2009). Recreational soccer is an effective health-promoting activity for
untrained men. British journal of sports medicine, 43(11), 825-831.
2) Ekstrand, Jan, Martin Hägglund, and Markus Waldén. "Epidemiology of muscle injuries in
professional football (soccer)." The American journal of sports medicine 39.6 (2011): 1226-
1232.
3) Woods, C., Hawkins, R., Hulse, M., & Hodson, A. (2002). The Football Association Medical
Research Programme: an audit of injuries in professional football—analysis of preseason
injuries. British journal of sports medicine, 36(6), 436-441.
4) Mackey, C., O'Sullivan, K., O'Connor, A., & Clifford, A. (2011). Altered hamstring strength
profile in Gaelic footballers with a previous hamstring injury. Isokinetics and Exercise Science,
19(1), 47-54.
5) Stanton, P., & Purdam, C. (1989). Hamstring injuries in sprinting—the role of eccentric
exercise. Journal of Orthopaedic & Sports Physical Therapy, 10(9), 343-349.
6) Opar, D., Williams, M., & Shield, A. (2012). Hamstring strain injuries: Factors that lead to
injury and re-injury [accepted manuscript].
7) Small, K., McNaughton, L., Greig, M., & Lovell, R. (2010). The effects of multidirectional
soccer-specific fatigue on markers of hamstring injury risk. Journal of Science and Medicine in
Sport, 13(1), 120-125.
8) Lee, J. W., Mok, K. M., Chan, H. C., Yung, P. S., & Chan, K. M. (2018). Eccentric hamstring
strength deficit and poor hamstring-to-quadriceps ratio are risk factors for hamstring strain
injury in football: A prospective study of 146 professional players. Journal of science and
medicine in sport, 21(8), 789-793.
9) Wright, J., Ball, N., & Wood, L. (2009). Fatigue, H/Q ratios and muscle coactivation in
recreational football players. Isokinetics and exercise science, 17(3), 161-167.
10) McAllister, M. J., Hammond, K. G., Schilling, B. K., Ferreria, L. C., Reed, J. P., & Weiss, L.
W. (2014). Muscle activation during various hamstring exercises. The Journal of Strength &
Conditioning Research, 28(6), 1573-1580.
26
11) Bennell, K., Wajswelner, H., Lew, P., Schall-Riaucour, A., Leslie, S., Plant, D., & Cirone,
J. (1998). Isokinetic strength testing does not predict hamstring injury in Australian Rules
footballers. British journal of sports medicine, 32(4), 309-314.
12) Askling, C., Karlsson, J., & Thorstensson, A. (2003). Hamstring injury occurrence in elite
soccer players after preseason strength training with eccentric overload. Scandinavian journal
of medicine & science in sports, 13(4), 244-250.
13) Chumanov, E. S., Heiderscheit, B. C., & Thelen, D. G. (2011). Hamstring musculotendon
dynamics during stance and swing phases of high speed running. Medicine and science in
sports and exercise, 43(3), 525.
14) Bakken, A., Targett, S., Bere, T., Eirale, C., Farooq, A., Mosler, A. B., ... & Bahr, R. (2018).
Muscle strength is a poor screening test for predicting lower extremity injuries in professional
male soccer players: A 2-year prospective cohort study. The American journal of sports
medicine, 46(6), 1481-1491.
15) van Dyk, N., Bahr, R., Whiteley, R., Tol, J. L., Kumar, B. D., Hamilton, B., ... & Witvrouw,
E. (2016). Hamstring and quadriceps isokinetic strength deficits are weak risk factors for
hamstring strain injuries: a 4-year cohort study. The American journal of sports medicine, 44(7),
1789-1795.
16) Van Hooren, B., & Bosch, F. (2017). Is there really an eccentric action of the hamstrings
during the swing phase of high-speed running? part I: A critical review of the literature. Journal
of sports sciences, 35(23), 2313-2321.
17) Thorborg, K., Krommes, K. K., Esteve, E., Clausen, M. B., Bartels, E. M., & Rathleff, M. S.
(2017). Effect of specific exercise-based football injury prevention programmes on the overall
injury rate in football: a systematic review and meta-analysis of the FIFA 11 and 11+
programmes. Br J Sports Med, 51(7), 562-571.
18) Meeuwisse, W. H. (1994). Assessing causation in sport injury: a multifactorial model.
19) Brockett, C. L., Morgan, D. L., & Proske, U. W. E. (2004). Predicting hamstring strain injury
in elite athletes. Medicine & Science in Sports & Exercise, 36(3), 379-387.
20) Cresswell, A. G., & Thorstensson, A. (1994). Changes in intra-abdominal pressure, trunk
muscle activation and force during isokinetic lifting and lowering. European journal of applied
physiology and occupational physiology, 68(4), 315-321.
27
21) Ekstrand, J., Hägglund, M., & Waldén, M. (2011). Injury incidence and injury patterns in
professional football: the UEFA injury study. British journal of sports medicine, 45(7), 553-558.
22) Opar, D., Williams, M., & Shield, A. (2012). Hamstring strain injuries: Factors that lead to
injury and re-injury.
23) Freckleton, G., & Pizzari, T. (2013). Risk factors for hamstring muscle strain injury in sport:
a systematic review and meta-analysis. Br J Sports Med, 47(6), 351-358.
24) Roe, M., Murphy, J. C., Gissane, C., & Blake, C. (2018). Hamstring injuries in elite Gaelic
football: an 8-year investigation to identify injury rates, time-loss patterns and players at
increased risk. Br J Sports Med, 52(15), 982-988.
25) Hegedus, E. J., McDonough, S., Bleakley, C., Baxter, G. D., DePew, J. T., Bradbury, I., &
Cook, C. (2016). Physical performance tests predict injury in National Collegiate Athletic
Association athletes: a three-season prospective cohort study. Br J Sports Med, 50(21), 1333-
1337.
28
7. Lekenabstract
Hamstringletsels zijn de meest voorkomende letsels in het voetbal, goed voor 12-15%
van alle voetballetsels. Naast de hoge incidentie heeft deze blessure ook een hoge re-
injury rate en krijgen spelers dus vaak opnieuw te maken met dezelfde blessure.
Daarom is het van groot belang om spelers die risico lopen op de blessure te kunnen
identificeren en om toekomstige blessures te kunnen voorspellen. In onze studie gaan
we dan ook na of dat mogelijk is. Dat doen we aan de hand van twee krachtmetingen.
Een eerste meting is een niet-functionele meting via een isokinetische dynamometer.
Een tweede is een functionele krachtmeting, in dit geval een Romanian deadlift. We
gaan in het prospectieve deel van deze studie na of het via de krachtmetingen mogelijk
is om blessures bij spelers te voorspellen. In het retrospectieve deel kijken we dan weer
of we aan de krachtmetingen kunnen zien welke spelers een verleden van
hamstringletsels hebben. Daarnaast zullen we ook onderzoeken of deze twee
metingen dezelfde resultaten geven.
De hypothese van deze studie was dat de functionele krachtmeting superieur zou zijn
aan de niet-functionele, omdat de functionele meer lijkt op de bewegingen die de
voetballers op het veld uitvoeren. Die hypothese werd door het onderzoek niet
bevestigd. We kunnen besluiten dat het niet mogelijk is om blessures te herkennen of
te voorspellen op basis van een enkele factor. In de toekomst zullen er meer complexe,
functionele tests gebruikt moeten worden om te proberen blessures te voorspellen.
29
8. Bewijs indiening ethisch comité
30
31
32
Ma Di Woe Do Vrij Za Zo
9. Appendix
9.1 Appendix 1
Beste kandidaat, gelieve een aantal minuten de tijd te nemen om onderstaande vragenlijst in
te vullen. Bij vragen of onduidelijkheden kan u zich steeds wenden tot de onderzoekers.
1. Demografie Naam/Code:…………….………………………………………………………………..………………… Geboortedatum: …………………………………………………………………………….…………….. Geslacht: ……………………………………………………………………………………….………….. Nationaliteit: ……………………………………………………………………………………….………. Beroep: ……………………………………………………………………………………………….……. Hobby’s: ………………………………………………………………………………………………….… Woonplaats: ………………………………………………………………………………………………..
2. Antropometrie Gewicht: ………kg Lengte: ………..cm Voorkeursbeen: Links / Rechts (omcirkel wat past)
3. Sport en Training Algemeen Gelieve hieronder per dag het aantal uur dat u aan sport doet in te vullen. Competitief Sport: …………………………………………………………………………………….…………………. Competitieniveau: ………………………………………………………………………………..……….. Ervaring: ………jaren Training: ………u/week Wedstrijd: .…….u/week Type trainingen die de club organiseert: (omcirkel wat past) Kracht / Lenigheid / Cardio (uithouding / interval) / Sportspecifiek
33
Andere: …………………………………………………………………………………………………….. Wordt er op training aandacht besteed aan lenigheid en kracht? Ja/Nee Zo ja, hoeveel? ……u/week
Aanvullend/recreatief Sport(en): 1) ………………………… ……u/week 2) ………………………… ……u/week 3) ………………………… ……u/week
4. Blessures Algemeen Heeft u op dit moment ergens klachten, pijn of een blessure? Ja / Nee Zo ja, waar? ……………………………………………………………………………………………….. Bent u hiervoor in behandeling bij een arts, kinesitherapeut, of andere? Ja / Nee Zo ja, welke behandeling? ……………………………………………………………………………...…………..…………………… Volgt u een aangepaste training? Ja / Nee Zo ja, welke aangepaste training? ………………………………………………………………………………………………………………. Verleden: 1) Klacht, pijn, blessure ( + datum): ….………….…….…………………………………. Behandeling, aangepaste training: ……………………………………………………. Tijd afwezig van training: ………………………………….……………………………. Tijd afwezig van wedstrijd: …………………………………………………………....... 2) Klacht, pijn, blessure ( + datum): ….………….…….…………………………………. Behandeling, aangepaste training: ……………………………………………………. Tijd afwezig van training: ………………………………….……………………………. Tijd afwezig van wedstrijd: …………………………………………………………....... 3) Klacht, pijn, blessure ( + datum): ….………….…….…………………………………. Behandeling, aangepaste training: ……………………………………………………. Tijd afwezig van training: ………………………………….…………………………….
34
Tijd afwezig van wedstrijd: …………………………………………………………....... Specifiek Heeft u al eens een hamstringblessure opgelopen? Ja/Nee Indien Ja: Type blessure: overbelasting / verrekking / scheur (omcirkel wat past) Locatie: links / rechts Omstandigheden: begin / einde van training / match lopen / trappen / springen / andere: …………………………………..
5. Opmerkingen ……………………………………………………………………………………………………….……………………………………………………………………………………………………………….……………………………………………………………………………………………………………….……………………………………………………………………………………………………………………….
35
9.2 Appendix 2
Recommended