1. style and fashion
2. footwear
3. shoes

AM02 Wedged shoes, A comfortable
alternative
Submitted by
Tan Wei Xiong Jude Alphonsus
U0706616E
Department of
Mechanical Engineering
In partial fulfilment of the
requirements for the Degree of
Bachelor of Engineering
National University of Singapore
Session 2010/2011
Summary
In this study, the relationship between uncomfortable shoes and plantar
pressure is investigated. Also, the hypothesis of wedged shoes being more
comfortable than normal stiletto styled shoes is presented.
It has revelance in the development of new shoe design as high heeled shoes
are popular in today’s society. While most studies delve into the numerous
changes in gait and posture, this study will focus on the possible discomfort on
the plantar surface that is directly derived from higher pressure loading.
It is first necessary to establish the relationship between the sensations of
discomfort on the plantar surface of the foot and quantifiable plantar pressure.
Unbiased opinion that was obtained through a series of blindfolded trials
yielded a positive, in favour of wedged shoes. 18 out of 25 subjects chose
wedged shoes as the more comfortable option.
Plantar pressure measurements explained the higher comfort rating given to
wedges shoes. It was attributed to the ability of the rigid sole to distribute
pressure and hence lowering the peak pressure experienced at the 1st
metatarsal heads.
Although the blindfolded test yielded positive results with a 90% confidence
interval, further population studies and finite element analysis might be
needed to reinforce the conclusions made in this report.
Acknowledgement
The author would like to express his sincere gratitude to the following
individuals and groups.
Associate Professor, Lee Heow Pueh
Dr Lee Shu Jin, Assistant Proffesor, Department of Surgery MBBS
Mr. Cheong Chee Hoong and his staff of the Defence Medical & Environmental
Research Institute, DSO National Laboratories (Kent Ridge)
Ms. Ng Zi Qi and Ms. Ye Huiping
Mr. Cheng Kok Sheng and the staff of the Applied Mechanics lab in the
National University of Singapore.
List of Figures
Figure 4.1 Comfort preferences of the different foot shapes ....................................... 21
Figure 4.2 Distribution of comfort rating scores ........................................................... 21
Figure 5.1 Subject 1 Barefoot ........................................................................................ 27
Figure 5.2 Subject 2 Heels ............................................................................................. 28
Figure 5.3 Subject 3 Wedges ......................................................................................... 28
Figure 5.4 Subject 2 Barefoot ........................................................................................ 29
Figure 5.5 Subject 2 Heels ............................................................................................. 29
Figure 5.6 Subject 2 Wedges ......................................................................................... 30
Figure 5.7 Video captures for subject 1 on first contact (a,b) Ascending (c,d)
Descending .................................................................................................................... 30
Figure 5.8 Video captures for subject 1 on first contact followed by toe off of the
same foot. Ascending (a,b),Descending (c,d) ................................................................ 31
Figure 5.9 Video captures for subject 1 on first contact followed by toe off of the
same foot Ascending (a,b),Descending (c,d) ............................................................... 31
Figure 5.10 Video captures for subject 2 on first contact followed by toe off of the
same foot Ascending (a,b),Descending (c,d) ................................................................. 31
Figure 5.11 Video captures for subject 1 on first contact followed by toe off of the
same foot Ascending (a,b),Descending (c,d) ............................................................... 32
Figure 5.12 Video captures for subject 2 on first contact followed by toe off of the
same foot Ascending (a,b),Descending (c,d) ............................................................... 32
Figure 5.13 Subject 1 Wedge......................................................................................... 36
Figure 5.14 Subject 1 Heel............................................................................................. 36
Figure 7.1 Free body diagram upon impact .................................................................. 41
Figure 11.1 A Pair of Wedged Shoes ............................................................................. 46
Figure 11.2 Side profile of the right wedge ................................................................... 46
Figure 11.3 A pair of Heels ............................................................................................ 47
Figure 11.4 Side profile of Heels ................................................................................... 47
Figure 11.5 Tekscan 3000 pressure sensors .................................................................. 48
Figure 11.6 Experimental Setup .................................................................................... 48
Figure 11.7 Graph of Pressure vs. time for different footwear for subject 1 ............. 49
Figure 11.8 Graphs for subject 2 .................................................................................. 55
Figure 11.9 Heel Left Trial 1 .......................................................................................... 60
Figure 11.10 Heel Left Trial 2 ........................................................................................ 60
Figure 11.11 Heel Right Trial 1 ...................................................................................... 60
Figure 11.12 Heel Right Trial 2 ...................................................................................... 61
Figure 11.13 Wedge Left Trial 1 .................................................................................... 61
Figure 11.14 Wedge Left Trial 2 ................................................................................... 61
Figure 11.15 Wedge Right Trial 1 ................................................................................. 62
Figure 11.16 Wedge Right Trial 2 ................................................................................. 62
List of Tables
Table 6.1 Weight of Wedge and Heel ........................................................................... 15
Table 7.1 Results of Blindfold Trial ................................................................................ 20
Table 8.1 Peak pressures of the left foot for both subjects .......................................... 33
Table 8.2 Peak Pressure Recorded ................................................................................ 35
Table 9.1 Weight of shoe .............................................................................................. 39
Table 9.2 Impact forces involved when shoes are dropped ......................................... 40
Table 10.1 Reaction forces acting on the shoe upon impact ........................................ 42
Table of Contents
Chapter 1:
Introduction............................................................................................. 8
1.1
Hypothesis Statement ..................................................................................... 8
1.2
History and Context......................................................................................... 8
1.3
Long and short term effects ............................................................................ 8
1.4
Purpose............................................................................................................ 9
1.5
Problem ........................................................................................................... 9
1.6
Scope ............................................................................................................. 10
Chapter 2:
Literature Review .................................................................................. 11
2.1
Changes in Lumbar Flexion Angle ................................................................. 11
2.2
Increase in Forefoot Pressure ....................................................................... 11
2.3
Intractable Plantar Keratosis ......................................................................... 12
2.4
Stair climbing gait changes ............................................................................ 12
Chapter 3:
3.1
Methodology ......................................................................................... 14
The Shoes ...................................................................................................... 14
3.1.1
High heel................................................................................................ 15
3.1.2
Wedge ................................................................................................... 15
Chapter 4:
Blindfolded Comfort Test ...................................................................... 16
4.1
Aim ................................................................................................................ 16
4.2
Limits ............................................................................................................. 16
4.3
Calculation of sample size ............................................................................. 16
4.4
Calculation of required positives................................................................... 17
4.5
Purpose.......................................................................................................... 17
4.6
Conduct ......................................................................................................... 18
4.6.1
Selection ................................................................................................ 18
4.6.2
Brief and Consent .................................................................................. 18
4.6.3
Personal Particulars ............................................................................... 19
4.7
Results ........................................................................................................... 19
4.8
Graphs ........................................................................................................... 21
4.9
Discussion of results ...................................................................................... 22
4.10
Further Investigation ..................................................................................... 23
Chapter 5:
In-Shoe Pressure Analysis...................................................................... 24
5.1
Aim ................................................................................................................ 24
5.2
Background.................................................................................................... 24
5.3
Conduct ......................................................................................................... 24
5.4
Selection Criteria ........................................................................................... 26
5.5
Data Collection Method ................................................................................ 26
5.6
Results and Discussions ................................................................................. 27
5.6.1
Video Capture Analysis .......................................................................... 30
5.7
Graph Analysis ............................................................................................... 32
5.8
Peak Pressures............................................................................................... 33
5.9
Differences in design and possible explanations .......................................... 35
Chapter 6:
Impact Test ............................................................................................ 39
6.1
Aim ................................................................................................................ 39
6.2
Conduct ......................................................................................................... 39
6.3
Results ........................................................................................................... 39
6.3.1
Impact Graphs. ...................................................................................... 40
Chapter 7:
Analysis .................................................................................................. 41
Chapter 8:
Limitations ............................................................................................. 43
8.1
Limited study done with pressure sensors.................................................... 43
8.2
Gait and foot profile variation ....................................................................... 43
8.3
Minute differences with the shoes ............................................................... 43
Chapter 9:
Conclusion ............................................................................................. 44
Chapter 10:
Recommendations for further work ..................................................... 45
Chapter 11:
Appendices ............................................................................................ 46
Chapter 12:
References ............................................................................................. 63
Chapter 1: Introduction
1.1
Hypothesis Statement
Wedged shoes are supported more uniformly than normal stilleto high heeled
shoes, so they distribute the plantar pressure more uniformly and hence have
a higher comfort rating.
1.2
History and Context
At first sight, wedged shoes (Appendix Fig. 11.1) seem to provide more support
and hence comfort, compared to high heeled shoes (Appendix Fig. 11.2).
Wedged shoes seem more comfortable, but are they? The modern woman
wears high heeled shoes not merely to increase her height. Some don it
because it is a requirement of the office wear; some do it to make their legs
look longer and sexier, yet others wear them because of the posture it forces
the body to adopt, making the body tilt forward, emphasizing the body shape
and contour. High heeled shoes have been around since the middle ages. Ever
since it was popularized by King Louis XIV of France [1], it has been an integral
part of women’s fashion. Although high heeled shoes promotes good posture
to a certain extent, but it has its drawbacks.
1.3
Long and short term effects
Much work has been done on the physiological effects, both short and long
term, on wearing high heeled shoes on flat ground [2]. However, few studies
have analysed the effects of wearing high heeled shoes in ascending and
descending a flight of steps. There are numerous studies on stair ascent and
decent, but these studies are usually done barefooted [3]. There is also a study
that investigates the different muscle used when ascending stairs [4]. This
study concentrates on the muscle groups used during climbing, but not the
plantar pressure exerted on the foot.
1.4
Purpose
It is not merely enough to simply investigate the short and long term effects of
wearing high heeled shoes. The modern society dictates that high heels are a
requirement for women, and there is a need to investigate the comfort of
shoes that serves the function to raise the height of the modern female.
1.5
Problem
There has been much hype about wedged shoes, shoes that purportedly
boasts better comfort for its users. These shoes (Appendix Fig. 11.1) have a
supported midsole, supporting the high heeled shoe from the forefeet to the
heel. Unlike a normal high heel shoe (Appendix Fig. 11.4), the wedge shoe does
not make a point heel contact with the floor. On first inspection, the wedge
shoes look more supported since they have a rigid support from the balls of
the feet (metatarsals heads) all the way to the heel. Au and Goonetilleke [5]
have qualitatively related the effects of plantar pressure and the feeling of
discomfort and pain. However, there is no comprenhensive research relating
the general comfort of the wedge shoes compared to the high heeled shoes of
the same height and sole last.
1.6
Scope
This study will first ascerain whether if there is a significant difference in the
perceived comfort level, between high heel shoes and wedges shoes. It will
then use actual quantifiable pressure data gathered from an in-shoe pressure
measurement system to try and explain and account for any significant
difference, if there are any.
Chapter 2: Literature Review
To further understand the biomechanical interaction between the foot and a
high heeled shoe, some background knowledge is required.
2.1
Changes in Lumbar Flexion Angle
This is the angle that is measured along 3 points of reference on the sagittal
plane of the back. This gives an indication of how arched the back is when
standing in an upright posture and walking. The paper Biomedical effects of
wearing high heel shoes[6] concludes that the angle decreases with an
increase in heel height, making the back more arched and increses
compressive forces on the lower lumbar spine, causing back pain and
discomfort. There is a big change of 1 degree in the lumbar flexion angle for
each 1 cm increase in heel height.
The wearing of high heeled shoes not only causes discomort the the foot
directly contact with the shoes, but also changes other anlges in the body that
also contribute to the discomfort of the shoes.
2.2
Increase in Forefoot Pressure
The wearing of high heeled shoes redistributes the pressure that the foot
experiences when it its standing barefoot on the ground. As the heel is lifted
and the foot is tilted downwards, more pressure is concentrated onto the
metatarsal heads and the hallux. Pressure is shifted from the heels to the
forefoot; and as heel height increases, the peak pressure is shifted to the 1st
metartasal head and the hallux [7].
This shift in peak pressure causes discomfort for first time wearers since they
are not accustomed to having their 1st metartasal heads of the foot bearing
most of the body weight.
2.3
Intractable Plantar Keratosis
Prolonged exposure of the foot to high pressure will cause corns or bunions,
also known as calluses to form. These are formed as a body’s defense to cope
with a higher localised pressure loading. These hard growth are an
accumulation of dead epidermal cells that grows, and these growth causes
pain
to
the
foot
[8].
These
calluses
often
appear
under
the
metatarsophalangeal joint [8], a common problem faced by high heeled users.
High heels also aggrevates the calluses and bunions, exerting pressure and
causing them to grow.
By looking at the peak pressure spots in an in-shoe pressure-management
system these areas which are prone to callus formation can be identified and
discomfort levels can be measured.
2.4
Stair climbing gait changes
The characteristics of the gait patterm changes when a subject walks up a
flight of steps. Firstly, it is noted that there is always initial forefoot contact in
both ascending and desending directions, independent of inclination [3].
Walking on a flat ground would certainly show a typical initial heel strike. This
information is important in determining the comfort of wearing high heel or
wedge shoes while ascending or descending a flight of steps. However, this
data is only for subjects wearing normal shoes, not high heeled ones. There is a
need to investigate the high heeled stair climbing gait, to further explain the
differences in comfort, if any, between the high heeled shoes and the wedged
shoes.
Chapter 3: Methodology
To first understand the pervieved differences in levels of comfort between the
high heeled and wedged shoes, a blindfolded fitting trial was conducted with
25 healthy young females with the 2 different pairs of shoes. Next, another
experiment was conducted with 2 other female subjects, having them ascend
and descend a flight of 4 steps. An in-shoe pressure-management system was
then used to gather the pressure data from the stair climbing motion .
3.1
The Shoes
Both shoes are bought off the shelves from a local shoe boutique. They are
chosen with the help of 2 female subjects having almost similar foot profile
and size. Both subjects are of size 36 (UK) and have a relatively normal arch
with no under or over pronation issues. They were asked to try on both types
of shoes simultaneously, for example, a high heel shoe on the left foot and a
wedge shoe on the right. This fitting is repeated at numerous shops until 2
pairs of shoes with the same heel height and similar internal last are found.
They also have the same insole shape and size so that it will be easier to carry
out the pressure analysis. The shoes are chosen such that they have a similar
topline (Appendix Fig 11.1 to 11.4). They are both black in color and were
found to be of almost the same weight (Table 6.1). The 2 shoes essentially feel
the same, except for the different sole support, namely the single stiletto heel
and the wedged support. For the purpose of this report, these two types of
shoes shall be termed elevated shoes.
Table 6.1 Weight of Wedge and Heel
Wedge
Heel
Left
Right
0.171kg 0.172kg
0.174kg 0.179kg
Weighed using a digital weighing scale, Teraoka Seiko Co. Ltd Japan, model DS-673
3.1.1 High heel
The stiletto styled high heel shoes (Appendix Fig. 11.3) sports a single inverted
pyramidal heel support and it is molded together in the same piece of hard
plastic it has also some form of metal strip that supports the heel internally.
The heels only experience impact loading in the vertical direction but do not
experience any shear force in the horizontal direction. It is black and has a
heel-to-floor height of 6cm. There is minimal cushioning on the insole. The
shoe uppers are made of Polyvinyl Chloride (PVC). For the purpose of this
report, the stiletto styled high heel shoes shall be referred to as “high heels”.
3.1.2 Wedge
These shoes differ from normal high heels in its out sole support. Instead of a
single pointed support at the heel, it has a wedge support that extends from
the front of the shoe all the way to the back. This support is usually made of
hollow plastic, also joined to the outsole of the shoe via means of n adhesive.
This makes the midsole more rigid since there is a wedge that supports the
entire sole. The base of the wedge is in total contact with the ground. Some
other wedge shoes have an arched base, leaving a point contact only at the
heel. This shoe has also a PVC upper, and a minimally cushioned sole. For the
purpose of this report, these shoes will be referred to as “wedges”.
Chapter 4: Blindfolded Comfort
Test
4.1
Aim
To test the hypothesis that wedged shoes are more comfortable than high
heeled shoes.
4.2
Limits
Population group:
Female
University students
Weight between 40 to 60kg
Wears heels not more than 8 times a month
4.3
Calculation of sample size
Let H0 be the statement: There is no difference in perceived comfort between
wedged shoes and high heeled shoes. p=0.5
Let H1 be the statement: Wedged shoes are more comfortable than high
heeled shoes. p>0.5
Confidence interval = 10%
Confidence level = 90%; z score = 1.64
Proportion = 0.90
Then n, sample size;
z 2 ∗ P(1 − P) 1.642 ∗ 0.90(1 − 0.90)
n=
=
= 24.2
I2
0.12
Therefore, a minimum of 25 subjects would be required.
4.4
Calculation of required positives
Using the Pearson’s chi-square test,
2
n
χ =�
i=1
(Oi − Ei )2
Ei
Chi squared equals 4.840 with 1 degree of freedom. The two-tailed P value
equals 0.0278. By conventional criteria, this difference is considered to be
statistically significant. The minimum positive result out of 25 is 18, for the
null hypothesis to be rejected.
4.5
Purpose
The purpose of this experiment is to get an unbiased opinion of comfort on the
plantar pressure distribution. It is then used to find out which shoes, high
heeled or wedged, are more comfortable in comparison to the other.
As pointed out by Au and Goondtilleke [5], there are many facets to a
comfortable pair of high heel shoe. Some of the possible factors that an
individual
considers to
differentiate
a
comfortable
shoe
from
an
uncomfortable one include; internal humidity, styling, colour, sound of the
shoes hitting on the floor, temperature and lastly pain. Pain in the
Metatarsophalangeal region scored the most negative factor when it comes to
rating shoe discomfort. In another paper, the correlation between plantar
pressure and comfort [9] of sports shoes has been shown. This explains the
purpose of studying plantar pressure to access comfort of high heel shoes.
To make sure that other factors will not interfere with the perception of pain
and hence discomfort, a blindfolded fitting would be needed.
4.6
Conduct
4.6.1 Selection
25 female subjects would be randomly chosen, in a non-specific race manner,
from the student pool of the National University of Singapore. They would
have to have a foot size of UK 36 and have no history of ankle or leg injury.
They should also be infrequent wearers of high heel shoes. This is to ensure
that the feet of the test subjects will be more sensitive to discomfort due to
plantar pressure. It is noted that frequent wearers of high heeled shoes have
been desensitized to the sensations of increased pressure to the metatarsals.
4.6.2 Brief and Consent
Subjects will be first informed of the purpose of the experiment and the
conduct. They will be told that they will be testing out the comfort of two
shoes while being blindfolded. They will wear the shoes, one at a time, and
stand up for a total of 2 minutes. In order to eliminate experimenter bias, the
shoes will be placed in a bag, and randomly picked for the first pair of shoes
that will be tried on. Subjects will be allowed to walk on the spot and arch and
flex the feet with the shoes on. The subjects will be prompted to concentrate
on the sensations of pain the plantar surface of the foot. They will then sit
down and give a comfort rating on a scale of 1 to 10. The ends of the spectrum
were; 10 being the “most comfortable condition imaginable” and 1 being the
“least comfortable condition imaginable”.
They will be also be given the full freedom of choice to choose whether to
participate or refuse participation in the study. All subjects will make an
informed voluntary decision to take part in this study.
4.6.3 Personal Particulars
Details pertinent to this study will be noted down before the experiment is
carried out. The details are shown in the table below (Table 7.1). Only 4 details
will be written down by the subject; name, age, average frequency of wearing
high heels in a month and mass. They would not be told of the differences in
the shoes that will be fitted.
4.7
Results
A total of 25 female subjects participated in the survey. The subjects’ age
ranged from 19 to 24 years old, mean of 21.4 years old with standard deviation
(SD) of 1.44 years; their mass ranged from 42 to 48kg, with a mean of 49.4kg
and SD of 5.1kg. All of the subjects wore high heels 8 or less times in a month.
There were 19 subjects giving a higher score of comfort for wedges shoes, and
only 6 subjects giving a higher rating for high heeled shoes. The mean rating
for high heel shoe and wedges were 5.6 and 6.6 respectively. This exceeds the
minimum positive result of 18 to prove the null hypothesis “There is no
difference in perceived comfort between wedged shoes and high heeled
shoes” false. The results show that there is a significant difference in the
comfort of wedges shoes, based on sensations of the foot alone.
Table 7.1 Results of Blindfold Trial
Comfort Rating / 10
Subject
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Min
Max
Age
22
24
23
22
22
21
22
23
20
20
20
24
20
21
22
20
19
20
23
23
20
20
22
21
20
19.0
24.0
Freq
Weight
High
/
Mass (kg)
(N)
Heels
mth
4
52
510
1
47
461
1
58
569
0
42
412
2
50
491
6
44
432
2
48
471
2
43
422
3
58
569
4
58
569
2
49
481
0
49
481
3
45
441
4
50
491
0
50
491
8
43
422
1
52
510
0
44
432
2
55
540
1
45
441
0
50
491
8
42
412
0
53
520
3
56
549
2
52
510
0.0
8.0
42.0
58.0
412.0
569.0
Wedges
5
6
7
3
3
7
3
5
4
6
8
6
10
6
7
7
3
7
5
8
4
8
5
5
3
7
8
5
7
5
6
5
6
6
7
9
7
9
8
8
6
5
8
6
6
6
9
4
6
6
3.0
10.0
4.0
9.0
Mean
Std Dev
4.8
21.4
1.4
2.4
2.3
49.4
5.1
484.6
50.2
5.6
1.9
6.6
1.4
Graphs
Preference Distribution
Foot Type
High Arch
Normal Arch
Wedges
High Heels
Flat Foot
0
5
10
15
20
Number of subjects
Figure 4.1 Comfort preferences of the different foot shapes
Frequency of Comfort Ratings
Comfort Rating
10
8
6
4
Wedges
2
High Heels
0
0
2
4
6
Number of subjects
Figure 4.2 Distribution of comfort rating scores
8
10
4.9
Discussion of results
Several observations were made from the results as well as individual
interviews with the subjects.
1.
Subjects having flat foot commented on the support the wedge shoes
gave in comparison to the high heeled one. Subjects with normal or high
arched foot could not tell the difference between the ‘mid sole support’. They
could not distinguish the wedges from the high heels.
This point might be valid since subjects who have normal to high arched feet
might not have contact with the shoe in the mid sole plantar area.
2.
Only 2 subjects claim that high heels are “naturally” more comfortable,
citing that the high heeled shoe provides for more balance.
This pair of high heeled shoes is more flexible in torsion since there is no rigid
support throughout the base of the shoe.
3.
Subjects claim that wedge shoes are more comfortable, but their claims
did not meet the blindfolded test result.
This test was well rigged and carried out, not allowing preconceived
misjudgments to interfere with the experiment conduct.
4.
4 subjects felt that the pressure on the 1st metatarsal head was lower in
the wedges compared to the high heeled shoe. They also say that the toes
experience higher pressure when wearing high heels.
This re-iterates the point that discomfort is governed by the pain generated
when the metatarsal heads or toes undergo higher than normal pressure.
5.
3 subjects claim that heels were more stable and 3 subjects claim that
wedges are more stable.
This could possibly show that stability cannot be judged and differentiated just
by a 2 minute standing test.
4.10 Further Investigation
Several points brought up in the above discussion needs to be looked into. The
sensations of “lower” or “more evenly distributed” pressure needs to be
quantified and explained. Also, the contact area of the mid sole needs to be
qualitatively identified and measured to support or refute claims made by
subjects regarding the ability to feel the midsole support.
An in-shoe pressure-management system would be a suitable system to look
into the plantar pressure in the shoe.
Chapter 5: In-Shoe Pressure
Analysis
5.1
Aim
To explain the higher comfort rating given to wedged shoes in comparison to
high heeled shoes.
5.2
Background
Many studies have already been conducted to study the effects of wearing
high heel shoes and walking on flat ground. They have found that there is a
shorter stride length, higher forefoot pressure [7] amongst other observations.
However, there is only one paper that discusses the use of high heel shoes on
ascending and descending stairs. It only focuses on the differences in the
activity of the muscles in the lower limb, with and without heel contact,
proposing that heel contact is better. There is no paper that discusses the
differences in plantar pressure observed when using a high heeled and a
wedged shoe.
5.3
Conduct
Using plantar pressure as a basis to quantify the sensations of discomfort, an
experiment was designed to investigate the relationship between localized
pressure and discomfort. The contact pressures at specific areas of interest of
the foot were collected and analyzed.
The subjects were asked to walk up and down a flight of 4 steps with an
inclination of 36.5°, each step measuring 0.20m in rise and 0.27m in run
(Appendix Fig 11.6). The F-Scan ® System by Tekscan was used together with
the Tekscan 3000 sensor (Appendix Fig 11.5) to collect data of the pressures
that the foot exerts on the shoe during stair ascent and descent. The sampling
rate was set to 100Hz since the subjects walked up the stairs, taking on
average 1s per step, making 100Hz in the range for capturing the required
changes in pressure
Three trials were done with each subject. The first was with a sock to hold the
sensors in place to simulate bare feet walking. The second was done with a
high heeled shoe that has a heel height of 6cm. The height of the heel was
measured via the perpendicular distance from point at the end of the shoe to
the ground. The third was a wedge shoe with exactly the same last as the
normal high heeled shoes, with exactly the same heel height of 6cm. the
subjects were told to walk normally at a pace they were comfortable with.
Both subjects ascended and descended with their whole foot on the steps, for
all 3 tests.
After each trial, the subjects were asked to identify which area(s) of the foot
experienced the most discomfort. They were asked to highlight the area(s) of
discomfort separately for ascending and descending. They were then asked to
rate the overall level of comfort of walking barefooted, with normal heels and
wedged shoes. A video recording was also taken to correlate the actual gait to
the pressure readings.
5.4
Selection Criteria
2 healthy females with no prior musculoskeletal injuries were selected to
perform this experiment. Both of them have normal arch. Both of them wore
high heeled shoes for 1 day in a month or less. Subjects that are infrequently
exposed to high heels have been selected for this trial so that there are no
changes to the normal biomechanical structure of their feet and their gait.
Also, they would be more sensitive to high pressure areas that the feet
experiences, as opposed to frequent high heeled shoe wearers, who have
become desensitized to the pain that the high heeled shoes cause. This is due
to possible adaptation of their foot, forming calluses to adapt to the higher
pressure loading [8].
5.5
Data Collection Method
The data that was logged from the pressure sensors was then segmented into
4 portions; the Hallux, the 1st metatarsal head, the 2nd to the 5th metatarsal
heads and the heel. The 2nd to the 5th metatarsal heads were not segmented
separately as they were difficult to distinguish from each other, and the
sensations of discomfort in the 2nd to the 5th metatarsal heads were always
group together. The midsole was also not studied in detail as they were found
to have very little contact with the sole of the shoe, and hence insignificant
readings (Fig 5.2, 5.3,5.5, 5.6). Each area of interest was selected in the
Tekscan F-scan system via a 4X4 pixel box, the pixel size corresponding to the
density of the pressure sensors on the pressure pads.
5.6
Results and Discussions
Subject 1 was found to be weighing 51.92kg and subject 2 weighed 42.96kg
when loaded with the pressure sensing apparatus. In general, they found
wedges to be more comfortable compared to heels. Preliminary findings
indicate that the perception of discomfort is directly linked with the area of
highest pressure reflected in the data measured by the pressure sensors.
When the 2 subjects were asked to mark down the area of discomfort on the
sole on a footprint diagram, it mapped out quite accurately the area of highest
pressure. The pressure mappings are taken from the Tekscan system. It shows
the peak pressure recorded during the entire phase of the stair climb.
Figure 5.1 Subject 1 Barefoot
Figure 5.2 Subject 1 Heels
Figure 5.3 Subject 1 Wedges
Figure 5.4 Subject 2 Barefoot
Figure 5.5 Subject 2 Heels
Figure 5.6 Subject 2 Wedges
5.6.1 Video Capture Analysis
From the analysis of the video capture, it is observed that for the barefoot
trial, both subjects land on their metatarsals first, followed by the heel. The toe
off is also similar in both subjects.
5.6.1a) Barefoot
(a)
(b)
(c)
(d)
Figure 5.7 Video captures for subject 1 on first contact (a,b) Ascending (c,d)
Descending
(a)
(b)
(c)
(d)
Figure 5.8 Video captures for subject 1 on first contact followed by toe off of
the same foot. Ascending (a,b),Descending (c,d)
This would form the basis of analysis for the high heeled shoe and wedged
shoe. On preliminary analysis, the readings from the pressure sensors show
that the hallux and the metatarsal heads experience a peak in plantar pressure
when the foot is in the toe off position.
5.6.1b) High heeled shoes
(a)
(b)
(c)
(d)
Figure 5.9 Video captures for subject 1 on first contact followed by toe off of
the same foot Ascending (a,b),Descending (c,d)
(a)
(b)
(c)
(d)
Figure 5.10 Video captures for subject 2 on first contact followed by toe off of
the same foot Ascending (a,b),Descending (c,d)
The high heeled stair climbing gait is somewhat different from the barefoot
gait as the heel strikes the ground first followed by the forefoot. However,
looking at the pressure analysis, the forefoot still experiences more pressure
than the heel, contrary to intuitive inspection.
5.6.1c) Wedged shoes
Figure 5.11 Video captures for subject 1 on first contact followed by toe off of
the same foot Ascending (a,b),Descending (c,d)
Figure 5.12 Video captures for subject 2 on first contact followed by toe off of
the same foot Ascending (a,b),Descending (c,d)
The wedge shoes gait is also similar to the high heeled gait in that the heel
strikes the ground first before the forefoot.
5.7
Graph Analysis
To further analyze the pressure values measured, graphs were plotted using
the data collected from the in-shoe pressure pads. The summation of the total
pressure at any point in time was also plotted together with the individual
pressure values at the 4 specified areas; namely the hallux, the first metatarsal
head, the 2nd to the 5th metatarsal heads and the heel.
5.8
Peak Pressures
The plantar pressure distribution on the barefoot takes a different profile
when it is compared with the heels. Several observations are made.
1. The sums of all the pressures have 2 separate peaks in both cases. The
first peak is always lower that the second peak in both the barefoot and
the heel profile on the ascending phase in both subjects.
This illustrates that more pressure is exerted on the forefoot when the
foot pushes off.
2. However, the difference in the peak varies. Typically, the difference in
peak pressure is greater for the high heels than for the barefoot.
Analysing the data from the left foot of the subjects, the differences are
as follows.
Table 8.1 Peak pressures of the left foot for both subjects
Subject 1
Ascending
Descending
Barefoot
1st
2nd
Peak Peak
(kPa) (kPa)
227
241
305
341
Subject 2
Ascending
Descending
192
348
264
281
14
36
Heels
1st
2nd
Peak Peak
(kPa) (kPa)
266
394
324
408
72
67
268
328
∆
(kPa)
405
225
128
84
Wedges
1st
2nd
Peak Peak
(kPa) (kPa)
266
392
312
321
137
103
252
339
∆
(kPa)
372
310
∆
(kPa)
126
9
120
29
It is observed that the highest difference in peak pressures comes from
the heels. This could explain the initial hypothesis of wedges being
more comfortable than high heels as lesser pressure is exerted on the
hallux and the metatarsal heads when the foot leaves the steps. It is
even more evident on the descending phase. The differences are 84
kPa on the heels and 9 kPa on the wedges. A greater difference in
pressure means that there is unequal distribution of weight on the
plantar surface, hence a more uncomfortable walking phase.
Taking a look at the pressure graphs for the wedge shoes (Appendix
11.5 to 11.6), it is evident that ∆, the difference in pressures are lower
compared to the barefoot trial. It would support the feedback gathered from
the blindfolded fitting experiment, that wedge shoes in fact distribute
pressure more evenly over the gait cycle.
3. The 2nd peak value, which is mainly due to forefoot contact, is generally
higher in the heels than compared to the wedges. In subject 1 for the
descending phase, a reading of 408 kPa compared to 321 kPa for the
wedges. As discussed earlier, higher plantar pressure directly translates
to perceiving the heels as uncomfortable, in addition to higher chances
of callus formation.
4. When analyzing the individual peak pressures of the 4 specified areas,
the first metatarsal head experiences the most pressure when wearing
elevated shoes. This is consistent with findings illustrated in a journal
[7] where the peak pressure exerted on the foot moves towards the 1st
metartasal head with increasing heel height. The minor differences in
area where the highest pressures was recorded could be attributed to
the different gait kinetics that the individual subject posses. It is also
noted that the peak pressures exerted is generally lowest compared to
heels and barefoot. It further emphasises the hypothesis that wedges
distributes weight more evenly throughout the stair climbing gait cycle,
making wedges more comfortable.
This quantifies the observation made from the blindfold test where test
subjects said that they felt lesser pressure on the 1st metartasal head
when wearing wedges.
Table 8.2 Peak Pressure Recorded
Subject 1
Barefoot
Max
Heels Max
Wedges
Max
Subject 2
Barefoot
Max
Heels Max
Wedges
Max
5.9
Region
Left
Pressure
(kPa)
Right
Region Pressure
(kPa)
2-5M
1M
170
178
Toe
2-5M
210
202
1M
162
1M
193
Toe
1M
161
194
Toe
1M
268
197
Toe
150
1M
322
Differences in design and possible explanations
The differences in design could provide possible explanations as to why
wedges seem to be better at spreading out pressure as compared to heels.
1. Wedges have a very rigid mid-sole support, that transfered the load to
the feet evenly. At first impact, the impulse is translated to all the other
parts at the same time, as shown in the 2 figures below. These are
taken from the left foot of subject 1 on the ascending phase.
Wedge Left Ascending
200
P, KPa
150
Toe
100
1M
50
2-5M
0
Heel
-50
4.7
5.2
5.7
6.2
6.7
t
Figure 5.13 Subject 1 Wedge
Heel Left Ascending
150
P, KPa
100
toe
1M
50
2-5M
0
4.3
4.8
-50
5.3
5.8
heel
t
Figure 5.14 Subject 1 Heel
It is clear that the curve of all the individual pressures in the wedge
follows a similar patern, reaching their individual first peak pressure at
approximately the same time. It is evident from the initial increase in
pressure to around t=5.2s, where the gradient of the curves are very
similar. While for the heel, the lines tend to diverge at the start, proving
that the heel is indeed not so adapt at distributing the pressure evenly.
The wedge shoe distributes more pressure to the heel, where lower
pressure is experienced. This in turn reduces pressure on the other
areas of the foot.
2. This also illustrates the qualitative feedback that is gathered from the
blindfolded trial where subjects claim that heels are more stable
because the front and the heel of the heels can flex and bend
independently. This is largely due to the less ridgid midsole of the heels
which accounts for the lower torsional stiffness of the shoe. This lower
torsional stiffness allows more torsional force to be exerted by the foot
when balencing, for example when only the heel stub misses a footing.
On the other hand, wedges having a more ridgid midsole and thus a
higher torsional stiffness, will impede any effort made by the foot to
right a footing once the heel area of the wedge starts to tilt, causing an
inversion ankle sprain.
The stability of the shoes is another possible factor that might affect
the comfort rating of the shoes.
3. As mentioned earlier, the 2 types of elevated shoes alters the normal
gait kinetics of the stair ascending and descending motion. Both the
shoes prevent the heel from lowering down to the same level as the
forefoot (Fig. 5.1 (c) & 5.2 (b) ). This reduces the need for the lowering
of the heel at first contact and subsequent raising before the toe off.
The shoes keep the foot in the ‘midway position’ instead of letting the
heel come in contact with the stairs.
4. The human foot, when elevated by the heel, forms an arch under the
midsole. This explains the lack of contact at the midsole, between the
plantar surface and the shoe. This refutes claims made by the subjects
in the previous trial, claiming that they can feel the mid sole support of
the wedges.
Chapter 6: Impact Test
6.1
Aim
To find out if there were significant impact forces affecting the pressure
readings of the pressure sensors
6.2
Conduct
Each shoe was weighed, using the digital weighing scale (Model DS-673,
Teraoka Seiko Co. Ltd Japan). The individual shoes were then attached with a
transducer (Type 4371, Brüel & Kjær, Nærum Denmark) to measure its
acceleration upon impact with the floor. This transducer was then wired up to
an oscilloscope that logged the voltage output from the transducer. The
sensitivity at the data logger was set at 0.316mV per 1m/s2 and the upper and
lower sensitivity limit of the oscilloscope was set at 2Hz and 3kHz respectively.
These limits were tuned during the experiment to eliminate the noise that was
generated from the accelerometer. The data points from the oscilloscope were
saved and recorded in an excel file.
6.3
Results
Table 9.1 Weight of shoe
Item
Tekscan 3000 Pressure Sensor (Left)
Tekscan 3000 Pressure Sensor (Right)
Wedge shoes (Left)
Wedge shoes (Right)
High heel shoes (Left)
High heel shoes (Right)
6.3.1
Weight (kg)
0.014
0.017
0.171
0.172
0.179
0.174
6.3.2 Impact Graphs.
The Acceleration vs Time graphs of the impact was plotted (Appendix Fig. 11.9
-11.16). The downward direction is taken to be negative.The shoes were
originally at a height of 0.3m and released midway in the recording period of
the oscilloscope. It is observed that the acceleration increased when released
and then took a sudden spike upon contact. The spike is in the negative
direction as the shoe experiences a sudden acceleration in the upward
direction to bring the shoe to a halt.
These are the data for the highest acceleration values and forces with the
respective shoes. The acceleration measured is the record of the negative
acceleration from the graphs. This acceleration is the amount of acceleration
the shoes experiences to stop it from going through the ground.
Table 9.2 Impact forces involved when shoes are dropped
Trial
Heels Left Trial 1
Heels Left Trial 2
Heels Right Trial 1
Heels Right Trial 2
Wedge Left Trial 1
Wedge Left Trial 2
Wedge Right Trial
1
Wedge Right Trial
2
Weight (kg)
0.179
0.174
0.171
0.172
Amplitude of Max
Acceleration (m/s2)
5.585
2.748
2.385
0.246
2.030
3.322
3.735
3.735
Force (N)
1.000
0.492
0.415
0.043
0.347
0.568
0.642
0.642
Chapter 7: Analysis
From the results obtained above, a simple model could be used to study the
forces that might play a part in affecting the results of the pressure readings
taken by the Tekscan pressure sensor.
Rground
ma
mg
Figure 7.1 Free body diagram upon impact
Drawing a free body diagram of the shoe upon impact, there are 2 evident
forces acting on the shoes. With the equation
Rground – mg = ma
Rground = ma - mg
Substituting the relevant data from table 2, the following Rground were obtained.
Table 10.1 Reaction forces acting on the shoe upon impact
Trial
Heels Left Trial
1
Heels Left Trial
2
Heels Right
Trial 1
Heels Right
Trial 2
Wedge Left
Trial 1
Wedge Left
Trial 2
Wedge Right
Trial 1
Wedge Right
Trial 2
Weight (kg)
0.179
Amplitude of Max
Acceleration
(m/s2)
5.585
Force (N)
Rground (N)
1.000
1.577
2.748
0.492
1.668
0.174
2.385
0.415
0.246
0.043
2.030
0.347
3.322
0.568
3.735
0.642
1.635
1.699
0.171
1.618
1.580
0.172
1.577
3.735
0.642
1.577
Chapter 8: Limitations
8.1
Limited study done with pressure sensors
As the experiment with the in-sole pressure sensors were done with the
goodwill of the DSO lab, a full scale test could not be carried out due to the
lack of funds to purchase or loan the entire system. Hence the experiment was
only limited to 2 female subjects who were of normal arched foot profile.
However, the 6 trials made it possible to qualify some of the feedback raised
about the plantar pressure during the blindfold fitting trial.
8.2
Gait and foot profile variation
It was difficult to quantitatively compare the results obtained as each step the
subjects took on the steps varied from each other. The first and last steps were
always different from the ones in the middle. A very long flight of steps might
have more consistent results.
8.3
Minute differences with the shoes
Although the selection of the shoes was as stringent as possible, it was difficult
to find actual off the rack shoes which only differed from each other by the
variation of the heel type.
Moreover, the shoes were reasonably similar as blindfolded subjects could not
tell the difference between the shoes whilst blindfolded.
Chapter 9: Conclusion
This study investigates the relationship between perceived comfort and actual
plantar measurements. It has made the following conclusions based on results
obtained from the 3 conducted experiments.
An unbiased preference of wedges over heels in 25 university going female
individuals.
A normal healthy individual can feel pain as a result of higher pressure loading
on specific areas of the plantar surface of the foot.
The peak pressure experienced by the 1st metatarsal head is lower in wedges
than in heels.
Wedges are more comfortable due to the ability of the rigid sole to distribute
pressure and hence lowering the peak pressure experienced at the 1st
metatarsal heads. It is contary to popular belief that the wedges support the
midsole.
Chapter 10: Recommendations
for further work
Due to the time and facilities constraint, the authour was unable to complete
the following to further substantiate the results obtained. These include:
A full population study of the plantar pressures involved in the stair ascending
and descending motion.
Finite Element Analysis on the shoe foot interaction to verify that the heels
does indeed deform under pressure and is unable to provide a ridgid support
to the foot.
A custom made pair of wedges and high heeled shoes that is exactly the same
except fot the sole support.
Chapter 11: Appendices
Figure 11.1 A Pair of Wedged Shoes
Figure 11.2 Side profile of the right wedge
Figure 11.3 A pair of Heels
Figure 11.4 Side profile of Heels
Figure 11.5 Tekscan 3000 pressure sensors
Figure 11.6 Experimental Setup
Heels
500
Pressure kPa
400
300
LEFT
200
RIGHT
100
0
-100
0
500
1000
1500
2000
2500
Time
Wedge
600
Pressure kPa
500
400
300
Left
200
Right
100
0
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
2500
2600
-100 0 1002003004005006007008009001000
Time
Barefoot
600
Pressire kPa
500
400
300
LEFT
200
RIGHT
100
0
-100 0
500
1000
1500
2000
Time
Figure 11.7 Graph of Summed Pressure vs. time for different footwear for
subject 1
2500
Pressure kPa
Heel Left Ascending
500
450
400
350
300
250
200
150
100
50
0
-50 2
TOE
1M
2-5M
HEEL
SUM
3
4
5
6
7
8
Time
Pressure kPa
Wedge Left Ascending
450
400
350
300
250
200
150
100
50
0
-50 3
TOE
1M
2-5M
HEEL
SUM
4
5
6
7
8
9
Time
Barefoot Left Ascending
500
Pressire kPa
400
Toe
300
1M
200
2-5M
100
Heel
0
SUM
-100
2
3
4
5
Time
6
7
8
Heels Right Ascending
500
Pressure kPa
400
TOE
300
1M
200
2-5M
HEEL
100
SUM
0
-100
2
3
4
5
6
7
8
Time
Wedge Right Ascending
600
Pressure kPa
500
400
TOE
300
1M
200
2-5M
100
HEEL
0
-100 4
5
6
7
8
9
SUM
Time
Right Barefoot Ascending
600
Pressire kPa
500
400
Toe
300
1M
200
2-5M
Heel
100
Sum
0
-100
3.5
4
4.5
5
Time
5.5
6
6.5
Heel Left Descending
500
Pressure kPa
400
TOE
300
1M
200
2-5M
100
HEEL
0
SUM
-100
13
15
17
19
21
Time
Pressure kPa
Wedge Left Descending
450
400
350
300
250
200
150
100
50
0
-50 16
TOE
1M
2-5M
HEEL
SUM
17
18
19
20
21
22
23
Time
Barefoot Left Descending
500
Pressire kPa
400
Toe
300
1M
200
2-5M
100
Heel
0
SUM
-100
15
16
17
Time
18
19
Pressure kPa
Heel Right Descending
450
400
350
300
250
200
150
100
50
0
-50 15
TOE
1M
2-5M
HEEL
SUM
16
17
18
19
20
21
Time
Wedge Right Descending
600
Pressure kPa
500
400
TOE
300
1M
200
2-5M
100
HEEL
0
-100 16
17
18
19
20
21
22
23
SUM
Time
Right Barefoot Descending
600
Pressire kPa
500
400
Toe
300
1M
200
2-5M
100
Heel
0
-100 14
15
16
17
Time
18
19
SUM
Heels
500
Pressure kPa
400
300
Left
200
Right
100
0
-100
0
500
1000
1500
2000
Time
Wedge
700
Pressure kPa
600
500
400
300
LEFT
200
RIGHT
100
0
0
500
1000
Time
1500
2000
Barefoot
700
600
Pressure kPa
500
400
300
LEFT
200
RIGHT
100
0
-100 0
500
1000
1500
2000
Time
Figure 11.8 Graphs for subject 2
Heels Left Ascending
500
Pressure kPa
400
TOE
300
1M
200
2-5M
100
HEEL
0
SUM
-100
1
2
3
4
5
Time
Heels Right Ascending
500
Pressure kPa
400
TOE
300
1M
200
2-5M
100
HEEL
0
SUM
-100
2
2.5
3
3.5
Time
4
4.5
5
Wedge Left Ascending
500
Pressure kPa
400
TOE
300
1M
200
2-5M
100
HEEL
0
SUM
-100
2
2.5
3
3.5
4
4.5
5
Time
Wedge Right Ascending
700
600
Pressure kPa
500
TOE
400
1M
300
2-5M
200
100
HEEL
0
SUM
-100 1
2
3
Time
4
5
Barefoot Left Ascending
300
Pressure kPa
250
200
TOE
150
1M
100
2-5M
50
HEEL
SUM
0
-50 2.2
3.2
4.2
5.2
Time
Barefoot Right Ascending
700
600
Pressure kPa
500
TOE
400
1M
300
2-5M
200
HEEL
100
SUM
0
-100 2.2
3.2
4.2
Time
5.2
Pressure kPa
Heels Left Descending
450
400
350
300
250
200
150
100
50
0
-50 13
TOE
1M
2-5M
HEEL
SUM
14
15
16
17
Time
Pressure kPa
Heels Right Descending
450
400
350
300
250
200
150
100
50
0
-50 13
TOE
1M
2-5M
HEEL
SUM
14
15
16
17
Time
Pressure kPa
Wedge Left Descending
450
400
350
300
250
200
150
100
50
0
-50 13
TOE
1M
2-5M
HEEL
SUM
14
15
Time
16
17
Wedge Right Descending
500
Pressure kPa
400
TOE
300
1M
200
2-5M
100
HEEL
SUM
0
-100
13
14
15
16
17
Time
Barefoot Left Descending
400
350
Pressure kPa
300
250
TOE
200
1M
150
2-5M
100
HEEL
50
SUM
0
-50 12.5
13.5
14.5
15.5
Time
Barefoot Right Descending
700
600
Pressure kPa
500
TOE
400
1M
300
2-5M
200
HEEL
100
SUM
0
-100 12.5
13.5
14.5
Time
15.5
2
0
-2
0
1000
2000
3000
-4
-6
Figure 11.9 Heel Left Trial 1
1
0
-1
0
1000
2000
3000
-2
-3
Figure 11.10 Heel Left Trial 2
1.000
0.000
-1.000 0
1000
2000
-2.000
-3.000
Figure 11.11 Heel Right Trial 1
3000
0.1
0.05
0
-0.05 0
-0.1
-0.15
-0.2
-0.25
-0.3
1000
2000
3000
Figure 11.12 Heel Right Trial 2
1
0.5
0
-0.5 0
1000
2000
3000
-1
-1.5
-2
-2.5
Figure 11.13 Wedge Left Trial 1
2
1
0
-1 0
1000
2000
-2
-3
-4
Figure 11.14 Wedge Left Trial 2
3000
2
1
0
-1 0
1000
2000
3000
-2
-3
-4
-5
Figure 11.15 Wedge Right Trial 1
2
1
0
-1 0
1000
2000
-2
-3
-4
-5
Figure 11.16 Wedge Right Trial 2
3000
Chapter 12: References
1.
2.
3.
4.
5.
6.
7.
8.
9.
Linder, M. and C.L. Saltzman, A history of medical scientists on high heels.
International Journal of Health Services, 1998. 28(2): p. 201-225.
Lee, Y.H. and W.H. Hong, Effects of shoe inserts and heel height on foot
pressure, impact force, and perceived comfort during walking. Applied
Ergonomics, 2005. 36(3): p. 355-362.
Riener, R., M. Rabuffetti, and C. Frigo, Stair ascent and descent at different
inclinations. Gait & Posture, 2002. 15(1): p. 32-44.
Yoon, J.Y., et al., Differences in activities of the lower extremity muscles with
and without heel contact during stair ascent by young women wearing highheeled shoes. Journal of Orthopaedic Science, 2009. 14(4): p. 418-422.
Au, E.Y.L. and R.S. Goonetilleke, A qualitative study on the comfort and fit of
ladies' dress shoes. Applied Ergonomics, 2007. 38(6): p. 687-696.
Lee, C.M., E.H. Jeong, and A. Freivalds, Biomechanical effects of wearing highheeled shoes. International Journal of Industrial Ergonomics, 2001. 28(6): p.
321-326.
Mandato, M.G. and E. Nester, The effects of increasing heel height on forefoot
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