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Effects of High Heeled Shoes Wearing Experience and Heel Height on Human Standing Balance and Functional Mobility a
Vaniessa Dewi Hapsari & Shuping Xiong
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Department of Human and Systems Engineering, School of Design and Human Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, South Korea Accepted author version posted online: 09 Jul 2015.
Click for updates To cite this article: Vaniessa Dewi Hapsari & Shuping Xiong (2015): Effects of High Heeled Shoes Wearing Experience and Heel Height on Human Standing Balance and Functional Mobility, Ergonomics, DOI: 10.1080/00140139.2015.1068956 To link to this article: http://dx.doi.org/10.1080/00140139.2015.1068956
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Publisher: Taylor & Francis Journal: Ergonomics DOI: http://dx.doi.org/10.1080/00140139.2015.1068956
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Vaniessa Dewi Hapsari and Shuping Xiong* Ergonomics and Applied Biomechanics Laboratory
School of Design and Human Engineering
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Department of Human and Systems Engineering
Ulsan National Institute of Science and Technology (UNIST)
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Ulsan, 689-798, South Korea
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*Corresponding author
Telephone: +82-052-217-2716, Fax: +82-052-217-2708
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Email:
[email protected]
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Running head: High Heels on Standing Balance and Mobility
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Effects of High Heeled Shoes Wearing Experience and Heel Height on Human Standing Balance and Functional Mobility
Effects of High Heeled Shoes Wearing Experience and Heel Height on Human
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This study aimed to examine the effects of high heeled shoes (HHS) wearing experience and heel height on human standing balance and functional mobility. Thirty young and
healthy females (ten experienced and twenty inexperienced HHS wearers) participated in
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a series of balance tests when they wore shoes of four different heel heights: 1cm(flat),
4cm(low), 7cm(medium), and 10cm(high). Experimental results show that regardless of
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the wearing experience, the heel elevation induces more effort from lower limb muscles (particularly calf muscles) and results in worse functional mobility starting at 7cm heel height. While the heel height increased to 10cm, the standing balance also becomes
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worse. Experienced HHS wearers do not show significantly better overall performance on standing balance and functional mobility than inexperienced controls, even though they have better directional control (76.8% vs. 74.4%) and larger maximum excursion (93.3%
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vs. 89.7%). To maintain standing balance, experienced wearers exert less effort on tibialis anterior, vastus lateralis and erector spinae muscles at the cost of more intensive effort
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from gastrocnemius medialis muscle.
Keywords: High heeled shoes; standing balance; fall risk; experience; functional
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mobility
Practitioner summary: Many women wear high heeled shoes (HHS) to increase female attractiveness. This study shows that HHS induce more muscular effort and worse human
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Standing Balance and Functional Mobility
standing balance and functional mobility, especially when heel height reaches 10cm. HHS wearing experience only provides certain advantages to wearers on limits of stability in terms of larger maximum excursion and better directional control.
1. Introduction High heeled shoes (HHS) are considered by many women as an essential part of a fashionable outfit. Many women all over the world wear HHS at some time in their lives
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and may even wear them regularly to increase their female attractiveness (Srivastava,
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Medical Association (2003) conducted a survey on HHS use of 503 women. It was
reported that 72% of women wore HHS and 39% wore HHS on a daily basis. Another
survey conducted by Hotter Shoes (2010) on 3,000 women who wear HHS revealed that
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10% of women had to receive medical attention or even be hospitalized because of their shoes and nearly 50% of women twisted their ankles. The top injuries caused by HHS
were broken ankles, twisted knees, infected blisters, bunions and torn tendons. However,
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above 60% of women were ready to continue wearing HHS despite suffering pain and injuries (Hotter Shoes 2010). Previous research studies reported that wearing HHS could
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cause changes on joint kinematics (Opila-Correia 1990; Snow and Williams 1994; Lee, Jeong, and Freivalds 2001) and postural control (Lindemann et al. 2003; Chien, Lu, and Liu 2013; Chien, Lu, and Liu 2014), alter foot pressure distribution and impact forces
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during gait (Lee and Hong 2005), increase lower extremity muscular activity and fatigue level (Gefen et al. 2002; Srivastava, Mishra, and Tewari 2012; Hong et al. 2013), and alter gait kinematics (Merrifield 1971; Soames and Evans 1987; de Lateur et al. 1991;
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Cowley, Chevalier, and Chockalingam 2009). Heel elevation can also be associated with an increased risk of falling (Snow
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1994; Blachette, Brault, and Powers 2011). Studies have shown that wearing HHS caused lumbar flattening (decreased the lumbar flexion angle) (Opila et al. 1988; Lee, Jeong, and Freivalds 2001), a pelvic backward rotation and a reduction of the distance of the ankle and knee joints from the line of gravity (Opila et al. 1988), creating an abnormal and
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Mishra, and Tewari 2012; Schaefer and Lindenberger 2013). The American Podiatric
unstable posture which induces challenges to the human balance system (Lee, Jeong, and Freivalds 2001). Balance describes the dynamics of body posture to prevent falling
(Winter 1995) and it is the ability to maintain, achieve or restore the body’s center of mass (COM) relative to the base of support (BOS), or more generally, within the limits of stability (Pollock et al. 2000; Mancini and Horak 2010; Chien, Lu, and Liu 2013). In
order to achieve balance, a person needs a complex set of sensorimotor control systems that include the sensory input from vision, proprioception, and the vestibular system; the integration of that sensory input; and the motor output to body muscles. Since the height of COM will be increased with higher heels and the base of support (BOS) will become
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smaller with reduced supporting base of HHS when compared with barefoot or flat shoes,
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Xu, and Su 2012; Chien, Lu, and Liu 2014). The difference between the vertical projection of the COM (i.e., center of gravity, COG) and center of pressure (COP) has also been recognized as the variable that provides a good assessment of spontaneous
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sway during quiet standing (Winter 1995). During quiet standing, the use of 7cm HHS
increases the oscillation of the COP when compared with barefoot standing (Gerber et al., 2012). During walking, the COG-COP inclination angles and their rate of changes have
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been used to describe the body’s dynamic control (Pai and Patton 1997; Chien, Lu, and Liu 2013). Previous experimental studies showed that compared with when barefooted or
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wearing walking shoes of heel lower than 2cm, women with dress shoes of heel higher than 4 cm performed significantly worse on the Functional Reach and Timed Up and Go tests (Arnadottir and Mercer 2000). Additionally, during high heeled gait, the increased
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heel heights corresponded to decreased gait speed and step length (de Lateur et al. 1991) and a lack of foot mediolateral stability (Gefen et al. 2002). Chien, Lu, and Liu (2013) reported that the primary factor for the reduction of the normalized walking speed and
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frontal inclination angles was the reduced base of the heels, not the height of heels. Even though previous studies have shown that HHS can cause various changes on kinematics,
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kinetics, and muscle activity of the musculoskeletal system, which could induce challenges to the human balance system and result in higher fall risks, they had major methodological limitations related to the shoes used in experiments. For example,
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wearing HHS could induce difficulties of maintaining balance (Menant et al. 2008; Cai,
Speksnijder et al. (2005) had their participants walk in their own shoes. Henderson
(2004) used flat sandals and high-heeled open toed shoes that were completely different in the experiment. Ebbeling, Hamill, and Crussemeyer (1994) and Lee and Hong (2005) used commercially available shoes that were similar only in very limited design parameters. Without strong controls on other shoe parameters (shoe type, material, heel
contact area, heel pattern etc), the experimental results could be biased since the effects
can be caused by not only the heel height but also other confounding factors (Witana et al. 2009; Srivastava, Mishra, and Tewari 2012). Furthermore, very few studies (Gerber et al., 2012; Chien, Lu, and Liu 2013) have explicitly measured the changes of human balance from different heights of shoes’ heels.
Therefore,
this study provided
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standardized shoes with different heel heights to examine the effect of heel height on
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Biomechanical accommodations to HHS were found to vary with experience in wearing HHS. Csapo et al. (2010) reported that long-term wearing of HHS induces
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shortening of the gastrocnemius medialis muscle fascicles and increases Achilles tendon stiffness, reducing the active range of motion of the ankle. Experienced wearers were also reported to have much greater increases in knee flexion during the stance phase of high
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heeled gait, which may cause knee abnormalities such as osteoarthritis (Opila-Correia 1990). Schaefer and Lindenberger (2013) found that experienced wearers adapted their
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walking more flexibly to shoe type and also when they were given different levels of cognitive load. During high heeled gait, they had more flexible adjustments of movement patterns. Very few studies have further investigated the consequences of these changes
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from HHS wearing experience on human balance. One recent study by Chien, Lu, and Liu (2014) examined the effects of long-term wearing HHS on the balance control during walking using the COG-COP inclination angles and their rate of changes. It was reported
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that when compared with inexperienced controls, experienced HHS wearers showed more conservative and stable body control during single-limb support, but a fast weight
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transfer during double-limb support. However, the effect of HHS wearing experience on human balance in terms of standing balance and functional mobility remains largely
unknown, even though both standing balance and functional mobility are critical
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human balance.
components of a person’s ability to perform daily activities and have been widely used in assessing human balance and the risk of falling (Winter 1995; Tang, Moore, and Woollacott 1998; Arnadottir and Mercer 2000; Browne and O'Hare 2001; Wallmann 2001; Garland et al. 2003; Mancini and Horak 2010; Kasser et al. 2011; Gerber et al. 2012).
Therefore, the objective of this study is two-fold. The first aim is to investigate the effect of heel height on human standing balance and functional mobility. We will determine whether or not wearing HHS impairs human standing balance and functional mobility. If yes, up to which level of heel height will induce significant impairment? The
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It was hypothesized that the heel elevation
would degrade human performance on standing balance and functional mobility.
2. Methods 2.1. Participants and Experimental Shoes
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However, HHS wearing experience would help counteract the performance degradation.
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Thirty young and healthy female participants with ages ranging from 18 to 30 years and shoe sizes ranging from 23.5cm to 25.0cm participated in this experiment. None of the
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subjects reported having any musculoskeletal or neuromuscular disorders that restrict the range of lower extremity motion, which can make the wearing of HHS painful (Srivastava, Mishra, and Tewari 2012). Participants were sorted into two groups, ten of
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them as experienced wearers and the other twenty as inexperienced wearers, based on their experience of wearing HHS. An experienced HHS wearer was defined as an individual who had worn shoes with narrow heels of more than 4cm height at least two
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times per week, 8 hours per day for at least one year (Henderson 2004; Lee and Hong 2005). An inexperienced wearer wore HHS less than once per week. The detailed
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characteristics of the subjects are given in table 1. Differences in age, weight and shoe size between groups were not significant (independent t-tests, p=0.263-0.794), however, the experienced group (stature: 159.87 ± 4.98 cm) was significantly (p=0.049) shorter than the inexperience group (stature: 163.86 ± 5.06 cm) even though the group mean
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standing balance and functional mobility.
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second aim of this study is to examine the effect of HHS wearing experience on human
difference was within 2.5%. All subjects gave their informed consents to participate in the study, which had been previously approved by the university institutional review board. [Insert Table 1 about here]
Four shoes with different heel heights (Figure 1, left) were used in this investigation and all shoes were made by the same manufacturer (CauseU, South Korea). Except the flat shoes as the baseline condition, all experimental shoes were women’s dress shoes with stiletto heels (12.5mm × 12mm, Figure 1, right). The shoe style, material,
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and heel pattern were kept the same for every shoe, with variation only in the heel height.
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classified as flat, low, medium, and high heel (Lee, Jeong, and Freivalds 2001; Lee and Hong 2005). The heel height order was randomly assigned to each participant.
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[Insert Figure 1 about here]
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2.2 Experimental Design
A mixed within-subject (heel height, 4 levels) and between-subject (wearing experience, 2 levels) design was used for this experiment. Sensory Organization Test (SOT) and
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Limits of Stability (LOS) were conducted to measure each participant’s standing balance, while Functional Reach (FR) and Timed Up and Go (TUG) tests were performed to measure functional mobility. SOT and LOS are two types of tested used with
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computerized dynamic posturography, which assesses body sway by measuring shifts in the COG as a person moves within the available stability limits (Wallmann 2001;
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Neurocom 2008; Mancini and Horak 2010). The SOT is designed to quantify an individual's ability to maintain standing balance in a variety of complex sensory
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conditions while the LOS test measures volitional control of the COG while standing (Neurocom 2008). FR and TUG tests reflect the basic functional mobility that would be required for performing activities of daily living (Duncan et al. 1990; Podsiadlo and Richardson 1991; Newton 2001) and they have been the two most commonly used tools
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The actual heel heights for four shoes were: 1cm, 4cm, 7cm, and 10cm and they can be
in the clinical field for assessing balance control and fall risks (Arnadottir and Mercer 2000; Mancini and Horak 2010). The FR captures the ability to control movement of the
COG over a fixed base of support and TUG include the ability to adjust the COG continuously over a moving base of support (Duncan et al. 1990; Duncan and Studenski 1994; Arnadottir and Mercer 2000).
SOT (Figure 2a) objectively identifies overall performance and abnormalities in the participant's effective
use of three sensory systems (visual,
vestibular and
proprioceptive) that contribute to postural control and balance (Chaudhry et al. 2004; NeuroCom 2008). The postural sway of participants during quiet standing was measured
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by a commercially available force platform system, PRO Balance Master (NeuroCom®
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lasts 20 seconds and was repeated 3 times, as specified in the operation guide of PRO
Balance Master. The outcome measures are equilibrium score and postural control
strategy score. Equilibrium score quantifies the participant’s COG sway or postural
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stability under each experimental trial and scores range from 0-100. An equilibrium score
of 100 indicates no or little sway whereas a score of 0 indicated a sway exceeding the limit of stability which without the restraint would have required a person to move his/her
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foot or would have resulted in a fall (NeuroCom 2008; Fong, Tsang, and Ng 2012). Strategy score quantifies the relative amount of movement about the ankles (ankle
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strategy) and about the hips (hip strategy) the participant used to maintain balance during each trial. A strategy score approaching 100 represents the participant predominantly uses an ankle strategy to maintain equilibrium, while a score near 0 reveals that the participant
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predominantly uses a hip strategy (Fong, Tsang, and Ng 2012). In order to understand the roles that muscles play in maintaining standing balance when wearing HHS, activities of gastrocnemius medialis(GM), gastrocnemius lateralis(GL), tibialis anterior(TA), vastus
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medialis(VM), vastus lateralis(VL) and erector spinae(ES) muscles were recorded (Henderson 2004;
Srivastava,
Mishra,
and
Tewari 2012; Hong et al.
2013)
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simultaneously with SOT using surface EMG sensors and the Myomonitor EMG System (Myomonitor® IV Wireless EMG System, Delsys Inc., Boston, MA, USA). [Insert Figure 2 about here]
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Balance Master®, NeuroCom International Inc., Clackamas, OR, USA). Each test trial
LOS (Figure 2b) test quantifies the maximum distance a person can intentionally
displace their COG without losing balance, stepping, or reaching for assistance. During this test, the participants need lean their bodies in a given direction (in total 8 directions) as fast and accurate as possible toward the highlighted target when they hear the auditory signal and hold the position for 10 seconds (Newton 2001; Goulding et al. 2003; Islam et
al. 2004). The outcome measures are reaction time, COG movement velocity, directional control, endpoint excursion, and maximum excursion (Hapsari, Xiong, and Yang 2014). Reaction time represents the amount of time from the auditory signal until the movement is initiated. Movement velocity provides information regarding the average speed of the
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COG movement to the target in degrees per second. Directional control represents a
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extraneous movement away from the target. Endpoint excursion represents the distance
the COG is displaced toward the target during the primary movement. Maximum excursion represents the maximum distance the COG is displaced toward the target over
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the entire trial duration. Both endpoint excursion and maximum excursion are expressed
as percentage of the distance toward the target. A person with delayed reaction time, slowed COG movement velocity, restricted excursions, and worsened directional control
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is at increased risk to fall or instability during weight shifting activities (Rogers et al. 2003; NeuroCom 2008).
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FR (Figure 2c) test measures the difference between arm’s length and maximal forward reach while subjects standing independently. TUG (Figure 2d) test is a simple test used to assess a person’s mobility and requires both static and dynamic balance. It
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measures the time that a person takes to rise from an arm chair, walk three meters, turn around, walk back to the chair, and sit down. The long completion time in TUG test and
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short functional reach distance indicate poor functional mobility. 2.3 Experimental procedures
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The experiment was conducted in a quiet, temperature (22°C) controlled laboratory room. All of the participants were briefed about the experimental procedures and asked to read and sign a consent form. The participant’s basic characteristics (age, stature, weight, shoe size) and the history of wearing HHS were then recorded. After cleaning the participant’s
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comparison of the amount of movement in the intended direction toward the target and
skin with alcohol, Delsys surface EMG recording electrodes were placed on 5 lower limb muscles
(gastrocnemius
medialis,
gastrocnemius
lateralis,
tibialis
anterior,
vastus
medialis, vastus lateralis) of the dominant leg and 1 low back muscle (erector spinae). All electrodes were taped to the skin to reduce movement artifacts and remained in place throughout the study (Srivastava, Mishra, and Tewari 2012).
After EMG recording preparation, three trials of maximum voluntary contractions (MVC) for each muscle were performed. The contractions were maintained for 5 seconds with 1 minute rest between them. The average of the three trials was used for
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normalization of the electrical activity of each muscle (Burden and Bartlett 1999; do
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1) on a PRO Balance Master for all shoe conditions. EMG recordings during the SOT test were simultaneously acquired at a sampling frequency of 1000Hz from six muscles. The
EMG system was then detached to minimize its possible interference on functional
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mobility and natural movements of the subject in two following functional mobility tests.
Thereafter, three test trials of the TUG and FR were conducted for each shoe condition. To prevent fatigue, each subject took a minimum of 5-minute rest between each shoe
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condition, and the whole experiment lasted for approximately 3.5 hours.
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2.4 Data processing
PRO Balance Master system software was used to automatically obtain equilibrium score and strategy score for the SOT test at each shoe condition. Five outcome measures from
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the LOS test including reaction time, COG movement velocity, directional control, endpoint excursion and maximum excursion were also determined from the PRO Balance Master system software (NeuroCom 2008; Hapsari, Xiong, and Yang 2014). All EMG
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data were processed using EMGworks Analysis Software (EMGworks® 4.0, Delsys Inc., Boston, MA, USA). Root mean square (RMS) amplitudes were calculated with windows
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length of 0.2s and windows overlap of 0.1s. The average RMS value of each muscle for SOT trials was then normalized to the average RMS value of each muscle for three maximum voluntary contraction (MVC) trials to account for individual differences
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Nascimento 2014). Each subject first participated in the SOT and then LOS tests (Figure
(Bolgla and Uhl 2007). The maximum reach distance of three FR trials and the completion time of three TUG trials were imported and averaged using Microsoft Excel 2013 for further statistical analysis. 2.5 Statistical analysis
Analysis of variance (ANOVA) was conducted to check the effects of heel height (withinsubject factor) and HHS wearing experience (between-subject factor) on each outcome measure. A Bonferroni post-hoc test was further conducted if the effect was statistically significant. Statistical software including Minitab (Minitab® 16, Minitab Inc., State
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College, PA, USA) and SAS (SAS® 9.2, SAS Institute Inc., Cary, NC, USA) were used
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Results
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The descriptive statistics (means and standard deviations) of outcome measures from SOT, LOS, FR, TUG and muscular activity tests at each heel height condition are summarized for inexperienced and experienced groups respectively (Table 2). The
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detailed statistical analysis results are described in the following subsections. [Insert Table 2 about here]
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3.1 Sensory Organization Test
Table 3 shows that the main effect of heel height is significant (p0.05). The post hoc tests indicate that both the equilibrium and strategy scores significantly decreased as the heel height increased to 10cm when compared with heel
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heights at 1cm and 4cm (Figure 3, top), indicating overall performance of integrating three sensory systems for maintaining standing balance was worse and the wearer
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employed more hip strategy (less ankle strategy) to control the standing posture.
[Insert Table 3 about here] [Insert Figure 3 about here]
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for data analysis at a significance level of 0.05.
3.2 Limits of Stability
The main effect of the heel height is significant for all five stability limit measures except reaction time (p=0.164) (Table 3). The main effect of wearing experience is also significant
for
two
stability
limit
measures
(directional
control
and
maximum
excursions), but the two-way interaction (heel height × wearing experience) is not significant (p>0.05). The post hoc tests show participants had significantly smaller
excursions and poorer directional control starting at 7cm heel height, while COG movement velocity at 10cm heel height was significantly slower than that at 4cm heel height (Figure 3, bottom). Regarding the wearing experience, experienced HHS wearers showed significantly better directional control (76.8% for experienced group vs. 74.4%
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for inexperienced group) and larger maximum excursion (93.3% for experienced group
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Further analysis on detailled directions showed that the experienced wearers had better directional control in the forward direction and larger excursions in both forward and back directions (Figure 4, bottom).
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[Insert Figure 4 about here]
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3.3 Functional mobility
As shown in table 3, the heel height and wearing experience have a significant main effect on both the completion time in TUG test and maximum reach distance in FR test
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(p0.05). The post hoc tests suggest that the wearers with heel heights of 7cm and 10cm had significantly shorter maximum functional reach distance and longer TUG completion
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time as compared with the flat shoes of 1cm heel height (Figure 5, top). Furthermore, the experienced group displayed significantly shorter maximum functional reach distance and longer TUG completion time than the inexperienced group (Figure 5, bottom).
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[Insert Figure 5 about here]
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3.4 Muscular activities
Results shown in table 3 suggest that the main effect of heel height is significant for the activity levels of four lower limb muscles (gastrocnemius medialis, gastrocnemius
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vs. 89.7% for inexperienced group) compared to inexperienced wearers (Figure 4, top).
lateralis, tibialis anterior, and vastus lateralis) out of total six investigated muscles. The main effect of wearing experience is significant for the activity levels of gastrocnemius medialis, tibialis anterior, vastus lateralis and erector spinae. The two-way interaction
(heel height × wearing experience) is not significant for all muscular activities. The post hoc tests show that the gastrocnemius medialis and gastrocnemius lateralis muscles
became significantly more active starting at 7cm heel height when compared with the flat shoes, while the tibialis anterior and vastus lateralis muscles became more active at 10cm heel height (Figure 6, top). Cross-comparison of normalized EMG data of four active muscles showed that when the heel height increased to 10cm, two calf muscles
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(gastrocnemius medialis, gastrocnemius lateralis) achieved nearly 20% MVC, while
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Regarding the wearing experience, experienced wearers exerted significantly more muscular effort from gastrocnemius medialis muscle and less effort from vastus lateralis,
tibialis anterior and erector spinae muscles compared to inexperienced controls (Figure 6,
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bottom). [Insert Figure 6 about here]
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The overall experimental results are summarized in table 4, where the effects from heel height and HHS wearing experience on human standing balance and functional
[Insert Table 4 about here]
Discussion
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mobility are given.
The purpose of the present study was to investigate the effects of heel height and wearing experience on human standing balance using SOT and LOS, and on functional mobility
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using FR and TUG. It was found that regardless of the wearing experience, the heel elevation induces more effort from lower limb muscles (particularly calf muscles) and
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results in worse functional mobility starting at 7cm heel height. While the heel height increased to 10cm, the standing balance also becomes worse. The results support the first part of our hypothesis on the effect of heel height. The findings suggest that compared
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activity levels of both tibialis anterior and vastus lateralis were within 10% MVC.
with standing on the flat shoes (H=1cm) or low heeled shoes (H=4cm), young women can still maintain similar performance on standing balance when they wear HHS with 7cm heel height by a compensatory increase in most lower limb muscles activities. However, when they wear HHS with 10cm heel height, the standing balance is worsened even though the wearers exert more muscle effort. When compared with inexperienced HHS controls, the experienced HHS wearers do not show significant improvements in all
measures of standing balance and functional mobility except two stability limit measures (maximum excursion and directional control). These results are different from the second part of our hypothesis on the effect of wearing experience. Wearing HHS appeared to impair human standing balance. A decrease in the
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equilibrium and strategy scores in the SOT test demonstrated that the wearer’s ability to
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postural control strategy is gradually shifted from an ankle strategy to a hip strategy. It is
well known that the ankle strategy is the first pattern for controlling upright body sway and an individual tends to shift to the hip strategy in more unstable conditions (Fong,
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Tsang, and Ng 2012). These findings are also consistent with previous studies which
reported that as the heel height increases, a women with a more upward displacement of the center of body mass will compensate for heel height by increasing the sway of her
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back to maintain balance (Rexford 2000; Cai, Xu, and Su 2012), thus more hip strategy is used to maintain the balance. To our knowledge, no previous research has been
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conducted to directly examine the effect of heel height on stability limits in different directions. We found that human stability limits in terms of COG movement velocity, directional control, and excursions were worsened when the heel height reached 7cm.
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The unstable posture caused by the increased heel height (Arnadottir and Mercer 2000; Lee and Hong 2005) can induce the fear of falling for the wearers which further restricts their movements, especially in the forward and back directions, signified by a slower
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speed of COG movement, worsened directional control, and reduced excursions. In the case of reaction time, there was no significant change, which should be reasonable as all
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participants in this study were healthy females and the reaction time was mainly associated with difficulties in cognitive processing and motor diseases (Rogers et al. 2003).
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integrate three sensory systems for maintaining standing balance is worsened and the
Simultaneously recorded EMG data during quiet standing in the SOT test showed
that balanced standing on higher heeled shoes elicited the increasing of the electrical activity from gastrocnemius medialis, gastrocnemius lateralis, tibialis anterior and vastus
lateralis muscles. However, there was no significant difference on EMG activity of the vastus medialis and erector spinae muscles. These findings are largely consistent with many previous studies on EMG activity of five lower extremity muscles (Joseph 1968;
Árnadóttir, Kjartansdóttir, and Magnúsdóttir 2011; Srivastava, Mishra, and Tewari 2012; do Nascimento et al. 2014). EMG activity of the erector spinae muscle was contradictory with results of some other studies. Pannell (2012) reported that wearing HHS leads to an unstable posture and larger compressive force in one’s low back, increasing the activity
t
of the erector spinae to maintain balance which may result in low back pain. Lee, Jeong,
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activity of the erector spinae. The insignificant difference on erector spinae muscle found
in this study could be caused by the less demanding balance disturbance on the task
(quiet standing) provided by this experiment. During the experiment, the participants
us
predominantly used an ankle strategy (reflected by all mean strategy scores were higher than 90, see Figure 3, top) to maintain their balance and lower leg muscles could be sufficient to support the movements around the ankle and knee areas (EMG activity is
an
within 20% MVC) and as a result, upper leg muscles, including thigh and low back muscles, may not be activated for this task. Furthermore, when the participants wear
M
shoes of 10cm heel, both calf muscles (gastrocnemius medialis and gastrocnemius lateralis) play more active roles (EMG activities about 20% MVC) than tibialis anterior and vastus lateralis (EMG activities
