Revalidatiewetenschappen en Kinesitherapie

Academiejaar 2014-2015

Functional Movement Screen and Y-balance test:

validity in hamstring injury risk prediction?

A prospective study

Masterproef voorgelegd tot het behalen van de graad van

Master of Science in de Revalidatiewetenschappen en Kinesitherapie

Van pellicom Bert

Vanmaele Ruben

Welvaert Mathieu

Promotor: Prof. Dr. Damien Van Tiggelen

Co-promotor: Mevr. Joke Schuermans

Revalidatiewetenschappen en Kinesitherapie

Academiejaar 2014-2015

Functional Movement Screen and Y-balance test:

validity in hamstring injury risk prediction?

A prospective study

Masterproef voorgelegd tot het behalen van de graad van

Master of Science in de Revalidatiewetenschappen en Kinesitherapie

Van pellicom Bert

Vanmaele Ruben

Welvaert Mathieu

Promotor: Prof. Dr. Damien Van Tiggelen

Co-promotor: Mevr. Schuermans Joke

Foreword

We would like to thank everyone who has guided us in creation of our master scription. Our greatest

gratitude goes out to some individuals in particular.

First of all we would like to thank our promotor Prof. Dr. Damien Van Tiggelen and our co-promotor

Joke Schuermans for their support and accurate feedback in the past 2 years during the testing and

writing of our paper.

We wish to express our sincere appreciation for all the subjects who participated to the testing

voluntarily.

Likewise, we would like to thank the Faculty of Medicine and Health Sciences and the department of

Rehabilitation Sciences and Physiotherapy for putting the research labs, testing equipment and

computers to our disposal.

As a last a special word of gratitude to our family and friends who supported us during these tough

years. Because of them, we had the opportunity to write this thesis.

Before the beginning of our study, we were already very fascinated in the sports dimension of

physiotherapy and the sciences of rehabilitation. Especially in soccer we were particularly interested.

We were very delighted when we knew that we could write our study around this topic.

Fully encouraged, we started to browse the great amount of literature regarding this subject. This

has led to our literature study in the first year. In the beginning of the second year we could start

screening soccer players ourselves. This essay is the final outcome of a tremendous amount of

reading, testing, processing of results and writing.

I

Table of Contents

1 ABSTRACT ……………………………………………………………………………………………………………….. 1

1.1 Abstract ( English ) …………………………………………………………………………………………. 1

1.2 Abstract ( Dutch ) …………………………………………………………………………………………… 2

2 INTRODUCTION ………………………………………………………………………………………………………. 3

2.1 Functional screening tools ……………………………………………………………………………… 4

2.1.1 Functional Movement Screen ……………………………………………………………. 4

2.1.2 Y-balance test ……………………………………………………………………………………. 5

2.2 General conclusion ………………………………………………………………………………………… 5

2.3 Research question …………………………………………………………………………………………. 5

3 METHODS ………………………………………………………………………………………………………………. 6

3.1 Recruitment study population ………………………………………………………………………. 6

3.2 Testing protocol ……………………………………………………………………………………………. 6

3.2.1 Functional Movement Screen ………………………………………………………….. 7

3.2.2 Y-balance test ………………………………………………………………………………….. 8

3.3 Follow-up ……………………………………………………………………………………………………… 9

3.4 Statistical analysis …………………………………………………………………………………………. 10

4 RESULTS ………………………………………………………………………………………………………………… 11

4.1 Subject characteristics ………………………………………………………………………………….. 11

4.2 Retrospective research …………………………………………………………………………………. 12

4.2.1 FMS and YBT performance in association with hamstring injury history 12

4.2.1.1 Functional Movement Screen ………………………………………………. 12

4.2.1.2 Y-balance test ………………………………………………………………………. 14

4.2.2 Questionnaire in association with hamstring injury history ………………. 15

II

4.3 Prospective research ……………………………………………………………………………………. 16

4.3.1 Functional Movement Screen performance in association with future

hamstring injury risk ………………………………………………………………………… 16

4.3.2 Y-balance test in association with future hamstring injury risk ………… 20

5 DISCUSSION ………………………………………………………………………………………………………….. 21

5.1 Functional Movement Screen ………………………………………………………………………. 21

5.1.1 Deep squat ………………………………………………………………………………………. 21

5.1.1.1 Core stability ……………………………………………………………………….. 21

5.1.1.2 Ankle dorsiflexion ………………………………………………………………… 22

5.1.1.3 Eccentric hamstring power …………………………………………………... 23

5.1.1.4 Hamstring and quadriceps co-contraction ……………………………. 23

5.1.2 Active straight leg raise …………………………………………………………………….. 24

5.1.2.1 Hamstring flexibility …………………………………………………………….. 25

5.1.2.2 Rectus femoris flexibility ……………………………………………………… 26

5.1.2.3 Neural extensibility ……………………………………………………………… 27

5.1.3 FMS composite score of deep squat and active straight leg raise test 27

5.1.4 Other FMS component tests …………………………………………………………….. 28

5.2 Y-balance test ……………………………………………………………………………………………….. 28

5.3 New insights in the clinical use of FMS and YB ………………………………………………. 29

5.4 Reoccurence of hamstring injury …………………………………………………………………… 29

5.5 Similar research …………………………………………………………………………………………….. 30

6 LIMITATIONS …………………………………………………………………………………………………………..31

7 CONCLUSION …………………………………………………………………………………………………………. 33

8 ACKNOWLEDGEMENTS ………………………………………………………………………………………….. 33

9 REFERENCES …………………………………………………………………………………………………………. 34

III

10 ABSTRACT ……………………………………………………………………………………………………………… 41

10.1 Abstract ( layman’s terms ) …………………………………………………………………………… 41

11 APPENDICES ………………………………………………………………………………………………………… 42

11.1 Functional Movement Screen …………………………………………………………………….. 42

11.2 Y-balance test …………………………………………………………………………………………….. 56

11.3 Questionnaire pre-testing ………………………………………………………………………….. 58

11.4 Questionnaire after 6 months follow-up ……………………………………………………. 60

11.5 Score sheet FMS ………………………………………………………………………….…………….. 62

11.6 Score sheet YBT ……………………………………………………………………………….….…….. 63

11.7 Informed consent ………………………………………………………………………….…………… 64

IV

Table of Tables

Table 1: subjects characteristics ………………………………………………………………………….......................... 11

Figure 1: FMS results ………………………………………………………………………………………………………………….. 12

Figure 2: trunk stability push up results ……………………………………………………………………………………… 12

Table 2: FMS results …………………………………………………………………………………………………………………… 13

Figure 3: distribution of the component test scores ( control – previous injury) ………………………… 13

Table 3: Y-Balance and variables characteristics ………………………………………………………………………… 14

Table 4: Y-balance results ………………………………………………………………………………………………………….. 15

Table 5: Comparison of players with and without injuries during the season …………………………….. 16

Figure 4: Boxplot DS and ASLR score ………………………………………………………………………………………….. 17

Figure 5 and 6: Histogram Deep Squat and Active Straight Leg Raise …………………………………………. 18

Table 6: 2 x 2 contingency table: DS & ASLR score x hamstring injury ………………………………………… 19

Table 7: Influence of the DS & ASLR on first hamstring injury ……………………………………………………. 19

Table 8: Influence of the DS & ASLR on subsequent hamstring injury ……………………………………….. 19

V

Table of abbreviations

FMS: Functional Movement Screen YBT: Y-balance test

FMS LL: FMS lower limb Y Balance C: Y balance control

DS: Deep squat Y Balance I: Y balance injury

HS: Hurdle step YB_A_C: Y balance anterior control

ILL: In-line lunge YB_A_I: Y balance anterior injury

SM: Shoulder mobility YB_PM_C: Y balance postero-medial control

ASLR: Active straight leg raise YB_PL_C: Y balance postero-lateral control

TS: Trunk stability push-up YB_PM_I: Y balance postero-medial injury

RS: Rotary stability YB_PL_I: Y balance postero-lateral injury

SEBT: star excursion balance test

RTP: Return to play

Cf: confer

Eg.: example given

Etc.: Et cetera

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1 Abstract

1.1 Abstract ( English )

Background: Among muscle injuries, hamstring injuries present the highest incidence and

reoccurrence rates in explosive field sports like soccer. There are many screening tools which try to

identify an increased risk of hamstring (re)injuries, two of those are the Functional Movement Screen

(FMS) and the Y-balance test (YBT). Both are functional tests which have the capacity to screen the

entire kinetic chain. Besides, they evaluate the most essential motor competences that are majorly

important in soccer athlete’s performance and injury vulnerability.

Purpose: To analyze if the functional screening tools FMS and Y-balance are useful in predicting an

increased risk of sustaining hamstring strain injuries in the population of male soccer players.

Methods: In the pre-season period of July 2014, an injury-group consisting of 28 male soccer players

with a hamstring injury history and a matched control group consisting of 30 male soccer players,

were tested on FMS and Y-balance testing performances. An additional cohort of 10 soccer players (3

with and 7 without hamstring injury history), was screened for FMS performance only. After testing,

the injury incidence of all 68 players was registered during a follow-up period of 6 months (half a

season). Data analysis evaluated the association between functional testing performance and the risk

of sustaining a hamstring injury during follow-up.

Results: Cross sectional data analysis did not reveal an association between the FMS total-score, FMS

LL –score or Y-balance testing performance and the presence/absence of a hamstring injury history.

Nevertheless, the injury-group scored significant lower on the trunk stability push-up test (p=0.047).

For the prospective data analysis, no association between FMS and Y-balance scores and the

incidence of hamstring injuries during follow-up could be demonstrated. Only a poor performance on

the deep squat test (p=0.043) and the active straight leg raise test (p=0.041) was associated with a

significantly higher risk of sustaining a hamstring injury. Unlike FMS- and Y-balance total scores, a

new component score taking deep squat and active straight leg raise performances together ( with a

total score ranging from 0-6), has the ability to predict future hamstring injury. When assessing its

association with getting injured for the first time and re-injuries separately, this combined screening

tool clearly presented the highest validity in terms of a first injury risk detection (p=0.006). In the re-

injury group, there are likely more different covariates that could influence the result, giving no

significant correlation.

We were able to demonstrate that the relative risk of sustaining an index hamstring injury was 27%

for players who scored less than 4 out of 6, and was reduced to 0% in players who scored 4 or more

out of 6.

Conclusion: The FMS in total does not have the ability to predict the risk of sustaining a hamstring

injury. The FMS component tests ‘deep squat’ and ‘active straight leg raise’ are able to predict future

hamstring injury, this especially for the group of players who sustained first hamstring injury. Based

on our results, we propose that the combined score of these two tests provides a valid prediction of

the index hamstring injury risk in soccer players. In this study, the Y-balance did not appear to be a

valid test to predict future hamstring injury.

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1.2 Abstract ( Dutch )

Achtergrond: Van alle spierletsels kennen hamstringletsels niet alleen de hoogste incidentiecijfers, maar hebben ze bovendien ook het meest recidief karakter bij explosieve veldsporten zoals voetbal. Er zijn verschillende testbatterijen die trachten het risico op hamstring (her)aandoeningen te identificeren, waarvan de Functional Movement Screen (FMS) en Y-balance test (YBT) er twee zijn. Beide zijn functionele testen die de capaciteit hebben om de volledige kinetische keten te screenen. Bovendien evalueren zij de meeste essentiële motorische vaardigheden die voornamelijk belangrijk zijn voor de prestatie en letselgevoeligheid van de voetbalspeler. Doel: Analyseren in welke mate de functionele testbatterijen FMS en Y-balance bruikbaar zijn om een verhoogd risico op hamstringletsels te voorspellen bij mannelijke voetbalspelers. Methode: In het voorseizoen (juli 2014) werden een patiëntengroep van 28 spelers met een verleden van een hamstringletsel en een overeenkomstige controlegroep van 30 spelers getest op de FMS en Y-balance. Bij een bijkomende cohorte van 10 spelers (3 met en 7 zonder hamstringletsel in het verleden) werd enkel de FMS afgenomen. Na testing werd de letselincidentie van alle 68 spelers geregistreerd tijdens een follow-up periode van 6 maanden (een half seizoen). Data-analyse evalueerde het verband tussen de functionele testprestaties en het risico een hamstringletsel op te lopen tijdens de follow-up periode. Resultaten: cross-sectioneel onderzoek kon geen verband aantonen tussen de totale FMS-score, de FMS LL-score of de Y-balance prestatie en de aan– of afwezigheid van een hamstringletsel in het verleden. Anderzijds scoorde de patiëntengroep wel significant lager op de trunk stability push-up test (P=0.047). Voor de prospectieve data-analyse kon er geen verband aangetoond worden tussen de FMS en Y-balance scores en de incidentie van een hamstringletsel gedurende de follow-up periode. Enkel een zwakke score op de deep squat test (p=0.043) en de active straight leg raise test (p=0.041) resulteerde in een significant hoger risico op een hamstringletsel. In tegenstelling tot de totale FMS- en Y-balance scores had een nieuwe componentscore, samengesteld uit de deep squat –en active straight leg raise resultaten (met een totale score variërend tussen 0-6), wel de mogelijkheid om een toekomstig hamstringletsel te voorspellen. Wanneer we voor dit verband een onderscheid maken tussen het oplopen van een eerste of een nieuw hamstringletsel, toonde deze gecombineerde testbatterij de hoogste validiteit op het vlak van blessurepreventie bij spelers zonder hamstringletsel in het verleden (p=0.006). Bij spelers met een verleden van een hamstringletsel zijn er waarschijnlijk meerdere covariaten van invloed. We waren in staat aan te tonen dat het relatief risico om een index hamstringletsel op te lopen 27% was voor spelers die minder scoorden dan 4 op 6, en dit daalde tot 0% voor deze die 4 of meer scoorden op 6. Conclusies: De FMS test in totaal heeft niet de predictieve waarde om het risico om hamstringblessures op te lopen te voorspellen. De FMS componenttesten ‘deep squat’ en ‘active straight leg raise’ zijn in staat om een hamstringletsel te voorspellen, dit vooral bij spelers die een eerste hamstringblessure opliepen. Gebaseerd op onze resultaten, stellen we dat de gecombineerde score van deze twee testen een valide voorspelling voorziet van het index hamstringletsel risico bij voetbalspelers. In deze studie bleek de Y-balance geen valide test is om een toekomstig hamstringletsel te voorspellen.

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2 Introduction

Hamstring injuries are amongst the most common non-contact injuries in explosive field sports27. In

soccer for example, they account for 10% - 23% of all acute non-contact injuries2,21,66-67. Even more

troublesome than their high incidence rates, are their exceptionally high reoccurrence rates in

football players. (16-60%)23, because those recurring injuries often result in more time loss and

subsequent financial consequences than the original insults8,23. In the context of hamstring strain

injuries, intrinsic risk factors related to individual features, seem to be of a higher value in predicting

future hamstring injury risk than the extrinsic ones50. The most common non-modifiable intrinsic risk

factors that are currently acknowledged in literature are age3,65,71, previous injury3,19,65 and black or

aboriginal ethnic origin65,71. The most common modifiable risk factors are bilateral strength

imbalances, strength deficits and low antagonist ratios17,19,72 , muscle fatigue19,72 , hamstring

tightness70 , insufficient warm-up procedures19,72 , morphological and anatomical hamstring muscle

features71 , poor lumbar posture and core stability35, and knee joint angle of concentric hamstring

peak torque7. Given the high injury and re-injury rates, and personal/financial costs associated with

the hamstring injuries, it is clear that better screening tools to identify athletes at risk for hamstring

injuries are needed

Previous research revealed that there are many screening tools to evaluate readiness for Return To

Play (RTP) or performance, which try to identify an increased risk of hamstring (re)injuries in

explosive fields sports (like soccer) in order to (1) decrease their (re)occurence, (2) enhance player’s

performance, and (3) ultimately improve quality of life. However this research is inconsistent and

unclear concerning which of those screening tools have the highest validity to achieve this main goal

[45].

In our systematic review: ‘Which functional screening tools are able to predict hamstring injuries in

explosive field sports’ we aimed at providing a literature to establish the effectiveness of current

functional screening tools for hamstring injury risk detection. In this review, we particularly

investigated the value of the commonly implemented ‘Functional Movement Screen’ and ‘Y-balance

test’, for the purpose of hamstring strain injury prediction and -prevention in explosive field athletes.

We chose to narrow the scope of our literature search down to these two functional screening tools

because of their international popularity and user-friendliness.

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2.1 Functional screening tools

2.1.1 Functional Movement Screen

In our previous systematic research we particularly focused on the Functional Movement Screen

(FMS). The FMS is a relatively new comprehensive evaluation tool, not intended to diagnose

orthopaedic problems, but rather to assess the quality of fundamental movement patterns to

identify functional movement deficits and asymmetries [39, 62]. Functional movement is the ability

to produce and maintain a balance between mobility and stability along the kinetic chain while

performing fundamental patterns with accuracy and efficiency.

This testing tool incorporates the evaluation of all major motor requirements in athletes such as

muscle strength, flexibility, range of motion, coordination, balance, and proprioception. It is known

as a time-efficient, noninvasive, inexpensive and user friendly screening tool14. Plisky et al. (2006)

hypothesized that tests, such as the FMS, which assesses multiple domains of functioning

simultaneously, may improve the accuracy of identifying athletes at risk for hamstring injury through

pre-participation assessment. When the score reached ≤14/21, the subject had a greater risk of

injury. 55

In our systematic review we could state that this test has a good to moderate intrarater

reliability31,58,62 and a good interrater reliability46,58,62. The reliability of the component test for the

‘shoulder mobility’ is high, and for the ‘hurdle step’ is poor. The other tests scored a good

reliability49, indicating moderate to good reliability when making an average for all component tests.

At this moment there is a lack of knowledge about the predictive value of the FMS in terms of the

identification of athletes at risk for future injury. The results of our review showed that the FMS Is

mostly reliable within the group of college students, but further investigation is needed within the

group of explosive field athletes such as soccer players. Certainly in terms of hamstring injury-specific

FMS screening and outcome, no research is available to date.

For our study we were curious to find out to what extent the FMS can be attributed to establish an

increased risk of sustaining hamstring strain injuries in the population of male soccer players.

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2.1.2 Y-balance test

The Y-Balance Test (YBT) assesses the athlete’s balance by challenging his postural control system in

3 (anterior, posteromedial, and posterolateral) of the 8 SEBT (star excursion balance test) directions

and has been advocated as a method for assessing dynamic balance (requires strength, flexibility and

proprioception). As these motor requirements are of capital importance in muscle injury prevention

and rehabilitation, this test could be valuable in hamstring injury risk assessment as well. The Y-

balance test (YBT) is one of the few field expedient tests that has shown predictive validity in terms

of the identification of injury risk in an athletic population. Amongst other risk factors, impaired

balance has been associated with an increased risk of lower extremity injuries.

The clinical application of the SEBT led to the development of the Y-Balance Test (YBT). The goal of

the YBT is to maintain single leg stance on one leg while reaching as far as possible with the

contralateral leg. Almost perfect agreement on the interrater test–retest reliability of the maximal

reach for the 3 reach directions (anterior, posteromedial, and posterolateral). Also, almost perfect

agreement on the interrater test–retest reliability of the average reach of 3 trails. Specifically, Plisky

et al. (2006) identified that individuals with anterior left/right asymmetries greater than 4 cm on the

YBT were 2.5 times more likely to sustain a lower extremity injury. Further, they reported that the

sum of three reach directions (anterior, posteromedial, and posterolateral) were predictive of lower

extremity injury.

2.2 General conclusion

The FMS and the Y-balance test are functional tests, unlike isokinetic testing etc., that have the

capacity to screen the entire kinetic chain and are very easy to administer. They evaluate the most

essential motor competences that are majorly important in the soccer athlete’s load bearing

capacity and thus their performance and injury vulnerability.

2.3 Research question

In current literature, evidence about the predictive value of these field tests for the purpose of

(secondary) hamstring injury prevention is non-existing. That is why we have chosen to assess the

validity of both the FMS and the Y-balance screening tools in hamstring injury risk detection in a

population at risk, like male soccer players.

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3 Methods

3.1 Recruitment study population

In order to find suitable patients and control subjects, we principally used social media or contacted

soccer clubs. Finally, we had a group of 28 patients who had a hamstring injury in the past (injury-

group) and 30 control subjects who voluntarily participated in our survey at UZ Gent to perform the

FMS and YBT. We also recruited 10 field players, but only the FMS assessment was conducted within

this smaller sample.

To subcategorize the potential candidates to the injury- or control group, we applied quite a few

inclusion –and exclusion criteria. Included athletes had to meet following requirements:

- male soccer field players between the age limits of 18 and 35 years

- active in amateur soccer competition (provincial divisions),

- never having sustained any (serious) lower limb injuries that required surgical interventions

For the injury-group, the key requirement was that they had at least one hamstring injury in the past

and that this injury or re-injury occurred in the last season.

3.2 Testing protocol

Before examining the subjects, they were asked to fill in a questionnaire (cf. appendix). The first part

contained administrative data, medical history, and current health. The second part contained

questions regarding the most recent soccer related hamstring injury and corresponding rehabilitation

period, so was only filled in by the injury group.

After this questionnaire, the investigators explained the purpose and content of the testing series,

after which the participants were asked to sign informed consent forms. Subsequently, each

participant performed a 5 min warm-up on a stationary bike before the actual testing commenced.

The functional screening of all subjects commenced with the Functional Movement Screen

(recorded by 2 investigators), followed by the Y-balance test (recorded by only 1 investigator), with

an overall duration of approximately 25-30 minutes. When a researcher wasn’t recording a test, they

could give a second opinion if there was some doubt or disagreement. All tests were performed

wearing soccer shoes and comfortable sports clothing.

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3.2.1 Functional Movement Screen

After filling in the questionnaire, all the participants were examined using the Functional Movement

Screen in the first place. This test contains 7 sub-tests: deep squat, hurdle step, in-line lunge,

shoulder mobility, active straight leg raise, trunk stability push-up and rotary stability; which were

always evaluated in the same order to advance standardization. Since the quality of movement

patterns is the most important goal, clear instructions and a short demonstration were given in a

standardized way. Each player was given three trials on each of the seven sub-tests and received a

score from zero to three on each. Scoring criteria were as follows: 0) pain was reported during the

movement; 1) failure to complete the movement or loss of balance during the movement; 2)

completion of the movement with compensation; and 3) performance of the movement without any

compensation. Each test was scored by at least 2 evaluators. One evaluator checked the frontal

plane, the other took account with requirements in the sagittal plane. When there was doubt, we

scored low. For each sub-test, the highest score from the three trials was recorded. For the sub-tests

that were assessed bilaterally, the lowest score was used. Three of the sub-tests (shoulder mobility,

trunk stability push-up and rotary stability) also have associated clearing exams (impingement

clearing test, press-up clearing test, posterior rocking clearing test), performed before each sub-test,

and are scored as either positive or negative with a positive response indicating that pain was

reproduced during the examination. Should there have been a positive result on a clearing sub-test;

the score for that movement would be zero regardless of how well the subject could perform the

movement. An overall composite FMS score with a maximum value of 21 was then calculated and

participants were informed of their score.

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3.2.2 Y-balance test

After the FMS evaluation, each participant was immediately submitted to the Y-balance assessment,

as the investigator’s instruction allowed the participants to rest for a moment, without needing a

second warming up session prior to testing.

The Y Balance Test Kit™ consists of a stance platform to which three pieces of PVC bars are attached

in the anterior, posteromedial, and posterolateral reach directions. The posterior bars are positioned

at 135 degrees from the anterior bar, with 45 degrees between both posterior bars. Each bar is

marked in 5 millimeter increments for performance measurement. The subject was asked to push a

target (reaching- indicator) along the bar with the reaching foot, by simultaneously bending through

the hip-, knee- and ankle-joints of the supporting leg, which was subject of dynamic stability testing.

When the subject reached his limit, he had to return to the starting position without pushing off with

the reaching foot and without losing his balance, so solely by using muscle strength and control in

the supporting leg and core. When the reaching-indicator was moved during the returning phase,

this trial was discarded, making the determination of reach distance more precise.

The Y-balance test was thoroughly explained and demonstrated by the raters. The subjects practiced

3 trials on each leg in each of the three reach directions prior to formal testing, giving the time

management and avoiding a certain learning effect. The subjects were tested directly after

practicing. The subjects took place on the center platform of the Y-balance kit on his right leg (which

was tested first), with his toes just behind the red line, indicating the attempted position of the

supporting leg on the Y-balance platform. While maintaining single leg stance, the subject was asked

to reach with the free limb in the anterior, posteromedial, and posterolateral directions. In order to

improve the reproducibility of the test and establish a consistent testing protocol, a standard testing

order was developed and utilized. The testing order was three trials standing on the right foot

reaching in the above mentioned direction with the left foot. Per direction, 3 trials were registered

and taken along for data-analysis. Afterwards the three tests were repeated standing on the left foot.

The subjects were motivated by the raters to really trying to reach their optimal performance. One

rater noted the reaching distance and one rater took care of trial registration. The raters dependently

determined if a successful trial was completed (i.e. that the foot was positioned correctly behind the

line and that all of the criteria were met for a successful trial). The maximal reaching distance was

measured by reading the tape measure at the edge of the reaching-indicator. The trial was discarded

and repeated if the subject: 1) failed to maintain unilateral stance on the platform (e.g. touched

down to the floor with the reach foot or fell off the stance platform), 2) failed to maintain reach foot

contact with the reach indicator on the target area while it was in motion (e.g. kicked the reach

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indicator), 3) used the reach indicator for stance support (e.g. placed foot on top of reach indicator),

or 4) failed to return the reach foot to the starting position under control. We allowed a one minute

break between the tests for the right and left leg.

To conclude the functional screening, lower limb length was measured for the analysis of the Y-

balance scores. This was done with the subject lying down supine on an examination table. The

subject’s limb length was then measured in centimeters by assessing the distance between the

anterior superior iliac spine and the most distal portion of the medial malleolus with a cloth tape

measure.

The data were analyzed for each subject for the right limb in the anterior, posterolateral, and

posteromedial reaching directions. Means and standard deviations were calculated for the reaching

distance in each direction. Since reach distance is related to limb length, reaching distance was

normalized to limb length to allow inter-subject comparison. To express reaching distance as a

percentage of limb length, the normalized value was calculated as reaching distance divided by limb

length, and then multiplied by 100. Composite reaching distance was obtained by taking the sum of

the three reaching distances in the different directions divided by three times limb length, and then

multiplied by 100.

3.3 Follow up

Players were tested pre-season in July, after which they were included in injury follow-up during the

first half of the subsequent season. They were asked to contact the investigators immediately when

they sustained a hamstring injury which would prevent them from participating in training or

competition for at least 1 session of exposure. The investigators also contacted each participant by

mail or Facebook, making sure no injury could have been missed due to lost to follow-up. We started

contacting the players from the beginning of December until the end of February.

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3.4 Statistical analysis

All data were imported in the SPSS Statistics software, version 22.

First, descriptive statistics were performed to assess covariate distribution in our test sample. In this

way, normality-assessment could be performed and basic parameters could be summarized (mean,

SD).

The Kolmogorov-Smirnov and Shapiro-Wilkinson test were performed to prove the level of normal

distribution of these data.

Retrospectively, we investigated if there were significant differences within continuous and

categorical variables. Hypothesis testing for continuous variables was performed by using General

Linear Models. In the case of categorical variables, Fisher’s Exact Test was performed.

Prospectively, to assess a possible relationship between testing results and subsequent injury

incidence, we used Independent Sample T-test and one-way Anova test for starters. Binary Logistic

and Ordinal Regression analyses were attributed to make a prediction model, assessing the validity of

both functional tests for future injury risk detection.

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4 Results

4.1 Subject characteristics

The control– and injury group present similar physical characteristics (weight, height, BMI).

Concerning the age of both groups, we can see that the injury-group (mean: 24.31 year; SD [ 2,94 y] )

is significant ( p=0.001) older than the control group ( mean: 21.94 year ; SD [1.92 y]). This difference

is statistically from high significance. The average competition level was also the same for both

groups, with the majority of participants playing in 2nd provincial division.

Variable Hamstring injury P value

Without ( n=37) With ( n=31)

Characteristics Age (year) 21.94 +- 1.92 24.31 +- 2.94 0.001

Height (cm) 182.2 +- 6.64 181.0 +- 5.15 0.407

Weight (kg) 74.68 +- 7.76 74.90 +- 5.75 0.893

BMI (kg/m2) 22.47 +- 1.80 22.87 +- 1.40 0.327

Table 1.

- 12 -

4.2 Retrospective research

4.2.1 FMS and Y-balance performance in association with hamstring injury history

When looking at the FMS and Y-balance scores in the formerly injured and the control groups, the

average FMS-score for the control group appeared to be a little bit higher (15.35 vs 14.94). This

minor difference was also seen in the average FMS-LL-score (FMS-Lower Limb; 8.81 vs 8.52). At last,

the Y-balance-score was more or less equal in both groups, with very symmetrical results in both

legs. None of the above mentioned discrete differences were of statistical significance. Chi Square

hypothesis testing revealed no association between the FMS total (p=0.169) - or FMS-LL (p=0.596)

scores and the presence or absence of a hamstring injury history, indicating that having a history of a

hamstring injury has no influence on the FMS total - or FMS LL-score.

4.2.1.1 Functional Movement Screen

Even though we could not demonstrate a difference in FMS score based on the presence or absence

of a hamstring injury history, categorical hypothesis testing revealed that the subjects who sustained

a hamstring strain injury in the past, scored significant lower on the trunk stability push-up test.

(p=0.047)

Figure 1. Figure 2.

- 13 -

Variable Hamstring injury P value

Without ( n=37) With ( n=31)

FMS FMS total score 15.35 +- 1.814 14.94 +- 1.931 0.364

FMS lower limb 8.81 +- 1.221 8.52 +- 1.288 0.337

Deep squat 2.24 +- 0.495 2.16 +- 0.374 0.440

Hurdle step 2.16 +- 0.374 2.29 +- 0.461 0.219

In-line lunge 2.68 +- 0.475 2.58 +- 0.502 0.426

Active straight leg raise 2.11 +- 0.774 2.23 +- 1.023 0.591

Trunk stability push up 1.73 +- 0.769 1.48 +- 0.724 0.182

Rotary stability 2.14 +- 0.347 2.03 +- 0.315 0.208 Table 2.

Figure 3.

0

20

40

60

80

100

DS HS ILL ASLR TSPU RS

FMS Score

- 14 -

4.2.1.2 Y-balance test

Although no association was found between the hamstring injury history and the performance on the

Y-balance test, we found a correlation between player’s age and the score on the Y-balance in the

injured group. Older subjects had a weaker Y-balance performance and this in both the injured leg

(p=0.043) and the control leg (p=0.036). Playing division could also be associated with Y-balance

testing performance. In the injury group, players competing in lower levels tended to have poorer Y-

balance results than their colleagues in higher division (p=0.045).

Table 3.

6,36 ± 1,446 3,03 ± 1,629 2,79 ± 1,343

0 2,04 ± 1,347

72,133 ± 9,2586 73,036 ± 6,3559 1992,6 ± 1,958

1990,43 ± 2,937 5,7 ± 1,512

YES

MEAN ± SD

102,581 ± 9,711 101,894 ± 7,0179 102,237 ± 8,1563 101,854 ± 6,7826

118,422 ± 12,5567 116,239 ± 10,793

117,956 ± 12,7411 116,762 ± 9,9575

117,633 ± 10,7939 115,952 ± 10,45051

116,944 ± 9,6101 116,573 ± 9,2017 71,367 ± 7,6345 72,68 ± 5,6618

NO YES NO

NO YES NO YES NO YES NO YES NO YES NO

History of injury

YES NO YES NO YES NO YES NO YES

YB_PL_C

YB_PM_C

YB_A_I

YB_A_C

BIRTHYEAR

DIVISION

PLAYING POSITION

MUSCLE

TEST

YB_PM_I

Y BALANCE I

Y BALANCE C

YB_PL_I

- 15 -

Table 4.

4.2.2 Questionnaire results in association with hamstring injury history

Additionally, hypothesis testing revealed a significant association between division and injury history

(p= 0.011), as players participating in lower divisions seem to report a higher injury history than

athletes active in higher levels of competition.

VARIABLE

MUSCLE

0,043

0,036

0,068

0,027

0,121

0,008

0,045

0,025

0,025

0,035

0,061

0,092

BIRTHYEAR

DIVISION

Significance (p<0,05)

YB_PL_C

YB_PM_C

Y BALANCE I

YB_PL_I

YB_PM_I

PLAYING POSITION

YB_PM_C

YB_A_I

YB_A_I

TEST

YB_PM_I

Y BALANCE I

Y BALANCE C

YB_PL_I

- 16 -

4.3 Prospective research

4.3.1 Functional Movement Screen performance in association with future hamstring injury risk

In total, 68 players were screened in this study. Of those 68, 31 have had one or more hamstring

injuries in the past. We followed these players during the season. Of these 68 players, 14 players got

a hamstring injury (20.6%) during follow-up. 3 players got a hamstring injury for the first time, so

78.6% got a re-injury of their hamstring. Of those 11 players, 5 got injured at the same side of their

first injury and 6 got a hamstring injury on the other leg.

For the prospective statistical analysis we can conclude that, when performing poorer on the deep

squat (p=0.043) and active straight leg raise (p=0.041) , there is significant higher risk of sustaining

hamstring injury. (cf. table 5)

Variable Hamstring injury P value

Without ( n=54) With ( n=14)

Characteristics Age (year) 23,04 +-2,840 23,09 +- 1,950 0,948

Height (cm) 181,9 +- 6,06 180,5 +- 5,83 0,432

Weight (kg) 74,96 +- 6,659 74,07 +- 7,849 0,668

BMI (kg/m2) 22,64 +- 1,55 22,72 +- 1,99 0,873

FMS FMS total score 15.26 +- 1.845 14,79 +-1,968 0,401

FMS lower limb 8.80 +- 1.234 8,21 +-1,251 0,122

Deep squat 2.26 +- 0.442 2,00 +- 0,392 0,043*

Hurdle step 2.19 +- 0.392 2,36 +- 0,497 0,246

In-line lunge 2.65 +- 0.482 2,57 +- 0,514 0,602

Active straight leg raise 1.70 +- 0.786 1,29 +- 0,611 0,041*

Trunk stability push up 2.17 +- 0.795 2,14 +- 1,231 0,946

Rotary stability 2.07 +- 0.328 2,14 +- 0,363 0,496

* P<0.05

TABLE 5.

- 17 -

Figure 4.

Ordinal regression analysis revealed borderline non-significance when assessing the predictive value

of the Deep Squat (=0.077) and the Straight Leg Raise (p=0.053) testing performances in identifying

future hamstring injury risk. The score on the Deep Squat tended to explain 9.2% of the variance

around the observations for ‘prospective injury [yes/no]’, whereas the SLR could explain about 7.2%

of the observed variance.

- 18 -

Figure 5.

Figure 6.

- 19 -

When performing binary logistic regression on the deep squat – and active straight leg raise score,

without distinguishing between sustaining first or subsequent hamstring injury, the test result on

each test wasn’t able to predict future injury. However, the total score (0-6) from the deep squat and

active straight leg raise test has, in the contrary, the ability to predict a subsequent injury. When the

score of this composite FMS increased by one, the risk of future hamstring injury reduced with 65%.

This model is in the ability to predict 10% of the observed incidence of injury.

Furthermore, separating between sustaining first of subsequent hamstring injury didn’t revealed any

correlation between the individual scores of these two test.

Separate cohorts were subjected to chi-square testing. When combining the combination of the deep

squat and straight leg raise test, there could be made a prediction of future hamstring injury. The

validity is clearly more for the group of players who sustained first hamstring injury ( p=0.006 ). Here,

when the score reached ≥4, the risk was decreased to nothing (RR = 0%), opposed to the players who

scored ≤3 ( RR = 27%). No significant result was found when we considered the group of subsequent

injury ( p=0.236 ), probably because of the influence of various covariates.

Variable Hamstring injury

Without ( n=54) With ( n=14)

FMS

DS & ASLR score ≤ 3 20 11

DS & ASLR score ≥ 4 34 3

TABLE 6.

OR P value

DS & ASLR score ≤ 3 27.27% 0.006

DS & ASLR score ≥ 4 0,00%

TABLE 7.

OR P value

DS & ASLR score ≤ 3 88.89% 0,236

DS & ASLR score ≥ 4 27.27%

TABLE 8.

- 20 -

4.3.2 Y-balance test in association with future hamstring injury risk

Research showed us that the Y-balance test, however, is unfortunately not able to predict hamstring

injury in the future. For each direction of this test.

- 21 -

5. Discussion In our study we examined if the FMS has a predictive value on sustaining hamstring injuries. We can

conclude that the FMS isn’t a specific test battery on predicting hamstring injuries. The positive tests

are the DS and the ASLR. The last one confirms what is proven in other studies. We think that

strength assessment of the hamstring is absent in the FMS protocol. Butler et al. (2013) found by

ROC curve analysis that a FMS cut score of ≤ 14 was able to discriminate between those at a greater

risk for injury. Further research is still needed because there’s a lack of research of the predictive

value of the FMS in athletes, and especially in our interest in soccer players. After all, we can assume

that the FMS is a general and not a specific test battery.

5.1 Functional Movement Screen

5.1.1 Deep squat

Based on the results of this mixed cross-sectional – prospective cohort study, we can conclude that,

soccer players who scored lower on the deep squat FMS component test, have an increased risk of

sustaining a hamstring injury. The squat is a movement that is essential within most closed kinetic

chain sports and corresponding movement requirements. It is the “ready position” and is required

for the majority of powerful movements involving the lower extremities. The deep squat component

test challenges total body mechanics, when performed properly. It is used to assess bilateral

symmetry and functional mobility of the hip-, knee-, and ankle joints. The bar that needs to be held

overhead assesses bilateral, symmetrical mobility of the shoulders and the thoracic spine, as well as

stability and motor control of the core musculature. Poor performance of this test can be the result

of several factors. Limited mobility in the upper torso can be attributed to poor glenohumeral and

thoracic spine mobility. Limited mobility in the lower extremity including poor closed kinetic chain

dorsiflexion of the ankles or poor flexion of the hips may also cause poor test performance, as well as

limited stability/motor control of the core.

5.1.1.1 Core stability

Surprisingly, the subtests of the FMS that contain core stability evaluation such as the trunk stability

push up and the rotary stability test, did not show significant results in predicting hamstring injuries.

We thought this was rather conflicting because we think core stability and core muscle endurance

- 22 -

are essential in performance as well as in injury prevention. Lumbopelvic/core stability is a major

factor during those 2 tests. Dewitt et al. (2014) concluded that restoration of core stability,

neuromuscular control and lengthening eccentric hamstring interventions are proposed key

components to reduce hamstring re-injury. Rehabilitation programs consisting of lengthened state

eccentric loading and lumbopelvic stability training, have shown to be effective in reducing

recurrence after injury. The implementation of lumbopelvic stability interventions, should (in theory)

enhance the length tension capacity of the hamstring muscle group by stabilizing the proximal

muscle attachments, thus avoiding unnecessary tension in the early phases of rehab which may limit

tissue healing. However, Okada et al. (2011) reported no significant relationships between any of the

core stability and FMS variables. Although dynamic, the FMS requires stabilization of the core to

complete the tasks for each screen. One would believe a strong core would be necessary to achieve

endeavour. Therefore, the lack of significant correlations is rather odd. Until further evidence is

available, current practice and widely published rehabilitation protocols cannot either be supported

or refuted. Bennell et al. (1999) evaluated the relationship between hamstring- and lumbar spine

flexibility on one hand and the incidence of hamstring injuries, on the other. In this cohort, the toe-

touch test did not appear to be a useful screening tool to identify footballers at risk for hamstring

strains. However, we can conclude that neuromuscular control, adequate eccentric strength and

musculotendinous elasticity are key components to achieve (1) a correct alignment in the three

planes of motion and (2) a balanced interaction between the internal –and external joint moments.

5.1.1.2 Ankle dorsiflexion

A second plausible cause of poorer deep squat performance could be a restricted ankle dorsiflexion.

When the subject was unable to reach the DS position, he was allowed to place the bar underneath

his heels, allowing a slight plantar flexion in the ankle joint. In this way, it was more likely to reach

the terminal deep squatting position without other major compensations, the athlete was assigned a

score 2. Via this slight modification, the actual presence of a dorsiflexion restriction was confirmed.

Gabbe et al. (2006) proved that a dorsiflexion restriction in the ankle is a risk factor for sustaining a

hamstring injury. In his study, a cohort of 222 Australian football players underwent a baseline

measurement in the form of a self-reported questionnaire and a musculoskeletal screening, of which

an ankle dorsiflexion lunge range, during the pre-season period of the 2002 Australian football

season, after which this cohort was submitted to follow up for registration of hamstring injury

incidence. Players with restricted ankle dorsiflexion on the lunge test were at elevated risk of

sustaining a hamstring injury but this was not significant. The nature of this relationship is unclear

and has not been investigated previously.

- 23 -

Hamstring injuries are believed to occur during the terminal swing phase of sprinting, or at early

ground contact with the foot in a relatively plantar flexed position61,72. Given this, the relationship

between reduced dorsiflexion and hamstring injury risk is not obvious. Potentially, dorsiflexion

stiffness could be associated with the presence of another possible but yet to be identified risk

factor, like poor proprioception. Poor proprioception or neuromuscular control could impact

hamstring functioning during the terminal swing phase of the sprinting cycle, increasing the

likelihood of hamstring injury at this point. Further studies could assess the relationship between

dorsiflexion stiffness and sprinting mechanics or could target improvement in ankle dorsiflexion

range as a potential prevention strategy for hamstring injuries.

5.1.1.3 Eccentric hamstring power

A deep squat requires negative/eccentric work of the hamstrings. Hamstring injuries tend to occur

during a deceleration or landing task suggesting the negative work may be a key component in the

hamstrings injury risk. Recent research has suggested that the hamstrings musculature has the

highest injury rate of lower extremity musculature54, mostly occurring during negative work

associated with deceleration54,71. The high rate of hamstring injuries may be associated with the

exaggerated load placed on these muscles in response to diminished gluteal function or gluteal

amnesia, or just because of eccentric strength deficits within the hamstring muscle complex, without

involvement of the gluts. Given the high rate of hamstring injuries in sport, a need emerges to

determine the precise role of the hamstrings, the gluts and their synergistic interplay during athletic

movements (especially squat positions) involving shortening and lengthening contractions as well as

the stretch-shortening cycle.

5.1.1.4 Hamstring and quadriceps co-contraction

The high incidence of hamstring injuries in athletes can be attributed to a combination of muscular

and mechanical factors including muscle activation and external loading. Most of these injuries occur

during highly dynamic movements with rapid changes in direction. During an unloaded squat,

hamstring and quadriceps co-contraction has been documented and explained via a co-contraction

hypothesis. This hypothesis suggests that the hamstring provide a stabilizing force at the knee during

a posteriorly-directed force on the tibia to counteract the anterior tibial force imparted by the

quadriceps. In contrast with this suggestion, Isear et al. (1997) reported that at no time during the

squat, however, did the hamstrings demonstrate significantly greater EMG activity than the

quadriceps even though both muscles demonstrated their greatest EMG activity during the 90-60°

- 24 -

arc of knee angle. Since the hamstrings appear to be minimally active during closed kinetic chain

activities such as an unloaded squat, perhaps other factors, such as compressive forces ( e.g., axial

loading) and joint geometry ( e.g., 9% posterior tilt of the proximal articulation surface of the tibia),

play more integral roles in knee joint stability than does muscular co-contraction of the hamstrings

and quadriceps. To further question the importance of the hamstrings during an unloaded squat, we

reviewed Wickiewicz et al. (1983) cadaveric study of lower extremity muscle architecture which

demonstrated that the cross-sectional area of the hamstrings was approximately 40% smaller than

that of the quadriceps. Thus, to offset the large forces imparted by the quadriceps, we believe that

the hamstrings would need to demonstrate significantly more relative EMG activity than the

quadriceps regardless of any advantages that might be realized as a result of line of pull or muscle

length relationships. Isear et al. (1997), however, demonstrated hamstring activity of more than five

times less than that of the quadriceps. Therefore, we believe these data provide adequate support

from which to question the notion, as suggested by the co-contraction hypothesis, that hamstring

muscle activity is sufficient to provide the necessary posterior tibial shear forces to counteract

adequately the anterior tibial shear forces imparted by the quadriceps, thus providing a stabilizing

force at the knee during an unloaded squat.

5.1.2 Active straight leg raise

Aside from poorer performance on the Deep Squat test, a weaker score on the Active straight Leg

Raise test (ASLR) , could also be associated with a higher risk of sustaining a hamstring injury. The

ASLR evaluates the ability to disassociate the lower extremity from the trunk, as the testing leg needs

to be lifted maximally with an extended knee and ankle, while maintaining stability in the torso. The

ASLR test assesses active hamstring and gastro‐soleus flexibility while maintaining a stable pelvis and

core, and active extension of the opposite leg. The ability to perform the ASLR test requires

functional hamstring, gluteal, and iliotibial band flexibility, all essential for adequate (soccer)

performance. This is different from passive flexibility, which is more commonly assessed. Next to

(active) muscle flexibility, adequate hip extension ROM in the opposite leg and pelvic and core

stability are required.

Poor performance during this test can be the result of several factors. First, the athlete may lack

functional hamstring flexibility. Second, the athlete may have inadequate mobility of the opposite

hip, possible due to iliopsoas tightness, associated with an anteriorly tilted pelvis. If this limitation is

considerable, true active hamstring flexibility cannot be assessed. Consecutively, ASLR performance

is highly dependent on contralateral hip extension mobility and the results should be interpreted as

- 25 -

such. Next to the ASLR, the Hurdle Step component test is also highly dependent on adequate hip

mobility (both in flexion and extension directions); however, this test directly scores the flexibility of

the hamstrings, gluts and iliopsoas and the results are less likely to be biased.

5.1.2.1 Hamstring flexibility

We found that 2 studies measured the hamstring flexibility with a passive knee extension test. They

came to the same conclusion, that there is no association between hamstring flexibility and an

increased risk of sustaining a hamstring injury3,24.

One study, using an active knee extension test, presented that a decrease of active hamstring

flexibility, showed an association with the incidence or former presence of hamstring injuries, with a

correlation that approached significance.28

Two other tests, measuring the flexibility of the hamstring, are the active and passive Straight leg

raise test (SLR). For the active SLR-test, authors demonstrated that for every 1° decrease in the active

hip flexion range of motion, the propensity for injury increased x 1,29.34

The passive SLR was used as screening tool in two studies. The first study approached a significant

correlation between a preseason decrease in hamstring flexibility and a higher risk of hamstring

injury during the season31. The second study presented contradictory results, and found no

correlation between hamstring flexibility and hamstring injury, measured with the passive SLR-test38.

The supine straight leg raise test is often recognized as the gold standard for measuring hip ROM and

concordant hamstring flexibility, also because this test allows unilateral measurement20.

For the SLR test, we need to notice that it is important to make a difference between the passive and

active SLR. The results show us that the active range of hip-flexion is a predictor of hamstring injury38,

in contrast to the passive ROM of hip-flexion, for which we found contradictory results 31,38.

Furthermore, considering the small number of observed hamstring injuries in the study of Gabbe et

al. (2005), the power of the study was not high which means that their conclusion must be

interpreted carefully.

Lockie et al. (2015) found a positive correlation between the unilateral sit-and-reach test (both

sides), which assess lower body flexibility (hamstring flexibility), and active straight leg raise test

(p=0,027). The left-leg active straight leg raise also best predicted the left-and-right-leg sit-and-reach.

The between-leg sit-and-reach difference had negative correlations with the left-leg active straight-

leg raise. Limitation of this study is that it had a small sample size (n=9) and that the subjects were

healthy female athletes.

- 26 -

5.1.2.2 Rectus femoris flexibility

Lastly, we found one screening tool, the Modified Thomas test, that could prove that flexibility of the

hip flexors, especially Rectus Femoris flexibility, is an independent risk factor of hamstring injury31.

However, a second study of the same author refuted former statement and showed that hip flexor

flexibility is not a risk factor for hamstring injury up until the football player reaches the age of 25,

after which it is significantly associated with an increased HSI vulnerability30. However, this is in

contrast with our results that only showed one player, of 11 players older than 25, who became

injured in the season after testing. Hagel et al. (2005) also concluded (after adjustment for exposure)

that younger age was associated with a lower relative risk of injury, as were quadriceps flexibility and

active knee extension range of motion. They conclude that it’s highly probable that there is an

association between a decrease in muscle flexibility, especially hamstring flexibility and possibly

iliopsoas flexibility, and a higher risk of hamstring injury. A plausible mechanism may involve

alteration in the mechanics of running and sprinting. In both studies the RF (hip flexors) flexibility was

tested in the modified Thomas test position. This position mimics the terminal stance and pre-swing

position of the leg during running and sprinting. At this point, the bi-articular Rectus Femoris is

lengthened over both hip and knee, and is acting eccentrically to control extension of the hip and

flexion of the knee. As it stretches, the tendon of the rectus femoris absorbs energy, which is

released during the active flexion of the hip and extension of the knee through mid to late swing

phase, accelerating the forward movement of the leg. Before initial ground contact, the hamstrings

must contract eccentrically to decelerate the forward momentum of the tibia. During this forceful

eccentric action, the hamstrings are susceptible for strain injury. The higher the running speed, the

higher the muscle loading and thus the higher the injury risk. When the Rectus Femoris is very tight,

this might increase the positive elastic recoil of the tendon, increasing the acceleration of hip flexion

and knee extension, which must be counteracted by the eccentrically contracting hamstrings.

Therefore a greater load may be placed on the hamstring muscles, potentially increasing their risk of

future 31. This study also gives another plausible explanation for this association, namely that the

reduction in hip flexor length could result in a restriction of hip extension in sprinting. Compensation

with increased movement at the lumbar spine, could be required to gain sufficient hip extension.

Over time, reliance on lumbar spine movement to compensate for restricted hip extension could lead

to joint hypermobility, irritation of the neural structures and activation problems within the

hamstring muscles, resulting in increased injury

However, in the study of Gabbe et al. (2006), quadriceps (RF) flexibility could not be identified as a

predictor of hamstring injuries across all ages.32

- 27 -

5.1.2.3 Neural extensibility

Lastly, Bennell et al. (1998) suggest that the SLR may be more of an indicator of the magnitude of

neural extensibility, rather than hamstring muscle length, which the reader should acknowledge as

well It has been suggested that neural extensibility may play a role in hamstring injury vulnerability63

In cases where neural pathology produces altered tension in the hamstring muscles, the intensity or

synergy of muscle contraction may be altered and injury to the musculotendinous unit may occur. It

is possible that momentary stretch on irritated neural tissue may cause a protective reflex

contraction in the hamstring muscles, resulting in an uncoordinated agonist-antagonist action.

Regarding the possible influence of contralateral iliopsoas flexibility on the hamstring injury risk, no

literature is available to date. Therefore, further research is needed.

5.1.3 FMS composite score of deep squat and active straight leg raise test

The binary logistic regression analysis revealed that a score of ≤3 on the DS & ASLR, influenced the

incidence of sustaining first hamstring injury after adjusting for subjects’ characteristics ( RR=27%),

unlike those who scored ≥4 ( RR=0%). The relatively strong predictability of running injuries according

to the DS & ASLR score was attributed to the following reasons. First, the DS test by itself had a

strong predictability of injuries, which was in accordance with the result of Butler et al.’s study36. The

DS test assesses bilateral, symmetrical mobility, especially mobility of hips, ankles, and thoracic

spine, and coordination in the close kinetic chain. Renström et al. (1993) reported that poor flexibility

and deficit in neuromuscular coordination can cause running injuries. Additionally, excessive

pronation and knee-in during testing, which was one of the causes that decreased the score on the

DS test14, was also reported to be a risk factor for injury45. Second, the ASLR test was also found to be

related to running injuries; it assesses active hamstring and gastric-soleus flexibility while maintaining

a stable pelvis. This finding agreed with the study by Yagi et al. (2013), who also reported that limited

SLR ability increased the injury risk in high school runners. Additionally, Lysholm et al. (1987)

reported that flexibility of the hamstrings was a risk factor for injury. Consequently, deficits in the DS

and ASLR tests are likely to induce asymmetric or compensatory movement patterns and thus result

in running injuries. Thus, the FMS contains both helpful and less helpful movement tests for

predicting injury risk in competitive male runners.36

- 28 -

5.1.4 Other FMS component tests

The HS test assesses stepping ability, which requires mobility and stability of the legs as well as

coordination. The ILL test requires mobility and stability in the split stance as well as coordination.

Although these 2 tests seem to be relevant for running, they were not significantly associated with

incidence of running injury because most subjects received a score of 2 (91.7% for HS, 86.9% for ILL).

Due to their ceiling effects, these 2 tests were ineffective in screening injury risk. As a result, the FMS

composite score had low predictability. For the SM, TSPU, and RS tests, there is no solid evidence

that shoulder mobility and core-stability influence the incidence of running injuries.36

5.2 Y balance test

Next to the value of the FMS in hamstring injury risk identification, we also evaluated the possible

role of the Y-balance test (YBT). We can conclude that the YBT is not able to differentiate players with

a low or high risk of sustaining future injury, nor has the capacity to identify athletes with a

hamstring injury history.

Overmoyer et al. (2015) examined how deficits in flexibility are related to the Y-Balance testing

performance, because joint flexibility, bilateral asymmetries in flexibility, and bilateral asymmetries

in performance of the Y Balance Test have been associated with injuries. . Based on their results,

when used with recreationally active healthy adults, the Y-Balance Test may help identify lower

extremity flexibility deficits and flexibility asymmetries in the ankle and hip regions, but may need to

be used in conjunction with additional tests to understand the broader picture regarding the

association between functional movement quality and injury risk. Especially for an athletic

population and regarding the predictive value for injuries. Recently, Smith et al. (2015) did some

interesting findings. The YBT has been proposed as a screen for injury risk; however, limited research

is available concerning the actual association between YBT performance and future injury risk. The

purpose of the study of Smith et al. (2015) was to examine the association between YBT (asymmetry

and composite score (CS)) and noncontact injury in a sample of Division I (DI) college athletes from

multiple sports. ROC curves determined that bilateral asymmetry of more than 4 cm would be the

associated with an elevated injury risk. Only asymmetry in the anterior direct was significantly

associated with noncontact injury. CS in this sample of DI athletes was not associated with increased

risk of injury.

- 29 -

Muscle fatigue is related to a decline in force output and proprioception. These can ultimately have

an adverse effect on neuromuscular control and functional performance. Local muscle fatigue has

been shown to have adverse consequences on dynamic standing balance. However, physical

therapists should be aware of the adverse influence distant fatigue may exhibit on neuromuscular

control in muscles not actively involved in the fatiguing exercise. The balance deficits noted may

indicate an increased risk of injury with muscle fatigue in muscles not directly contributing to

standing balance. (Wassinger et al. (2014))68 Therefore, this is obviously an important view in making

an overall screening tool, because when upper limb testing is followed by the Y balance test, or even

the Functional Movement screen, this could affect the results of these last two tests.

5.3 New insights in the clinical use of FMS and YB

Recently, a couple of new papers concerning the FMS and Y-balance tests were published. Chimera

et al. (2015) found that research is limited regarding the effects of injury or surgery history and sex

on the Functional Movement Screen (FMS) and Y Balance Test (YBT). Their findings suggest, lower

overall FMS component scores were found in athletes with a history of hip-, elbow- and hand injuries

as well as subject with a history of shoulder surgery. Worse FMS movement pattern performance

was observed in athletes with a history of knee surgery, hip injury, hip surgery, shoulder injury and

shoulder surgery. Female athletes performed worse in FMS movement patterns for trunk and rotary

stability but better in the lunge, shoulder mobility and straight-leg raise. Anterior asymmetry was

greater for male athletes.

5.4 Reoccurence of hamstring injury

We can confirm the results of previous studies, indicating that previous hamstring injury is a great

risk factor of sustaining a new hamstring injury. Previous injury is often proposed to be a risk factor

for soccer injuries, but most studies rely on players reporting their own medical history and are thus

potentially subject to recall bias. Little is known about the natural variation in injury pattern between

seasons. Hägglund et al. (2006) investigated whether prospectively recorded injuries during one

season are associated with injuries sustained during the following season, and to compare injury risk

and injury pattern between consecutive seasons. Players who were injured in the 2001 season were

at greater risk of any injury in the following season compared with the non-injured players. Players

with a previous hamstring injury, groin injury, and knee joint trauma were 2 to 3 times more likely to

sustain an identical injury in the following season, whereas no such relation was found for ankle

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sprain. However age was not associated with an increased injury risk. Engebretsen et al. (2010) found

similar results. Previous acute hamstring injury was found to be a significant risk factor for new

hamstring injuries. Previously injured players have more than twice as high a risk of sustaining a new

hamstring injury.

5.5 Similar research

In 2013, Lehr et al. ( 2013) did a similar prospective study as ours. In athletics, efficient screening

tools are sought to curb the rising number of noncontact injuries and associated health care costs.

The authors hypothesized that an injury prediction algorithm incorporating a functional movement

screen, demographic information, and injury history, can accurately categorize the magnitude of the

risk of noncontact lower extremity (LE) injury. It is unrealistic to individually test for each of the

known risk factors. Therefore, a screening process that uses field-expedient tests that incorporates

multiple potential risk factors, along with proper weighting of these factors, may be useful. The

above mentioned author used the Lower Quarter Y-Balance test and the FMS-test for injury risk

assessment. Athletes were then prospectively followed for noncontact LE injury. 12% of the study

sample sustained a hamstring injury. Subsequent analysis divided the sample into two risk

categories: Low (normal and slight) and High (moderate and substantial) risk of sustaining future

injury. Athletes subcategorized in the ‘high risk’ group, were at a significantly greater risk of

noncontact LE injury during the season. These results suggest that an injury prediction algorithm

composed of performance on efficient, low-cost, field-ready tests can help identify individuals at

elevated risk of noncontact LE injury. It is unknown if an athlete’s risk category can be altered with

injury prevention systems. However, individual components of the injury risk algorithm are

modifiable. A neuromuscular training program has been shown to be able to elevate the YBT-LQ

composite scores above the injury threshold in high school soccer players.47 The study of Lehr et al.

(2013) used bench marks for injury risk that were sports, gender, and age specific. The sports

medicine clinician can immediately apply the results of this study in two ways. First, the YBT-LQ, FMS

and injury prediction algorithm can be implemented in pre- participation screening to identify

athletes with the highest injury risk so that these athletes can be remediated via individual

prevention strategies before the start of a new season. Furthermore, these field-expedient tests and

the Move2Perform algorithm can be used for return to sport decisions.

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6 Limitations

First, our study relies on players reporting their own medical history and are thus potentially subject

to recall bias. We can wonder if you may believe the self-report of the players concerning which

hamstring muscle was injured and if the injury was proximal or distal in the muscle. This is why we

could not meet the influence of the exact location of a hamstring injury on functional score as re-

injury risk.

During the testing at the UZ of Ghent, the functional screening was consequently conducted by the

same 3 researchers (RV, BVP, MW). In that way scoring could be performed quite objectively, with

mutual agreement. However, the field testing was done by only one assessor, so this evaluation was

more subjective.

A limitation of the FMS is that there is no specific test that the hamstring strength examines. Yeung

et al. (2009) concluded that quadriceps peak torque ratio assessments may be useful to identify

sprinters susceptible to hamstring injury. Van der horst et al. (2014) proved that eccentric hamstring

strength exercises are hypothesized to reduce the incidence of hamstring injury among male

amateur soccer players by 70%. The prevention of such injuries will be beneficial to soccer players,

clubs, football associations, health insurance companies and society.

Another huge limitation of the FMS in our study is that we did not incorporated the shoulder mobility

test in our analysis. We just focused on the FMS lower limb and core stability tests. A lack of shoulder

mobility could be an injury risk factor for hamstring injury, perhaps because of the compensation in

the lower kinetic chain that is the immediate consequence. This need to be investigated by future

research, in combination with the Y-balance upper limb test. In that way, we could get a view if a lack

of upper limb dysfunction could predict injuries in the lower kinetic chain.

A limitation of the Y-balance test is that due to the fact that this test is dynamic, difficulties can occur

in attempting to accurately assess the maximal reach point and what criteria constitutes a successful

reach (e.g. how much movement of the stance foot is allowed or if the reach foot is allowed to touch

down). Touching down with the reach foot introduces error by making it difficult to quantify the

amount of support gained from that touchdown. If touchdown is not allowed, standardizing the

distance from the ground that the person reaches is difficult, as well as instantaneously marking the

maximal reach point. In addition, it is difficult for examiners to determine how much movement of

the stance foot is allowed. Precise determination of the heel or forefoot lift off from the surface is

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difficult due to the contours of the foot and the rapid position changes due to co-contraction of the

lower limb muscles during unilateral stance.

In both the FMS and Y-balance test, error could have been introduced by fatigue and practice effect.

The last limitation in our study is that we didn’t do a follow-up through the whole season. That

wasn’t practical attainable. Our follow-up went till the end of February. When we would have a done

a follow-up till now, till the end of the season, we expect we would have more injuries. Injuries occur

more at the end of the season when the players are more fatigue.

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7 Conclusion

The functional screening tool FMS itself is not useful to predict an increased risk of sustaining

hamstring strain injuries in the population of male soccer players.

However, The FMS component tests ‘deep squat’ and ‘active straight leg raise’ are able to predict

future hamstring injury, this especially in terms of the risk of sustaining a hamstring injury for the first

time. For this purpose, a combined screening tool of these two tests should be created for a good

prediction of future hamstring injury.

The Y-balance is not a specific valid test to predict hamstring injury. It’s a more useful screening tool

to evaluate the knee –and ankle stability.

8 Acknowledgements

The authors would like to extend their sincere appreciation to our promotor Prof. Dr. Damien Van

Tiggelen and our co-promotor Joke Schuermans who helped us when we had some issues during the

2 years we wrote our thesis. We would also like to thank our fellow students Xavier Verstraeten,

Thomas De Jonghe, Alexander Blondeel, Elien Boulangier and Naomi Fevery for the good teamwork

during the testing in the summer.

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9 References

1. Alter MJ. Science of flexibility (3rd ed.). Champaign, IL: Human Kinetics, 2004.

2. Arnason A1, Gudmundsson A, Dahl HA, Jóhannsson E. Soccer injuries in Iceland. Scand J Med

Sci Sports. 1996 Feb;6(1):40-5.

3. Arnason A, Sigurdsson SB, Gudmundsson A, Holme I, Engebretsen L, Bahr R. Risk factors for

injuries in football. Am J Sports Med. 2004 Jan-Feb;32(1 Suppl):5S-16S.

4. Bennell K1, Wajswelner H, Lew P, Schall-Riaucour A, Leslie S, Plant D, Cirone J. Isokinetic

strength testing does not predict hamstring injury in Australian Rules footballers. Br J Sports

Med. 1998 Dec;32(4):309-14.

5. Bennell K1, Tully E, Harvey N. Does the toe-touch test predict hamstring injury in Australian

Rules footballers? Aust J Physiother. 1999;45(2):103-109.

6. Bradley PS1, Portas MD. The relationship between preseason range of motion and muscle

strain injury in elite soccer players. J Strength Cond Res. 2007 Nov;21(4):1155-9.

7. Brockett CL1, Morgan DL, Proske U. Predicting hamstring strain injury in elite athletes. Med

Sci Sports Exerc. 2004 Mar;36(3):379-87.

8. Brooks JH, Fuller CW, Kemp SP, Reddin DB. Incidence, risk, and prevention of hamstring

muscle injuries in professional rugby union. Am J Sports Med 2006 Aug;34(8):1297-306. Epub

2006 Feb 21.

9. Butler RJ1, Southers C, Gorman PP, Kiesel KB, Plisky PJ. Differences in soccer players' dynamic

balance across levels of competition. J Athl Train. 2012 Nov-Dec;47(6):616-20. doi:

10.4085/1062-6050-47.5.14.

10. Butler RJ1, Contreras M, Burton LC, Plisky PJ, Goode A, Kiesel K. Modifiable risk factors

predict injuries in firefighters during training academies. Work. 2013 Jan 1;46(1):11-7. doi:

10.3233/WOR-121545.

11. Cameron M, Adams R. Kicking footedness and movement discrimination by elite Australian

Rules Footballers. J Sci Med Sport. 2003 Sep;6(3):266-74

12. Chimera NJ, Smith CA, Warren M. Injury History, Sex, and Performance on the Functional

Movement Screen and Y Balance Test. J Athl Train. 2015 Mar 11. [Epub ahead of print]

- 35 -

13. Ciullo JV, Zarins B. Biomechanics of the musculotendinous unit: relation to athletic

performance and injury. Clin Sports Med. 1983 Mar;2(1):71-86. No abstract available.

14. Cook G, Burton L, Hoogenboom B. Pre-participation screening: the use of fundamental

movements as an assessment of function - part 1. N Am J Sports Phys Ther. 2006

May;1(2):62-72.

15. Cook G, Burton L, Hoogenboom B. Pre-participation screening: the use of fundamental

movements as an assessment of function - part 2. N Am J Sports Phys Ther. 2006

May;1(2):62-72.

16. Coughlan GF1, Fullam K, Delahunt E, Gissane C, Caulfield BM. A comparison between

performance on selected directions of the star excursion balance test and the Y balance test.

J Athl Train. 2012 Jul-Aug;47(4):366-71. doi: 10.4085/1062-6050-47.4.03.

17. Croisier JL1, Forthomme B, Namurois MH, Vanderthommen M, Crielaard JM. Hamstring

muscle strain recurrence and strength performance disorders. Am J Sports Med. 2002 Mar-

Apr;30(2):199-203.

18. DeWitt J1, Vidale T2. Recurrent hamstring injury: consideration following operative and non-

operative management. Int J Sports Phys Ther. 2014 Nov;9(6):798-812.

19. Drezner JA. Practical management: hamstring muscle injuries. Clin J Sport Med. 2003

Jan;13(1):48-52.

20. Ekstrand J, Gillquist J. The frequency of muscle tightness and injuries in soccer players. Am J

Sports Med. 1982 Mar-Apr;10(2):75-8.

21. Ekstrand J, Gillquist J. Soccer injuries and their mechanisms: a prospective study. Med Sci

Sports Exerc 1983;15(3):267–70.

22. Ekstrand J, Hagglund M, Walden M. Injury incidence and injury patterns in professional

football – the UEFA injury study. British Journal of Sports Medicine 2010: Epub ahead of

print.

23. Ekstrand J1, Hägglund M, Waldén M. Epidemiology of muscle injuries in professional football

(soccer). Am J Sports Med. 2011 Jun;39(6):1226-32. doi: 10.1177/0363546510395879. Epub

2011 Feb 18.

- 36 -

24. Engebretsen AH1, Myklebust G, Holme I, Engebretsen L, Bahr R. Intrinsic risk factors for

hamstring injuries among male soccer players: a prospective cohort study. Am J Sports Med.

2010 Jun;38(6):1147-53. doi: 10.1177/0363546509358381. Epub 2010 Mar 24.

25. Fousekis K1, Tsepis E, Poulmedis P, Athanasopoulos S, Vagenas G. Intrinsic risk factors of non-

contact quadriceps and hamstring strains in soccer: a prospective study of 100 professional

players. Br J Sports Med. 2011 Jul;45(9):709-14. doi: 10.1136/bjsm.2010.077560. Epub 2010

Nov 30.

26. Freckleton G1, Cook J, Pizzari T. The predictive validity of a single leg bridge test for

hamstring injuries in Australian Rules Football Players. Br J Sports Med. 2014 Apr;48(8):713-

7. doi: 10.1136/bjsports-2013-092356. Epub 2013 Aug 5.

27. Fyfe JJ1, Opar DA, Williams MD, Shield AJ. The role of neuromuscular inhibition in hamstring

strain injury recurrence. J Electromyogr Kinesiol. 2013 Jun;23(3):523-30. doi:

10.1016/j.jelekin.2012.12.006. Epub 2013 Feb 9.

28. Gabbe BJ, Finch CF, Bennell KL, Wajswelner H. Risk factors for hamstring injuries in

community level Australian football. Br J Sports Med 2005;39(2):106–10.

29. Gabbe BJ, Bennell KL, Finch CF, Wajswelner H, Orchard JW. Predictors of hamstring injury at

the elite level of Australian football. Scand J Med Sci Sports. 2006 Feb;16(1):7-13.

30. Gabbe BJ, Bennell KL, Finch CF. Why are older Australian football players at greater risk of

hamstring injury? J Sci Med Sport 2006a;9(4):327–33.

31. Gribble PA1, Brigle J, Pietrosimone BG, Pfile KR, Webster KA. Intrarater reliability of the

functional movement screen. J Strength Cond Res. 2013 Apr;27(4):978-81. doi:

10.1519/JSC.0b013e31825c32a8.

32. Hagel B. Hamstring injuries in Australian football. Clin J Sport Med. 2005 Sep;15(5):400.

33. Hagglund M, Walden M, Ekstrand. Previous injury as a risk factor for injury in elite football: a

prospective study over two consecutive seasons. Br J Sports Med. 2006;40:767-772

34. Henderson G1, Barnes CA, Portas MD. Factors associated with increased propensity for

hamstring injury in English Premier League soccer players. J Sci Med Sport. 2010

Jul;13(4):397-402. doi: 10.1016/j.jsams.2009.08.003. Epub 2009 Oct 2.

35. Hennessey L1, Watson AW. Flexibility and posture assessment in relation to hamstring injury.

Br J Sports Med. 1993 Dec;27(4):243-6.

- 37 -

36. Hotta T1, Nishiguchi S, Fukutani N, Tashiro Y, Adachi D, Morino S, Shirooka H, Nozaki Y, Hirata

H, Yamaguchi M, Aoyama T. Functional Movement Screen for Predicting Running Injuries in

18-24 Year-Old Competitive Male Runners. J Strength Cond Res. 2015 Apr 3. [Epub ahead of

print]

37. Isear JA Jr1, Erickson JC, Worrell TW. EMG analysis of lower extremity muscle recruitment

patterns during an unloaded squat. Med Sci Sports Exerc. 1997 Apr;29(4):532-9.

38. Jarvinnen TA, Kaariainen M, Jarvinen M, Kalimo H. Muscle strain injuries. Curr Opin

Rheumatol. 2000;12:155-161

39. Kiesel K, Plisky PJ, Voight ML. Can Serious Injury in Professional Football be Predicted by a

Preseason Functional Movement Screen? N Am J Sports Phys Ther. 2007 Aug;2(3):147-58.

40. Lehr ME1, Plisky PJ, Butler RJ, Fink ML, Kiesel KB, Underwood FB. Field-expedient screening

and injury risk algorithm categories as predictors of noncontact lower extremity injury. Scand

J Med Sci Sports. 2013 Aug;23(4):e225-32. doi: 10.1111/sms.12062. Epub 2013 Mar 20.

41. Lisman P1, O'Connor FG, Deuster PA, Knapik JJ. Functional movement screen and aerobic

fitness predict injuries in military training. Med Sci Sports Exerc. 2013 Apr;45(4):636-43. doi:

10.1249/MSS.0b013e31827a1c4c.

42. Lockie R1, Schultz A2, Callaghan S3, Jordan C2, Luczo T4, Jeffriess M5. A preliminary

investigation into the relationship between functional movement screen scores and athletic

physical performance in female team sport athletes. Biol Sport. 2015 Mar;32(1):41-51. doi:

10.5604/20831862.1127281. Epub 2014 Nov 3.

43. Lysholm J, Wiklander J. Injuries in runners. Am J Sports Med. 1987 Mar-Apr;15(2):168-71.

44. Meeuwisse WH1, Fowler PJ. Frequency and predictability of sports injuries in intercollegiate

athletes. Can J Sport Sci. 1988 Mar;13(1):35-42.

45. Messier SP1, Pittala KA. Etiologic factors associated with selected running injuries. Med Sci

Sports Exerc. 1988 Oct;20(5):501-5.

46. Minick KI1, Kiesel KB, Burton L, Taylor A, Plisky P, Butler RJ. Interrater reliability of the

functional movement screen. J Strength Cond Res. 2010 Feb;24(2):479-86. doi:

10.1519/JSC.0b013e3181c09c04.

- 38 -

47. Myer GD1, Ford KR, Brent JL, Hewett TE. Differential neuromuscular training effects on ACL

injury risk factors in"high-risk" versus "low-risk" athletes. BMC Musculoskelet Disord. 2007

May 8;8:39.

48. Okada T1, Huxel KC, Nesser TW. Relationship between core stability, functional movement,

and performance. J Strength Cond Res. 2011 Jan;25(1):252-61. doi:

10.1519/JSC.0b013e3181b22b3e.

49. Onate JA1, Dewey T, Kollock RO, Thomas KS, Van Lunen BL, DeMaio M, Ringleb SI. Real-time

intersession and interrater reliability of the functional movement screen. J Strength Cond

Res. 2012 Feb;26(2):408-15. doi: 10.1519/JSC.0b013e318220e6fa. 50

50. Orchard JW. Intrinsic and extrinsic risk factors for muscle strains in Australian football. Am J

Sports Med. 2001 May-Jun;29(3):300-3.

51. Overmoyer GV1, Reiser RF 2nd. RELATIONSHIPS BETWEEN LOWER-EXTREMITY FLEXIBILITY,

ASYMMETRIES AND THE Y-BALANCE TEST. J Strength Cond Res. 2015 Feb 21. [Epub ahead of

print]

52. Padulo J, Tiloca A, Powell D, Granatelli G, Bianco A, Paoli A. EMG amplitude of the biceps

femoris during jumping compared to landing movements. Springerplus. 2013 Oct 9;2:520.

doi: 10.1186/2193-1801-2-520. eCollection 2013.

53. Parchmann CJ1, McBride JM. Relationship between functional movement screen and athletic

performance. J Strength Cond Res. 2011 Dec;25(12):3378-84. doi:

10.1519/JSC.0b013e318238e916.

54. Petersen J, Thorborg K, Nielsen MB, Budtz-Jørgensen E, Hölmich P. Preventive effect of

eccentric training on acute hamstring injuries in men's soccer: a cluster-randomized

controlled trial. Am J Sports Med. 2011 Nov;39(11):2296-303. doi:

10.1177/0363546511419277. Epub 2011 Aug 8.

55. Plisky PJ1, Rauh MJ, Kaminski TW, Underwood FB. Star Excursion Balance Test as a predictor

of lower extremity injury in high school basketball players. J Orthop Sports Phys Ther. 2006

Dec;36(12):911-9.

56. Renström AF. Mechanism, diagnosis, and treatment of running injuries. Instr Course Lect.

1993;42:225-34.

- 39 -

57. Shaffer SW1, Teyhen DS, Lorenson CL, Warren RL, Koreerat CM, Straseske CA, Childs JD. Y-

balance test: a reliability study involving multiple raters. Mil Med. 2013 Nov;178(11):1264-

70. doi: 10.7205/MILMED-D-13-00222.

58. Shultz R1, Anderson SC, Matheson GO, Marcello B, Besier T. Test-retest and interrater

reliability of the functional movement screen. J Athl Train. 2013 May-Jun;48(3):331-6. doi:

10.4085/1062-6050-48.2.11. Epub 2013 Feb 20.

59. Smith CA1, Chimera NJ, Warren M. Association of y balance test reach asymmetry and injury

in division I athletes. Med Sci Sports Exerc. 2015 Jan;47(1):136-41. doi:

10.1249/MSS.0000000000000380.

60. Smith CA1, Chimera NJ, Wright NJ, Warren M. Interrater and intrarater reliability of the

functional movement screen. J Strength Cond Res. 2013 Apr;27(4):982-7. doi:

10.1519/JSC.0b013e3182606df2.

61. Stanton P, Purdham C. Hamstring injuries in sprinting - the role of eccentric exercise. J

Orthop Sports Phys Ther. 1989;10(9):343-9.

62. Teyhen DS1, Shaffer SW, Lorenson CL, Halfpap JP, Donofry DF, Walker MJ, Dugan JL, Childs

JD. The Functional Movement Screen: a reliability study. J Orthop Sports Phys Ther. 2012

Jun;42(6):530-40. doi: 10.2519/jospt.2012.3838. Epub 2012 May 14.

63. Turl S, George K. Adverse neural tension: a factor in repetitive hamstring strain. J Orthop

Sports Phys Ther 1998;27:16-21

64. van der Horst N1, Smits DW1, Petersen J2, Goedhart EA3, Backx FJ1. The preventive effect of

the Nordic hamstring exercise on hamstring injuries in amateur soccer players: study

protocol for a randomised controlled trial. Inj Prev. 2014 Aug;20(4):e8. doi:

10.1136/injuryprev-2013-041092. Epub 2013 Dec 13.

65. Verrall GM1, Slavotinek JP, Barnes PG, Fon GT, Spriggins AJ. Clinical risk factors for hamstring

muscle strain injury: a prospective study with correlation of injury by magnetic resonance

imaging. Br J Sports Med. 2001 Dec;35(6):435-9; discussion 440.

66. Waldén M1, Hägglund M, Ekstrand J. Injuries in Swedish elite football--a prospective study on

injury definitions, risk for injury and injury pattern during 2001. Scand J Med Sci Sports. 2005

Apr;15(2):118-25.

- 40 -

67. Waldén M1, Hägglund M, Ekstrand J. UEFA Champions League study: a prospective study of

injuries in professional football during the 2001-2002 season. Br J Sports Med. 2005

Aug;39(8):542-6.

68. Wassinger CA1, McKinney H1, Roane S1, Davenport MJ1, Owens B1, Breese U1, Sokell GA1.

The influence of upper body fatigue on dynamic standing balance. Int J Sports Phys Ther.

2014 Feb;9(1):40-6.

69. Wickiewicz TL, Roy RR, Powell PL, Edgerton VR. Muscle architecture of the human lower limb.

Clin Orthop Relat Res. 1983 Oct;(179):275-83.

70. Witvrouw E1, Danneels L, Asselman P, D'Have T, Cambier D. Muscle flexibility as a risk factor

for developing muscle injuries in male professional soccer players. A prospective study. Am J

Sports Med. 2003 Jan-Feb;31(1):41-6.

71. Woods C1, Hawkins RD, Maltby S, Hulse M, Thomas A, Hodson A; Football Association

Medical Research Programme. The Football Association Medical Research Programme: an

audit of injuries in professional football--analysis of hamstring injuries. Br J Sports Med. 2004

Feb;38(1):36-41.

72. Worrell TW. Factors associated with hamstring injuries. An approach to treatment and

preventative measures. Sports Med. 1994 May;17(5):338-45.

73. Yagi S1, Muneta T, Sekiya I. Incidence and risk factors for medial tibial stress syndrome and

tibial stress fracture in high school runners. Knee Surg Sports Traumatol Arthrosc. 2013

Mar;21(3):556-63. doi: 10.1007/s00167-012-2160-x. Epub 2012 Aug 9.

74. Yeung SS1, Suen AM, Yeung EW. A prospective cohort study of hamstring injuries in

competitive sprinters: preseason muscle imbalance as a possible risk factor. Br J Sports Med.

2009 Aug;43(8):589-94. doi: 10.1136/bjsm.2008.056283. Epub 2009 Jan 27.

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10 Abstract

10.1 Abstract ( Layman’s terms )

Achtergrond: Hamstringletsels (achterste dijbeenspier) horen bij de meest voorkomende letsels in het voetbal en kennen bovendien een groot risico op herval. De FMS en Y-balance zijn 2 functionele testen die trachten het risico op een hamstring(her)aandoening op te sporen door de belangrijke bewegingsvaardigheden te evalueren die bepalend zijn voor de prestatie en letselgevoeligheid van de voetbalspelers. Doel: Onderzoeken in welke mate de functionele testen FMS en Y-balance bruikbaar zijn om een verhoogd risico op hamstringletsels te voorspellen. Methode: In het voorseizoen (juli 2014) werd een groep van 28 spelers met een verleden van een hamstringletsel (patiëntengroep) en 30 spelers zonder verleden (controlegroep) getest in het UZ Gent. Een andere groep van 10 spelers (3 met en 7 zonder verleden) werd op het voetbelveld getest, maar enkel de FMS werd afgenomen bij deze kleine groep. Alle 68 spelers werden gedurende de eerste helft van het daaropvolgende seizoen opgevolgd om te kijken of ze een (nieuw) hamstringletsel opliepen. Resultaten: Er was geen belangrijk verschil tussen de patiënten en controlegroep wat betreft de totale scores van de FMS en Y-balance. Maar, de patiëntengroep behaalde wel een duidelijk lagere score op de Trunk-stability push-up (deeltest van de FMS). Een zwakke score op de deeltesten (1) deep squat en (2) active straight leg raise vertoonde een verband met de hamstringblessuregevoeligheid tijdens de opvolgperiode. Een gecombineerde test van deze twee testen bleek in staat te zijn om een verhoogd risico op een toekomstig hamstringletsel te detecteren, dit voornamelijk bij spelers die nog nooit een blessure hebben opgelopen aan de hamstring. Een score van minder dan 4 op 6 ging gepaard met een risico van 27%, terwijl het risico op een toekomstige hamstringblessure voor de spelers die op deze gecombineerde score 4 of meer scoorden, tot 0 werd reduceerd. Conclusie: De totale FMS score heeft geen voorspellende waarde op het voorspellen van hamstringblessure. De twee deeltesten FMS deep squat en active straight leg raise kunnen een hamstringletsel voorspellen, voornamelijk bij spelers zonder verleden van een hamstringletsel. Om een goede voorspelling te maken van het risico moet wel een gecombineerde test worden gemaakt van deze twee testen. De Y-balance is geen goede test om dit risico te voorspellen.

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11 Appendices

11.1 Functional Movement Screen

1.Deep squat Purpose: The ability to perform the deep squat requires appropriate pelvic rhythm, closed-kinetic chain dorsiflexion of the ankles, flexion of the knees and hips. Extension of the thoracic spine and flexion and abduction of the shoulders as well as stability and motor control of the core musculature.

- placing his/her feet approximately shoulder width apart and the feet aligned in the sagittal plane.

- adjusts their hands on the dowel to assume a 90‐degree angle of the elbows with the dowel overhead

- instruction: descend as far as they can into a squat position while maintaining an upright torso, keeping the heels and the dowel in position. Hold the descended position for a count of one, and then return to the starting position. As many as three repetitions may be performed.

- Not achieved? the athlete is then asked to perform the test with a 2x6 block under the heels.

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Score 3: Upper body // tibia Femur below the horizontal Knees above feet Dowel above feet

Score 2: Upper body // tibia or vertical Femur below horizontal Knees above feet Dowel above feet Block under heels

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Score 1: Upper body and tibia not // Femur not below the horizontal Knees not above feet Dowel not above feet

2. Hurdle step Purpose: The movement requires proper coordination and stability between the hips and torso during the stepping motion as well as single leg stance stability. The hurdle step assesses bilateral functional mobility and stability of the hips, knees and ankles. Performing the hurdle step test requires stanceleg stability of the ankle, knee and hip as well as maximal closed-kinetic chain extension of the hip. The hurdle step also requires step-leg open-kinetic chain dorsifl exion of the ankle and fl exion of the knee and hip. In addition, the subject must also display adequate balance because the test imposes a need for dynamic stability.

- placing the feet together and aligning the toes touching the base of the hurdle. The hurdle is then adjusted to the height of the athlete's tibial tuberosity.

- The dowel is grasped with both hands and positioned behind the neck and across the shoulders.

- maintain an upright posture and step over the hurdle, raising the foot toward the shin, and maintaining alignment between the foot, knee, and hip, and touch their heel to the floor (without accepting weight) while maintaining the stance leg in an extended position.

- The moving leg is then returned to the starting position. - If one repetition is completed bilaterally meeting the criteria provide, a “3”is given.

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Score 3: Hips, knees and ankles remain aligned in the sagittal plane. Minimal to no lumbar movement Dowel // hurdle

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Score 2: Alignment is lost between the hips, knees, and ankles. Movement is noted in the lumbar spine The dowel and hurdle do not remain //

Score1: Contact with hurdle Loss of balance

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3. In-line lunge Purpose: This test assesses torso, shoulder, hip and ankle mobility and stability, quadriceps flexibility and knee stability. The ability to perform the in-line lunge test requires stance-leg stability of the ankle, knee and hip as well as apparent closed kinetic chain hip abduction. The in-line lunge also requires step-leg mobility of the hip, ankle dorsiflexion and rectus femoris flexibility. The subject must also display adequate stability due to the rotational stress imposed.

- Place the end of their heel on the end of the board or a tape measure taped to the floor.

- The previous tibial measurement is then applied from the end of the toes of the foot on the board and a mark is made.

- The dowel is placed behind the back touching the head, thoracic spine, and middle of the buttocks. The hand opposite to the front foot should be the hand grasping the dowel at the cervical spine. The other hand grasps the dowel at the lumbar spine.

- Both toes must point forward, and feet must begin flat. - The individual then lowers the back knee enough to touch the surface behind the

heel of the front foot, while maintaining an upright posture, and then returns to the starting position.

- The lunge is performed up to three times bilaterally in a slow controlled fashion.

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Score 3: the dowel remains vertical Dowel in contact with the head, thorax and sacrum there is no torso movement noted the dowel and feet remain in the sagittal plane Knee touches block

Score 2: If 1 of upper conditions is not fulfilled

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Score 1: Loss of balance Athlete fails

4. Shoulder mobility Purpose: assesses bilateral shoulder range of motion, combining internal rotation with adduction and external rotation with abduction. It also requires normal scapular mobility and thoracic spine extension.

- The tester first determines the hand length by measuring the distance from the distal wrist crease to the tip of the third digit in inches.

- The individual is then instructed to make a fist with each hand, placing the thumb inside of the fist.

- They are then asked to assume a maximally adducted, extended, and internally rotated position with on shoulder and a maximally abducted, flexed, and externally rotated position with the other.

- The tester then measures the distance between the to closest bony prominences. - The flexed shoulder identifies the side being scored.

Score 3: Fists are within one hand length.

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Score 2: Fists are within one and one half hand lengths.

Score 1: Fists are not within one and one half hand lengths.

An impingement clearing exam should be performed at the end of the shoulder mobility test. This movement is not scored; rather it is performed to observe a pain response. If pain is produced, a score of zero is given to the entire shoulder mobility test.

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5. Active straight Leg Raise Purpose: assesses active hamstring, gastroc-soleus, gluteal and iliotibial flexibility while maintaining a stable pelvis and active extension (iliopsoas flexibility) of the opposite leg. The ability to perform the active straight-leg raise test requires functional hamstring flexibility, which is the flexibility that is available during training and competition.

- The individual first assumes the starting position by lying supine with the arms in anatomical position, legs over the 2 × 6 board, and head flat on the floor.

- The tester then identifies the mid‐point between the anterior superior iliac spine, and the midpoint of the patella of the leg on the floor, and a dowel is placed at this position.

- Next the individual is instructed to slowly lift the test leg with a dorsiflexed ankle and an extended knee. During the test the opposite knee (the down leg) must remain in contact with the ground and the toes pointed upward, and the head in contact with the floor.

Score 3: the vertical line of the malleolus of the tested leg resides between the mid‐thigh and the SIAS. The non‐moving limb must remain in neutral position.

Score 2: the vertical line of the malleolus of the tested leg resides between the mid‐thigh and the knee joint line. The non‐moving limb must remain in the neutral position.

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Score 1: Note the vertical line of the malleolus of the tested leg resides below the knee joint line. The non‐moving leg must remain in the neutral position.

6. Extension test en trunk stability test Purpose: The ability to perform the trunk stability push-up requires symmetric trunk stability in the sagittal plane during a symmetric upper extremity movement.

- The individual assumes a prone position with the feet together. - The hands are placed shoulder width apart at the appropriate position per the

described criteria. - During this test, men and women have different starting arm positions. Men begin

with their thumbs at the top of the forehead, while women begin with their thumbs at chin level.

- The individual is asked to perform one push‐up in this position. The body should be lifted as a unit; no “lag” (or arch) should occur in the lumbar spine when performing the movement.

- If the individual cannot perform a push‐up in this position, the thumbs are moved to the next easiest position, chin level for males, shoulder level for females, and the push‐up is attempted again.

- The trunk stability push‐up can be performed a maximum of three times.

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Score 3: Men perform a repetition with thumbs aligned with the top of the head Women perform a repetition with thumbs aligned with the chin

Score 2: M: thumbs//chin F: thumbs //clavicle

Score 1: M: thumbs not // chin F: thumbs not //clavicle

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A clearing exam is performed at the end of the trunk stability push‐up test. This movement is not scored; the test is simply performed to observe a pain response. If pain is produced, positive is recorded on the score sheet and a score of zero is given for the test.

7. Rotary stability test Purpose: a complex movement requiring proper neuromuscular coordination and energy transfer from one segment of the body to another through the torso. The rotary stability test assesses multi-plane trunk stability during a combined upper and lower extremity motion. The ability to perform the rotary stability test requires asymmetric trunk stability in both sagittal and transverse planes during asymmetric upper and lower extremity movement.

- The individual assumes the starting position in quadruped, their shoulders and hips at 90‐degree angles, relative to the torso, with the 2 × 6 board between their hands and knees.

- The individual then flexes the shoulder and extends the same side hip and knee. - The same shoulder is then extended and the knee flexed enough for the elbow and

knee to touch. - This is performed bilaterally, for up to three attempts each side. - If the individual cannot complete this maneuver (score a “3”), they are then

instructed perform a diagonal pattern using the opposite shoulder and hip in the same manner as described for the previous test.

Score 3: The subject performs a correct unilateral repetition.

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Score 2: The subject performs a correct diagonal repetition.

Score 1: The subject is unable to perform a diagonal repetition.

A clearing exam is performed at the end of the rotary stability test. This movement is not scored; it is performed to observe a pain response. If pain is produced, a positive is recorded on the score sheet and a score of zero is given for the test.

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11.2 Y-balance test

FIGURE 1 and 2. Starting position Y-balance test / Anterior reach Y-balance test.

FIGURE 3 and 4. Posteromedial reach Y-balance test / Posterolateral reach Y-balance test.

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Participants.

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11.3 Questionnaire pre-testing

IDENTIFICATIE EN SPECIFICATIE VAN HET RISICOPROFIEL OP ‘HAMSTRING STRAIN INJURY’ BIJ DE

VOETBALSPELER

ADMINISTRATIEVE VRAGENLIJST

Naam Club en divisie Adres

Telefoonnummer Email-adres Geboortedatum Lengte Gewicht Dominant been Hoelang voetbalt u reeds (in jaren)? Spelpositie? Beoefent u naast voetbal nog een andere sport? Zo ja, welke?

Wordt er tijdens de trainingen systematisch voldoende aandacht besteed aan een adequate gedoseerde warming up en cooling down?

Medische voorgeschiedenis? => gelieve hiernaast uw voormalige sportblessures zo volledig mogelijk te noteren, met vermelden van datum/periode van voorkomen en duur van de revalidatieperiode (hoelang u ingevolge het letsel niet voluit hebt kunnen deelnemen aan training en competitie)

Letsel Datum letsel Duur revalidatie

1.

2.

3.

4.

5.

6.

7.

8.

9.

Heeft u momenteel ergens last van (bewegingsapparaat)? Waar precies?

Maakt u gebruik van een supplementaire ‘beschermende’ voetbaluitrusting? (dragen van thermische shorts, braces, steunkousen, ed. )

Rookt u? Bent u bewust bezig met het consumeren van evenwichtige voeding?

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Hoeveel liter water drinkt u dagelijks? (bij benadering)

Enkel voor letselgroep:

Hoeveel keer liep u reeds een hamstringletsel op?

Kan u een benaderende datum geven aan elk van deze letsels? Zo niet, geef dan enkel de datum van uw laatste hamstringblessure:

Hoelang kon u ingevolge uw letsel niet deelnemen aan trainingen en wedstrijden? Wat was met andere woorden de omvang van uw Time-Loss?

Waar was dit laatste letsel exact gesitueerd? Duid aan:

Geef aan hoe omvangrijk uw laatste blessure was aan de hand van volgende vragen:

Betrof het een verrekking of een echte scheur?

Hoe groot was de omvang van uw functioneel deficiet? Welke bewegingen en/of activiteiten kon u niet meer uitvoeren door uw letsel? (sprinten, passen, schieten op doel, lopen, jogging, stappen, trappen doen,..?)

Bent u tevreden over de medische begeleiding en de kwaliteit van uw revalidatie/kinesitherapie na uw laatste hamstringblessure? Gelieve deze revalidatie een score tussen 0 en 10 te geven (waarbij 0 = helemaal niet tevreden over het gevolgde revalidatieprotocol en 10 = geen betere revalidatie denkbaar)

Vat hieronder kort samen waar precies aandacht aan besteed werd bij uw revalidatie / kinesitherapeutische behandelingen (manuele therapie, frictie, massage, elektrotherapie, oefentherapie onderste lidmaat, oefeningen op core-stability, sportspecifieke- en veldtrainingen,..):

In hoeverre voelt u zich voldoende uit gerevalideerd? Hoe zelfzeker voelt u zich in het hervatten van intensieve trainingen en competitie? Geef een score tussen 0 (zeer onzeker en bang om opnieuw gekwetst te raken) en 10 (sterker dan ooit tevoren en absoluut geen zorgen over letselrecidief):

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11.4 Questionnaire after 6 months follow-up

Vragenlijst voetballers winterstop 2014

1/ Algemene vragen

-Naam en voornaam:

-Club + divisie:

-Lengte(cm):

-Gewicht:

-Dominant been(schopbeen li/re):

2/ Sport specifieke vragen

-Hoeveel trainingen gemiddeld per week meegedaan?

-Welke blessures zijn er in de periode van de testing tot nu (december 2014) voorgevallen?

Soort letsel + (li/re) Datum opgelopen letsel Duur revalidatie/out

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-Specifiek hamstringblessures:

Vragen Antwoord( zo specifiek mogelijk aub)

Wanneer (datum)

Hoe is het letsel ontstaan

(lopen/trappen…/tijdens match of training?)

Linker of rechter been

Aan zelfde zijde als vorig hamstring letsel: ja/nee

Locatie letsel:

1) Binnenzijde/buitenzijde been 2) Bovenaan(bil)/midden/onderaan(thv

knieholte)

1)

2)

Heeft u een kinesitherapeut/ arts

geconsulteerd?

Werd er medische beeldvorming uitgevoerd?

ja: wat was de diagnose?

nee: hoe werd diagnose gesteld?

Duur revalidatie

Indien revalidatie: wat werd er gedaan?

Hoeveel trainingen gemist

Hoeveel matchen gemist

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11.5 Score sheet FMS.

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11.6 Score sheet YBT.

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11.7 Informed consent

Informed Consent

Ik ondergetekende, .........................................................................., verklaar hierbij dat ik, als participant aan

een onderzoek van de masterscriptie ‘ Does the Functional Movement Screen and Y balance test have the

ability to predict hamstring injuries in male soccer players?’ (Universiteit Gent):

(1) de informatiebrief heb gelezen. Die geeft uitleg over de aard van de vragen, taken, opdrachten en stimuli

die tijdens het onderzoek zullen worden aangeboden. Op elk ogenblik wordt me de mogelijkheid geboden om

bijkomende informatie te verkrijgen.

(2) totaal vrijwillig deelneem aan het onderzoek.

(4) de toestemming geef aan de proefleiders om mijn resultaten op anonieme wijze te bewaren, te verwerken

en te rapporteren.

(5) de toestemming geef fotomateriaal, getrokken tijdens mijn onderzoek, te mogen gebruiken / publiceren.

(6) op de hoogte ben van de mogelijkheid om mijn deelname aan het onderzoek op ieder moment stop te

zetten.

(7) ervan op de hoogte ben dat ik een samenvatting van de onderzoeksbevindingen kan krijgen.

Gelezen en goedgekeurd te .............................(plaats) op ............. (datum)

Handtekening van participant:

……………………………………