Effects of Raised Heel Insole on Muscle Activity during ankle Sudden
Inversion in Normal Adults
JONGSUNG CHANG1, SEUNGMIN NAM2,*
1Department of Physical Therapy,
Yeungnam University College,
Daegu,
SOUTH KOREA
2Department of Sports Rehabilitation,
Yeungnam University College,
Daegu,
SOUTH KOREA
Abstract: - Raised heel insoles increase the plantar flexion angle of the ankle and cause ankle inversion sprain.
The purpose of this study was to artificially create an ankle sudden inversion situation, which is a mechanical
situation of actual ankle joint damage, and investigate the effect of the raised heel insole on ankle joint muscle
activity. The subjects of this study were forty subjects with normal adults. The subjects performed sudden ankle
inversion on the trapdoor with no raised heel insole, insole heights of 3cm, and insole heights of 7cm. The
application of the raised heel insole was conducted randomly. The subjects performed the trapdoor test three
times using dominant feet with a 60-second rest period between tests. This study assessed muscle activity
during sudden ankle inversion three times. Raised heel insoles showed a significant decrease in Tibialis
Anterior, Peroneus Longus, and Peroneus Brevis muscle activity than no raised heel insole (p<.05). Raised heel
insoles showed a significant increase in Gastrocnemius muscle activity than no raised heel insole (p<.05).
Raised heel insoles increase the risk of ankle sprain injury by reducing tibialis anterior and peroneus muscle
activity during sudden ankle inversion.
Key-Words: - Raised Heel Insole, Ankle Joint, Ankle Sprain, Ankle Sudden Inversion, Muscle Activity,
Normal Adults.
Received: April 13, 2024. Revised: August 17, 2024. Accepted: October 6, 2024. Published: November 13, 2024.
1 Introduction
Gait is a basic movement necessary for locomotion
during active daily living, and is defined as
locomotion by moving the body from one point to
another by alternately moving the lower extremity
and trunk, [1]. The normal gait cycle consists of a
stance phase and a swing phase and is a movement
that locomotion the body forward while
maintaining stability and balance, [2]. However,
when gait, the body receives an impact 2-3 times
the weight, and it has been reported that a lot of
impact is applied to the rare foot, especially during
the stance phase, [3]. Therefore, shoes contribute to
injury prevention by alleviating the impact on the
body. Also, shoes are a basic tool to protect the
body and have the function of supporting the body
and absorbing shock when gait. In other words, in
the case of shoes, the functional aspect is
important, [4]. However, recently, apart from
functional factors, there is a tendency to prefer high
heels as the cosmetic aspect is emphasized to
simply compensate for small height or make the
legs look longer, [5].
In heel shoes, the normal gait of the lower
extremity is difficult, and as the positions of the
vertebral column and low extremity joint change,
the center of gravity of the body changes, and the
longitudinal arch becomes higher, [6].
Additionally, stability is reduced due to a high heel,
causing compensation in the knee joint and hip
joint. Additionally, high-heeled shoes increase
plantar flexion of the ankle joint during gait and
affect supination and pronation motion of the foot
during gait, [7]. These changes cause
musculoskeletal problems such as muscle
weakness, ligament damage, joint adhesion, and
improper body alignment at the ankle joint, [8].
Balance refers to a process caused by coordinated
activities in the proprioceptor and mechanical
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aspects. Continuous wearing of high heel shoes
causes abnormalities in the Somatosensory system
and proprioceptor around the ankle joint and
changes the normal mechanism of the foot,
affecting balance function, [9]. It was said to bring
about change. This can lead to various adverse
effects on balance, gait, and ankle. According to
previous studies, it has been reported that wearing
Raised heel insoles has a negative effect on balance
and gait, [10].
In particular, ankle sprains can be caused by
high heels, and ankle sprains are the main cause of
activity disorder, and symptoms such as pain,
edema, muscle weakness, and instability appear,
[11]. Damage to the Anterior Talofibular Ligament
(ATL) and Calcaneofibular Ligament (CFL) is
common in most ankle sprains. Due to this damage,
the stability between the talus and fibula and
between the calcaneus and fibula decreases, leading
to chronic ankle instability, [12].
According to many previous studies, using high
heels has a negative effect on balance and gait
function and the body as a whole. However, there is
a lack of research on the effects of high heels on the
ankle joint in the context of actual mechanical
processes and injury mechanisms. In addition,
despite the increasing use of raised heel insoles by
modern people, there is a lack of research on the
risks and negative effects of raised heel insoles.
Therefore, the purpose of this study was to
artificially create an ankle sudden inversion
situation, which is a mechanical situation of actual
ankle joint damage, and investigate the effect of
raised heel insoles on ankle joint muscle activity.
And, this study aims to investigate the relationship
between raised heel insoles and ankle injuries.
2 Methods
2.1 Subjects
The subjects were 60 normal adults attending Y
University College from September to October
2023. The criteria for determining a normal ankle
joint were that there was no clear history of ankle
joint damage through a questionnaire, no ankle
symptoms such as pain or swelling, and no
instability due to the talar tilt test or anterior drawer
test through a physical examination. The data
analysis of this study was approved by the
Institutional Review Board of Daegu University.
2.2 Study Protocol
To evaluate the effect of raised heel insole on normal
adults, bare feet and insole heights of 3cm and 7cm
were applied to the subjects. The order of application
of the insole was determined randomly. The subject
was asked to stand on a trap door wearing bare feet
or shoes with insoles, and an ankle sudden inversion
situation was applied. Additionally, because vision
can affect the experimental results, measurements
were made with eyes closed. Muscle activity was
measured before and after measurement. The
reference value of muscle activity was expressed as
a ratio of the average value of activity measured for
2 seconds from the onset of muscle activity when
inversion of the ankle joint was induced. The
measurements were made 3 times on bare feet, with
insole heights of 3cm and 7cm, and the average
value was used. Since muscle fatigue may increase
during measurement, sufficient rest of 5 minutes was
provided between measurements (Figure 1).
Fig. 1: Raised Heel Insole
2.3 Measurement Tools and Measurement
Methods
2.3.1 Trap Door
For examination, a trap door was employed to
analyze the ankle injuries kinematically, [13]. The
subject is asked to stand on a trap door with the leg
to be tested on the active board and the leg not
being tested on the stationary board, with both feet
parallel, and then place both arms naturally and
look straight ahead. To prevent the subject from
predicting, a trap door is activated to induce an
inversion motion of the ankle joint. The trapdoor
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platform rotated in an inverted manner by 25° from
the neutral standing position. The subjects
performed the trapdoor test three times using
dominant feet with a 60-second rest period between
tests (Figure 2).
Fig. 2: Trap door
2.3.2 Electromyography
Electromyography measurements were performed
at the tibialis anterior, peroneus longus, peroneus
brevis, and gastrocnemius of the dominant leg
using surface electromyography (MP35, Biopac,
Goleta, CA, USA) in the setting of sudden ankle
inversion. To measure electromyography, surface
electrodes were attached after hair removal and
ethyl alcohol disinfection of the electrode
attachment area. The electrodes were placed as
described by the surface EMG for non-invasive
assessment of muscles (SENIAM) protocol, [14].
To measure the tibialis anterior, it was attached at
the upper 1/3 of the line between the tip of the
fibula and medial malleolus, to measure the
peroneus longus, it was attached at a point 3cm
distal to the fibular head, and to measure the
peroneus brevis, it was attached at a point 5cm
proximal to the lateral malleolus. It was attached to
the tendon behind the fibula, and to measure the
gastrocnemius, it was attached to the upper third of
the line between the fibular head and the calcaneus.
To eliminate noise caused by the movement of the
wire and ensure that the electrode adheres well to
the skin, tape and elastic bands were used to fix the
wire and electrode. Electromyography signals were
collected at a signal acquisition rate of 1000Hz
sampling rate and processed by full-wave
rectification. Data were stored using the Biopac
student lab PRO 3.7.1 (Biopac System, USA)
program and were section-filtered from 30 to 500
Hz and filtered at 60 Hz to remove noise. The
muscle activity signal evaluated in each muscle was
processed as a root mean square value and then
normalized as a percentage of the root mean square
value of maximal voluntary isometric contraction
(MVIC) (%MVIC). Evaluation of maximum
voluntary isometric contraction was performed in
the manual muscle strength testing position and
was recorded as the root mean square value of each
muscle measured when contracted for 5 seconds.
The maximal voluntary isometric contraction was
assessed three times, and the average value was
calculated and used (Figure 3).
Fig. 3: Electrode placement
2.4 Statistical Analyses
The data collected in this study were analyzed
using the Windows SPSS version 26.0 (SPSS Inc,
Chicago, IL, USA) program. The general
characteristics of the subjects were tested for
homogeneity using an independent sample t-test.
The collected data were tested for normality of
variables through the Shapiro-Wilk test, and as a
result of the test, all data were normally distributed,
so a parametric test was adopted. To determine the
effect of insole height on ankle muscle activity,
one-way repeated ANOVA was performed.
Mauchly's mauchly's sphericity test was satisfied
(p>0.05), and univariate analysis and within-subject
effect test were performed. Also, there was a
difference between variables, so a post-hoc analysis
was performed. The statistical significance level α
was set at 0.05.
3 Results
The demographic statistics of a single group are
shown in Table 1. Sixty subjects (gender: male 36,
female 24; age: 23.52±1.82years; height:
170.17±7.67cm; weight: 65.45±13.29kg). Raised
heel insoles showed a significant decrease in
Tibialis Anterior, Peroneus Longus, and Peroneus
Brevis muscle activity than no raised heel insole
(p<.05). Additionally, as a result of post-hoc
analysis, there were significant differences in no
raised heel insole, insole heights of 3cm, and insole
heights of 7cm in the Tibialis Anterior and
Peroneus Longus muscles (p<.05). There was a
significant difference between the no raised heel
insole and the raised heel insole in the Peroneus
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Brevis muscle (p<.05), but there was no difference
according to height (p>.05).
Table 1. General characteristics of subjects
Group (N=60)
Gender (M/F)
36/24
Age (year)
23.52±1.82
Height (cm)
170.17±7.67
Weight (kg)
65.45±13.29
Table 2. Comparison of the ankle muscle activity between the no-raised heel insole and the raised heel insole
Raised heel insoles showed a significant
increase of Gastrocnemius muscle activity than no
raised heel insole (p<.05). Additionally, as a result
of post-hoc analysis, there were significant
differences in no raised heel insole, insole heights
of 3cm, and insole heights of 7cm in the
Gastrocnemius muscle (p<.05) (Table 2).
4 Discussion
The shoes focus on the functional aspect to absorb
shock to the foot during gait and ensure proper
alignment of the body. However, with the recent
emphasis on cosmetic aspects and increasing the
heel or insole of shoes, the risk of musculoskeletal
diseases such as ankle sprains is increasing, [15].
Accordingly, this study was conducted in normal
adults to provide an ankle sudden inversion
situation, which is a mechanical situation of actual
ankle joint damage, and to determine the effect of
raised heel insole on ankle muscle activity. For this
study, insoles with no raised heel insole, insole
heights of 3cm, and insole heights of 7cm were
randomly applied to each subject. Then, standing
on the trap door, a sudden ankle inversion was
performed. The hypothesis of this study is that
during ankle sudden inversion, ankle muscle
activity decreases as the insole increases, causing
ankle instability and having a negative effect in
terms of prevention.
As a result of this study, the muscle activity of
the tibialis anterior significantly decreased by
28.81±10.90% in the no-raised heel insole,
25.73±12.08% in the insole heights of 3cm, and
17.84±4.45% in the insole heights of 7cm. In
addition, peroneus longus was significantly
decreased to 54.83±15.15% in no raised heel
insole, 39.42±9.81% in insole heights of 3cm, and
35.68±9.08% in insole heights of 7cm. These
findings suggest that the higher the height of the
insole, the muscle activity of the ankle muscles in
the situation of the ankle sudden inversion. I think
this is the cause of not properly protecting the
ankle.
According to previous studies, tibialis anterior
is the agonist of the ankle dorsiflexion, and
peroneus longus is the agonist of the ankle
eversion. In other words, the tibialis anterior and
peroneus longus are muscles that protect the ankle
joint and prevent damage when the ankle sprains in
the inversion and plantarflexion, [16]. To prevent
and protect ankle sprains, wearing raised heel
insoles should be limited. Wearing of the raised
heel insole must be limited to allow the tibialis
anterior and peroneus longus to function normally.
As the ankle plantar flexion angle increases, the
risk of ankle sprains increases, [17]. In addition,
high heel insoles move the center of gravity
forward, negatively affecting balance and gait, [18].
As a result of this study, the muscle activity of
the peroneus brevis decreased as the height of the
insole increased. However, there was no difference
MVIC%
Nonea
(Mean±SD)
3cmb
(Mean±SD)
7cmc
(Mean±SD)
p
post-hoc
Tibialis Anterior
28.81±10.90
25.73±12.08
17.84±4.45
.001*
a > b > c
Peroneus Longus
54.83±15.15
39.42±9.81
35.68±9.08
.000*
a > b > c
Peroneus Brevis
17.12±6.77
12.94±4.58
12.68±4.61
.037*
a > b,c
Gastrocnemius
49.86±11.73
57.47±6.59
68±6.49
.000*
c > b > a
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in muscle activity between the insole height of 3cm
and 7cm. It is thought that it was difficult to
selectively record electrical activity in peroneus
brevis using surface electrodes. In other words, the
peroneus brevis is a synergist of the peroneus
longus, and it is believed that it does not have a
significant effect on ankle stability during sudden
ankle inversion compared to the peroneus longus,
[19].
As a result of this study, the muscle activity of
Gastrocnemius significantly increased to
49.86±11.73% at no raised heel insole,
57.47±6.59% at insole heights of 3cm, and
68±6.49% at insole heights of 7cm. These research
results are because Gastrocnemius is an agonist of
ankle plantar flexion, and as the heel insole
increases, the ankle plantar flexion angle increases.
According to previous research, as the insole height
increases, the ankle joint uses plantar flexion to
adapt the body to the high heel insole, which is
consistent with the research results showing that
gastrocnemius contraction increases, [20].
Additionally, muscle activity of Gastrocnemius was
significantly higher with eyes closed than with eyes
open between no raised heel insole and insole
heights of 7cm. These results were consistent with
research results showing that when visual cue
deprivation occurs, the demand for muscle
contraction to maintain balance increases, [21]. In
addition, the gastrocnemius provides ankle stability
in static situations, but it is consistent with the
research results that reported that the dorsiflexion
strength is reduced and the risk of ankle sprain is
greater when the gastrocnemius responds quickly,
[22]. These results provide insight into the injury
mechanism and causes of injury, and thus improve
the existing preventive appliances.
Limitations of this study include that the age
was limited to those in their 20s and only
removable insoles were applied. In future studies, it
is necessary to compare fixed insoles as well as
removable height-elevating insoles with adults of
various ages or patients with ankle instability.
Additionally, it is believed that further research
should be conducted on kinematic analysis and
injury factors in ankle sudden inversion during gait,
[23].
5 Conclusion
To summarize the results of this study, a raised heel
insole increases the risk of ankle sprain injury by
reducing tibialis anterior and peroneus muscle
activity during ankle sudden inversion. Although a
raised heel insole may be helpful in cosmetic
aspects, the load generated during repeated gaits
has a negative effect on the ankle joint. In other
words, scientific evidence can be provided that
raised heel insoles can increase the risk of injury in
normal adults. It may also contribute to ankle joint
damage prevention. This is expected to reduce
treatment costs due to damage and reduce social
expenditures such as medical expenses.
Acknowledgement:
This research was supported by the Yeungnam
University College Research Grants in 2023.
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
- JongSung Chang has organized and executed the
experiments.
- SeungMin Nam was responsible for the Statistics.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
This research was supported by the Yeungnam
University College Research Grants in 2023.
Conflict of Interest
The authors have no conflicts of interest to declare.
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