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. . . Published ahead of Print

A Multi-station Proprioceptive Exercise Program Prevents Ankle

Injuries in Basketball

Eric Eils1,2, Ralf Schrter1, Marc Schrder1, Joachim Gerss3, and Dieter Rosenbaum1

1 Funktionsbereich Bewegungsanalytik (Movement Analysis Lab), Orthopaedic Department,

University Hospital Muenster, Muenster, Germany2 Institute of Sport Science, Motion Science, University of Muenster, Muenster, Germany3 Department of Medical Informatics and Biomathematics, University Hospital Munster,

Muenster Germany

Accepted for Publication: 28 March 2010

Medicine & Science in Sports & Exercise Published ahead of Print contains articles in unedited

manuscript form that have been peer reviewed and accepted for publication. This manuscript will undergo

copyediting, page composition, and review of the resulting proof before it is published in its final form.

Please note that during the production process errors may be discovered that could affect the content.

Copyright 2010 American College of Sports Medicine

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A Multi-Station Proprioceptive Exercise Program Prevents Ankle Injuries in Basketball

Eric Eils1,2 PhD, Ralf Schrter1 MD, Marc Schrder1, Joachim Gerss3 PhD, Dieter

Rosenbaum1 Prof.,

1 Funktionsbereich Bewegungsanalytik (Movement Analysis Lab), Orthopaedic Department,

University Hospital Muenster, Domagkstrasse 3, 48149 Muenster, Germany

2 Institute of Sport Science, Motion Science, University of Muenster, Horstmarer Landweg

62b, 48149 Muenster, Germany

3 Department of Medical Informatics and Biomathematics, University Hospital Munster,

Domagkstrasse 9, 48149 Muenster Germany

Correspondence to:

Priv. Doz. Dr. Eric Eils,

Institute of Sport Science, Motion Science

University of Muenster,

Horstmarer Landweg 62b,

48149 Muenster, Germany

Phone: ++49-251-8334866; Fax: ++49-251-8334872

Email: [email protected]

Running title: Exercise program to prevent ankle injuries

This study was funded by a research grant of the Bundesinstitut fr Sportwissenschaft

(Federal Institute of Sports Science). Grant number: VF 0407(01/68/2004).

Medicine & Science in Sports & Exercise, Publish Ahead of Print

DOI: 10.1249/MSS.0b013e3181e03667

Copyright 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.

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Abstract

Purpose: To investigate the effectiveness of a multi-station proprioceptive exercise program

for the prevention of ankle injuries in basketball players using a prospective randomized

controlled trial in combination with biomechanical tests of neuromuscular performance.

Methods: 232 players participated in the study and were randomly assigned to a training or

control group following the CONSORT-statement. The training group performed a multi-

station proprioceptive exercise program and the control group continued with their normal

work-out routines. During one competitive basketball season the number of ankle injuries

was counted and related to the number of sports participation sessions using logistic

regression. Additional biomechanical pre-post tests (angle reproduction, postural sway) were

performed in both groups to investigate the effects on neuromuscular performance.

Results: In the control group 21 injuries occurred, while in the training group 7 injuries

occurred. The risk for sustaining an ankle injury was significantly reduced in the training

group by approximately 35%. The corresponding numbers-needed-to-treat (NNT) was 7.

Additional biomechanical tests revealed significant improvements in joint position sense and

single limb stance in the training group.

Conclusion: The multi-station proprioceptive exercise program effectively prevented ankle

injuries in basketball players. NNT-analysis clearly showed the relatively low prevention

effort that is necessary to avoid an ankle injury. Additional biomechanical tests confirmed the

neuromuscular effect, and confirm a relationship between injury prevention and altered

neuromuscular performance. With this knowledge, proprioceptive training may be optimized

to specifically address the demands in various athletic activities.

Key Words: Proprioceptive training, Prospective randomized controlled trial, Prevention and

rehabilitation, Biomechanical tests; neuromuscular performance


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Introduction

Paragraph Number 1 Sporting activities like basketball, soccer, team handball and

volleyball are high-risk activities especially for lateral ligament injuries of the ankle joint

complex (8). In basketball, every other injury that occurs affects the ankle joint (21, 27).

These injuries often result in a considerable amount of time off for the injured players;

typically one or more weeks (16) or five to six sessions (18). Players may be unavailable for

their team in important phases during the season thus causing a serious problem particularly

for professional or semi-professional teams.

Paragraph Number 2 Different intervention methods have been recommended for the

prevention of ankle injuries (17). There is evidence that ankle braces are effective in the

prevention of acute, as well as recurrent, ankle sprains but there is still controversy

concerning the effectiveness of special training procedures (8). It was reported that

proprioceptive training is not effective as a primary prevention in healthy subjects (4);

however, recent results seem promising in underlining its effect as secondary prevention in

subjects with recurrent ankle injuries (3, 11).

Paragraph Number 3 The effectiveness of specific training programs has been evaluated

using prospective randomized controlled trials or laboratory based studies (5-7, 9, 11, 24,

26). In prospective randomized intervention trials, a training group and a control group are

monitoredduring a season and differences in the number of injuries at the end of one season

are indicative for the effectiveness of the training program. In laboratory-based studies,

different test procedures are performed before and after a training period. Differences in

neuromuscular performance are indicative of the effectiveness of the training program.

However, both approaches are insufficient for a thorough understanding of ankle injury

prevention. For example, when investigating the effectiveness of training programs, the

reasons for possibly reduced injury rates might remain unclear. On the other hand,


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investigating the effects of a pre-post test design does not implicate that changes in

neuromuscular parameters are effective with respect to injury reduction. A combination of

both approaches may help to improve our understanding of the relationship of ankle injury

prevention and neuromuscular performance in athletes.

Paragraph Number 4 Therefore, the aim of the present investigation was to simultaneously

evaluate the effectiveness of an intervention program for the prevention of ankle injuries as

well as the effects of laboratory-based trials on neuromuscular performance during a

basketball game season. The intervention trial was conducted as prospective randomized

controlled trial, with a laboratory-based aspect involving neuromuscular measurements in a

subgroup before and after the training period. The underlying hypothesis was that there will

be a significant reduction in the number of ankle sprains in the training group and, in

addition, neuromuscular performance changes related to the specific multi-station

proprioceptive exercise program will be found in the training group.

Methods

Subjects

Paragraph Number 5 The CONSORT statement was followed in the design of the study (1).

The study contained a prospective randomized controlled trial and a pre-post laboratory-

based test of a selected subgroup. The respective number of athletes recruited and

investigated in the course of the trial is shown in Fig. 1.

Paragraph Number 6 In total, 232 players on 35 teams in the vicinity of Muenster,

Germany, participated in the study (Tab. 1). All players played basketball on a regular basis

and the performance level of the players varied between the seventh highest (Kreisliga) and

the highest league (Bundesliga) in Germany. Prior to participation, all subjects signed an


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informed consent form. The tests were approved by the local human ethics committee and all

procedures were performed in accordance to the principles of the Declaration of Helsinki.

Subjects were free of injuries at the start of the study. To evaluate the effect of the multi-

station proprioceptive exercise program on injury incidence, all subjects who wore external

stabilizing devices (braces, tape) or who had previously performed proprioceptive exercises

were excluded from the study. The remaining 198 subjects were randomly assigned to the

control or the training group usinga stratified randomization design with the strata defined

by performance (high, middle, low) and sex (male, female). It has to be noted that subjects

were allocated to the groups as teams because the balance training program had to be

integrated in the normal training process. Teams were assigned using random numbers (0

and 1) that were generated by a computer program. The randomization list was established

in advance and strictly maintained. This finally resulted in two randomized groups that were

comparable in terms of performance and sex.

Training program

Paragraph Number 7 The control group consisted of 102 players who continued with their

normal work-out routines. The training group consisted of 96 players who performed a multi-

station proprioceptive exercise program that was designed in cooperation with the School of

Physiotherapy of the University Hospital. The program was integrated within the regular

training routines and was especially designed for basketball work-outs. At the beginning of

the season, each coach obtained an eight-page training manual which contained a detailed

description of the set-up, all exercises (including the different difficulty levels) and additional

background information concerning posture corrections and proprioception. In addition, a

physiotherapist introduced this program to all players and coaches on site and gave detailed

instructions for correct execution. This was repeated for each difficulty level. During the


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season, the coaches were encouraged to contact us and were contacted by us on a regular

basis to keep them motivated and to help with questions or problems .

Paragraph Number 8 The multi-station program was adapted from a program presented by

Eils and Rosenbaum (5). It was performed once a week and consisted of six stations that were

performed twice (barefoot) at the beginning of the normal training routine (Fig. 2). The

exercise period took 20 minutes (including set-up and removal). The exercises were

performed for 45 s followed by a 30 s break where subjects transferred to the next station.

The correct posture of the lower leg of the subjects was controlled (slight external rotation of

the foot, slightly flexed knee and the patella over the metatarsophalangeal joint) during the

exercise. The intensity and difficulty of the exercises were increased during the season twice

by minor modifications for each station.

Injuries:

Paragraph Number 9 From the beginning of the season, all injuries of the players in a team

were registered by a person in charge of the team (coach, physiotherapist, player) using a

specific injury questionnaire that was filled out and returned in case of an injury.To reduce

reporters bias to an acceptable degree, we contacted the coach and the player to obtain

further information about the circumstances, the severity and the medical diagnosis. All

injuries were reported but the contact to the coaches and players was only arranged in case

of ankle injuries. An injury was defined as an event that forced the subject to terminate the

ongoing basketball activity and, in addition, prevented further participation in the next

scheduled basketball activity.

Biomechanical tests:

Paragraph Number 10 Additional biomechanical tests were performed in a subgroup of

both, the control and the training group in order to investigate the influence of the training


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program on neuromuscular performance. The subgroup was randomly selected using a

stratified randomization design as mentioned above. Subsequently, players within these

teams were randomly selected and asked for participation in the study. Finally 24 subjects

(11 in the control group, 13 in the training group) were enrolled and performed the pre-tests

in angle reproduction and postural sway. During the season, 8 players of this group (3

control group, 5 training group) were lost due to different reasons (see Fig. 1). Finally, data

of 16 players (8 of each group) who performed both pre- and post tests could be analysed.

Paragraph Number 11 A pressure distribution platform (Emed ST4, Novel GmbH, Munich,

Germany) was used to measure postural sway in single-limb stance (Fig. 3). No instructions

concerning the posture were given to the subjects except to avoid contact of the legs and to

focus on a point on the wall directly ahead. Individual posture was noted and subjects were

informed to use the same style as in the pre-test when it deviated in the post-test. For each

foot, three trials of single limb stance (10 sec. each) were performed. For analysis, the sway

variation and the sway amplitude of the center of pressure (CoP) in medio-lateral and

anterior-posterior direction as well as the total sway distance (total length of the CoP-line)

were determined and averaged.

Paragraph Number 12 A custom-built device was used for testing joint position sense in a

passive angle reproduction test. It consisted of a footplate in combination with a Penny &

Gilles goniometer (Biometrics Ltd, Gwent, UK). Subjects sat in front of the measuring device

and placed the foot on the horizontal footplate (Fig. 4). The rotation axis of the device was

aligned with the medial malleolus. The knee joint was placed over the ankle. This position

was defined as the neutral position (0). Subjects were unable to see their feet throughout the

examination and had their eyes closed to concentrate on the measurements. For the passive

angle reproduction test, the foot was brought into one of the two testing positions (10

dorsiflexion, 15 plantarflexion) and was held for two seconds. Then it was brought back to


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the neutral position and back towards the testing position until the subjects indicated that they

felt to have reached the same position. The foot was returned to the neutral position and the

next angle was chosen. Angles were tested in random order and each angle was tested three

times. All joint position tests were performed by the same investigator. The differences

between predefined and reproduced angles were saved for analysis.Lower leg strength was

not tested in this study because it was shown that deficits in ankle strength are not related to

chronic ankle instability or subjects who previously sustained sprains without instability as a

complaint (12, 19, 28).

Statistics:

Paragraph Number 13 To calculate the injury incidence of the groups, the number of

injuries was related to the number of sports participation sessions (game and practice

sessions combined). The data was then analyzed by logistic regression. The results were

presented as odds ratios of injury as well as the numbers needed to treat (NNT). Pre- post-

test-analysis was performed using the dependent non-parametric Wilcoxon signed-rank test.

Differences between groups (training, control) were tested using the independent Students t-

test (whole group) and the independent Mann-Whitney U-Test (biomechanical subgroup).

Prediction intervals based on the data of the total study population were used to test the

representativeness of the biomechanical subgroup. In all statistical procedures, p-values

below 0.05 were regarded as significant. The statistical analyses were performed by means of

SPSS17 (SPSS Inc., Chicago, Illinois).


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Results

Paragraph Number 14 During the season, 21 ankle injuries occurred in the control group

and 7 injuries in the training group. Significant differences were found when focusing on the

preventive effect of the multi-station proprioceptive exercise program (Tab. 2). The logistic

regression revealed a significantly reduced odds ratio of 0.355 for training vs. control group

(95% CI: 0.151 - 0.835, p=0.018). The NNT-analysis revealed a value of 360 for the training

group. Due to the fact that the observation unit is not the player but the single participation in

sports, the NNT-values have to be reconsidered. Therefore, with an average of 55 sports

participation sessions in our investigation (average of both groups), NNT-values have to be

corrected to 360/55 = 6.5. This indicates that 7 basketball players (NNT-values are rounded

to the next number to avoid underestimation) have to perform the multi-station proprioceptive

exercise program to prevent one ankle injury during 55sports participation sessions, i.e. in a

time period of 18 weeks for recreational (assuming 2 work-outs per week, 1 game per week)

or nine weeks for professional players (assuming 5 work-outs per week, 1 game per week).

Paragraph Number 15 Analysis of players who had previously sustained an ankle injury

revealed an odds ratio of 1.6 (95% CI: 0.755-3.553, p=0.212) indicating an increased but

non-significant risk (factor 1.6) of sustainingan ankle injury.

Paragraph Number 16 Players of the training group showed a significantly more stable

single limb stance concerning medio-lateral and overall sway parameters (Tab. 3). Sway in

antero-posterior direction was also decreased in the post-test but not found to be significant.

Players in the control group also showed slightly decreased values in the post-test but none of

the differences were significant.

Paragraph Number 17 A clear effect of the training program is apparent for the angle

reproduction test. The degree of error for 10 dorsiflexion, 15 plantarflexion and the mean

was significantly reduced for the post-test in the training but not in the control group (Tab. 4).


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Discussion

Paragraph Number 18 The present investigation evaluated the effectiveness of a multi-

station proprioceptive exercise program for prevention of ankle injuries using a prospective

randomized controlled trial in combination with a laboratory based pre-post test. The results

suggest that the training program is effective in reducing the incidence of ankle injuries in

basketball players and also leads to specific changes in neuromuscular performance;

specifically in terms of proprioception and postural sway. In summary, these findings

indicate that improvements in these neuromuscular parameters may be a key factor for an

effective reduction in ankle injury risk.

Paragraph Number 19 The multi-station proprioceptive exercise program led to a

significant reduction of ankle injuries in basketball players. The riskof sustainingan ankle

injury was reduced by 35.5% and the NNT-analysis revealed that 7 players have to be treated

with this training program to prevent one ankle injury during 55sports participation sessions.

This underlines the potential benefit of an active injury prevention protocol, especially in

professional sport. Results for risk reduction and NNT calculation are comparable to results

in the literature. For example, Hupperets et al. recently reported a similar NNT value of 9 and

a relative risk reduction of 35% in the training group compared to the control group in a

randomized controlled trial using home based proprioceptive training on recurrences of

ankle sprains (11). In the present study, a frequency of 4.31 injuries per 1000 sports

participation sessions was comparable to results of McKay et al. who reported 3.85 ankle

injuries per 1000 sportsparticipation sessions in Australian basketball players (16).

Paragraph Number 20Neuromuscular training programs consisting mainly of exercises on

an ankle disk, performed several times per week, were found to be effective in the reduction

of ankle injury incidence (6, 9, 20, 23), although Handoll and colleagues questioned the


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efficacy in an evidence-based review of the literature due to a limited amount of high quality

studies (8).Preliminary evidence was only given for those with previous ankle injuries. Eils

and Rosenbaum speculated that specific training on an ankle disk probably generated only

single stimulation and therefore introduced a six-week multi-station proprioceptive exercise

program that addressed strength and coordination in multiple ways and was performed only

once a week (5). The authors showed that this program led to significant improvements

within the neuromuscular system in the training group but not in the control group. However,

it still remained unclear whether the measured effects of this low-frequency and high

stimuli program would lead to a reduction in the number of ankle injuries. The results of the

present study underlined the effectiveness of such a program and suggest that training-

induced changes within the neuromuscular system may be related to the reduced incidence of

ankle injuries. It must be noted that a direct one-to-one relationship cannot be established

since only a subgroup of the entire cohort was evaluated in the lab due to organizational

concerns. However, although the sample was small, it was randomly drawn and

representative. A post-hoc analysis using prediction intervals based on data of the total study

population revealed that the sample is proven to be representative of the total study

population except for the rate of high performance players. Furthermore, significant

differences were found between pre- and post-tests. The study design involving a randomized

controlled trial combined with laboratory based testing is important in more appropriately

identifying the relationship between ankle injury prevention and neuromuscular

performance, compared to independent randomized controlled trials and laboratory based

testing. This relationship will help to better understand the complex interaction between

injury prevention and neuromuscular performance.


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Paragraph Number 21 Recently, the importance and efficacy of complex intervention

programs consisting of a variety of exercises, have also been reported for volleyball players

(26) and in athletes with acute ankle sprains (10-11). Therefore, there is new evidence that

proprioceptive training programs with challenging exercises to create multiple stimuli may be

recommended for the prevention of ankle injuries. The effects of proprioceptive training have

been well documented in the past and laboratory-based studies concerning alterations in joint

position sense, sway regulation in single limb stance, muscle strength or peroneal reaction

times have been performed (5-7, 9, 12-15, 24-25). Despite differing findings (22) , there

appears to be a trend of characteristic neuromuscular performance adaptations due to

specific training programs.

Paragraph Number 23 In the present investigation, the results of the angle reproduction test

show a significant improvement in neuromuscular performance. The results for the sway

regulation are similar but not all improvements in the training group were significant. The

training program seems to be more effective in improving sway reduction in medio-lateral

direction. This is comprehensible because movement in medio-lateral direction is mainly

controlled in the subtalar joint whereas the movement in antero-posterior direction is more

regulated in the tibiotalar joint. A similar result was reported by Eils and Rosenbaum (2001)

when evaluating the effects of a multi-station proprioceptive exercise programs in patients

with ankle instability (5).

Paragraph Number 24 In previous studies, the relationship between training-related

changes within the neuromuscular system and effectiveness of injury prevention was vague.

In the present investigation, this relationship was evaluated for the first time with parallel

biomechanical testing in a smaller subgroup, including angle reproduction and postural

sway testing. Although we analyzed only a small subgroup and are aware of the fact that

other factors may play a role in this context, we believe that the results of the present study


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underline a more direct relationship between measured alterations within the neuromuscular

system and effectiveness of injury prevention than shown in previous studies due to the fact

that the sample was randomly selected and representative. The results of the postural sway

analysis in single-limb stance and angle reproduction showed significant differences within

the training group but not in the control group for selected parameters. Therefore, an

improved ability to detect a predetermined angle (improved joint position sense) and the

ability to regulate sway in single-limb stance appear to be related to a reduction of lateral

ankle injuries. These improvements may help athletes to prevent ankle injuries in potentially

dangerous circumstances, e.g. in cutting and landing movements, due to an improved joint

position sense of the foot and ankle complex.

Paragraph Number 25 At this point, it will be of interest how exercises have to be designed

to be most effective. For example, what are the effects of a typical ankle disk training

compared to a more complex exercise on a neurophysiologic basis? Is it possible to derive

some typical characteristics or key aspects that make an exercise more suitable for

proprioceptive training? However, this remains speculative and has to be addressed in

additional biomechanical studies.

Paragraph Number 26 One aspect that needs clarification in the present investigation is the

influence of proprioceptive training on subjects with and without previous ankle injuries. It

has been stated that a beneficial effect is most pronounced for athletes with previous ankle

injuries and that there is only a small or no effect of training in healthy subjects (4, 8). We

found an increased chance (factor 1.6) of obtaining an ankle injury in subjects with previous

injuries. However, this increase was not significant. Only players who never performed

proprioceptive exercises or wore ankle stabilizing devices before were included in the present

investigation. Therefore, a high percentage of players with previously injured ankles have

probably been excluded resulting in a similar percentage of players (about 50% each) with


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and without previous injuries. This explains why the effect for players with previous injuries

is not as pronounced as in other investigations (2, 16, 26).

Paragraph Number 27 Significant differences between players age and sports activity were

initially found between the training and control group. The players in the training group were

significantly younger (22.6 vs. 25.5 years) and more active (3.5 vs. 2.8 times per week) than

the controls. These group differences actually emphasize the findings because it can be

argued that younger and more active individuals would have a greater risk of injury due to

increased exposure.

Paragraph Number 28 The results of the present investigation show that the number of

ankle injuries was reduced but there was no information concerning other injuries. This

might be a limitation in the present study because it would be of interest to know whether

ankle injuries may be replaced by injuries in other areas. We were not able to derive this

information from our data because coaches and players were only contacted in case of ankle

injuries. However, a systematic Cochrane review focusing on interventions for preventing

ankle ligament injuries did not report an apparent effect on the incidence of other leg

injuries (8). This leads us to trust that there is no significant shift of injuries to other body

areas.

Conclusion

Paragraph Number 29 The results of the present investigation show that a specific multi-

station proprioceptive exercise program performed only once a week significantly reduced

the frequency of ankle injuries in a population of basketball players. In addition,

characteristic and significant improvements in neuromuscular performance were found in

biomechanical tests of proprioception and postural sway that may be directly related to the

risk of ankle injury. This is the first study to directly underline a relationship between injury


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incidence and alterations in neuromuscular performance. The evaluation of injury incidence

as well as objective parameters from biomechanical tests warrants the recommendation of

such exercises for the prevention of ankle injuries.

Paragraph Number 30 Although the population were basketball players, it may be safe to

assume that the program is also applicable to other sports or high-risk activities like team

handball, volleyball or soccer.

Acknowledgement

Paragraph Number 31 The authors wish to thank M. Overbeck and colleagues for their help

in setting up the exercise program. This study was funded by a research grant of the

Bundesinstitut fr Sportwissenschaft (Federal Institute of Sports Science). Grant number: VF

0407(01/68/2004). None of the authors of this article have any conflicts of interest or

financial conflicts to disclose. The results of the present study do not constitute endorsement by

American College of Sports Medicine.


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25. Verhagen E, Bobbert M, Inklaar M, van Kalken M, van der Beek A, Bouter L, and van

Mechelen W. The effect of a balance training programme on centre of pressure excursion in

one-leg stance. Clin Biomech (Bristol, Avon). 2005; 20(10):1094-100.

26. Verhagen EA, van der Beek A, Twisk J, Bouter L, Bahr R, and van Mechelen W. The

Effect of a Proprioceptive Balance Board Training Program for the Prevention of Ankle

Sprains. A Prospective Controlled Trial.Am J Sports Med. 2004; 32(6):1385-93.

27. Wang HK, Chen CH, Shiang TY, Jan MH, and Lin KH. Risk-factor analysis of high

school basketball-player ankle injuries: a prospective controlled cohort study evaluating

postural sway, ankle strength, and flexibility.Arch Phys Med Rehabil. 2006; 87(6):821-5.

28. Willems T, Witvrouw E, Verstuyft J, Vaes P, and De Clercq D. Proprioception and

Muscle Strength in Subjects With a History of Ankle Sprains and Chronic Instability.J Athl

Train. 2002; 37(4):487-93.


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List of Figures

FIGURE 1: Flowchart of number of athletes participating in this study.

FIGURE 2: Exercises and variations of the multi-station proprioceptive exercise program.

Please note that this is only a short description of the program and the exercises.

FIGURE 3: Measurement of postural sway in single-limb stance on the pressure distribution

platform and an example of the derived parameters (excursions of the center of pressure CoP

in medio-lateral and antero-posterior directions as well as total sway distance).

FIGURE 4: Joint position sense testing in a custom-built device in combination with an

electrogoniometer. The foot of the subjects was passively moved into 10 of dorsiflexion and

15 of plantarflexion. Deviations between predefined and reproduced angles were derived for

analysis.


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Figure 1

Players assessed foreligibility (n=232)

198 Players were enrolled and agreed toparticipate in the study.

Allocated to controlgroup

(n=102)

Allocated totraining group

(n=96)

Excluded (n=34)Previous use of braces (13 playe rs)Previous performing proprioceptive / neuromuscular

training programs (9 players)

Did not return questionnaire (7)Other reason s (11 players)

Analyzed(n=91)

Lost to follow-up:(n=15)

Reasons:Did not return questionnaire ofparticipations in spo rts

(9 players)Sustained other injuries (3players)

Unknown reasons (3 players)


Reasons:Did not return questionnaire ofparticipations in sports

(6 players)Sustained other injuries (2players)

Unknown reasons (3 players)

Analyzed(n=81)

Biomechanical pre-post subgroup

analysis (n=24)


Reasons:Did not participate inpost-test (2 p layers)

Erroneous data (1player)Unknown reasons (5

players)

Analyzed(n=16)


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Figure 2

Exercise 1Basic Exercise:

Walking slowly back

and forth on a balancebeam (1 step=3

seconds). Thecontralateral leg swings

through and nearly

touches the ground

Variation 1:Walking faster than

before on the balance

beam. Way back: slowlywith same execution as

above.

Variation 2:

Stance on a balancebeam. The contralateral

leg moves a basketballthat lies on the groundin circles. Focus on the

supporting leg.


Single leg stance on

exercise mat with thecontralateral leg flexed.

Lower and raise thebody. Distribute load on

the foot. Only small

knee movemen ts to theleft and right are

allowed.

Variation 1:

Single limb stance asabove opposite to a

partner. A basketball ispassed to the partner.After catching the ball,

the position is controlledfor 2 seconds. Pass the

ball back and forth.

Variation 2:

Single leg stance on asoft mat. Balance a ball

(tennis ball, basketball)on the dorsum of theelevated contralateral

foot.


Jump from one leg to

the other on an exercisemat and control landing

for 4 seconds. Raise thecontralateral leg

Variation 1:Jump from one leg to

the other (exercise mat)with a partner. Disturbeach other during the

flight phase (handcontact) and control the

landing and stance for 4seconds.

Variation 2:As before, but on a soft

mat.


Walk up and down an

inclined surface anddribble the ball.

Variation 1:Walk on inclined surface

up and down anddribble the ball . In

addition, an elastic strapis wrapped around theknees. Walk forwards

and backwards. Focuson wide steps.

Variation 2:Walk up and down an

inclined surface. Anopposite partner is

doing the same. Passthe ball between

partners and move up

and down with only theforefoot in ground

contact.


Maintain balance in

single-leg stanceelevating the

contralateral leg againstresistance of an elastic

strap.

Variation 1:

Maintain balance insingle-leg stance (eyes

closed) elevating the

contralateral leg againstresistance of an elastic

strap.

Variation 2:

Maintain balance insingle-leg stance

moving the contralateralleg sideways against

resistance of an elastic

strap. Evert the lateraledge of the contralateral

foot.


Maintain balance in

single-leg stance oninversion-eversion tilt

board. The contralateralleg is rested on an

inclined surface nearly

without being loaded.

Variation 1:The same as above witha partner. Pass the ball

and control stance aftercatching the ball.

Variation 2:Maintain balance in

single-leg stance oninversion-eversion

board. The contralateralleg is elevated.


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Figure 3


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Figure 4


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TABLE 1. Anthropometric data of the whole (upper part) and the biomechanical subgroup

(lower part)

Whole group Training group (n=81) Control group (n=91) P-level

Mean SD Range Mean SD Range

Age (years) 22.6 6.3 14-43 25.5 7.2 15-43 p

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TABLE 2. Number of ankle injuries, participations in sports, injury frequency related to 1000

participations in sports, odds ratio and number needed to treat (NNT).

Training group Control group

Absolute number of injuries 7 21Total number of participations

in sports

4565 4876

Injury frequency per 1000 sport

participations

1.53 4.31

Odds ratio (95% CI); p-value 0,355 (0.151-0.835); p=0.018 1

Number needed to treat (NNT) 7 /


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TABLE 3. Postural sway parameters (mean standard deviation).


Pre test Post test Pre test Post test

Postural sway [mm] Mean SD Mean SD P level Mean SD Mean SD P level

Standard deviation medio-lateral 5.8 0.7 5.1 0.8

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TABLE 4. Angular errors in the joint position test from predetermined angles (mean standard deviation).


Pre test Post test Pre test Post test

Degrees of error [] Mean SD

Mean

SD

P level

Mean

SD Mean

SD

P level

10 dorsiflexion 2.0 0.5 1.2 0.5

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