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Effects of long-term wearing of high-heeled shoes on the control of the body's center of mass motion in relation to the center of pressure during walking
Gait & Posture 39 (2014) 1045–1050
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Effects of long-term wearing of high-heeled shoes on the control of the body’s center of mass motion in relation to the center of pressure during walking Hui-Lien Chien a, Tung-Wu Lu a,b,*, Ming-Wei Liu c a b c
Institute of Biomedical Engineering, National Taiwan University, Taiwan, ROC Department of Orthopaedic Surgery, School of Medicine, National Taiwan University, Taiwan, ROC Department of Surgery, Taiwan Adventist Hospital, Taiwan, ROC
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 June 2013 Received in revised form 2 December 2013 Accepted 12 January 2014
High-heeled shoes are associated with instability and falling, leading to injuries such as fracture and ankle sprain. This study investigated the effects of habitual wearing of high-heeled shoes on the body’s center of mass (COM) motion relative to the center of pressure (COP) during gait. Fifteen female experienced wearers and 15 matched controls walked with high-heeled shoes (7.3 cm) while kinematic and ground reaction force data were measured and used to calculate temporal-distance parameters, joint moments, COM–COP inclination angles (IA) and the rate of IA changes (RCIA). Compared with inexperienced wearers, experienced subjects showed significantly reduced frontal IA with increased ankle pronator moments during single-limb support (p < 0.05). During double-limb support (DLS), they showed significantly increased magnitudes of the frontal RCIA at toe-off and contralateral heel-strike, and reduced DLS time (p < 0.05) but unaltered mean RCIA over DLS. In the sagittal plane experienced wearers showed significantly increased mean RCIA (p < 0.05) and significant differences in the RCIA at toe-off and contralateral heel-strike (p < 0.05). Significantly increased hip flexor moments and knee extensor moments at toe-off (p < 0.05) were needed for forward motion of the trailing limb. The current results identified the change in the balance control in females after long-term use of high-heeled shoes, providing a basis for future design of strategies to minimize the risk of falling during high-heeled gait. ß 2014 Elsevier B.V. All rights reserved.
Keywords: Gait High heels Balance Habitual Inclination angle
1. Introduction In modern society, many women wear high-heeled shoes in both professional and social settings [1], with up to 39% of American women [2,3] and 78% of British women wearing them on a daily basis [4,5]. High-heeled shoes often result in a reduced supporting base compared with barefoot, increasing the difficulty of maintaining balance, and the risk of falling [6,7]. Compared to barefoot gait, experienced wearers of high-heeled shoes adopted a conservative strategy for controlling the motion of the body’s center of mass (COM) in relation to the center of pressure (COP) during high-heeled gait [8]. Whether long-term wearing of highheeled shoes would help improve the balance control during highheeled gait remained unclear.
* Corresponding author at: Institute of Biomedical Engineering, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei 100, Taiwan, ROC. Tel.: +886 2 33653335; fax: +886 2 33653335. E-mail address: [email protected] (T.-W. Lu). 0966-6362/$ – see front matter ß 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gaitpost.2014.01.007
Habitual wearers of high-heeled shoes were reported to experience chronic adaptations in muscle-tendon architecture, including shortening of the gastrocnemius medialis fascicles [9,10] and increased Achilles tendon stiffness [9]. These adaptations could shift the stretch distribution of a muscle-tendon unit away from the tendinous tissues toward the muscle fascicles during gait, altering neural activation patterns and reducing muscle-tendon unit efficiency [11]. Reduced endurance of the gastrocnemius lateralis and peroneus longus muscles was also reported [12]. Habitual and inexperienced wearers were found to accommodate differently to walking in high-heeled shoes when compared to low-heeled shoes, the former subjects showing decreased rotations of the upper trunk and exaggerated motions of the pelvis, and the latter showing the opposite [13]. Habitual wearers also had a shorter stride length than inexperienced wearers. These kinematic changes suggest that both groups adopt a cautious gait style, particularly the inexperienced group [13]. Differences in the changes of gait kinematics and muscletendon architecture between habitual and inexperienced wearers suggest that the two groups may have different balance control
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during high-heeled gait. Menant et al. [7] studied the effects of wide base, elevated shoe heels on gait stability using the minimum COM–BOS margin during SLS, but the effects of long term use were not considered. Since the dynamic stability of gait depends on both the position and the velocity of the COM with respect to the BOS [14], the minimum COM–BOS margin alone may not be sufficient to describe the body’s stability. The continuously varying BOS during double-limb support (DLS) presents another difficulty in the definition of the COM–BOS margin. Chien et al. [8] used COM– COP inclination angles (IA) to describe the body’s dynamic control in experienced wearers. The experienced wearers were found to adopt a conservative balance control strategy when compared with barefoot, with reduced normalized walking speed, reduced frontal IA throughout the high-heeled gait cycle, and also a reduced frontal and sagittal rate of change of IA (RCIA) during DLS. During high-heeled gait the BOS is reduced both in the anterior–posterior and in the medial–lateral directions compared with barefoot. During single-limb support (SLS), the BOS is reduced mainly as a result of the reduced area of the heel. During DLS, the reduced BOS is a result not only of the reduced area of the heel, but also of the reduction in the step width and stride length [8]. The reduced BOS was found to be a major factor affecting the observed conservative control strategy in habitual wearers compared to the barefoot condition [8]. However, whether this strategy was adopted immediately or whether it was a result of long-term adaptation to high-heeled shoes has not been explored. The purposes of this study were to investigate the long-term effects of wearing high-heeled shoes on the body’s COM motion in terms of IA and RCIA during high-heeled gait. It was hypothesized that during high-heeled walking, experienced wearers would decrease the frontal IA throughout the gait cycle, and the frontal and sagittal RCIA during DLS when compared with the inexperienced controls. 2. Materials and methods 2.1. Subjects Fifteen female habitual wearers of high-heeled shoes (experienced group; age: 24.4 3.4 years; height: 158.9 5.7 cm; mass: 49.2 5.1 kg) and 15 matched controls (inexperienced group; age: 24.9 4.1 years; height: 161.0 4.2 cm; mass: 50.3 3.7 kg) participated in the current study with informed written consent, as approved by the Institutional Research Board. None of the subjects suffered from any neuromusculoskeletal pathology that might have affected their normal gait. Experienced wearers had worn shoes with narrow heels of more than 3 cm height a minimum of three times per week, six hours per day for at least two years. The inexperienced wearers wore high-heeled shoes less than twice per month. 2.2. Data collection Each subject walked in high-heeled shoes (height: 7.3 cm) at a self-selected pace on an 8-m walkway. The shoes were narrowheeled (heel base: 2.0 cm 1.6 cm; mass: 0.2 kg) and were commercially available [8]. Subjects were fitted with the most suitable test shoes from several different sizes, and were allowed to familiarize themselves with the walkway before data collection. Each subject wore 39 retroreflective markers for tracking motions of the body segments [15]. Markers for the heels, big toes and fifth metatarsal bases were attached to the corresponding positions on the shoes. Markers on the navicular tuberosity and malleoli were not affected by the shoes. Three-dimensional trajectories of the markers were measured using a motion capture system (Vicon 512, OMG, UK) at a sampling rate of 120 Hz, and were low-pass filtered using a fourth-order Butterworth filter with
a cut-off frequency of 5 Hz [16]. The ground reaction forces (GRF) were collected from two forceplates (AMTI, USA) at a frequency of 1080 Hz [15]. Six successful trials, three for each limb, were obtained. 2.3. Data analysis The body was modeled as a system of 13 rigid segments, namely the head and neck, trunk, pelvis, arms, forearms, thighs, shanks and feet [15,17]. Coordinates of the markers gathered during a static calibration trial were used to define the anatomical coordinate system of each of the body and foot/shoe segments, with the positive x-axis directed anteriorly, the positive y-axis superiorly and the positive z-axis to the right. A Cardanic rotation sequence (z–x–y) was used to describe the rotational movements of each joint [15]. In order to minimize the errors owing to skin movement artifacts, a global optimization method was used [18]. With the measured GRF and kinematic data, inverse dynamics were used to calculate the inter-segmental forces and moments at the lower limb joints. Inertial properties for each body segment were obtained using an optimization method [19], using Dempster’s coefficients as the initial guess [17]. In the shod condition, the mass of the foot/shoe unit was determined as the sum of the masses of the foot and the shoe, with the center of mass taken as that of the foot as an approximation. All the calculated joint moments were normalized to body weight (BW) and leg length (LL) that was defined as the sum of the shoe height and the distance between the anterior superior iliac spine and the medial malleolus [20]. The body’s COM position was calculated as the weighted sum of the positions of all 13 model body segments. The COP position was calculated using forces and moments measured by the forceplates [21]. The medial/lateral positions of the COM and COP were described relative to the line of progression that bisected the medial/lateral range of motion of the COM during a gait cycle, a positive value being to the side of the contralateral limb [22]. The anterior/posterior positions of the COM and COP were described parallel to the direction of progression, a zero value being the position of heel-strike and a positive value being anterior to that position. The IA in the sagittal plane (a) and frontal plane (b) were then calculated as follows [16] (Fig. 1). * *! * P COM COP Z t¼ (1) * jP COM COP j
a ¼ sin1 ðt x Þ
(2)
b ¼ sin1 ðty Þ
(3)
*
where P COM COP was the vector pointing from the COP to the COM, * and Z was the unit vector of the global vertical axis. With the current forceplate setup, a and b were calculated from the beginning of SLS to the subsequent heel-strike. The RCIA for a and b were also calculated by smoothing and differentiating their trajectories using the GCVSPL method [23]. During the gait cycle, the transitions between SLS and DLS, i.e., heel-strike of the contralateral leg and toe-off of the ipsilateral leg, are critical instances at which maintaining body stability is expected to be more difficult [16]. Therefore, the values of the IA, RCIA and the joint moments at these instances were obtained. The values of IA, RCIA and the joint moments were averaged over the DLS and SLS, respectively. The ranges of motion (ROM) of IA during DLS and SLS, as well as the peak RCIA during DLS, were obtained. Temporaldistance parameters (gait speed, stride length, step width, stride time, cadence, stance time, DLS time and SLS time) for all conditions were also calculated. For between-group comparisons, gait speed,
[(Fig._1)TD$IG]
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Fig. 1. Ensemble-averaged COM–COP inclination angle (IA) and rate of changes of IA (RCIA) in the (a) frontal and (b) sagittal planes in experienced wearers of high-heeled shoes (solid) and inexperienced controls (dashed) during high-heeled gait. (HS, heel-strike; CTO, toe-off of the contralateral leg; CHS, heel-strike of the contralateral leg; TO, toe-off; SLS, single-limb support; DLS, double-limb support; CSLS, single-limb support of contralateral limb.) *p < 0.05.
stride length, step width, stride time, cadence, and COP and COM positions were normalized following Hof [24]. The values of the variables from both limbs were averaged for each subject for subsequent statistical analysis. Comparisons of all the calculated variables between groups were performed using independent ttests. All statistical analyses were performed using SPSS (version 17.0, SPSS Inc., USA) with a significance level of 0.05. 3. Results No significant between-group differences in any temporal-distance parameters were found, except that the experienced group showed increased SLS time
but reduced stance time, DLS time, step width and normalized step width (Table 1). In the frontal plane, compared with the inexperienced group, all variables of the IA in the experienced group were significantly reduced except the averaged values over the SLS and their ROM during DLS (Fig. 1 and Table 2). The experienced group also showed significantly increased lateral RCIA at toe-off (p < 0.0001) and contralateral heel-strike (p = 0.0002) (Fig. 1 and Table 2). The experienced group showed increased mean ankle pronator moments over SLS (p = 0.040) and at contralateral heel-strike (p = 0.009) (Fig. 2 and Table 3). In the sagittal plane, no significant between-group differences were found in any variables of the IA, except that the experienced group showed increased ROM during SLS (p = 0.027) (Fig. 1 and Table 2). The experienced group also showed increased posterior RCIA at toe-off (p < 0.0001) and contralateral heel-strike (p < 0.0001), and increased mean values of the posterior RCIA over DLS (p = 0.001)
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Table 1 Means (standard deviations) of temporal-distance parameters during high-heeled gait for experienced wearers of high-heeled shoes and inexperienced controls. Parameters
Inexperienced
Gait speed m/s 1.08 (0.10) Dimensionless 0.37 (0.03) Stride length m 1.16 (0.06) %LL 130.0 (8.2) Step width cm 8.09 (2.93) %LL 9.1 (3.3) Stride time second 1.08 (0.08) Dimensionless 3.57 (0.30) Cadence steps/min 112.32 (9.44) Dimensionless 0.57 (0.06) Stance time % 66.6 (0.9) Double-limb suport time % 15.6 (1.0) Single-limb support time % 34.9 (1.4) *
Experienced
p
1.07 (0.09) 0.37 (0.03)
0.774 0.980
1.16 (0.05) 132.0 (6.5)
0.803 0.488
5.85 (2.10) 6.6 (2.3)
0.023* 0.028*
1.08 (0.08) 3.62 (0.27)
0.888 0.660
111.40 (7.81) 0.56 (0.04)
0.772 0.555
64.2 (1.4)
<0.0001*
13.3 (1.4)
<0.0001*
36.6 (1.6)
0.003*
p < 0.05.
(Fig. 1 and Table 2). No significant between-group differences were found in the two peaks of the sagittal RCIA. The experienced group showed increased hip flexor moments and knee extensor moments at toe-off (hip, p = 0.012; knee, p < 0.001) (Fig. 2 and Table 3).
4. Discussion The current study aimed to investigate the effects of habitual wearing of high-heeled shoes on the body’s COM motion in terms of IA and RCIA during walking. The results supported the hypothesis, except for the frontal and sagittal RCIA during DLS. The current results provide a basis for future design of strategies to minimize the risk of falling during high-heeled gait. Compared with inexperienced wearers, experienced wearers showed more stable body control during SLS with reduced IA in the frontal plane, i.e., reduced COM–COP separation, which was achieved mainly through increased pronator moments at the
ankle (Fig. 2 and Table 3). They also showed reduced ROM of IA in the frontal plane during DLS owing to the reduced BOS in the medial–lateral direction as a result of the reduced step width (Tables 1 and 2). Control of the body’s medio-lateral motion is important for gait stability [25]. Impaired medio-lateral motion control can cause a sideway fall in the elderly, a major risk factor for hip fractures [25]. Increased medio-lateral COM–COP separation, as indicated by the increased frontal IA, was found in elderly fallers, leading to loss of balance, especially under unexpected postural disturbances such as tripping or slipping [26]. Compared to barefoot gait, reduced frontal IA in experienced wearers of shoes with narrow high heels is helpful for the body’s stability [8]. The current results showed that inexperienced wearers were yet to develop the same strategy as the experienced wearers, suggesting that they were subject to a higher fall risk during high-heeled gait. Increased pronator moments appeared to be used by the experienced wearers to improve the overall dynamic balance control during high-heeled gait. On the one hand, increased activity of the ankle evertors helps to move the COP medially and the COM laterally during SLS of barefoot gait [12,27], contributing to the reduction of the COM and COP separation, and thus maintaining the body’s balance. On the other hand, increased pronator activity helps to provide the necessary torque at the ankle to reduce its medio-lateral instability [28] that may be induced by shoes with narrow high heels. Such activity also helps to stabilize the ankle from foot flat to push-off during barefoot gait [29,30]. However, increased muscle activity may increase the metabolic cost of gait and result in accelerated muscle fatigue and discomfort [10]. The peroneus longus was found to be more vulnerable to fatigue among habitual wearers of high-heeled shoes, which could in turn alter the stability of the feet during prolonged walking [12]. Since increased pronator activity is important in the strategy used by experienced wearers, weakness of the pronators, resulting from aging, for example, or from early fatigue owing to muscular architectural changes, could lead to an increased risk of falling similar to inexperienced wearers. While the experienced wearers adopted a conservative body control in the frontal plane with reduced IA and unaltered mean RCIA during the gait cycle, they showed a faster weight transfer between SLS and DLS, with increased magnitudes of the RCIA at toe-off and contralateral heel-strike, which were different from the hypothesis. The increased pronator activity in SLS continued
Table 2 Mean (standard deviations) of the frontal and sagittal COM–COP inclination angle (IA) and their rates of change (RCIA) at heel-strike of contralateral leg (CHS), toe-off (TO), and their mean values during single-limb support (Mean/SLS) and double-limb support (Mean/DLS), as well as the range of motion (ROM) of IA and the two RCIA peaks during high-heeled gait for experienced wearers of high-heeled shoes and inexperienced controls. COM–COP inclination angle (8) Inexperienced Frontal CHS TO Mean/DLS Mean/SLS ROM/DLS ROM/SLS Peak 1 Peak 2
2.2 2.6 0.2 2.3 4.8 1.0 – –
(0.8) (0.8) (0.3) (0.6) (1.4) (0.2)
Sagittal CHS TO Mean/DLS Mean/SLS ROM/DLS ROM/SLS Peak 1 Peak 2
8.0 10.7 1.5 0.7 19.5 19.2 – –
(0.7) (1.1) (0.9) (0.8) (1.0) (1.0)
*
p < 0.05.
Rate of change of COM–COP inclination angle (8/s)
Experienced 1.6 2.0 0.1 1.7 3.6 0.9 – –
(0.5) (0.4) (0.3) (0.3) (0.7) (0.1)
8.5 11.0 1.2 0.5 19.7 20.3 – –
(1.2) (1.2) (0.7) (0.4) (1.8) (1.6)
p
Inexperienced
0.017* 0.018* 0.990 0.004* 0.009* 0.802 – –
1.8 1.1 26.6 0.5 – – 50.1 96.6
0.202 0.472 0.494 0.594 0.670 0.027* – –
46.7 50.7 104.5 51.8 – – 205.8 500.9
(6.6) (6.0) (8.7) (0.7)
(25.2) (30.3)
(17.4) (23.0) (9.9) (4.9)
(91.1) (82.9)
Experienced 10.5 12.5 24.9 0.5 – – 50.9 76.1
48.1 10.6 135.5 50.4 – – 271.9 465.0
(9.2) (3.8) (6.1) (0.3)
(16.9) (25.8)
(64.5) (21.9) (28.8) (5.1)
(88.4) (110.3)
p 0.0002* <0.0001* 0.530 0.663 – – 0.917 0.056 <0.0001* <0.0001* 0.001* 0.469 – – 0.053 0.322
[(Fig._2)TD$IG]
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(a)
(b)
Hip Ext (+)/Flex (-)
%BW*LL
20
DLS
SLS
DLS
10
10
0
0
DLS
SLS
DLS
CSLS
-10
* Knee Ext (+)/Flex (-)
Knee Abd (+)/Add (-)
10
%BW*LL
Hip Abd (+)/Add (-)
CSLS
20
-10
1049
10
5 5
0 -5
0
-10
*
Ankle Plant (+)/Dorsi (-)
Ankle Pronator (+)/Supinator (-)
20
%BW*LL
4 10 2 0
0
-10
20
HS
40
CTO
60 CHS
80
100
-2 HS
HS
TO
20 CTO
% Gait Cycle
40
*
60
CHS
80 TO
100 HS
% Gait Cycle
Fig. 2. Ensemble-averaged joint moments at the hip, knee and ankle in the sagittal (a) and (b) frontal planes in experienced (solid) and inexperienced wearers (dashed) during high-heeled gait. (Ext/Flex, extensor and flexor moments; Plant/Dorsi, plantarflexor and dorsiflexor moments; Abd/Add, abductor and adductor moments; HS, heel-strike; CTO, toe-off of the contralateral leg; CHS, heel-strike of the contralateral leg; TO, toe-off; SLS, single-limb support; DLS, double-limb support; CSLS, single-limb support of contralateral limb.) *p < 0.05.
during DLS to provide the necessary stability of the support ankle, and thus the whole body stability, when the COM was moving away from the supporting ankle, and to achieve better end-point control of the contralateral swing limb, especially at heel-strike. Long-term use of high-heeled shoes appeared to help the experienced wearers acquire a better function from the ankle pronators for a faster weight transfer from SLS to DLS. This is critical because falls or ankle sprains often happen during a rapid shifting movement at foot contact. Insufficient foot evertor strength may compromise the stability of the supporting ankle
and the end-point control of the contralateral swing limb at heelstrike, increasing the fall risk during high-heeled gait. The faster weight transfer during DLS in the experienced wearers was even more evident in the sagittal plane, as indicated by the significantly increased means of the RCIA over DLS, increased RCIA at toe-off and contralateral heel-strike, and reduced DLS time (Tables 1 and 2). At the contralateral heel-strike, the frontal stability achieved by the increased pronator moments at the ankle may also be helpful for the weight transfer in the sagittal plane. At toe-off, increased hip flexor moments and knee extensor
Table 3 Means (standard deviations) of joint moments at heel-strike of contralateral leg (CHS), toe-off (TO) and their mean values during single-limb support (Mean/SLS) and doublelimb support (Mean/DLS) in experienced wearers of high-heeled shoes and inexperienced controls. Units: %BW LL. Parameters
Hip Inexperienced
Knee Experienced
Ankle
p
Inexperienced
Experienced
p
Inexperienced
Experienced
p
13.3 0.9 6.8 4.8
(1.1) (0.6) (0.9) (1.1)
12.7 0.8 6.5 4.9
(1.5) (0.8) (1.1) (0.9)
0.229 0.018 0.313 0.944
1.2 0.0 0.7 0.7
(0.5) (0.1) (0.3) (0.3)
1.8 0.1 0.9 1.0
(0.6) (0.1) (0.3) (0.3)
0.009* 0.904 0.131 0.040*
Extensor (+)/flexor () moment CHS 6.3 (2.3) TO 2.7 (0.8) Mean/DLS 5.4 (1.3) Mean/SLS 0.5 (1.5)
6.4 3.5 5.8 1.1
(1.9) (0.8) (1.3) (1.7)
0.926 0.012* 0.375 0.291
0.2 0.4 0.9 2.2
(1.4) (0.3) (0.7) (1.4)
0.6 0.9 1.0 1.6
(1.3) (0.4) (0.8) (1.4)
0.452 <0.001* 0.900 0.237
Abductor (+)/adductor () moment CHS 9.5 (1.3) TO 0.4 (0.5) Mean/DLS 3.8 (0.7) Mean/SLS 8.3 (0.7)
10.4 0.6 4.3 8.8
(1.9) (0.4) (1.2) (1.3)
0.156 0.150 0.179 0.291
4.4 0.3 1.4 3.6
(1.3) (0.2) (0.7) (0.9)
4.7 0.4 1.5 3.8
(0.8) (0.2) (0.5) (0.8)
0.478 0.160 0.491 0.542
*
p < 0.05.
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moments were needed to push the trailing limb forward so that the COM could catch up with the fast anteriorly moving COP for stable control during the subsequent SLS of the contralateral limb. Pai and Patton [14] showed that the control of the stability of the body depends not only on the position of the COM with respect to the base of support, but also on the velocity of the COM. During DLS where the BOS was greater than during SLS, increased mean RCIA in experienced wearers may be helpful for maintaining the continuing progress of the COM without compromising the stability. Shoes with narrow high heels have been shown to be related to the increased risk of falling previously noted in the elderly [6,7]. The current study identified the changes in the balance control in young females after long-term wearing of high-heeled shoes, which serve as the baseline data. Further study on the older population is needed to identify the mechanisms responsible for the increased risk of falling in the elderly who wear high-heeled shoes. 5. Conclusions Experienced wearers of high-heeled shoes appeared to adopt a specific control strategy during high-heeled gait when compared with inexperienced wearers. In the frontal plane, experienced wearers showed more conservative body control during SLS, but a faster weight transfer during DLS where the BOS was greater than SLS, both benefited by increased ankle pronator moments. In the sagittal plane where the main body motion occurred, the even faster weight transfer during DLS in experienced wearers was seen primarily by the fast increase of the COM and COP separation with increased mean RCIA. Increased hip flexor moments and knee extensor moments at toe-off were needed for the forward motion of the trailing limb. The current study identified the changes in the balance control in females after long-term use of high-heeled shoes, providing a basis for future design of strategies to minimize the risk of falling during high-heeled gait. Acknowledgement The authors gratefully acknowledge the financial support from Taiwan Adventist Hospital of Taiwan (100-E-11). Conflict of interest None declared. References [1] Hsue BJ, Su FC. Kinematics and kinetics of the lower extremities of young and elder women during stairs ascent while wearing low and high-heeled shoes. J Electromyogr Kinesiol 2009;19:1071–8. [2] American Podiatric Medical Association (APMA). High heel survey; 2003, http://www.apma.org/s_apma/doc.asp?CID=1233&DID=17112.2003/.
[3] Yoon JY, An DH, Yoo WG, Kwon YR. Differences in activities of the lower extremity muscles with and without heel contact during stair ascent by young women wearing high-heeled shoes. J Orthop Sci 2009;14:418–22. [4] The Ogilvy Group. British women’s daily battle with high heels; 2007, http:// www.feetforlife.org/cgibin/item.cgi?id=1850&d=pnd&h=0&f=0&dateformat=%25o%20%25B%20%25Y [accessed 25.10.09]. [5] Curran SA, Holliday JL, Watkeys L. Influence of high heeled footwear and prefabricated orthoses on energy efficiency in ambulation. Foot Ankle Online J 2010;3(3):1–11. [6] Tencer AF, Koepsell TD, Wolf ME, Frankenfeld CL, Buchner DM, Kukull WA, et al. Biomechanical properties of shoes and risk of falls in older adults. J Am Geriatr Soc 2004;52(11):1840–6. [7] Menant JC, Perry SD, Steele JR, Menz HB, Munro BJ, Lord SR. Effects of shoe characteristics on dynamic stability when walking on even and uneven surfaces in young and older people. Arch Phys Med Rehabil 2008;89(10): 1970–6. [8] Chien HL, Lu TW, Liu MW. Control of the motion of the body’s center of mass in relation to the center of pressure during high-heeled gait. Gait Posture 2013;38(3):391–6. [9] Csapo R, Maganaris CN, Seynnes OR, Narici MV. On muscle, tendon and high heels. J Exp Biol 2010;213:2582–8. [10] Cronin NJ, Barrett RS, Carty CP. Long-term use of high-heeled shoes alters the neuromechanics of human walking. J Appl Physiol 2012;112(6):1054–8. [11] Kim Y, Lim JM, Yoon B. Changes in ankle range of motion and muscle strength in habitual wearers of high-heeled shoes. Foot Ankle Int 2013; 34(3):414–9. [12] Gefen A, Megido-Ravid M, Itzchak Y, Arcan M. Analysis of muscular fatigue and foot stability during high-heeled gait. Gait Posture 2002;15(1):56–63. [13] Opila-Correia KA. Kinematics of high-heeled gait with consideration for age and experience of wearers. Arch Phys Med Rehabil 1990;71(11):905–9. [14] Pai YC, Patton J. Center of mass velocity-position predictions for balance control. J Biomech 1997;30(4):347–54. [15] Lu TW, Chien HL, Chen HL. Joint loading in the lower extremities during elliptical exercise. Med Sci Sports Exerc 2007;39(9):1651–8. [16] Hsu WC, Wang TM, Liu MW, Chang CF, Chen HL, Lu TW. Control of body’s center of mass motion during level walking and obstacle-crossing in older patients with knee osteoarthritis. J Mech 2010;26(2):229–37. [17] Dempster WT, Gabel WC, Felts WJ. The anthropometry of the manual work space for the seated subject. Am J Phys Anthropol 1959;17:289–317. [18] Lu TW, O’Connor JJ. Bone position estimation from skin marker co-ordinates using global optimisation with joint constraints. J Biomech 1999;32:129–34. [19] Chen SC, Hsieh HJ, Lu TW, Tseng CH. A method for estimating subject-specific body segment inertial parameters in human movement analysis. Gait Posture 2011;33(4):695–700. [20] Magee DJ. Orthopedic physical assessment. Canada: Saunders Elsevier; 2008. [21] Hsieh HJ, Lu TW, Chen SC, Chang CM, Hung C. A new device for in situ static and dynamic calibration of force platforms. Gait Posture 2011;33(4):701–5. [22] Huang SC, Lu TW, Chen HL, Wang TM, Chou LS. Age and height effects on the center of mass and center of pressure inclination angles during obstaclecrossing. Med Eng Phys 2008;30(8):968–75. [23] Woltring HJ. A FORTRAN package for generalized, cross-validatory spline smoothing and differentiation. Adv Eng Softw 1986;8:104–13. [24] Hof AL. Scaling gait data to body size. Gait Posture 1996;4:222–3. [25] Greenspan SL, Myers ER, Kiel DP, Parker RA, Hayes WC, Resnick NM. Fall direction, bone mineral density, and function: risk factors for hip fracture in frail nursing home elderly. Am J Med 1998;104(6):539–45. [26] Lee HJ, Chou LS. Detection of gait instability using the center of mass and center of pressure inclination angles. Arch Phys Med Rehabil 2006;87(4):569– 75. [27] Winter DA. Human balance and posture control during standing and walking. Gait Posture 1995;3(4):193–214. [28] Hopkins JT, McLoda T, McCaw S. Muscle activation following sudden ankle inversion during standing and walking. Eur J Appl Physiol 2007;99(4):371–8. [29] Winter DA, Yack HJ. EMG profiles during normal human walking: stride-tostride and inter-subject variability. Electroencephalogr Clin Neurophysiol 1987;67(5):402–11. [30] Rodgers MM. Dynamic foot biomechanics. J Orthop Sports Phys Ther 1995; 21(6):306–16.
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Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Effects of long-term wearing of high-heeled shoes on the control of the body’s center of mass motion in relation to the center of pressure during walking Hui-Lien Chien a, Tung-Wu Lu a,b,*, Ming-Wei Liu c a b c
Institute of Biomedical Engineering, National Taiwan University, Taiwan, ROC Department of Orthopaedic Surgery, School of Medicine, National Taiwan University, Taiwan, ROC Department of Surgery, Taiwan Adventist Hospital, Taiwan, ROC
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 June 2013 Received in revised form 2 December 2013 Accepted 12 January 2014
High-heeled shoes are associated with instability and falling, leading to injuries such as fracture and ankle sprain. This study investigated the effects of habitual wearing of high-heeled shoes on the body’s center of mass (COM) motion relative to the center of pressure (COP) during gait. Fifteen female experienced wearers and 15 matched controls walked with high-heeled shoes (7.3 cm) while kinematic and ground reaction force data were measured and used to calculate temporal-distance parameters, joint moments, COM–COP inclination angles (IA) and the rate of IA changes (RCIA). Compared with inexperienced wearers, experienced subjects showed significantly reduced frontal IA with increased ankle pronator moments during single-limb support (p < 0.05). During double-limb support (DLS), they showed significantly increased magnitudes of the frontal RCIA at toe-off and contralateral heel-strike, and reduced DLS time (p < 0.05) but unaltered mean RCIA over DLS. In the sagittal plane experienced wearers showed significantly increased mean RCIA (p < 0.05) and significant differences in the RCIA at toe-off and contralateral heel-strike (p < 0.05). Significantly increased hip flexor moments and knee extensor moments at toe-off (p < 0.05) were needed for forward motion of the trailing limb. The current results identified the change in the balance control in females after long-term use of high-heeled shoes, providing a basis for future design of strategies to minimize the risk of falling during high-heeled gait. ß 2014 Elsevier B.V. All rights reserved.
Keywords: Gait High heels Balance Habitual Inclination angle
1. Introduction In modern society, many women wear high-heeled shoes in both professional and social settings [1], with up to 39% of American women [2,3] and 78% of British women wearing them on a daily basis [4,5]. High-heeled shoes often result in a reduced supporting base compared with barefoot, increasing the difficulty of maintaining balance, and the risk of falling [6,7]. Compared to barefoot gait, experienced wearers of high-heeled shoes adopted a conservative strategy for controlling the motion of the body’s center of mass (COM) in relation to the center of pressure (COP) during high-heeled gait [8]. Whether long-term wearing of highheeled shoes would help improve the balance control during highheeled gait remained unclear.
* Corresponding author at: Institute of Biomedical Engineering, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei 100, Taiwan, ROC. Tel.: +886 2 33653335; fax: +886 2 33653335. E-mail address: [email protected] (T.-W. Lu). 0966-6362/$ – see front matter ß 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gaitpost.2014.01.007
Habitual wearers of high-heeled shoes were reported to experience chronic adaptations in muscle-tendon architecture, including shortening of the gastrocnemius medialis fascicles [9,10] and increased Achilles tendon stiffness [9]. These adaptations could shift the stretch distribution of a muscle-tendon unit away from the tendinous tissues toward the muscle fascicles during gait, altering neural activation patterns and reducing muscle-tendon unit efficiency [11]. Reduced endurance of the gastrocnemius lateralis and peroneus longus muscles was also reported [12]. Habitual and inexperienced wearers were found to accommodate differently to walking in high-heeled shoes when compared to low-heeled shoes, the former subjects showing decreased rotations of the upper trunk and exaggerated motions of the pelvis, and the latter showing the opposite [13]. Habitual wearers also had a shorter stride length than inexperienced wearers. These kinematic changes suggest that both groups adopt a cautious gait style, particularly the inexperienced group [13]. Differences in the changes of gait kinematics and muscletendon architecture between habitual and inexperienced wearers suggest that the two groups may have different balance control
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during high-heeled gait. Menant et al. [7] studied the effects of wide base, elevated shoe heels on gait stability using the minimum COM–BOS margin during SLS, but the effects of long term use were not considered. Since the dynamic stability of gait depends on both the position and the velocity of the COM with respect to the BOS [14], the minimum COM–BOS margin alone may not be sufficient to describe the body’s stability. The continuously varying BOS during double-limb support (DLS) presents another difficulty in the definition of the COM–BOS margin. Chien et al. [8] used COM– COP inclination angles (IA) to describe the body’s dynamic control in experienced wearers. The experienced wearers were found to adopt a conservative balance control strategy when compared with barefoot, with reduced normalized walking speed, reduced frontal IA throughout the high-heeled gait cycle, and also a reduced frontal and sagittal rate of change of IA (RCIA) during DLS. During high-heeled gait the BOS is reduced both in the anterior–posterior and in the medial–lateral directions compared with barefoot. During single-limb support (SLS), the BOS is reduced mainly as a result of the reduced area of the heel. During DLS, the reduced BOS is a result not only of the reduced area of the heel, but also of the reduction in the step width and stride length [8]. The reduced BOS was found to be a major factor affecting the observed conservative control strategy in habitual wearers compared to the barefoot condition [8]. However, whether this strategy was adopted immediately or whether it was a result of long-term adaptation to high-heeled shoes has not been explored. The purposes of this study were to investigate the long-term effects of wearing high-heeled shoes on the body’s COM motion in terms of IA and RCIA during high-heeled gait. It was hypothesized that during high-heeled walking, experienced wearers would decrease the frontal IA throughout the gait cycle, and the frontal and sagittal RCIA during DLS when compared with the inexperienced controls. 2. Materials and methods 2.1. Subjects Fifteen female habitual wearers of high-heeled shoes (experienced group; age: 24.4 3.4 years; height: 158.9 5.7 cm; mass: 49.2 5.1 kg) and 15 matched controls (inexperienced group; age: 24.9 4.1 years; height: 161.0 4.2 cm; mass: 50.3 3.7 kg) participated in the current study with informed written consent, as approved by the Institutional Research Board. None of the subjects suffered from any neuromusculoskeletal pathology that might have affected their normal gait. Experienced wearers had worn shoes with narrow heels of more than 3 cm height a minimum of three times per week, six hours per day for at least two years. The inexperienced wearers wore high-heeled shoes less than twice per month. 2.2. Data collection Each subject walked in high-heeled shoes (height: 7.3 cm) at a self-selected pace on an 8-m walkway. The shoes were narrowheeled (heel base: 2.0 cm 1.6 cm; mass: 0.2 kg) and were commercially available [8]. Subjects were fitted with the most suitable test shoes from several different sizes, and were allowed to familiarize themselves with the walkway before data collection. Each subject wore 39 retroreflective markers for tracking motions of the body segments [15]. Markers for the heels, big toes and fifth metatarsal bases were attached to the corresponding positions on the shoes. Markers on the navicular tuberosity and malleoli were not affected by the shoes. Three-dimensional trajectories of the markers were measured using a motion capture system (Vicon 512, OMG, UK) at a sampling rate of 120 Hz, and were low-pass filtered using a fourth-order Butterworth filter with
a cut-off frequency of 5 Hz [16]. The ground reaction forces (GRF) were collected from two forceplates (AMTI, USA) at a frequency of 1080 Hz [15]. Six successful trials, three for each limb, were obtained. 2.3. Data analysis The body was modeled as a system of 13 rigid segments, namely the head and neck, trunk, pelvis, arms, forearms, thighs, shanks and feet [15,17]. Coordinates of the markers gathered during a static calibration trial were used to define the anatomical coordinate system of each of the body and foot/shoe segments, with the positive x-axis directed anteriorly, the positive y-axis superiorly and the positive z-axis to the right. A Cardanic rotation sequence (z–x–y) was used to describe the rotational movements of each joint [15]. In order to minimize the errors owing to skin movement artifacts, a global optimization method was used [18]. With the measured GRF and kinematic data, inverse dynamics were used to calculate the inter-segmental forces and moments at the lower limb joints. Inertial properties for each body segment were obtained using an optimization method [19], using Dempster’s coefficients as the initial guess [17]. In the shod condition, the mass of the foot/shoe unit was determined as the sum of the masses of the foot and the shoe, with the center of mass taken as that of the foot as an approximation. All the calculated joint moments were normalized to body weight (BW) and leg length (LL) that was defined as the sum of the shoe height and the distance between the anterior superior iliac spine and the medial malleolus [20]. The body’s COM position was calculated as the weighted sum of the positions of all 13 model body segments. The COP position was calculated using forces and moments measured by the forceplates [21]. The medial/lateral positions of the COM and COP were described relative to the line of progression that bisected the medial/lateral range of motion of the COM during a gait cycle, a positive value being to the side of the contralateral limb [22]. The anterior/posterior positions of the COM and COP were described parallel to the direction of progression, a zero value being the position of heel-strike and a positive value being anterior to that position. The IA in the sagittal plane (a) and frontal plane (b) were then calculated as follows [16] (Fig. 1). * *! * P COM COP Z t¼ (1) * jP COM COP j
a ¼ sin1 ðt x Þ
(2)
b ¼ sin1 ðty Þ
(3)
*
where P COM COP was the vector pointing from the COP to the COM, * and Z was the unit vector of the global vertical axis. With the current forceplate setup, a and b were calculated from the beginning of SLS to the subsequent heel-strike. The RCIA for a and b were also calculated by smoothing and differentiating their trajectories using the GCVSPL method [23]. During the gait cycle, the transitions between SLS and DLS, i.e., heel-strike of the contralateral leg and toe-off of the ipsilateral leg, are critical instances at which maintaining body stability is expected to be more difficult [16]. Therefore, the values of the IA, RCIA and the joint moments at these instances were obtained. The values of IA, RCIA and the joint moments were averaged over the DLS and SLS, respectively. The ranges of motion (ROM) of IA during DLS and SLS, as well as the peak RCIA during DLS, were obtained. Temporaldistance parameters (gait speed, stride length, step width, stride time, cadence, stance time, DLS time and SLS time) for all conditions were also calculated. For between-group comparisons, gait speed,
[(Fig._1)TD$IG]
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1047
Fig. 1. Ensemble-averaged COM–COP inclination angle (IA) and rate of changes of IA (RCIA) in the (a) frontal and (b) sagittal planes in experienced wearers of high-heeled shoes (solid) and inexperienced controls (dashed) during high-heeled gait. (HS, heel-strike; CTO, toe-off of the contralateral leg; CHS, heel-strike of the contralateral leg; TO, toe-off; SLS, single-limb support; DLS, double-limb support; CSLS, single-limb support of contralateral limb.) *p < 0.05.
stride length, step width, stride time, cadence, and COP and COM positions were normalized following Hof [24]. The values of the variables from both limbs were averaged for each subject for subsequent statistical analysis. Comparisons of all the calculated variables between groups were performed using independent ttests. All statistical analyses were performed using SPSS (version 17.0, SPSS Inc., USA) with a significance level of 0.05. 3. Results No significant between-group differences in any temporal-distance parameters were found, except that the experienced group showed increased SLS time
but reduced stance time, DLS time, step width and normalized step width (Table 1). In the frontal plane, compared with the inexperienced group, all variables of the IA in the experienced group were significantly reduced except the averaged values over the SLS and their ROM during DLS (Fig. 1 and Table 2). The experienced group also showed significantly increased lateral RCIA at toe-off (p < 0.0001) and contralateral heel-strike (p = 0.0002) (Fig. 1 and Table 2). The experienced group showed increased mean ankle pronator moments over SLS (p = 0.040) and at contralateral heel-strike (p = 0.009) (Fig. 2 and Table 3). In the sagittal plane, no significant between-group differences were found in any variables of the IA, except that the experienced group showed increased ROM during SLS (p = 0.027) (Fig. 1 and Table 2). The experienced group also showed increased posterior RCIA at toe-off (p < 0.0001) and contralateral heel-strike (p < 0.0001), and increased mean values of the posterior RCIA over DLS (p = 0.001)
H.-L. Chien et al. / Gait & Posture 39 (2014) 1045–1050
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Table 1 Means (standard deviations) of temporal-distance parameters during high-heeled gait for experienced wearers of high-heeled shoes and inexperienced controls. Parameters
Inexperienced
Gait speed m/s 1.08 (0.10) Dimensionless 0.37 (0.03) Stride length m 1.16 (0.06) %LL 130.0 (8.2) Step width cm 8.09 (2.93) %LL 9.1 (3.3) Stride time second 1.08 (0.08) Dimensionless 3.57 (0.30) Cadence steps/min 112.32 (9.44) Dimensionless 0.57 (0.06) Stance time % 66.6 (0.9) Double-limb suport time % 15.6 (1.0) Single-limb support time % 34.9 (1.4) *
Experienced
p
1.07 (0.09) 0.37 (0.03)
0.774 0.980
1.16 (0.05) 132.0 (6.5)
0.803 0.488
5.85 (2.10) 6.6 (2.3)
0.023* 0.028*
1.08 (0.08) 3.62 (0.27)
0.888 0.660
111.40 (7.81) 0.56 (0.04)
0.772 0.555
64.2 (1.4)
<0.0001*
13.3 (1.4)
<0.0001*
36.6 (1.6)
0.003*
p < 0.05.
(Fig. 1 and Table 2). No significant between-group differences were found in the two peaks of the sagittal RCIA. The experienced group showed increased hip flexor moments and knee extensor moments at toe-off (hip, p = 0.012; knee, p < 0.001) (Fig. 2 and Table 3).
4. Discussion The current study aimed to investigate the effects of habitual wearing of high-heeled shoes on the body’s COM motion in terms of IA and RCIA during walking. The results supported the hypothesis, except for the frontal and sagittal RCIA during DLS. The current results provide a basis for future design of strategies to minimize the risk of falling during high-heeled gait. Compared with inexperienced wearers, experienced wearers showed more stable body control during SLS with reduced IA in the frontal plane, i.e., reduced COM–COP separation, which was achieved mainly through increased pronator moments at the
ankle (Fig. 2 and Table 3). They also showed reduced ROM of IA in the frontal plane during DLS owing to the reduced BOS in the medial–lateral direction as a result of the reduced step width (Tables 1 and 2). Control of the body’s medio-lateral motion is important for gait stability [25]. Impaired medio-lateral motion control can cause a sideway fall in the elderly, a major risk factor for hip fractures [25]. Increased medio-lateral COM–COP separation, as indicated by the increased frontal IA, was found in elderly fallers, leading to loss of balance, especially under unexpected postural disturbances such as tripping or slipping [26]. Compared to barefoot gait, reduced frontal IA in experienced wearers of shoes with narrow high heels is helpful for the body’s stability [8]. The current results showed that inexperienced wearers were yet to develop the same strategy as the experienced wearers, suggesting that they were subject to a higher fall risk during high-heeled gait. Increased pronator moments appeared to be used by the experienced wearers to improve the overall dynamic balance control during high-heeled gait. On the one hand, increased activity of the ankle evertors helps to move the COP medially and the COM laterally during SLS of barefoot gait [12,27], contributing to the reduction of the COM and COP separation, and thus maintaining the body’s balance. On the other hand, increased pronator activity helps to provide the necessary torque at the ankle to reduce its medio-lateral instability [28] that may be induced by shoes with narrow high heels. Such activity also helps to stabilize the ankle from foot flat to push-off during barefoot gait [29,30]. However, increased muscle activity may increase the metabolic cost of gait and result in accelerated muscle fatigue and discomfort [10]. The peroneus longus was found to be more vulnerable to fatigue among habitual wearers of high-heeled shoes, which could in turn alter the stability of the feet during prolonged walking [12]. Since increased pronator activity is important in the strategy used by experienced wearers, weakness of the pronators, resulting from aging, for example, or from early fatigue owing to muscular architectural changes, could lead to an increased risk of falling similar to inexperienced wearers. While the experienced wearers adopted a conservative body control in the frontal plane with reduced IA and unaltered mean RCIA during the gait cycle, they showed a faster weight transfer between SLS and DLS, with increased magnitudes of the RCIA at toe-off and contralateral heel-strike, which were different from the hypothesis. The increased pronator activity in SLS continued
Table 2 Mean (standard deviations) of the frontal and sagittal COM–COP inclination angle (IA) and their rates of change (RCIA) at heel-strike of contralateral leg (CHS), toe-off (TO), and their mean values during single-limb support (Mean/SLS) and double-limb support (Mean/DLS), as well as the range of motion (ROM) of IA and the two RCIA peaks during high-heeled gait for experienced wearers of high-heeled shoes and inexperienced controls. COM–COP inclination angle (8) Inexperienced Frontal CHS TO Mean/DLS Mean/SLS ROM/DLS ROM/SLS Peak 1 Peak 2
2.2 2.6 0.2 2.3 4.8 1.0 – –
(0.8) (0.8) (0.3) (0.6) (1.4) (0.2)
Sagittal CHS TO Mean/DLS Mean/SLS ROM/DLS ROM/SLS Peak 1 Peak 2
8.0 10.7 1.5 0.7 19.5 19.2 – –
(0.7) (1.1) (0.9) (0.8) (1.0) (1.0)
*
p < 0.05.
Rate of change of COM–COP inclination angle (8/s)
Experienced 1.6 2.0 0.1 1.7 3.6 0.9 – –
(0.5) (0.4) (0.3) (0.3) (0.7) (0.1)
8.5 11.0 1.2 0.5 19.7 20.3 – –
(1.2) (1.2) (0.7) (0.4) (1.8) (1.6)
p
Inexperienced
0.017* 0.018* 0.990 0.004* 0.009* 0.802 – –
1.8 1.1 26.6 0.5 – – 50.1 96.6
0.202 0.472 0.494 0.594 0.670 0.027* – –
46.7 50.7 104.5 51.8 – – 205.8 500.9
(6.6) (6.0) (8.7) (0.7)
(25.2) (30.3)
(17.4) (23.0) (9.9) (4.9)
(91.1) (82.9)
Experienced 10.5 12.5 24.9 0.5 – – 50.9 76.1
48.1 10.6 135.5 50.4 – – 271.9 465.0
(9.2) (3.8) (6.1) (0.3)
(16.9) (25.8)
(64.5) (21.9) (28.8) (5.1)
(88.4) (110.3)
p 0.0002* <0.0001* 0.530 0.663 – – 0.917 0.056 <0.0001* <0.0001* 0.001* 0.469 – – 0.053 0.322
[(Fig._2)TD$IG]
H.-L. Chien et al. / Gait & Posture 39 (2014) 1045–1050
(a)
(b)
Hip Ext (+)/Flex (-)
%BW*LL
20
DLS
SLS
DLS
10
10
0
0
DLS
SLS
DLS
CSLS
-10
* Knee Ext (+)/Flex (-)
Knee Abd (+)/Add (-)
10
%BW*LL
Hip Abd (+)/Add (-)
CSLS
20
-10
1049
10
5 5
0 -5
0
-10
*
Ankle Plant (+)/Dorsi (-)
Ankle Pronator (+)/Supinator (-)
20
%BW*LL
4 10 2 0
0
-10
20
HS
40
CTO
60 CHS
80
100
-2 HS
HS
TO
20 CTO
% Gait Cycle
40
*
60
CHS
80 TO
100 HS
% Gait Cycle
Fig. 2. Ensemble-averaged joint moments at the hip, knee and ankle in the sagittal (a) and (b) frontal planes in experienced (solid) and inexperienced wearers (dashed) during high-heeled gait. (Ext/Flex, extensor and flexor moments; Plant/Dorsi, plantarflexor and dorsiflexor moments; Abd/Add, abductor and adductor moments; HS, heel-strike; CTO, toe-off of the contralateral leg; CHS, heel-strike of the contralateral leg; TO, toe-off; SLS, single-limb support; DLS, double-limb support; CSLS, single-limb support of contralateral limb.) *p < 0.05.
during DLS to provide the necessary stability of the support ankle, and thus the whole body stability, when the COM was moving away from the supporting ankle, and to achieve better end-point control of the contralateral swing limb, especially at heel-strike. Long-term use of high-heeled shoes appeared to help the experienced wearers acquire a better function from the ankle pronators for a faster weight transfer from SLS to DLS. This is critical because falls or ankle sprains often happen during a rapid shifting movement at foot contact. Insufficient foot evertor strength may compromise the stability of the supporting ankle
and the end-point control of the contralateral swing limb at heelstrike, increasing the fall risk during high-heeled gait. The faster weight transfer during DLS in the experienced wearers was even more evident in the sagittal plane, as indicated by the significantly increased means of the RCIA over DLS, increased RCIA at toe-off and contralateral heel-strike, and reduced DLS time (Tables 1 and 2). At the contralateral heel-strike, the frontal stability achieved by the increased pronator moments at the ankle may also be helpful for the weight transfer in the sagittal plane. At toe-off, increased hip flexor moments and knee extensor
Table 3 Means (standard deviations) of joint moments at heel-strike of contralateral leg (CHS), toe-off (TO) and their mean values during single-limb support (Mean/SLS) and doublelimb support (Mean/DLS) in experienced wearers of high-heeled shoes and inexperienced controls. Units: %BW LL. Parameters
Hip Inexperienced
Knee Experienced
Ankle
p
Inexperienced
Experienced
p
Inexperienced
Experienced
p
13.3 0.9 6.8 4.8
(1.1) (0.6) (0.9) (1.1)
12.7 0.8 6.5 4.9
(1.5) (0.8) (1.1) (0.9)
0.229 0.018 0.313 0.944
1.2 0.0 0.7 0.7
(0.5) (0.1) (0.3) (0.3)
1.8 0.1 0.9 1.0
(0.6) (0.1) (0.3) (0.3)
0.009* 0.904 0.131 0.040*
Extensor (+)/flexor () moment CHS 6.3 (2.3) TO 2.7 (0.8) Mean/DLS 5.4 (1.3) Mean/SLS 0.5 (1.5)
6.4 3.5 5.8 1.1
(1.9) (0.8) (1.3) (1.7)
0.926 0.012* 0.375 0.291
0.2 0.4 0.9 2.2
(1.4) (0.3) (0.7) (1.4)
0.6 0.9 1.0 1.6
(1.3) (0.4) (0.8) (1.4)
0.452 <0.001* 0.900 0.237
Abductor (+)/adductor () moment CHS 9.5 (1.3) TO 0.4 (0.5) Mean/DLS 3.8 (0.7) Mean/SLS 8.3 (0.7)
10.4 0.6 4.3 8.8
(1.9) (0.4) (1.2) (1.3)
0.156 0.150 0.179 0.291
4.4 0.3 1.4 3.6
(1.3) (0.2) (0.7) (0.9)
4.7 0.4 1.5 3.8
(0.8) (0.2) (0.5) (0.8)
0.478 0.160 0.491 0.542
*
p < 0.05.
1050
H.-L. Chien et al. / Gait & Posture 39 (2014) 1045–1050
moments were needed to push the trailing limb forward so that the COM could catch up with the fast anteriorly moving COP for stable control during the subsequent SLS of the contralateral limb. Pai and Patton [14] showed that the control of the stability of the body depends not only on the position of the COM with respect to the base of support, but also on the velocity of the COM. During DLS where the BOS was greater than during SLS, increased mean RCIA in experienced wearers may be helpful for maintaining the continuing progress of the COM without compromising the stability. Shoes with narrow high heels have been shown to be related to the increased risk of falling previously noted in the elderly [6,7]. The current study identified the changes in the balance control in young females after long-term wearing of high-heeled shoes, which serve as the baseline data. Further study on the older population is needed to identify the mechanisms responsible for the increased risk of falling in the elderly who wear high-heeled shoes. 5. Conclusions Experienced wearers of high-heeled shoes appeared to adopt a specific control strategy during high-heeled gait when compared with inexperienced wearers. In the frontal plane, experienced wearers showed more conservative body control during SLS, but a faster weight transfer during DLS where the BOS was greater than SLS, both benefited by increased ankle pronator moments. In the sagittal plane where the main body motion occurred, the even faster weight transfer during DLS in experienced wearers was seen primarily by the fast increase of the COM and COP separation with increased mean RCIA. Increased hip flexor moments and knee extensor moments at toe-off were needed for the forward motion of the trailing limb. The current study identified the changes in the balance control in females after long-term use of high-heeled shoes, providing a basis for future design of strategies to minimize the risk of falling during high-heeled gait. Acknowledgement The authors gratefully acknowledge the financial support from Taiwan Adventist Hospital of Taiwan (100-E-11). Conflict of interest None declared. References [1] Hsue BJ, Su FC. Kinematics and kinetics of the lower extremities of young and elder women during stairs ascent while wearing low and high-heeled shoes. J Electromyogr Kinesiol 2009;19:1071–8. [2] American Podiatric Medical Association (APMA). High heel survey; 2003, http://www.apma.org/s_apma/doc.asp?CID=1233&DID=17112.2003/.
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