Applied Ergonomics 36 (20

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Abstract

and shifts peak pressures from the third, fourth and fth

Clark, 1985; Snow et al., 1992; Eisenhardt et al., 1996).

employment criteria and/or fashion customs encouragedthe continuous use of high-heeled shoes. Studying theimpact of high heels on kinetic changes and perceived

ARTICLE IN PRESSdiscomfort provide a basis for designs that minimizeadverse effects.

0003-6870/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.apergo.2004.11.001

Corresponding author. Tel.: +886 2737 6339; fax: +8862737 6344.E-mail address: yhlee@im.ntust.edu.tw (L. Yung-Hui).Surveys of shoe choice have shown that 3769% ofwomen wear high-heeled shoes on a daily basis (TheGallup Organization, 1986; Frey et al., 1993). Wearinghigh-heeled shoes modies gait kinematics and kinetics(Esenyel et al., 2003; Snow et al., 1992; Mandato andNester, 1999; Voloshin and Loy, 1994; Kerrigan et al.,1998). Previous studies have demonstrated that walkingin high-heeled shoes alters lower-extremity joint func-tion (Esenyel et al., 2003), raises the peak pressure in theforefoot (Snow et al., 1992; Mandato and Nester, 1999),

In addition, wearing high-heeled shoes for walkinggenerates a force spike at the initial ground contact (i.e.,impact force) and the force is then transmitted upto the skeleton as a shock wave (Voloshin and Loy,1994). This shock wave appeared to damage soft tissues,which may result in leg and back-pain complaints(Wosk and Voloshin, 1981; Voloshin and Wosk, 1982)and eventually lead to degenerative joint disorders(Kerrigan et al., 1998). Despite concerns regarding theiradverse effects on human musculoskeletal system,minimize the adverse effects on the human musculoskeletal system. Previous studies demonstrated the effects of inserts on kinetics

and perceived comfort in at or running shoes. No study attempted to investigate the effectiveness of inserts in high heel shoes. The

purpose of this study was to determine whether increasing heel height and the use of shoe inserts change foot pressure distribution,

impact force, and perceived comfort during walking. Ten healthy females volunteered for the study. The heel heights were 1.0 cm

(at), 5.1 cm (low), and 7.6 cm (high). The heel height effects were examined across ve shoe-insert conditions of shoe only; heel cup,

arch support, metatarsal pad, and total contact insert (TCI). The results indicated that increasing heel height increases impact force

(po0:01), medial forefoot pressure (po0:01), and perceived discomfort (po0:01) during walking. A heel cup insert for high-heeledshoes effectively reduced the heel pressure and impact force (po0:01), an arch support insert reduced the medial forefoot pressure,and both improved footwear comfort (po0:01). In particular, a TCI reduced heel pressure by 25% and medial forefoot pressure by24%, attenuate the impact force by 33.2%, and offered higher perceived comfort when compared to the non-insert condition.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: High-heeled shoes; Insert; Impact force; Pressure distribution

1. Introduction metatarsal heads to the rst and second (Soames andStudying the impact of high-heeled shoes on kinetic changes and perceived discomfort provides a basis to advance the design andEffects of shoe inserts and heel heand perceived com

Lee Yung-Hui

Department of Industrial Management, National Taiwan U

Sec IV, Taipei

Received 26 January 200405) 355362

t on foot pressure, impact force,rt during walking

ong Wei-Hsien

sity of Science and Technology, No. 43, Kee-Lung Road,

an, 106 ROC

epted 12 November 2004

www.elsevier.com/locate/apergo

Engineering efforts to reduce foot loading caused bypeak pressure and impact force, and to improve shoecomfort, involved designing shoe inserts with differentshapes (Light et al., 1980; Chen et al., 1994; Hodge et al.,1999; Lee et al., 2004). The use of inserts is effective inredistributing the pressure beneath the foot andabsorbing energy in terms of reducing impact force.Various inert designs demonstrate different kineticmodication during gait. For example, a heel pad iseffective in reducing heel pressure and the magnitude ofthe heelstrike impact (Light et al., 1980; Jorgensen andEkstrand, 1988). An arch support was designed to resistdepression of the foot arch during weight bearingthrough skeletal support, thereby decreasing tensionin the plantar aponeurosis (Kogler et al., 1996). Ametatarsal pad has been found to reduce forefootpressure and transfer weight bearing to the longitudinaland metatarsal arches (Lee et al., 2004). Finally, a totalcontact insert (TCI) provided pressure relief in the heeland forefoot regions (Lord and Hosein, 1994; Chenet al., 2003). These studies, however, focused on insertsin at or running shoes. No study, insofar as we haveexamined, attempted to identify insert effectiveness in

2. Methods

2.1. Participants and materials

Ten healthy females volunteered for this study. Theaverage age of the subjects was 23 years (range 2028),average weight was 50 kg (range 4753), and averageheight was 160 cm (range 156162). None of the subjectshad suffered an injury to the lower extremity during thepreceding year. Four subjects had worn high-heeledshoes two-to-ve times per week for at least 1 year. Theother six had relatively limited experience. Writtenconsent was obtained from each subject before com-mencement of the experiment.The shoes used in this study were commercially

available items and were selected based on the similarityof construction such as foot contact points, supports,and pump style. The main difference among these shoeswas the height of the heel: a at (1.0 cm), a low (5.1 cm)and a high heel (7.6 cm) (Fig. 1). The mediolateral byanteroposterior dimensions of the heel of the shoes wereas follows: 2.8 3.0 cm and 2.4 2.6 cm (low and highheel, respectively). Each participant received ve insert

ARTICLE IN PRESS

. Fro

L. Yung-Hui, H. Wei-Hsien / Applied Ergonomics 36 (2005) 355362356high heels.The purpose of this study was to determine whether

increasing heel height and the use of various types ofshoe inserts would result in changes in foot pressuredistribution, impact force, and perceived comfort duringwalking. The types of shoe inserts used in the currentstudy included heel cup, arch support, metatarsal pad,and TCI.

Fig. 1. The shoes of three different heel heights were used in this studyFig. 2. The custom-made insertsconditions: (1) shoe only; (2) heel cup; (3) arch support;(4) metatarsal pad; and, (5) TCI (Fig. 2).The inserts were custom fabricated for each indivi-

dual. The fabricating steps were: (1) negative impressionof foot using Hydrogum alginate (Zhermack, SPA,Italy) set while the subject was wearing the high-heeledshoes in seating posture; (2) producing a positive cast ofthe feet by pouring plaster into the high-heeled shoes;

m left to right: a at (1.0 cm), a low (5.1 cm) and a high heel (7.6 cm).and their support positions.

and, (3) making semi-rigid inserts from Multiformmolded materials (AliMed Inc., Dedham, MA) thatwere contoured from the individual positive casts.Multiform is a thermoformable cross-linked polyethy-lene foam. The density of multiform provides goodsupport as well as cushioning (Lamb, 1991). To preventa tight feeling in the toe box, the TCI was designedto terminate at the distal border of the metatarsalheads (see Fig. 2). To avoid slipping around the inside ofthe shoe, the inserts were adjusted to appropriateposition and then attached inside the shoe while beingworn.

2.2. Apparatus

Pressure distributions were measured using the Pedar

ARTICLE IN PRESSL. Yung-Hui, H. Wei-Hsien / Appliedin-shoe pressure measurement system (Novel GmbH,Munich, Germany) (Fig. 3). The Pedar system consistsof A/D conversion electronics housed in a small unitattached to the subjects waist. Leads to each 99-sensorinsole (sample rate 50Hz) were connected to A/Dconversion electronics linked to a computer. Thepressure-measuring insole has a linear response toapplied loads of 050N/cm2 with minimal error, andno interference to normal gait characteristics has beendemonstrated (McPoil et al., 1995). A description of thePedar system and components have been previouslyreported (McPoil et al., 1995; Barnett et al., 2001). Formeasuring impact force external to the shoe, two AMTIforce plates (Model OR6-5-1000; Advanced Biomecha-nical Technology, Newton, MA) were installed on thewalkway (960Hz sampling rate). The Novel playersoftware (Novel GmbH, Munich, Germany) synchro-nized foot-pressure data with video and force-plates.The player is made for effortless synchronized playback,presentation or analysis of complex dynamic events.Fig. 3. The Pedar in-shoe pressure measurement system.2.3. Comfort measurement

The visual analogue scale (VAS) developed byMunermann et al. (2002) was a reliable measure toassess footwear comfort. The VAS was used to rate thefootwear comfort for each experimental condition inthis study. Comfort was rated by a ruler that consistedof a 100mm VAS with the left end of the scale labelednot comfortable at all (0 comfort point) and the rightend labeled the most comfortable condition imaginable(10 comfort points). To perceive uniform comfortableexperiences, we required participants to comfortably tinto the size and advised them not to take the effects ofshoe cosmetics and styles into comfort rating.

2.4. Procedures

In the study, all participants walked on a treadmill forwarm up and walked on a level walkway for datacollection. Firstly, each participant walked on a tread-mill for 5min at 130 cm/s to become habituated to eachheel height and walking speed. The speed of 130 cm/swas used because walking speed may inuence plantarpressure and ground reaction force (Schwartz et al.,1964; Murray et al., 1970). The comfortable speedsreported in previous studies about high heels rangedfrom 122 to 140 cm/s (Opila-Correia, 1990; Snow andWilliams, 1994; Esenyel et al., 2003).A split plot design was used in the study. Firstly, a

heel height was randomly assigned to the participant.For the same heel height, the order of inserts was thenrandomly selected. To prevent fatigue, each participanttook a 5-min rest in between. Data of three successfultrials were collected. The gait initiation and terminationphases were recorded and only the middle gait cycle wasused for analysis to each trial. A total of 450 trials (10subjects 3 heel heights 5 insert conditions 3 trials)were obtained for data analysis.

2.5. Data analysis

Novel Multimasks analysis software (Novel Electro-nics, Inc.) was used to calculate the peak plantarpressure, at the region of highest pressure during gaitcycle, for the six foot regions: heel, midfoot, lateral andmedial forefoot, toes, and hallux (big toe). The regionwas dened based on a percentage of the width and thelength of foot (Fig. 4A). A LabView (National Instru-ments, Austin, TX, US)-based program using a low-passlter with a cut-off frequency of 400Hz (Gillespie andDickey, 2003) was written to analyze ground reactionforce. Impact force obtained from ground reaction forcewas a force spike superimposed on the upslope of theinitial ground-reaction peak occurring right after theheelstrike (Whittle, 1999) (Fig. 4B). Impact force was

Ergonomics 36 (2005) 355362 357normalized to body weight (%BW). As described by

trials that showed the highest repeatability were chosen

ARTICLE IN PRESS

GRF

(%BW

)

80

1

1

1

(B)

rface

pliedfor averaging. All subsequent analyses were derivedfrom these averaged data sets.Analysis of variance (ANOVA) was employed to

study the effects of heel height and shoe insert. TukeysHSD test was used for post hoc comparison. To test forrelationships between comfort rating and pressure andimpact-force variables, Pearsons correlation coefcientswere calculated. An alpha level of 0.01 was used for alltests of statistical signicance to minimize the experi-ment-wise error rate.

3. Results

The assumption of homogeneity is examined and notviolated. Fig. 5 illustrates the comparisons of peakpressures in different foot regions and Table 1 lists theKadaba et al. (1989), a statistical assessment of thebetween-trial repeatability was performed by using thecoefcient of multiple correlations for each motionpattern per participant for each condition. Repeatabilitywas high between trials for each participant, the three

Heel

(A)

Midfoot

Me forefoot

Medi forefoot

Lateral forefoot

85%

58%

31%

0%

40%50%0% 100%

Medial

Medial forefoot

Fig. 4. (A) Denition of the six plantar-su

L. Yung-Hui, H. Wei-Hsien / Ap358comparisons of impact forces for each test condition.ANOVA results indicated a signicant heel height effecton peak pressure of the medial forefoot (F 2;18 42:6;po0:01), the heel (F 2;18 51:2; po0:01), and themidfoot (F 2;18 16:3; po0:01) regions, and impactforce (F 2;18 64:4; po0:01). Post hoc comparisonsusing Tukeys HSD test showed a signicantly higherpeak pressure in the medial forefoot region during high-heeled walking. On the contrary, peak pressure in theheel and the midfoot regions decreased as the heel heightwas increased. The impact force in high heel wassignicantly higher than in low heel and at shoes.ANOVA results also indicated a signicant insert

effect on peak pressure of the medial forefoot (F 4;36 25:6; po0:01), the heel (F 4;36 24:8; po0:01), and themidfoot (F 4;36 12:6; po0:01) regions, and impactforce (F 4;36 8:6; po0:01). Post hoc comparisonsshowed that peak pressure in the heel region wassignicantly reduced with the use of heel cup and TCIthan that with the use of metatarsal pad and shoe onlyin all heights. In the midfoot region, the peak pressurewas increased with the use of arch support, metatarsalpad, and TCI compared to the use of the heel cup andshoe only. In medial forefoot region, the peak pressurewas decreased with the use of arch support and TCIcompared to the use of shoe only, and peak pressurewith the use of TCI was also signicantly lower thanthat with the use of metatarsal pad in low and high heel(Fig. 5). The impact force was effectively attenuatedwith the use of heel cup and TCI compared to the use ofshoe only in all heights. Impact force with a use of TCIwas also signicantly lower than that with a use ofmetatarsal pad in high heel (Table 1).Fig. 6 illustrates the comparisons of comfort ratings

for each test condition. ANOVA results indicated asignicant heel height (F 2;18 46:8; po0:01) and insert(F 4;36 30:4; po0:01) effects for the comfort rating.Post hoc comparisons showed that comfort rating wassignicantly decreased with an increase of heel height.The comfort rating with the use of TCI was higher than

0

20

40

60

30 40 50 60 70Stance phase (%GC)20100

Impact forceImpact force

regions; (B) vertical ground reaction force.00

20

40 First peak vertical forceFirst peak vertical force

Ergonomics 36 (2005) 355362that with the use of metatarsal pad and shoe only in allheights, and the rating with the use of heel cup and archsupport were higher than that of the shoes only in lowand high heel.Table 2 lists the coefcients of correlation between

measures of biomechanical variables and comfort rating.The comfort ratings were signicantly correlated (po0:01)with peak pressure in medial forefoot (0.601), in themidfoot (0.356), and impact force (0.369).

4. Discussion

The results supported our hypotheses that increasingheel height would change pressure distribution under theplantar surface and increased impact force and per-ceived discomfort during walking. All inserts were

ARTICLE IN PRESSplied25

3035

(N/cm

2 )

Heelp

ARTICLE IN PRESSplied0

2

4

Com

fort

ratin

g

6

8

10

Flat shoe Low heel High heel

TCI

p

heels, indicating that higher heel lift might lead to more

vertical force and temporal parameters produced by an in-shoe

pressure measuring system and a force platform. Clin. Biomech. 16

height on forefoot loading. Foot Ankle 14 (3), 148152.

Eisenhardt, J.R., Cook, D., Pregler, I., Foehl, H.C., 1996. Change in

temporal gait characteristics and pressure distribution for bare feet

ARTICLE IN PRESSplieddiscomfort. VAS provided a reliable measure to assessfootwear comfort, as indicated in a previous study(Munermann et al., 2002). This was true for high-heeledambulation, as previous ndings indicate that mostpeople can rapidly distinguish between comfortable anduncomfortable footwear (Munermann et al., 2001). Themechanism underlying this perception and the function-ing of the feedback control system are not clearlyunderstood. Our comfort ratings were, however, nega-tively correlated with peak pressure in the medialforefoot (r 0:601) and impact force (r 0:369),but were positively correlated with peak pressure in themidfoot (r 0:356; po0:01). It appears reasonable tosuggest that our participants were able to perceive theextent of the comfort through realization of the changesin pressure distribution and impact force that character-ized the different inserts. The study indicated that theuses of some inserts were effective in improving comfortwhen wearing high-heeled shoes. In comparison withnon-insert shoes, the use of a heel cup improved comfortrating from 2.6 to 5.2, an arch support to 5.4, and a TCImore to 6.8. Therefore, the TCI offered superiorcomfort compared to non-insert condition when wear-ing high-heeled shoes.There are several limitations to the current study.

First, the experience of wearing high heels might be aconfounding factor in response to the experimentalconditions. Several subjects had limited experience usinghigh heels. In addition, this study was laboratory-basedand the tasks were preformed over a 2-h period. In arealistic work environment, the individual may bestanding for much of the work day. An experiment oflonger duration may provide better insight into thebehavioral and physical adaptations of each individualand reect the effects found in real work environments.Second, when examining pressures at the footshoeinterface using an insert as a measuring device, the factthat the presence of the insert itself could inuence theseparameters must not be neglected. There is no directway of measuring this. Therefore, the recorded pressuremay have small errors which are inevitable. However,participants perceptions of changes in comfort pro-duced by the insertion of the insole may give someindication of pressure distribution changes.

5. Conclusion

Increasing heel height increases medial forefootpressure, impact force, and perceived discomfort duringIncreasing heel height signicantly reduced footwearcomfort, however, the uses of the inserts were effectivein improving footwear comfort. The mean comfortrating in at shoe was 7.6 and reduced to 2.6 in high

L. Yung-Hui, H. Wei-Hsien / Apwalking. A custom-made insert with a heel-cup or anversus various heel heights. Gait Posture 4 (4), 280286.

Esenyel, M., Walsh, K., Walden, J.G., Gitter, A., 2003. Kinetics of

high-heeled gait. J. Am. Podiatr. Med. Assoc. 93 (1), 2732.

Frey, C., Thompson, F., Smith, J., Sanders, M., Horstman, H., 1993.

American Orthopaedic Foot and Ankle Society womens shoe

survey. Foot Ankle 14 (2), 7881.

Gillespie, K.A., Dickey, J.P., 2003. Determination of the effectiveness

of materials in attenuating high frequency shock during gait using

lterbank analysis. Clin. Biomech. 18 (1), 5059.

Hodge, M.C., Bach, T.M., Carter, G.M., 1999. Orthotic management

of plantar pressure and pain in rheumatoid arthritis. Clin.

Biomech. 14 (8), 567575.

Jorgensen, U., Ekstrand, J., 1988. Signicance of heel pad connement

for the shock absorption at heel strike. Int. J. Sports Med. 9 (6),(4), 353357.

Boulton, A.J., Franks, C.I., Betts, R.P., Duckworth, T., Ward, J.D.,

1984. Reduction of abnormal foot pressure in diabetic neuropathy

using a new polymer insole material. Diabetes Care 7 (1), 4246.

Chen, H., Nigg, B.M., de Koning, J., 1994. Relationship between

plantar pressure distribution under the foot and insole comfort.

Clin. Biomech. 9 (6), 335341.

Chen, W.P., Ju, C.W., Tang, F.T., 2003. Effect of total contact insoles

on the plantar stress redistribution: a nite element analysis. Clin.

Biomech. 18 (6), s17s24.

Corrigan, J.P., Moore, D.P., Stephens, M.M., 1993. Effect of heelarch-support mechanism for high-heeled shoes would beeffective for reductions of heel pressure and impact forceor medial forefoot pressure, and for an improvement infootwear comfort. In particular, a TCI, combined with aheel-cup and an arch-support mechanism, could reduceheel pressure by 25% and medial forefoot pressure by24%, attenuate the impact force by 33.2%, and offerbetter comfort when compared to not wearing an insert.It is suggested that these inserts may contribute torelieve foot pressure, reduced impact force, and morecomfort at work for women wearing high-heeled shoes.

Acknowledgements

This study was supported by a grant from theNational Science Council, ROC (Project No. NSC-92-2213-E-011-041). The authors also wish to acknowledgeMr. Liu Wen-Long, an orthotic technician from theDepartment of Physical Medicine and Rehabilitation,Chang Gung Memorial Hospital, for his assistance withthe fabrication of the custom-made inserts.

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Effects of shoe inserts and heel height on foot pressure, impact force, and perceived comfort during walkingIntroductionMethodsParticipants and materialsApparatusComfort measurementProceduresData analysis

ResultsDiscussionConclusionAcknowledgementsReferences