Wearing of high-heeled shoes increases load and forefoot-rearfoot load imbalance 13

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1 Original Paper Biomedical Human Kinetics, 6, 12 18, 2014 DOI: /bhk Non-habitual wearing of high-heeled shoes increases loading coefficient, stress and forefoot-rearfoot load imbalance in females as revealed by the modified velocity field diagram Sam Ibeneme 1, Ann Ekeanyanwu 2 1 Department of Medical Rehabilitation, Faculty of Health Sciences and Technology, College of Medicine, University of Nigeria, Enugu Campus, Enugu; 2 Department of Physiotherapy, Federal Medical Centre, Owerri, Imo Summary Study aim: To determine the effects of non-habitual wearing of high-heeled shoes on loading coefficient, loading stress and forefoot-rearfoot load imbalance in females Materials and methods: Fifty young adult female subjects were selected using a convenience sampling technique, and studied utilising crossover control research design. They walked barefoot and thereafter, in high-heeled shoes; for a distance of 10-metre measured out in a gait laboratory. They demonstrated their gait twice for each speed, along a 10 metres walkway, at five speeds varying from very slow to very fast. Mean values of steps and time were recorded and used to calculate the values of velocity, stride length, stride frequency, double-support, swing, single-support, and stance phases of stride. These were adopted to form a modified velocity field diagram (MVFD). The data obtained were statistically analysed using a t-test for correlated means, with alpha set at Results: The MVFDs revealed that the F/R load ratios were obtained as 0.67 and 1.5, while loading coefficient was 0.4 and 0.6, for barefoot and high-heeled walking, respectively. Loading coefficient and stress in high-heeled walking was 1.50 and 1.88 of the value in barefoot walking, respectively. Conclusions: Non-habitual wearing of high-heeled shoes increased F/R load imbalance, loading coefficient, and stress in the foot. However, there was no evidence of gait pathology in the subjects when they walked barefoot. Thus, non-habitual use of high-heeled shoes by the subjects did not translate to significant residual biomechanical derangements in the locomotor apparatus otherwise the kinematic data recorded for barefoot walking would have approximated the values obtained during high heeled walking. Keywords: Walking High-heeled shoes Forefoot/rearfoot load ratio Load imbalance Introduction Footwear is an important fashion accessory, which in addition to its aesthetic role protects the foot, especially the sole, from unexpected injury. The aesthetic value of footwear in clothing is globally acknowledged, especially high-heeled shoes, and currently generates billions of dollars in the fashion industry. In addition, shoes can be adapted to meet the specific needs of individuals in rehabilitation medicine, providing support, comfort, and enhancing postural stability during bipedal locomotion [9, 15]. Beyond its aesthetic values, the use of footwear is an apparent recognition of the need to enhance the foot s functions as a compliant deterministic machine that receives and distributes body mass, adapting to varied surface topography while serving as a rigid lever that pushes the body forward in walking [11]. Its anatomic architecture appears related to its primary function of weight bearing and shock absorption arising from ground reaction forces. Thus, the three plantar arches of the foot (medial and lateral longitudinal arches, and transverse arch) are designed to act as shock absorbers and distribute body mass on the feet [8]. However, footwear alters the alignment of the feet and eventually, either interferes with the transmission of information from the pressures on the available support areas or the movements needed while walking [16]. Thus, prolonged use of high-heeled footwear shortens the calf musculature [13], the Achilles tendon [16], and possibly creates load imbalance between the forefoot and the rearfoot as the foot is no longer freely floating. In fact, the Author s address Sam Ibeneme, Department of Medical Rehabilitation, Faculty of Health Sciences and Technology, College of Medicine, University of Nigeria, Enugu Campus, Enugu sam.ibeneme@unn.edu.ng

2 Wearing of high-heeled shoes increases load and forefoot-rearfoot load imbalance 13 elevation of the calcaneous through wearing high-heeled shoes affects functions of the foot, particularly at the ankle joint which is excessively plantar flexed [6, 1], thus adversely influencing gait kinematics (including velocity) leading to modifications in gait pattern and foot instability [14]. This could have a serious implication for individuals with foot deformities and may precipitate forefoot/rearfoot load imbalance [7]. It had also been highlighted [6] that when high-heel shoes are habitually used, one of the gastrocnemius muscles may act more intensively to produce the required propulsive forces necessary to raise the foot from midstance to push-off. The net effect is asymmetric muscle activity which could contribute to the forefoot/rearfoot load imbalance and possible foot instability. The possibility of a similar problem in non-habitual wearers requires investigation as a basis to educate women on its use. This is important as previous authors have suggested that such footwear can often have deleterious and irreversible biomechanical effects [12] which inform the assumptions that all women should avoid wearing highheeled shoes. Therefore the aim of the study was to determine the effects of non-habitual wearing of high-heeled shoes on loading coefficient, loading stress and forefootrearfoot load imbalance in females using a Modified Velocity Field Diagram Materials and methods Research design A repeated measure/cross-over control research design was used in this study. Area of study Setting: this study was carried out at the Gait Laboratory, Department of Medical Rehabilitation, Faculty of Health Sciences, University of Nigeria, Enugu Campus. Location of Study: this study was located at the University of Nigeria, Enugu Campus, Enugu. Subjects selection Fifty young adult female subjects were recruited at their halls of residence on campus. The sample was drawn using a convenience sampling technique. Selection criteria Inclusion criteria Only non-habitual high-heel shoe wearers must be recruited. Only size 38 shoe wearers must be selected. Only females of years of age must be involved Only undergraduate female students living in the halls of residence within the university campus must be selected. All subjects must abstain from alcohol at least 72 hours prior to the gait recording as alcohol use within 72 hours prior to gait recording has been found to influence gait [4, 10]. Only subjects that are not on sedative drugs, for at least 72 hours prior to the experiment must be involved as sedative drugs use within 72 hours prior to gait recording has been found to influence gait [2, 3]. All subjects must be experienced wearers of high-heeled shoes as evidenced by self-reported wearing usage of at least twice per month for not less than 5 years. Exclusion criteria All those who are blind or visually impaired, must be excluded. All those with a history of skin infections, especially those involving the feet, must be excluded. The subjects must be those that have reported not having any musculoskeletal or neuromuscular abnormalities that restrict the range of lower extremity motion, which might make the wearing of high-heeled shoes painful. Subjects with any history of pathology of neurological or orthopaedic nature, must be excluded Subjects description Barefoot Walking Condition: Initially, all the subjects were asked to walk barefoot, without shoes or stockings. High-Heeled Walking Condition: All subjects were also required to walk in the same pair of high-heeled shoes provided by the researcher. Ethical approval: ethical consideration Ethical approval from the Health Research Ethics Committee of the University of Nigeria Teaching Hospital, Ituku Ozalla, Enugu, was obtained. All participants had adequate information regarding the research, and gave their written informed consent prior to participation in the study. All subjects were also assured of confidentiality and anonymity. It was made clear to all subjects of the sample that they have the right to refuse to participate or to withdraw at any stage of the project. These rights were respected throughout the study. Quantitative gait assessment The purpose of the study was explained to the subjects prior to obtaining their informed consent to participate in the study. The subjects walked barefoot (which served as the control) and thereafter in high-heeled shoes, for a distance of 10 metres measured out on a walkway in a gait laboratory located in a remote campus building. Each subject walked the distance at five different selfselected speeds: ordinary, very slow, slow, fast, and very fast, in that order. The subjects walked twice the distance,

3 14 S. Ibeneme, A. Ekeanyanwu for each speed, during which the steps were counted and time taken to complete the distance obtained using a Stopwatch (model Hanbart, made in Germany), and the mean recorded. During high heeled walking, the subjects were required to demonstrate their gait using the same pair of high heeled shoes provided by the researcher, with a heel height of about 8.5 cm. Modified Velocity Field Diagram (VFD) The mean of the number of steps and time required to complete the distance at various speeds were used to calculate the mean values of stride length (L), stride frequency (F), and velocity (V) for each subject. Their regression lines were known as L-line, F-line, and V-line, respectively, which were then adapted to form a modified velocity field diagram (MVFD) earlier described by Ibeneme [7]. Speeds varying from very slow to very fast, were serially numbered 1 5, with units in velots, on the MVFD. The numbers were used for the X-axis, while the numerical values of velocity, stride length, and stride frequency were used on the Y-axis. These lines make up the primary features of the VFD [5]. With the regressions, it was possible to calculate the stride phase duration for each subject at each velotype. These values were plotted on the MVFD at the corresponding velotype. The phases of stride studied were, stance (ST), swing (SW), and double-support (DS).These regressions lines were projected on the MVFD as the ST-Line, SW-Line and DS-Line. The ST-Line intersected the L-line at a point known as ST L on the MVFD. The area between lines N TL- S TL to lines N 1 P 1 in the MVFD was known as the loading zone [7]. The slope of the line ST L -P 1, was also known as the loading coefficient (LC). In the normal features of the MVFD, the LC was taken to define the fraction of the body mass (load) borne on the forefoot. Conversely, when these features are reversed, the LC was taken to define the fraction of the body mass that is applied to the rearfoot [14]. A balance in load distribution between the forefoot and the rearfoot was taken to mean that the ratio of F/R load ratio is 1, and vice-versa when otherwise. The equality point of the numerical values of velocity and stride frequency (E 1 ) marked the upper limit of very slow speed and a speed transition to the path of minimal energy trajectory [5, 7]. Available data were analyzed for statistical significance using the independent t-test for paired samples at p < Results The results are presented in tables 1 3, and figs Analyses of the MVFDs (figs. 1 2) revealed changing dynamics of the loading zone (defined by line ST L -P 1 ) whose slope defined the loading coefficient (LC). The dimensions Table 1. Age, weight and height of subjects Range Mean Standard deviation Age (yrs) Weight (kg) Height (m) Table 2. Mean and standard deviation for the gait parameters for the same subjects in high heeled and barefoot walking conditions Velotypes Stride velocity Control 0.59 ± ± ± ± ± 0.29 High heel 0.65 ± 0.15* 0.83 ± ± 0.16** 1.27 ± 0.18*** 1.52 ± 0.25*** Stride frequency Control 0.66 ± ± ± ± ± 0.14 High heel 0.72 ± 0.01*** 0.81 ± 0.09*** 0.89 ± ± ± 0.15 Stride length Control 0.88 ± ± ± ± ± 0.15 High heel 0.89 ± ± ± 0.10*** 1.25 ± 0.10*** 1.33 ± 0.11*** 1 very slow walking speed, 2 slow walking speed, 3 ordinary walking speed, 4 fast walking speed, 5 very fast walking speed; significantly different from control: * p < 0.05, ** p < 0.01, *** p < 0.001,

4 Wearing of high-heeled shoes increases load and forefoot-rearfoot load imbalance 15 V-line V-line D E 2 F-line B 2 2 D 0 V, 1 and F (numerical) values 1.0 ST SW B-line P-line P 0 P 2 1 P 1 P 1 P B 1 E 1 B 0 B 2 SF D-line S D S-line 0.5 E 3 DS 0 N 1 BN DN N 2 N 3 5 Velotypes (velots) V = Velocity, L = stride Length, F = stride Frequency, ST = STance, SW = SWing, DS = Double-Support Fig. 1. Velocity field diagram for subjects while walking barefoot Table 3. Mean and Standard Deviation for the Phases of Stride for the Same Subjects in High Heeled and Barefoot Walking Conditions Velotypes Double support duration Control 0.19 ± ± ± ± ± 0.10 High heel 0.16 ± 0.06*** 0.11 ± 0.03*** 0.09 ± ± ± 0.04 Swing duration Control 0.58 ± ± ± ± ± 0.03 High heel 0.55 ± 0.05*** 0.51 ± 0.03*** 0.48 ± ± ± 0.02* Stance Duration Control 0.93 ± ± ± ± ± 0.11 High heel 0.83 ± 0.13*** 0.71 ± 0.11** 0.64 ± ± ± = very slow walking speed, 2 = slow walking speed, 3 = ordinary walking speed, 4 = fast walking speed, 5 = very fast walking speed; significantly different from control: * p < 0.05, ** p < 0.01, *** p < 0.001,

5 16 S. Ibeneme, A. Ekeanyanwu 2.0 V-line 1.5 L-line V, 1 and F (numberical) values 1.0 ST P 1 E B P P B E 2 P-line P 2 S E D 1 D 0 D-line F-line S D 0.5 SW B-line E 3 SW ST DD S-line E 1N 1 BN E 2N 2 4 DN 5 N 3 DD N 3 Figure 2. Velocity field diagram for subjects while walking in high-heeled shoes of the loading zone were obtained as 0.04, and 0.75 velots on the X-axis, for barefoot (fig. 1), and high-heeled walking (fig. 2), respectively. It suggested that the loading zone for high-heeled walking represented about 1.88 of the value obtained in barefoot (control) walking. The loading coefficient was taken as a measure of the body load on the forefoot of the subjects at E 1. This was obtained as 0.04/0.1 = 0.4; and 0.75/1.25 = 0.6, for barefoot, and highheeled walking, respectively. The loading coefficient obtained for high-heeled walking represents about 1.5 of the value obtained for barefoot walking. It further implies that with a mean body mass of about ± 6.27 kg, it is expected that about ( ± 6.27) or ± 2.51 kg; and ( ± 6.27) or ± 3.76 kg, of the body mass, of the same subjects, were borne on the forefoot during barefoot walking, and high-heeled walking, respectively. Thus, the remaining load constitutes the body mass impacted on the rear foot, and is obtained as the difference between the total body mass and the weight on the forefoot (i.e kg) or ± 3.76 kg for barefoot walking, and ( kg) or ± 2.51 kg, for high-heel walking, respectively. Consequently, the forefoot/rearfoot load ratio is obtained as 21.77/32.65 = 0.67, and 32.65/21.77 = 1.5. These ratios approximate to 1, and 2, respectively. It was further observed that the point of speed transition from slow to normal walking speeds, represented as equality point E 1 on the MVFDs, are variously obtained as 1.7, and 2.0 velots, for barefoot walking, and high-heeled walking, respectively. Discussions From the results, a F/R load ratio of 2 suggests load imbalance during high heeled walking such that twice the body mass was borne on the forefoot than the rearfoot. However, in the same subjects, a F/R load ratio of 1 was obtained and suggests a homogeneous load distribution between the forefoot and rearfoot during barefoot walking unlike high heeled walking. Therefore, in non habitual wearers, high heeled walking may predispose to forefootrearfoot load imbalance. It was also revealed (figs.1 2), that during high-heeled walking, in the same subjects, the loading zone (defined by the distance between points ST L and P 1 on the MVFDs figs. 1 2, which is an indicator of loading stress [7], and which corresponds to the distance between N TL and N 1 on the x-axis), increased reasonably, compared to barefoot walking (control). The value recorded for high-heeled walking was shown to represent about 1.88 of the value

6 Wearing of high-heeled shoes increases load and forefoot-rearfoot load imbalance 17 obtained in barefoot walking. When the dimension of the loading zone is compared between the barefoot and high heeled walking, it gives a ratio of about 1:3. This indicates that in the same subjects, the loading stress for the limbs was about 3 times higher in high-heeled walking than barefoot walking. Explanations for this observation were sought from the literature, which revealed that [6] when no heel lift is present (i.e. barefoot walking), gastrocnemius lateralis and gastrocnemius medialis are positioned at their resting lengths. However, when heel-lifts are used (i.e. highheeled walking), the fibre lengths shorten in such a manner that an active tension generated on the contraction of the muscles is not consistent with their anticipated lengthtension relations. The implication is that the deviation of the resultant force due to these two muscles, in highheeled walking, is transferred to the calcaneum through the Achilles tendon, probably resulting in an inverting moment that acts to incline the foot s skeletal structures laterally and thus enhance stability. The inverting moment is expected to place tremendous stress around the forefoot and lateral margins of the foot. This expectation was met in this study where the MVFD revealed that the loading stress was 3 times higher in high-heeled walking than in barefoot gait. Similarly, loading stress might have further increased during high heeled walking, as the heeled shoe steals [16] much of the propulsive power from the tendon and leg muscles thereby placing more stress on them to achieve the needed propulsion. It was further observed that with an increase in loading stress in high-heeled walking there was a concomitant increase in the loading coefficient compared to barefoot walking, such that it represented 1.50 of the value obtained for barefoot walking. This means that 1.50 of the body mass borne on the forefoot in barefoot walking is transmitted to the forefoot of the same subjects in high heeled walking. Apparently, heel raise, not body mass may be the determinant of the loading coefficient of the foot as captured by the MVFD. This is reasonable as this study involved the same subjects, with the same body mass, and yet the loading coefficient increased compared to barefoot walking, by about 150% in high-heeled walking. Invariably, the higher the heel, the greater the loading stress, and consequently loading coefficient. In summary, our findings suggest that in non-habitual/ occasional wearers, walking on high-heeled shoes creates F/R load imbalance, and increases the loading stress as well as the loading coefficient. However, there was no pathological gait after the shoes were removed and, as such, non-habitual use of high heeled shoes apparently poses no inherent risks. Had the many years of non-habitual use of high heeled shoes translated to significant residual biomechanical derangements in the locomotor apparatus, then kinematic data recorded for barefoot walking, in the same subjects, would have approximated what was obtained during high heeled walking. Nevertheless, the abnormal biomechanical changes suggested by the kinematic data for non-habitual wearers, while walking in high heeled shoes, are undesirable. 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7 18 S. Ibeneme, A. Ekeanyanwu 14. Nordin N., Frankel V.H. (2003) Biomecânica básica do sistema músculo esquelético. 3ª ed. Guanabara Koogan. p Olaogun M.O.B., Edewor N.S. (1994) The Effect of Foot Wear on Postural Stability. J. Nig. Soc. Physioth., 6: Rossi W.A. (1999) Why Shoes Make Normal Gait Impossible. Pediatry Management. Retrieved from www. unshod.org 17. Santos A. (2005) Postura corporal: um guia para todos. São Paulo: Summus editorial, p Received Accepted University of Physical Education, Warsaw, Poland