Do ankle braces provide similar effects on ankle biomechanical variables in subjects with and without chronic ankle instability during landing?

Songning Zhng *,Mihel Wortley ,Juli Freedmn Silvernil,Dniel Crson Mxime R.Pquette

a Biomechanics/Sports Medicine Laboratory,Department of Kinesiology,Recreation and Sport Studies,The University of Tennessee,Knoxville,TN 37934,USA

b Pellissippi State Community College,Knoxville,TN 37933,USA

c Department of Kinesiology,University of Massachusetts,Amherst,MA 01003,USA

Do ankle braces provide similar effects on ankle biomechanical variables in subjects with and without chronic ankle instability during landing?

Songning Zhanga,*,Michael Wortleyb,Julia Freedman Silvernailc,Daniel Carsona, Maxime R.Paquettea

aBiomechanics/Sports Medicine Laboratory,Department of Kinesiology,Recreation and Sport Studies,The University of Tennessee,Knoxville,TN 37934,USA

bPellissippi State Community College,Knoxville,TN 37933,USA

cDepartment of Kinesiology,University of Massachusetts,Amherst,MA 01003,USA

Purpose:The purpose of this study was to examine effects of a sport version of a semi-rigid ankle brace(Element?)and a soft ankle brace (ASO)on ankle biomechanics and ground reaction forces(GRFs)during a drop landing activity in subjects with chronic ankle instability(CAI) compared to healthy subjects with no history of CAI.

Methods:Ten healthy subjects and 10 subjects who had multiple ankle sprains participated in the study as the control and unstable subjects, respectively.The CAIsubjects were age,body mass index and gender matched with the controlsubjects.The arch index and ankle functions of the subjects were measured in a subject screening session.During the biomechanical test session,participants performed five trials of drop landing from 0.6 m,wearing no brace(NB),Element?brace and ASO brace.Simultaneous recording of three-dimensionalkinematic(240 Hz) and GRF(1200 Hz)data were performed.

Results:The CAI subjects had lower ankle functional survey scores.The arch index and deformity results showed greater arch deformity of Element?againsta static load than in NB and ASO due to greater initialarch position held by the brace.CAIparticipants had greater eversion velocity than healthy controls.The ASO brace reduced the first peak vertical GRF whereas Element?increased 2nd peak vertical GRF. Element?brace reduced eversion range ofmotion(ROM)and peak eversion velocity compared to NB and ASO.In addition,Element?reduced dorsiflexion ROM and increased peak plantarflexion moment compared to NB and ASO.

Conclusion:Results of static arch measurements and dynamic ankle motion suggestthatthe restrictions offered by both braces are in partdue to more dorsiflexed ankle positions at contact,and higher initial arch position and stiffer ankle for Element?.

Copyright?2012,Shanghai University of Sport.Production and hosting by Elsevier B.V.All rights reserved.

Drop landing;Lateralankle sprain;Recurrentankle sprain;Semi-rigid ankle brace;Softankle brace

1.Introduction

Ankle ligamentsprain is the mostcommon sports injury,1—4accounting for 15%of all sport injuries in 15 National Collegiate Athletic Association sports.4Among the ankle ligamentinjuries,lateralankle sprain is the mostcommon type and typically caused by excessive inversion,particularly when the ankle is in a plantarflexed position.5—8It was found that 73%of athletes who had previously sprained their ankle had a recurrence9and that 59%of them had significant residual symptoms and functional disability which is often referred to as chronic ankle instability(CAI).In addition,recurrent sprains have been linked to increased risk of osteoarthritis and articular degeneration at the ankle joint.10

Subjects with CAI have shown a greater first peak vertical ground reaction force(GRF)compared to the contralateral unaffected limb and lower relative time to peak compared to controls during a v-cut maneuver.11Rosenbaum et al.12showed no significant differences in objective data(i.e., vertical jumping height,single leg hopping time,sprint time, and side-cuttime)although significantdifferences between 10 braces were observed in subjective evaluation of performance restriction in subjects with CAI.Gribble and colleagues13found that a lace-up ankle brace does increase dynamic stability measured as resultant GRF vector time to stability in CAI subjects.These studies demonstrated mixed biomechanical and performance results of CAI subjects during dynamic movements.

Ankle braces are designed to prevent or treat ankle sprains or recurrences.Many athletes wear them in both games and practices in hope to prevent ankle sprains.It has been demonstrated that wearing ankle braces is effective in reducing ankle sprains.14,15We previously demonstrated effectiveness of a semi-rigid ankle brace with a heel strapping system(Element?)in an inversion drop and a lateral cutting maneuver.8In a landing study on flat and inverted surfaces, Zhang etal.16showed thatthe same ankle brace reduced time to 2nd peak vertical GRF,sagittal-plane ankle angle and dorsiflexion velocity at contact,maximum eversion velocity and plantarflexion velocity,contact inversion angle and peak eversion velocity during landing on both flat and inversion surfaces.Chen and colleagues17also showed that the semirigid ankle brace reduced ankle inversion atcontactand peak inversion angles as well as dorsiflexion range of motion (ROM)in both landings on an inverted surface and inversion drop on a trapdoor device.McCaw et al.18found a significantly reduced maximum sagittal-plane ankle angular velocity while wearing an ankle brace in soft and stiff landing.It was also found that the peak vertical GRF and its loading rate significantly increased while the contact ankle sagittal-plane angle significantly decreased during drop landing wearing an ankle brace compared to no brace(NB).19More recently, Gardner et al.20demonstrated decreased relative ankle work when wearing a boot ankle brace compared to NB condition during a single-leg landing.

The majority of previous research on ankle braces has been conducted on healthy subjects or in subjects with unknown histories of ankle sprains.Itis still unclear whether ankle braces can provide similar or greater ankle sprain protection in CAI subjects compared to healthy subjects during landing activities.Therefore,the purpose of this study was to examine effects of a sport version of the semi-rigid ankle brace(Element?)and a soft ankle brace(ASO)on ankle biomechanics and GRFs in a drop landing activity in CAIsubjects compared to healthy subjects with no history of CAI.We hypothesized that greater reduction of eversion ROM and peak eversion velocity would be observed in the sport ankle brace compared to the soft ankle brace and in CAI participants compared to healthy participants.It was also hypothesized that the ankle braces would yield greater reduction of eversion ROM and velocity in CAI participants compared to healthy participants.

2.Methods

2.1.Participants

Ten control subjects with no history of previous ankle sprains(age:24.1±5.4 years,mass:72.4±12.0 kg,height: 1.74±0.08 m)and 10 CAI subjects who had multiple ankle sprains(age:24.8±5.7 years,mass:73.03±9.31 kg,height: 1.75±0.09 m)were recruited to participate in the study.In each subject group,five females and five males were recruited.The CAI subjects were age and body mass index matched by the subjects in the control group.Potential subjects were asked to participate in a screening session for ankle functions and instability using Ankle Joint Functional Assessment Tool(AJFAT)20and arch index measurements.If a subject met the inclusion criteria(multiple ankle sprains in past 12 months and beyond,and no ankle sprains in past 3 months)for CAI group,he/she was then asked to participate in a biomechanical testing session.All participants signed an informed consent form approved by the Institution Review Board.

2.2.Experimentalprotocol

2.2.1.Screening session

The session began with the subject filling out the AJFAT survey21to document the condition of the reported CAI.Arch index was measured with the subjects in sitting(unloaded)and standing(loaded)positions in barefoot and in both ankle braces using an AHIMS(Arch Height Index Measurement System;JAK Tooland Model,LLC,Matawan,NJ,USA).The measurements were used to compute arch index(AID)22and arch deformity(AD)23using the following equations:

where dorsum height is the height of dorsum of the foot at 50%of foot length and the truncated foot length is measured from heel to the head of 1st metatarsal head.22

2.2.2.Biomechanical test session

Fig.1.The Element?(A)and ASO(B)ankle braces used in the study.

The biomechanical testing session began with a 5-min warm-up of jogging on a treadmill followed by a stretching routine of major muscle groups.Participants performed five trials in each of the three testing conditions:drop landing from an over-head bar from a height of 0.6 m,wearing NB (NB,lab running shoe:Grid Triumph,Saucony),Element? (DeRoyal Industries,Inc.,Rowell,TN,USA;Fig.1A)and ASO(ASO,Medical Specialties,Charlotte,NC,USA; Fig.1B).The Element?ankle brace is a semi-rigid brace with a hinge joint at the ankle allowing sagittal plane rotation and a heel strapping system designed to strap and stabilize the calcaneus with two cross-pattern straps to restrictankle frontal-plane motion.16The ASO brace is a soft elastic band ankle brace to restrict overall ankle mobility. The running shoes were also worn with the ankle braces on the unstable side of the CAIsubjects and the rightside of the control subjects.A seven-camera motion analysis system (240 Hz;Vicon Motion Analysis Inc.,Oxford,UK)was used to obtain the three-dimensional(3D)kinematics during the test.Reflective anatomicaland tracking markers were placed on both feet,ankles,legs,knees,thighs and on the pelvis during testing.For the pelvis,thigh,and leg,the tracking markers were attached to the respective segment via a semirigid thermoplastic shell.The three tracking markers for the heelsegmentwere placed directly to the skin of the posterior heelvia a custom made two-markerwand and the lateralheel marker via cutouts on the posterior and lateral heel counter. A separate static trial was collected prior to testing of NB, Element?and ASO conditions.The anatomical landmarks were marked with a marker pen to minimize placement errors when reapplying the static markers forthe 2nd and 3rd static trials.A force platform(1200 Hz,American Mechanical Technology Inc.,Walthertown,MA,USA)was used to measure the GRF and moments of forces simultaneously using the Vicon system.Participants were given ample time to become familiarwith the landing movementin all three brace conditions prior to testing.The brace conditions were randomized for all participants.

2.3.Data and statistical analyses

2.3.1.Data analysis

Visual3D(C-Motion,Inc.,Germantown,MD,USA)3D biomechanical analysis software suite was used to compute 3D kinematic and kinetic variables.Customized computer programs(VB_V3D and VB_Tables,MS Visual Basics) were used to generate scripts and modify models for Visual3D,determine critical events and compute additional variables,and organize the mean variable fi les needed for statistical procedures.The data were analyzed from the touchdown to 350 ms after touchdown.The 3D marker trajectories and GRF data were smoothed with a 4th-order Butterworth digital filter using cutoff frequencies of 8 and 50 Hz,respectively.The 3D angular kinematic angles were computed using a Cardan sequence(x-y-z).The polarity of 3D kinematic and kinetic variables was determined by the right-hand rule.The GRF were normalized to body weight (BW)and internal joint moments were normalized to body mass(Nm/kg).

2.3.2.Statistical analysis

The arch index,arch deformity,ankle ROM and AJFAT data were first analyzed by a one-way analysis of variance (ANOVA,17.0;SPSS Inc.,Chicago,IL,USA)to detect the group difference.The arch index and arch deformity were further analyzed using a 2×2×3(group×load×brace) mixed-designed ANOVA.The effects of ankle functional status and ankle braces on selected biomechanical variables of the dynamic movement tests were analyzed using a 2×3 (group×brace)mixed-design ANOVA for each movement. The post hoc comparisons were conducted for the selected biomechanical variables and theαlevelwas setat0.0167 with a Bonferroni procedure to adjust theαlevel for multiple comparisons.

3.Results

3.1.Ankle functions,static ROMs and arch index

The CAI subject had an average of 1.9±1.1(mean±SD) sprains within the last 12 months and 4.5±3.1 total sprains. The one-way ANOVA showed that healthy control subjects had a significantly greater AJFAT score(26.7±1.1)than CAI subjects(14.9±5.5).The ankle inversion(34.5±7.8°)and eversion(-18.3±3.7°)ROMs for control subjects were not significantly different from the inversion(40.1±8.3°)and eversion(-15.7±3.4°)ROMs of CAI subjects.

The unloaded(seated)and loaded(standing)arch indices were greaterforthe Element?(p＜0.001 and p＜0.001)and ASO(p＜0.001 and p＜0.001)than NB,respectively(Table1). The results on the arch deformity showed a significant brace effect(p=0.009).The post hoc comparisons showed greater arch deformity in Element?compared to NB(p=0.009)and ASO(p=0.011,Table 1).The three-way ANOVA results showed a significant brace×load interaction for arch index (p=0.009)and arch height(p=0.003),butno interaction was found for the truncated foot length.Paired t tests showed that Element?yielded significantly decreased arch index and dorsum height from the unloaded position to the loaded position.

Table 1Average arch index measurements and arch deformity(mean±SD).

3.2.GRF and center of pressure(COP)

A representative verticalGRF curve was presented in Fig.2. The 1stpeak verticalGRF(p=0.005)wassignificantly smaller in ASOcompared to NB(p=0.009)and Element?(p=0.035, Table 2).The 2nd peak vertical GRF(p=0.003)for NB was smaller than Element?(p=0.004).The time to the 2nd peak GRF(p＜0.001)was significantly shorter in Element?compared to NB(p＜0.001)and ASO(p=0.035),and in ASO compared to NB(p＜0.001,Table 2).

3.3.Ankle variables

The ankle dorsiflexion ROM(p＜0.001)was greaterin NB compared to Element?(p＜0.001)and ASO(p＜0.001, Table 3).The ankle angle at contact(p＜0.001)was less plantarflexed in Element?compared to NB(p＜0.001)and ASO(p=0.015)and in ASO compared to NB(p=0.001). The ankle eversion ROM(p=0.001)was smaller in Element?compared to ASO(p=0.003)and NB(p=0.005). The peak eversion velocity for the unstable group was greater than the control group(p=0.01).The post hoc comparison showed that it was smaller for Element?compared to NB (p＜0.001)and ASO(p=0.013).The peak ankle plantarflexor moment was significantly greater in Element?compared to NB(p=0.041)and ASO(p=0.037,Table 3). No significant differences were found in peak ankle eversion moment in early landing although there was a trend of brace main effect(p=0.054).

Fig.2.Representative ensemble curve of vertical ground reaction force curve in landing with ankle brace.

4.Discussion

The main purpose of the current study was to examine effects of the sport version of the semi-rigid ankle brace and a soft ankle brace in a drop landing activity in CAI subjects compared to healthy controls.The arch deformity derived from the unloaded and loaded arch indices showed that the Element?had the greatest amount of arch deformity.The ASO brace did not affect arch deformity.The greater arch deformity associated with the Element?brace is mainly due to the higher arch position compared to NB and ASO,and shorter truncated foot length compared to NB.Foot arch is involved in attenuating GRF,especially during movements that yield a forefoot-to-heelloading pattern such as landing or stair descent.The Element?brace has a heel to mid-foot cross-pattern strapping system that is designed to hold the arch in a higher position.As the arch is held in a higher position, the footlength is reduced.The higherinitialarch heightallows more range of motion in the foot and ankle for load attenuation.This is evidenced by the greater arch deformity under the loaded position forthe arch index measurements.Whetherthe arch is bottomed out in the loaded(standing)position cannot be fully understood from these semi-static measurements.

The CAI subjects had significantly lower ankle functional scores compared to healthy subjects based on the AJFAT survey suggesting that some residual deficiencies are still present.However,no differences were found in the inversion and eversion ROMs,arch indices,and arch deformity between groups.Most biomechanical variables during landing did not show any significant group differences or group×brace interactions.However,the peak ankle eversion velocity was significantly greater in CAI subjects than controls.These results suggestthatsubjects with CAImay experience greater functional deficits of the ankle complex during this high loading landing task,which may in turn increase the possibility of ankle sprain recurrence in these unstable ankles.Due to lack ofany interactive effects ofgroup and brace,the results suggest that Element?and ASO braces provide similar protection to the ankle complex for CAIsubjects compared to healthy controls.Previous research has demonstrated that the usage of an ankle brace reduced incidence of acute ankle sprains in basketball.15The ankle braces,particularly the Element?brace,reduced eversion ROM and peak eversion velocity providing restriction to the subtalar joint in thelanding condition.Dayakidis and Boudolos11showed greater first peak vertical GRF in unstable ankles compared to unaffected sides during a v-cut movement in their CAI subjects. However,we did notfind any significantchanges in the peak vertical or medial GRF variables in our CAI group compared to the control group.Furthermore,the performance related variables such as dorsiflexion ROM and peak plantarfl exion were not changed between the groups.Rosenbaum et al.12found that objective measurements such as sprint,hopping and cutting times and jump heights were not changed in CAI subjects compared to controls.These findings from literature supportourresults thatankle braces provide greater stability to unstable ankle joints even during violentdynamic movements such as drop landings while maintaining performance requirements.

Table 2Average GRF and COP variables(mean±SD).

The significant effects of ankle braces during landing were mostly associated with the Element?brace.Element?brace reduced peak eversion velocity compared to ASO and NB. These results suggest that the Element?brace is more effective in restricting rear-foot motion during landing movement and this result is consistentwith similar findings of the longer version of the brace in a previous drop landing study.16Element?and ASO braces also significantly reduced the ankle dorsiflexion ROM.However,the reduced ROM in the braced conditions is mostly related to reductions in ankle plantarflexion angle at contact.The Element?brace reduced the contact plantarflexion angle even more than ASO.Less plantarflexion at contact is beneficial in preventing lateral ankle sprains as the ankle is less stable in more plantarflexed position and lateralankle sprains occur mostfrequently when the ankle experiences excessive inversion in a more plantarflexed position.7The reduced dorsiflexion ROM also requires increased plantarflexor momentin the Element?brace.Zhang et al.16also showed similar effects of the original Element?brace on ankle angle at contact,peak dorsiflexion angle and peak plantarflexion moment in landing on flat and inverted surfaces.Chen at el.17also found reductions in ankle plantarflexion angle at contact in both landing on the inverted surface and inversion drop test with the original Element?brace.These results suggestthatthe semi-rigid ankle brace is effective in restricting ankle motion in frontal plane.The sagittal plane dorsiflexion ROM is more related to performance and is reduced in both braces,which is partially due to the less plantarflexed ankle angle at contact.It is not clear whetherthe braces would influence performance ofjumping or other activities.

The 1stand 2nd peak verticalGRFs are associated with the forefoot and heel contact,24,25which indicate magnitude of overall loading to the body during landing activities.In addition to the effects of ankle braces on ankle kinematics and kinetics,ASO also reduced the 1st peak vertical GRF compared to NB and Element?.The 2nd peak vertical GRF was increased in Element?compared to NB.During the landing movement,the braced conditions did not reduce thetotal mediolateral COP displacement as it was very small during landing.Although not statistically significant,Element?brace was shown to provide slightly greaterrestriction on peak eversion movement than NB(p=0.067).Peak eversion moment has been shown to decrease during landing on flat and inverted surfaces in the original Element?brace compared to NB.16The sport version of this brace provides similar butslightly reduced effects on peak eversion moment. The increased 2nd peak vertical GRF associated with landing wearing Element?may be related to the increased stiffness in the foot and ankle complex due to reduced dorsiflexion ROM. Previous research has demonstrated that the heightened stiffness of the lower extremity joints lead to increased peak vertical GRFs.25This effect was further enhanced by the shorter time to reach the 2nd peak GRF with Element?compared to NB and ASO.These data may suggest that landing with Element?may cause slight increases in ankle stiffness compared to landing without a brace.Whether the increased ankle stiffness and loading to the body would also increase loading to the other lower extremity joints is unknown.Even though the increased 2nd peak GRF may not have direct impact on ankle frontal-plane moment during landing on regular flat surface,it may increase external inversion momentapplied to ankle complex when landing on inverted surface(e.g.,landing on someone’s foot)and requires greater ankle internal eversion moment to minimize potential injurious effect on ankle.The stiffer ankle and added restriction due to Element?brace application may help reduce the risk of inversion ankle sprains in this kind of landing conditions.Further examination of knee and hip kinetics are needed to better understand effects of Element?on other lower extremity joints during drop landing.Many athletes wear an ankle brace and/or taping to prevent ankle sprains in competition as well as in practice.Effects of these practices on other lower extremity joints are largely unknown at this point.

Table 3Average ankle kinematic and kinetic variables(mean±SD).

In order to improve tracking of the rearfoot,wand markers were attached through the lateral and posterior heel cutouts in the shoe.This may lead to increased vibrations of the markers due to the extended wand shaft.However,we tried to minimize vibrations by using a relatively large base that conforms to the shape of heel,and a shortest possible wand shaft.The base was further secured to the heel with duct tape.A recent paper has demonstrated that the peak knee and hip moments may be exaggerated during a cutting movement when the kinematic and kinetic data were filtered at 10 and 50 Hz, respectively.26Although we filtered the kinematic and GRF data at 8 and 50 Hz,only ankle joint moments were analyzed in the current study.The paper did not present any data on ankle moments and therefore the effects of different cutoff frequencies on ankle moments are stillunknown.Although our CAI subjects demonstrated functional instability reflected in the lower AJFAT scores,mechanical instability was not assessed using a method recommended by Hartel.10However, the ankle inversion/eversion ROMs of CAI subjects did not differ from the controls.This lack of information on mechanical instability and differences of the ankle ROMs between the two groups may be one of the causes contributing to the lack of differences in the effects of ankle braces on ankle kinematic and kinetic variables between groups.It has been recently suggested that studies examining subjects with CAI should also demonstrate mechanical instability.27One limitation of the study is the small sample sizes,which may further contribute to the lack of differences between the subject groups.Future studies on CAI should also pay attention to individual differences in data analyses.

5.Conclusion

The results from this study showed that CAI subjects had lowerankle functionalscore.The CAIparticipants had greater eversion velocity butdid notdiffer in other variables from the control subjects.The sport version of the Element?brace with shorter semi-rigid arms but the same strapping system offered some restrictive effects in the landing movement partially supporting our hypothesis.The ASO brace reduced the first peak vertical GRF whereas Element?increased 2nd peak vertical GRF.Element?brace reduced eversion ROM and peak eversion velocity compared to NB and ASO.In addition,Element?reduced dorsiflexion ROM and increased peak plantarflexion moment compared to NB and ASO.The dynamic measurements suggested that these restrictions offered by both braces are in part due to more dorsiflexed ankle positions prior to contact.

Acknowledgment

This study was supported in part by DeRoyal Industries, Inc.,Powell,TN,USA.

1.Arendt E,Dick R.Knee injury patterns among men and women in collegiate basketballand soccer:NCAA data and review of literature.Am J Sports Med 1995;23:694—701.

2.Fong DT,Hong Y,Chan LK,Yung PS,Chan KM.A systematic review on ankle injury and ankle sprain in sports.Sports Med 2007;37:73—94.

3.Garrick JG.The frequency of injury,mechanism of injury,and epidemiology of ankle sprains.Am J Sports Med 1977;5:241—2.

4.Hootman JM,Dick R,Agel J.Epidemiology of collegiate injuries for 15 sports:summary and recommendations for injury prevention initiatives.J Athl Train 2007;42:311—9.

5.Cordova ML,Ingersoll CD,LeBlanc MJ.Influence of ankle support on jointrange of motion before and after exercise:a meta-analysis.J Orthop Sports Phys Therap 2000;30:170—7[discussion 178—82].

6.De Clercq DL.Ankle bracing in running:the effectofa push type medium ankle brace upon movements of the foot and ankle during the stance phase.Int J Sports Med 1997;18:222—8.

7.Wright IC,Neptune RR,van den Bogert AJ,Nigg BM.The influence of foot positioning on ankle sprains.J Biomech 2000;33:513—9.

8.Zhang S,Wortley M,Chen Q,Freedman J.Efficacy ofan ankle brace with a subtalar locking system in inversion control in dynamic movements.J Orthop Sports Phys Therap 2009;39:875—83.

9.Yeung MS,Chan KM,So CH,Yuan WY.An epidemiological survey on ankle sprain.Br J Sports Med 1994;28:112—6.

10.Hertel J.Functional anatomy,pathomechanics,and pathophysiology of lateralankle instability.J Athl Train 2002;37:364—75.

11.Dayakidis MK,Boudolos K.Ground reaction force data in functional ankle instability during two cutting movements.Clin Biomech(Bristol Avon)2006;21:405—11.

12.Rosenbaum D,Kamps N,Bosch K,Thorwesten L,Volker K,Eils E.The influence of external ankle braces on subjective and objective parameters of performance in a sports-related agility course.Knee Surg Sports Traumatol Arthrosc 2005;13:419—25.

13.Gribble PA,Taylor BL,Shinohara J.Bracing does not improve dynamic stability in chronic ankle instability subjects.Phys Therap Sport2010;11:3—7.

14.Pedowitz DI,Reddy S,Parekh SG,Huffman GR,Sennett BJ.Prophylactic bracing decreases ankle injuries in collegiate female volleyball players. Am J Sports Med 2008;36:324—7.

15.Sitler M,Ryan J,Wheeler B,McBride J,Arciero R,Anderson J,etal.The efficacy of a semirigid ankle stabilizer to reduce acute ankle injuries in basketball.A randomized clinical study at West Point.Am J Sports Med 1994;22:454—61.

16.Zhang S,Chen Q,Wortley M.Biomechanical characteristics of drop landing on an inverted surface with ankle brace.The 33th annualmeeting of the American Society of Biomechanics.State College,Pennsylvania, USA,August 26—29.2009.

17.Chen Q,Wortley M,Bhaskaran D,Milner CE,Zhang S.Is the inverted surface landing more suitable in evaluating ankle braces and ankle inversion perturbation?Clin J Sport Med 2012;22:214—20.

18.McCaw ST,Cerullo JF.Prophylactic ankle stabilizers affect ankle joint kinematics during drop landings.Med SciSports Exerc 1999;31:702—7.

19.Hodgson B,Tis L,Cobb S,Hhigbie E.The effectofexternalankle support on vertical ground-reaction force and lower body kinematics.J Sport Rehabil 2005;14:301—12.

20.Gardner JK,McCaw ST,Laudner KG,Smith PJ,Stafford LN.Effect of ankle braces on lower extremity joint energetics in single-leg landings. Med Sci Sports Exerc 2012;44:1116—22.

21.Rozzi SL,Lephart SM,Sterner R,Kuligowski L.Balance training for persons with functionally unstable ankles.J Orthop Sports Phys Ther 1999;29:478—86.

22.Williams DS,McClay IS.Measurements used to characterize the footand the medial longitudinal arch:reliability and validity.Phys Ther 2000;80:864—71.

23.Zifchock RA,Davis I,Hillstrom H,Song J.The effectof gender,age,and lateral dominance on arch height and arch stiffness.Foot Ankle Int 2006;27:367—72.

24.Dufek JS,Bates BT.Biomechanical factors associated with injury during landing in jump sports.Sports Med 1991;12:326—37.

25.Zhang S,Bates BT,Dufek JS.Contributions of lower extremity joints to energy dissipation during landings.Med Sci Sports Exerc 2000;32:812—9.

26.Kristianslund E,Krosshaug T,van den Bogert AJ.Effect of low pass filtering on joint moments from inverse dynamics:implications for injury prevention.J Biomech 2012;45:666—71.

27.Delahunt E,Coughlan GF,Caulfield B,Nightingale EJ,Lin CW, Hiller CE.Inclusion criteria when investigating insufficiencies in chronic ankle instability.Med Sci Sports Exerc 2010;42:2106—21.

Received 23 April 2012;revised 14 June 2012;accepted 2 July 2012

*Corresponding author.

E-mailaddress:szhang@utk.edu(S.Zhang)

Peer review under responsibility of Shanghai University of Sport.

Production and hosting by Elsevier

2095-2546/$-see front matter Copyright?2012,Shanghai University of Sport.Production and hosting by Elsevier B.V.All rights reserved. http://dx.doi.org/10.1016/j.jshs.2012.07.002