Running head: Total support moments in shod gait
Inter-joint sharing of total support moments in the lower extremities during gait in narrow-heeled shoes of different heights
Hui-Lien Chiena,+, Ming-Wei Liub,+, Tung-Wu Lua,c,*, Chien-Chung Kuoa,d and Pei-Chen Chunge
Hui-Lien Chien
aInstitute 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:
[email protected] Ming-Wei Liu
bDepartment of Surgery, Taiwan Adventist Hospital (TAH), No. 424, Sec. 2, Ba-De Road, Songshan District, Taipei 105, Taiwan, ROC., Tel: +886- 2-27816323, Fax: +886-2- 27816319, E-mail: [email protected]
Tung-Wu Lu
aInstitute of Biomedical Engineering, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei 100, Taiwan, R.O.C.
cDepartment of Orthopaedic Surgery, School of Medicine, National Taiwan University, No.1, Changde St., Zhongzheng Dist., Taipei 100, Taiwan, ROC.,
Tel: +886-2-33653335, Fax: +886-2-33653335, E-mail: [email protected] Chien-Chung Kuo
aInstitute of Biomedical Engineering, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei 100, Taiwan, R.O.C.
dDepartment of Orthopedics, China Medical University Hospital, 2 Yude Road, Taichung, 40447, Taiwan, R.O.C.
Tel: +886-4-22052121-5052, Fax: +886-4-22338592, E-mail: [email protected] Pei-Chen Chung
eDepartment of Rehabilitation Medicine, Taiwan Adventist Hospital (TAH), No. 424, Sec. 2, Ba-De Road, Songshan District, Taipei 105, Taiwan, ROC., Tel: +886- 2- 27718151 ext.2688, Fax: +886-2- 27118492, E-mail: [email protected]
Word Count: 4441
Second Revision Submitted to Ergonomics
___________________________________________________________________ +These authors contributed equally to the work
* Corresponding author: Professor Tung-Wu Lu, D.Phil., Institute of Biomedical Engineering, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei 100, Taiwan, ROC.
Abstract
The study aimed to investigate the influence of the base and height of shoe heels on the total support moment and individual joint contributions during gait. Fifteen healthy females walked barefoot and with narrow-heeled shoes (heel heights: 3.9, 6.3 and 7.3cm) while kinematic and kinetic data were measured. Compared to the barefoot condition, the subjects maintained unaltered total support moments in the sagittal plane in shod conditions. This was achieved by increasing the knee extensor moment to compensate for the diminished ankle plantarflexor moments in medium and high heel conditions. In the frontal plane, subjects in shod coditions had to sustain an increased total support moment for balance control during late single-leg stance with increased knee abductor and ankle pronator moments as a result of the reduced base of the heels. The results will be helpful for future shoe designs to reduce fall risks and prevent relevant musculoskeletal problems.
Keywords: gait; high heels; biomechanics; total support moment
Practitioner summary: Knowledge of the influence of narrow-heeled shoes on lower limb support moments helps in shoe design to address fall risks. Gait analysis showed that females in narrow-heeled shoes maintained unaltered sagittal total support moments but sustained an increased demand in the frontal plane during late single-leg stance.
Introduction
Shoe design and its effects on fall-related injuries and musculoskeletal problems have been a subject of extensive research . Among various types of shoes, health hazards for high-heeled shoe wearers have received much attention for more than 250 years . In modern society, many women wear high-heeled shoes in both professional and social settings . Surveys have shown that up to 39% of American women and 78% of British women wear high heels on a daily basis . High heels disrupt the synchronic interplay between the joints of the pelvis-leg apparatus during walking, affecting the temporal-spatial parameters , joint kinematics , muscle activity , energy consumption , and plantar foot pressures . The possible role of high-heeled shoes in falls in the elderly and the associated injuries such as fracture have also been noted. Knowledge of how individual joints work together while carrying different loads in order to maintain body balance during high-heeled gait may offer better insights into the ergonomic design or choice of high-heeled shoes to prevent relevant musculoskeletal problems.
Much research has been devoted to the study of the effects of heel height on the mechanics of the lower extremities during gait . The increased plantar flexion of the ankle during stance, associated with high-heeled shoes, causes changes in supination of normal barefoot walking . Compensations at other joints may also appear but are still controversial in the literature. Some authors suggested that knee flexion at heel strike and during stance
would be increased ; the range of motion of hip abduction and adduction would be decreased; and significant changes in the internal and external rotations at the hip and knee would also be present . However, others reported an unchanged range of flexion-extension, internal-external and valgus-varus motion at the knee joint and unaltered thigh motion during stance phase .
Controversies also exist regarding the effects of high-heeled shoes on joint kinetics during gait. During stance phase of gait, wearing high-heeled shoes was found to reduce the ankle plantar flexor moments significantly in previous studies . However, the effects of high heels on the loads in the other joints varied between studies. For example, Esenyel et al. found that high-heeled shoes did not alter the magnitudes of the hip extensor and knee abductor moments significantly, while greater hip extensor moments and knee abductors moments were reported by Kerrigan et al. . Most of these kinetic studies focused on the effects of heel-height on joint loadings, so even though limited simultaneous measurements of kinematic and kinetic data were available, no attempt was made to clarify the existing controversies in both the reported kinetic and kinematic changes with increased heel height. On the other hand, previous studies assessed high-heeled gait patterns mainly through data at individual joints. Note that individual joint moments represent the net effect of all agonist and antagonist muscle activity at the individual joint, indicating an integration of all the neural control acting at the joint . Analysis of only a single joint can lead to an erroneous diagnosis . Therefore, it appears that simultaneous consideration of kinematic and kinetic
coordination between multiple joints of the lower extremities is essential for a better understanding of the effects of heel height during high-heeled gait. This is associated with the multiple combinations of moments at the hip, knee, and ankle which could be used to produce the final kinematic gait pattern.
For a given kinematic configuration of the multi-link system of the lower limbs, proper combinations of joint moments are necessary to support the body weight (BW) and to prevent collapse of the lower limbs, which is an important subtask of gait . The total support moment (Ms), defined as the numerical sum of the extensor moments at the hip and knee, and the plantarflexor moment at the ankle, has been shown to be a useful measure for explaining how the lower extremity supports the upper body . It is also a less variable (i.e., a more reliable) measure of the kinetic chain synergy of the lower extremities when compared to the analysis of individual joint moments . A wide range of combinations of hip extensors and knee extensors could be used by individuals to achieve similar kinematic patterns . Comparisons of the individual joint moments as a percentage of the total support moment could be useful for quantifying the possible compensatory strategies in response to injury or intervention. For example, the total support moment and the contribution of individual joint moments to the total support moment (CMs) have been used to assess the weight-bearing strategy in healthy subjects , and patients with stroke , patellofemoral pain syndrome , and total knee replacement . No study has applied Ms and individual joint contributions to characterize quantitatively the
supportive synergies of the lower limb joints in response to high-heeled shoes.
While the total support moment and the contributions of the individual joint moments were calculated primarily in the sagittal plane, data for the frontal plane are also necessary for studying the control of high-heeled gait. This is because frontal balance control is especially critical considering the narrow width of the base of support (BOS) that makes it more difficult to maintain the body’s center of mass (COM) within the BOS . Maintaining frontal balance during weight-bearing can be accomplished by a collaboration of abductor muscles and non-contractile tissue at the joints of the lower limb. Since the ranges of motion of these joints are limited in the frontal plane, the distribution between the individual joint moments as a result of kinematic pattern changes, and thus the total support moment, may not be the same as that in the sagittal plane. The controversies on the effects of high heels on joint loads may be resolved by further quantifying the changes in the total support moment and the coordination between joints in the frontal plane, which to date remain unavailable.
The purposes of this study were to investigate the influence of the base and height of the shoe heels on the angles and moments of individual joints, as well as on the total support moment and the contributions of individual joints, both in the sagittal and frontal planes during gait. It was hypothesized that compared to barefoot, narrow-heeled shoes would increase the knee joint moment to compensate for the diminished ankle plantarflexor moments in order to maintain an unaltered total support moment in the sagittal plane; that in
the frontal plane, narrow-heeled shoes would increase the ankle abductor moment with increased knee abductor moment, and would thus increase the total support moment with altered individual joint contributions; and that these phenomena would not be affected by heel height.
Material and methods Subjects and shoes
Fifteen female adults (age: 24.4±3.4 years; height: 158.9±5.7 cm; mass: 49.2±5.1 kg) participated in the current study with informed written consent. They were free from any neuromusculoskeletal pathology that might have affected their normal gait. They had worn shoes with narrow heels of more than 3 cm height at least three times per week, six hours per day for at least two years. Permission to conduct this study was provided by the Institutional Research Board.
In a gait laboratory, each subject walked at a self-selected pace on an 8-m walkway barefoot, or with low-heeled shoes (3.9 cm), medium-heeled shoes (6.3 cm), or high-heeled shoes (7.3 cm). All the shoes were narrow-heeled (2.0 cm x 1.6 cm) and commercially available, and were selected to have similar construction, including foot contact points, vamp and shape of the toe box. Subjects were fitted with the most suitable test shoes from several different sizes, and were allowed to walk around in the lab for at least 20 minutes with each pair of test shoes to familiarize themselves with the walkway and to become accustomed to
the shoes.
Instrumentation and data analysis
Each of the subjects wore 39 infra-red retroreflective markers to track the motions of the body segments . Foot markers, namely big toe, fifth metatarsal base and heel, were placed on the corresponding positions on the shoes in shod conditions. Markers were placed directly on the navicular tuberosity and malleoli since they were not covered by the shoes. Three-dimensional trajectories of the markers were measured using a 7-camera motion capture system (Vicon 512, Oxford Metrics, UK) at a sampling rate of 120 Hz, and the ground reaction forces (GRF) and the center of pressure (COP) were gathered from two forceplates (OR6-7-100, AMTI, USA) placed next to each other along the direction of progression in the center of the walkway at a frequency of 1080 Hz . Six successful trials, three for each limb, for each of the four shoe conditions, were obtained. The order of the test conditions was randomized.
The pelvis-leg apparatus was modeled as a 7-link system . Coordinates of the markers gathered during a static calibration trial were used to define the anatomical coordinate system of each of the links (body segments and feet/shoes unit), 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 . In order to minimize the errors owing to skin movement artifacts, a global optimization method
was used . With the measured GRF and kinematic data, inverse dynamics were used to calculate the intersegmental forces and moments at the lower limb joints. Inertial properties for each body segment were obtained using Dempster’s coefficients . The mass of the foot/shoe unit was determined as the sum of the masses of the foot and the shoe (0.2 kg), with the center of mass taken as that of the foot as an approximation. Since the foot was in contact with the floor at low speed during stance, the effect of the inertia of the shoe on the joint moments was expected to be small and was thus ignored.
All the calculated joint moments were normalized to body weight (BW) and leg length (LL), defined as the distance between the ipsilateral ASIS and medial malleolus for barefoot gait , and this distance was added to the shoe height to get LL for shod gait. The total support moment during the stance phase was calculated as the sum of the extensor moments at the hip and knee, and the plantarflexor moment at the ankle in the sagittal plane (sagittal Ms); and the sum of the abductor moments at the hip, knee and ankle in the frontal plane (frontal Ms). The percent contribution to Ms for the hip, knee, and ankle joint moments was calculated by dividing the joint moment by the Ms and was expressed as a percentage of the Ms . The joint angles, moments, Ms and individual joint moment contributions were expressed against the percentage of the stance phase. The range of motion of joint angles during stance phase was obtained. The peak values of Ms (Ms1, Ms2) and their occurrence (P1, P2), as well as the peak values for all the calculated variables at P1 and P2, were extracted for subsequent
statistical analysis . The Ms, joint moments and their contributions to the Ms averaged over the single-leg stance (SLS) were also obtained. Gait speeds for all conditions were also calculated and normalized following Hof .
Statistical analysis
Since several of the calculated variables were correlated to the normalized gait speed, the normalized gait speed was taken as a covariate in the one-way repeated measures ANCOVA for all calculated variables (α=0.05). If a significant main effect was found, pair-wise comparisons between test conditions using an independent t-test with Bonferroni correction (α=0.05/6=0.0082) were performed. All statistical analysis was performed using SPSS (version 11.0, SPSS Inc., USA).
Results
Joint moments, Ms and CMs in the sagittal plane
In the sagittal plane, no significant differences in Ms were found between any test conditions, neither at P1 or P2, nor for the mean values during SLS (Figure 1 and Table 1). However, compared with barefoot, significantly reduced ankle plantarflexor moments were found for medium-heeled and high-heeled shoes at P1 (p=0.008) and P2 (p<0.0001). Significantly reduced mean ankle plantarflexor moments during SLS were also found for all shoe conditions, values for the medium-heeled and high-heeled shoes being smaller than for the
low-heeled shoes (p<0.0001). Medium-heeled and high-heeled shoes also had smaller ankle plantarflexor moments than low-heeled shoes at P2. Compared with barefoot, no significant differences were found in the hip and knee joint moments at P1 and P2 for all shoe conditions, but the mean values during SLS were significantly increased at the knee joint for medium-heeled and high-medium-heeled shoes (p=0.0006) (Table 1). The hip contributed the greatest component to the sagittal Ms at P1 for all conditions except for the high-heeled condition in which the knee contributed the greatest (Figure 2). At P2, the ankle plantarflexors had to work against the hip and knee (negative contributions) in order to provide the necessary sagittal Ms in all conditions (Figure 2). Given the changes of the moments of the individual joints, no significant differences in the joint contributions to the sagittal Ms were found between any conditions, neither at P1or P2, nor during SLS (Table 1).
Joint moments, Ms and CMs in the frontal plane
In the frontal plane, compared with barefoot, narrow-heeled shoes had greater Ms (p=0.002), knee abductor moments (p=0.0001) and ankle pronator moments (p<0.0001) at P2, and mean ankle pronator moments during SLS (p<0.0001) (Figure 1 and Table 1). Greater ankle pronator moments for narrow-heeled shoes were also found at P1, those for the medium-heeled and high-medium-heeled shoes being greater than for the low-medium-heeled shoes (p<0.0001). The contribution of the ankle joint to frontal Ms was significantly increased at P1 (p<0.0001), P2
(p<0.0001) and during SLS (p<0.0001) (Figure 2), the contributions in the medium-heeled and high-heeled conditions being greater than that in the low-heeled condition at P1. Greater knee abductor moments in all shoe conditions were also found at P2 but the contribution of the knee to frontal Ms was not altered. In contrast to the ankle and knee joints, the hip moments were not changed significantly but their contribution to frontal Ms was decreased at P1, P2 and during SLS when compared with the barefoot condition. Nonetheless, for all conditions the contribution of the hip at P1 and P2 was still the greatest, followed by the knee and the ankle (Figure 2).
Joint angles in the sagittal and frontal planes
No significant differences in the joint angles were found at the hip and knee for neither the sagittal, nor the frontal plane (Figure 3 and Table 2). The ankle was slightly dorsiflexed with barefoot and low-heeled shoes but significantly increased the plantarflexion with medium and high heels both at P1 and P2 (p<0.0001) (Table 2). Low-heeled shoes also had greater ankle plantarflexion than barefoot at P1 (Table 2). Medium-heeled and high-heeled shoes had significantly greater ankle supination angles than barefoot and low-heeled shoes at P1 (p<0.0001) and greater than barefoot at P2 (p=0.0001). High-heeled shoes also had greater supination angles than medium-heeled shoes at P1 (p<0.0001) and low-heeled shoes at P2 (p=0.0001). Narrow-heeled shoes had significantly smaller range of motion at the ankle joint
in the frontal plane during the stance phase.
Discussion
The current study aimed to investigate the influence of the base and height of shoe heels on the angles and moments of individual joints in two dimensions, as well as the total support moment and the contributions of individual joints, both in the sagittal and frontal planes during gait. The results support the hypotheses that compared to barefoot, narrow-heeled shoes would increase the knee joint moment to compensate for the diminished ankle plantarflexor moments in order to maintain an unaltered sagittal Ms; that in the frontal plane, narrow-heeled shoes would increase the ankle pronator moment with an increased knee abductor moment at P2, and would thus increase the frontal Ms with altered individual joint contributions; and that these phenomena would not be affected by heel-height. Women with narrow, high-heeled shoes appeared to adopt a control strategy to maintain an unaltered total sagittal Ms, but had to sustain an increased demand for balance control in the frontal plane as a result of the reduced base of the shoe heels, especially during late SLS.
Kinematic changes at the ankle in response to narrow-heeled shoes contributed to the observed decrease of the ankle plantarflexor moments and increase of the knee extensor moments during the first half of the SLS when compared with the barefoot condition. These individual joint moment changes were also found by Esenyel et al. . The more plantarflexed posture of the ankle while wearing high heels effectively shortened the leverarm available to
the ground reaction force about the ankle joint, thus reducing the counter-balancing plantarflexor moment. The increased plantarflexion moved the knee joint center relatively more anteriorly. To maintain balance, one would have to bring the COM backward, leading to a more posteriorly directed GRF and thus increased knee extensor moments. Increased knee flexion may accompany this strategy but the current subjects did not appear to do this. They managed to move the body’s COM posteriorly, most likely through a more posterior position of the trunk . The increased extensor moment helped resist the tendency of flexing the knee. This also appeared to be helpful for assisting the ankle plantarflexors in forward progression . However, as suggested by Kerrigan et al. , increased knee extensor moments during narrow-heeled shoes would require increased quadriceps forces, leading to increased strain of the patella tendon, and increased pressure across the patellofemoral joint. For frequent and prolonged walking with high-heels, these changes may lead to overuse syndromes or exacerbation of existing knee weakness or pain.
While narrow-heeled shoes altered individual joint moments and their contributions to sagittal Ms at the knee and ankle, the sagittal Ms remained largely unaltered among all test conditions during SLS. Unaltered sagittal Ms indicated that the base and height of the shoe heels did not affect the mechanical demand significantly in the standing limb in supporting the whole body. However, there was a trend of increased knee moment contribution and reduced ankle moment contribution to the unaltered sagittal Ms during the first half of SLS.
This trend of increased knee moment contribution appeared to be helpful for preventing the collapse of the lower extremities in compensation for the reduced plantarflexor moment contribution as a result of wearing high-heeled shoes. For a disrupted joint contribution to sagittal Ms, either due to injury or disease at the joint, or because of the footware, redistribution of the joint moment contributions is necessary in order to prevent the collapse of the limb . From the current results, since the line of action of the GRF tended to pass close to the COM which was close to the hip joint, it appeared more efficient to increase the knee extensor moment to compensate for the reduction of the ankle plantarflexion moment.
During the second half of SLS, the sagittal Ms remained statistically the same as that during the first half but the moment distributions among the joints were altered. Instead of extensor moments, the hip and knee showed negative contributions to the sagittal Ms. The main anti-collapse moment came from the ankle joint, which reduced with increased heel height. In response, the knee flexor moment also reduced with increased heel height. The ankle plantarflexors acted to provide the necessary sagittal Ms for propulsion while working against the hip and knee in all conditions. This contribution of the ankle moment to sagittal Ms remained unchanged with increased heel height, indicating a critical role of the ankle in the support of the body during this phase.
In the frontal plane, greater ankle pronator moments were needed to maintain the stability at the ankle when wearing narrow-heeled shoes of various heights. During the first
half of SLS, pronator moments for the narrow high heels were greater than those for barefoot. This was related to the distally displaced COP in narrow high heels compared to barefoot. Given the same GRF, a distally displaced COP would in effect shift the GRF medially to the ankle joint center, leading to an increased leverarm length availabe to the GRF about the subtalar joint axis (Figure 4). This phenomenon was further enhanced by the increased supination of the ankle with increased heel height, which was coupled with the increased ankle plantarflexion. The increased pronator moments were thus needed for the stability of the subtalar joints. Similar phenomena were found in the second half of SLS. The significantly increased ankle pronator moments indicated the increased demand for stability control of the ankle joint while wearing narrow-heeled shoes. Failure to provide sufficient pronator moments, such as a sudden increase in supination when encountering uneven terrain, may lead to an unstable ankle joint which has been associated with lateral ankle sprains .
The heights of the shoe heels did not affect the total support of the lower extrimities in the frontal plane but the effect of the reduced base was found during the second half of SLS. While the main contribution to the frontal Ms was from the hip, the increase in the frontal Ms due to the reduced base of the shoes was accompanied with an altered load sharing between joints, with increased ankle contribution, decreased hip contribution but unchanged knee contribution. It appeared that the ankle contribution was increased to compensate for the reduced contribution of the hip. Nonetheless, the hip remained the greatest contributor to the
frontal Ms, playing a critical role in the balance control during the second half of SLS. The increased ankle contribution may be needed for better control of the subsequent transfer of the body weight to the small base of the heel of the contralateral limb during the terminal double stance. It may also be helpful for reducing the risk of falling related to unsuccessful weight transfer to the narrow heels around contralateral heel-strike.
The differences in the total support of the limbs and the contributions from the individual joints between the frontal and sagittal planes appeared to be related to the differences in the functional anatomy of the limbs in these planes. The lower limb joints have greater ranges of motion in the sagittal plane than in the frontal plane. Therefore, the positions of the joints could be altered to a greater extend, thus allowing for a redistribution of the joint moments in the sagittal plane to adapt to the kinematic changes induced by the narrow, high heels to maintain an unchanged sagittal Ms. In contrast, the lower limb joints do not have a large range of motion in the frontal plane. Therefore, the sharing of the frontal Ms among the lower limb joints appeared to be related to the change of the lines of action of the GRF in relation to the longitudinal axis of the limb, leading to changes in individual joint moments in the same direction but with different magnitudes.
Narrow-heeled shoes have been shown to be related to the increased fall risks previously noted in the elderly (Lord and Bashford, 1996; Menant et al ., 2008 ; Tencer et al ., 2004 ). The current results with young subjects showed that increased knee extensor and abductor, and
ankle pronator activity were important in the strategy used by women to provide whole body support during high-heeled gait. Therefore, inability to recruit or weakness of these muscles, such as resulting from aging, may lead to an increased risk of falling, which warrants further similar studies on the older population. On the other hand, the reduced heel base instead of the heel height was found to be the primary factor for the altered total support moments and individual joint contributions for body balance control during gait. This suggests that the dimension of the base of the heel should be a major factor in future design of footwear with special consideration of walking balance or footware for the elderly. Further study would be neeed to provide a quantitative relationship between the dimension of heel base and the total support of the body for footwear design purposes.
Conclusions
Women with narrow, high-heeled shoes appeared to adopt a specific control strategy to maintain an unaltered sagittal Ms through increasing the knee extensor moment to compensate for the diminished ankle plantarflexor moments. In the frontal plane, they had to sustain an increased demand for balance control during late SLS by increasing knee abductor and ankle pronator moments as a result of the reduced base of the shoe heels. The narrow heel base instead of heel height as the primary factor affecting the total support moments and individual joint contributions for body balance control suggests that the dimension of the heel
base should be a major factor in future design of footwear for walking balance, especially for the elderly.
Acknowledgements
The authors wish to thank Hao-Ling Chen for her help with data analysis and gratefully acknowledge the financial support from Taiwan Adventist Hospital of Taiwan [100-E-11].
REFERENCES American Podiatric Medical
Figure Captions
Figure 1. Ensemble-averaged total support moments and individual joint moments at the hip, knee and ankle in the (a) sagittal and (b) frontal planes when walking barefoot (dotted curves) and wearing narrow-heeled shoes with low heels (dashed curves), medium-height heels (dashed-dotted curves) and high heels (solid curves). Vertical lines indicate the times of the first and second peaks of the total support moment. (Ext/Flex: extensor/flexor; Abd/Add: abductor/adductor; Plant/Dorsi: plantarflexor/dorsiflexor; Pro/Sup: pronator/supinator)
Figure 2. Individual joint contributions to the first and second peaks of the total support moment (Ms), and their average values during single-leg stance at the hip, knee and ankle in the (a) sagittal and (b) frontal planes when walking barefoot and with narrow-heeled shoes with low heel height, medium heel height and high heel height. Bare: barefoot; Low: low-heeled shoe; Medium: medium-low-heeled shoe; High: high-low-heeled shoe.
Figure 3. Ensemble-averaged angles at the hip, knee and ankle in the (a) sagittal and (b) frontal planes when walking barefoot (dotted curves) and wearing narrow-heeled shoes with low heels (dashed curves), medium-height heels (dashed-dotted curves) and high heels (solid curves). Vertical lines indicate the times of the first and second peaks of the total support moment. (Flex/Ext: flexion/extension; Add/Abd: adduction/abduction; Dorsi/Plant: dorsiflexion/plantarflexion; Sup/Pro: supination/pronation)
with low-heeled and high-heeled shoes. Compared with barefoot, the narrow high heels displaced the COP distally away from the ankle joint center, which in effect shifted the GRF medially, leading to increased leverarm lengths availabe to the GRF about the subtalar joint axis and supinating moments.
