The influence of variations in shoe midsole density on the impact

Transcription

The University of Toledo
The University of Toledo Digital Repository
Theses and Dissertations
2004
The influence of variations in shoe midsole density
on the impact force and kinematics of landing in
female volleyball players
Karen J. Nolan
Follow this and additional works at: http://utdr.utoledo.edu/theses-dissertations
Recommended Citation
Nolan, Karen J., "The influence of variations in shoe midsole density on the impact force and kinematics of landing in female volleyball
players" (2004). Theses and Dissertations. Paper 1528.
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An Abstract of
The influence of variations in shoe midsole density on the impact force and
kinematics of landing in female volleyball players
Karen J. Nolan
Submitted as partial fulfillment of the requirements for
the Doctor of Philosophy in
Exercise Science
May 2004
The purpose of this study was to examine the effect of changing the
midsole density of athletic shoes on impact forces upon landing during a nonrhythmic athletic activity. Previous studies showed that changing the density of
the midsole had neither a positive or negative effects on running, which is a
repetitive rhythmic athletic activity. This investigation examined the influence of
variations in athletic shoe midsole density on vertical ground reaction forces,
loading rates, peak joint moments, and examined which specific kinematic
variables were affected upon landing after a non-rhythmic vertical jump. Subjects
included 20 female, NCAA volleyball athletes (21.1 ± 2.84 years). Each subject
was tested in three different athletic shoe conditions: control midsole, soft
iii
midsole, and hard midsole. For each of the athletic shoe midsole conditions, the
subjects performed 10 volleyball approaches and spike jumps; landing onto two
force platforms to measure impact forces. Kinematic data was collected
simultaneously with the kinetic data using a six camera Motion Analysis system.
Data was collected for each subject for a total of 30 trials (10 trials X 3 midsole
conditions). A one-way repeated measures analysis of variance was used to
compare the three different shoe conditions (significance at α = .05). Results
indicated that variations in midsole density do not significantly affect impact
forces or loading rates upon landing. Kinematic variables failed to sufficiently
explain this result. It is possible that athletes may use neuromuscular adaptations
to account for changes in midsole density during impact. More research is
needed to determine if changes in muscle activity are used as a possible strategy
during landing to affect impact forces. Further research is needed on the effects
of athletic shoe midsole density during landings from non-rhythmic athletic
activities.
iv
Dedication
This dissertation is dedicated to all those who helped me along the way to
achieve my goals.
v
Acknowledgements
The completion of this dissertation would not have been possible without
the support, assistance and guidance of many people. I would like to first thank
my dissertation committee: Charles W. Armstrong, Ph.D., Richard A. Yeasting,
Ph.D., and Phillip A. Gribble, Ph.D., ATC-L.
I am extremely grateful that Charles W. Armstrong, Ph.D., has been my
advisor during my entire course of study at the University of Toledo. I sincerely
appreciate all of the challenges and opportunities he provided. I would like to
thank him for his optimistic support and confidence in my abilities. I am most
grateful to have had Dr Armstrong as a mentor.
I would like to thank Richard A. Yeasting, Ph.D., for serving on my
dissertation committee and being a supportive reviewer of my research. I would
like to further thank him for providing me a thorough knowledge of anatomy and
challenging me to think beyond the obvious. I consider myself lucky to have had
such a competent professor in my minor field of study, anatomy.
I would like to thank Phillip A. Gribble, Ph.D., ATC-L for serving on my
committee and being an interested and enthusiastic reviewer of my dissertation.
He was generous with his time, knowledge, and provided a careful analysis of my
study.
I would like to acknowledge the generous support of Fila USA for
providing the prototype athletic shoes designed for this investigation. I would like
to extend a very special thank you to Craig Wojcieszak, Director of Advanced
vi
Research and Product Testing, Fila USA, who showed enough interest in my
initial research to allow this project to get started. I would further like to thank him
for his dedication to this project and his contributions along the way.
I would to thank Bruce Kwiatkowski, M.A. for the generous use of his time
providing technical support. I would also like to thank Donald B. White, Ph.D. for
all of his assistance and statistical support.
I appreciate the cooperation of Coach Kent Miller and the Women’s
Volleyball Team from the University of Toledo, and Coach Kim Berrington and
the Women’s Volleyball Team from Eastern Michigan University. The athletes
from both teams provided me with excellent and cooperative subjects for this
investigation. It was a pleasure to work with both teams.
I am especially grateful for the never ending support and encouragement
from my family. I would especially like to acknowledge my husband John for his
constant support while I pursued my degree.
vii
Table of Contents
Abstract ........................................................................................................ iii
Dedication .................................................................................................... v
Acknowledgments ........................................................................................ vi
Table of Contents .........................................................................................viii
List of Tables ................................................................................................ ix
List of Figures ............................................................................................... xii
I.
Introduction ............................................................................. 1
II.
Review of Literature ................................................................ 9
III.
Methodology ..........................................................................50
IV.
Results ....................................................................................66
V.
Discussion............................................................................ 105
VI.
References........................................................................... 119
VII.
Appendix A........................................................................... 126
VIII.
Appendix B........................................................................... 129
IX.
Appendix C .......................................................................... 131
X.
Appendix D .......................................................................... 133
XI.
Appendix E........................................................................... 135
XII.
Appendix F ........................................................................... 137
XIII.
Appendix G .......................................................................... 139
XIV.
Appendix H .......................................................................... 141
XV.
Appendix I ............................................................................ 143
XVI.
Appendix J ........................................................................... 146
List of Tables
Page
Table 1.
Anthropometric Data of Subjects
58
Table 2.
Means and Standard Deviations: Peak Vertical Ground
Reaction Forces
71
Statistical Summary of Athletic Shoe Midsole Density on
Left and Right Peak Vertical Ground Reaction Force
71
Table 3.
Table 4.
Means and Standard Deviations: Total Peak Vertical Ground
Reaction Forces
72
Table 5.
Statistical Summary of Athletic Shoe Midsole Density on Total
Peak Vertical Ground Reaction Force
72
Table 6.
Means and Standard Deviations: Left and Right Peak Vertical
Ground Reaction Force
73
Table 7.
Means and Standard Deviations: Total Peak Vertical Ground
Reaction Forces
74
Table 8.
Means and Standard Deviations: Loading Rate
Table 9.
Statistical Summary of Athletic Shoe Midsole Density on Left
and Right Loading Rate
75
Table 10.
Means and Standard Deviations: Peak Ankle Joint Moments
Table 11.
and Right Peak Ankle Joint Moments
76
Table 12.
Means and Standard Deviations: Peak Knee Joint Moments
Table 13.
and Right Peak Knee Joint Moments
77
Table 14.
Means and Standard Deviations: Peak Hip Joint Moments
Table 15.
and Right Peak Hip Joint Moments
78
Table 16.
Means and Standard Deviations: Ankle Position at Initial
Contact with the Ground
ix
75
76
77
78
84
Table 17.
Table 18.
Table 19.
Table 20.
Table 21.
Ankle Position at Initial Contact with the Ground
84
Means and Standard Deviations: Ankle Position at Peak
Vertical Ground Reaction Force
85
Ankle Position at Peak Vertical Ground Reaction Force
85
Means and Standard Deviations: Maximum Angular
Displacement of the Ankle
86
Maximum Angular Displacement of the Ankle
86
Table 22.
Means and Standard Deviations: Left Ankle Range of Motion 87
Table 23.
Means and Standard Deviations: Right Ankle Range of
Motion
88
Means and Standard Deviations: Knee Position at Initial
89
Knee Position at Initial Contact with the Ground
89
Means and Standard Deviations: Knee Position at Peak
90
Knee Position at Peak Vertical Ground Reaction Force
90
Displacement of the Knee
91
Maximum Angular Displacement of the Knee
91
Table 30.
Means and Standard Deviations: Left Knee Range of Motion
92
Table 31.
Means and Standard Deviations: Right Knee Range of
Motion
93
Means and Standard Deviations: Hip Position at Initial
94
Table 24.
Table 25.
Table 26.
Table 27.
Table 28.
Table 29.
Table 32.
x
Table 33.
Statistical Summary of Athletic Shoe Midsole Density on Hip
Position at Initial Contact with the Ground
94
Means and Standard Deviations: Hip Position at Peak
95
Statistical Summary of Athletic Shoe Midsole Density on Hip
Position at Peak Vertical Ground Reaction Force
95
Displacement of the Hip
96
Maximum Angular Displacement of the Hip
96
Table 38.
Means and Standard Deviations: Hip Range of Motion
97
Table 39.
Means and Standard Deviations: Vertical Hip Displacement
98
Table 40.
Vertical Hip Displacement
98
Table 41.
Means and Standard Deviations: Vertical Hip Position
99
Table 42.
Means and Standard Deviations: Time to Maximum Flexion
Angle of the Ankle
101
Time to Maximum Flexion Angle of the Ankle
101
Angle of the Knee
102
Time to Maximum Flexion Angle of the Knee
102
Angle of the Hip
103
Time to Maximum Flexion Angle of the Hip
103
Post Participation Questionnaire Results
104
Table 34.
Table 35.
Table 36.
Table 37.
Table 43.
Table 44.
Table 45.
Table 46.
Table 47.
Table 48.
xi
List of Figures
Figure 1.
Typical Athletic Shoe Construction
Page
11
Figure 2.
Anatomy of an Athletic Shoe
13
Figure 3.
Fila Athletic Shoes used for data collection, soft midsole,
Control midsole, and hard midsole
53
Figure 4.
Position of 6 cameras, frontal, sagittal and transverse views
56
Figure 5.
Alignment of the force plates
56
Figure 6.
Frontal View of Experimental Set Up, testing area, position
of six cameras, force plates and Crush It volleyball
57
Figure 7.
Retroflective Marker and Sacral Wand
60
Figure 8.
Position of 31 retroflective markers during static trial
61
Figure 9.
Peak Vertical Ground Reaction Forces: After Initial Contact
with the Ground
71
Total Peak Vertical Ground Reaction Force: After Initial
72
Figure 11.
Left Peak Vertical Ground Reaction Force
73
Figure 12.
Right Peak Vertical Ground Reaction Force
73
Figure 13.
Total Peak Vertical Ground Reaction Force
74
Figure 14.
Loading Rate: Time to Peak Vertical Ground Reaction Force
75
Figure 15.
Peak Ankle Joint Moments
76
Figure 16.
Peak Knee Joint Moments
77
Figure 17.
Peak Hip Joint Moments
78
Figure 18.
84
Figure 19.
85
Figure 20.
86
Figure 10.
xii
Figure 21.
Left Ankle Range of Motion: From Initial Foot Contact to 0.75
sec Post Impact
87
Figure 22.
Right Ankle Range of Motion: From Initial Foot Contact to
0.75 sec Post Impact
88
Figure 23.
89
Figure 24.
90
Figure 25.
91
Figure 26.
Left Knee Range of Motion: From Initial Foot Contact to 0.75
sec Post Impact
92
Figure 27.
Right Knee Range of Motion: From Initial Foot Contact to 0.75
sec Post Impact
93
Figure 28.
Hip Position at Initial Contact with the Ground
94
Figure 29.
Hip Position at Peak Vertical Ground Reaction Force
95
Figure 30.
96
Figure 31.
Hip Range of Motion: From Initial Foot Contact to 0.75 sec
Post Impact
97
Figure 32.
Vertical Hip Displacement – (a measurement of jump height)
98
Figure 33.
Vertical Hip Position: Maximum Vertical Hip Position during
the Jumping Phase and Hip Position in Static Stance
99
Figure 34.
101
Figure 35.
102
Figure 36.
103
xiii
Chapter One
INTRODUCTION
The function of athletic shoes is to protect the feet from the stresses of
athletic activity while permitting the athlete to achieve their maximum potential.
During physical activity a large amount of force passes through the foot and
lower extremities every time an athletic shoe strikes the ground.25 A basketball
player landing after jumping for a rebound can experience a landing force that
exceeds five times their body weight.67 Athletic shoes are designed to protect the
athlete, and prevent injury. The midsole of an athletic shoe, in particular, can be
modified to help control the amount of force attenuated during impact with the
ground.25 The degree of shock absorption provided by an athletic shoe is
determined by the material characteristics and construction of its midsole.
The differences in design and variations in material, weight, lacing
characteristics and other factors engineered into athletic shoes are meant to
protect the areas of the feet that encounter the most stress.25 The typical
construction of an athletic shoe consists of an insole, a midsole and an outsole.
The insole is in direct contact with the foot, and is usually made of compressible
foam that conforms to the foot to improve comfort and provide a minimal amount
of shock absorption.12, 25, 52 The midsole is located between the insole and the
outsole, it provides cushioning and support.25 The outsole is the treaded layer
1
2
that is in direct contact with the ground; it provides traction and resists wear.6, 21,
56
The midsole design of athletic shoes has evolved over the past 25 years
from shoes that were relatively flat, for example Converse All Stars, to the current
designs that utilize a significantly increased heel thickness. This increased heel
thickness is used to provide better shock absorption and cushioning, especially
during jumping and pounding activities.40, 50
The midsole of an athletic shoe requires a delicate balance of support and
cushioning. The support or stability provided by the midsole helps control
excessive foot movements. Athletic shoes may contain different densities of foam
or more rigid devices in specific areas of the midsole to aid in controlling
abnormal foot motion.4, 26 The primary purpose of cushioning in athletic shoe
midsoles is to protect the body from the consequences of repeated impacts
between the foot and the ground.
Various materials have been used in athletic shoe midsoles to improve
cushioning.61 The cushioning provides an interface for shock absorption by
spreading out the force of impact so it is not transferred directly to the feet and
legs of the athlete.25 Athletic shoe midsoles attempt to attenuate impact force by
inserting a soft material at the foot-ground interface. The additional deformation
of the midsole should act to reduce the stiffness of the impacting system,
therefore, reducing impact force.38 The modeling research by Gerritsen, van den
Bogert and Nigg supported these presumptions.28
3
The attenuation of impact forces during landing is important because the
initial contact of the foot with the ground results in significant impact force. High
impact forces and impact loading rates have been related to cartilage
degeneration, fatigue fractures, shin splints, Achilles tendon problems, and
hematological problems. It has been demonstrated that many of these injuries
occur due to the excessively high forces acting on the body, rather than
insufficient structural properties of the human body. It is the job of a well
designed athletic shoe to reduce this impact force for the athlete without
interfering with performance.40, 61
Impact force can be defined as the force generated by a collision between
two objects. The shock absorbing capability of an athletic shoe midsole should
attenuate the impact forces between the athlete’s foot and the ground.25 There is
general consensus among the researchers that cushioning is needed in athletic
shoes for shock absorption and comfort.15, 25, 38-40, 46, 50, 59-61, 71, 77 The ability of an
athletic shoe midsole to attenuate impact forces is important for the prevention of
pain and the development of musculoskeletal overuse injuries related to
repetitive impacts.10, 29 Schwellnus, Jordon and Noakes71 indicated that improved
shock absorption in athletic footwear could reduce the incidence of injury.
Conversely, lack of cushioning in shoes was implicated as a cause of athletic
injuries.71
There is controversy, however, regarding how much cushioning should be
in the midsole of an athletic shoe. Nigg and Segesser61 suggested that changes
in cushioning properties relate more to comfort than injury prevention. Robbins
4
and Gouw69 caution that increased cushioning can actually lead to injury by
reducing the sensory feedback coming from the plantar surface of the foot. Their
research indicated that increased cushioning in an athletic shoe increased impact
force with the ground upon landing.69 Midsole cushioning is important in reducing
impact loads, however, too much cushioning has been associated with instability
and greater likelihood of injury.15
Nigg, Bahlsen, Denoth, Luethi and Stacoff52 found that, in studies of
athletic shoes that were identical except for the midsole density, ground reaction
forces were not what was expected, when compared to material tests. They
found no significant difference in ground reaction forces during running;
attributing the similarities in ground reaction forces to kinematic adaptations of
the athletes during their running gait. They suggested that athletes were able to
increase knee flexion while wearing the harder midsoles, to compensate for the
changes in impact force. Their research indicates that athletes are able to
compensate for variations in midsole density during rhythmic athletic activities,
such as running.52
Further evidence that knee activity changes with changes in midsole
density comes from Frederick, Clarke and Larsen23. They found a correlation
between knee flexion velocity, caused by midsole hardness, and oxygen
consumption. When the knee is more flexed the muscles have to work harder,
requiring additional effort to consistently use knee flexion to attenuate impact
forces.23 Increased knee flexion initially appears to reduce impact peaks when
running, but these increased knee flexion angles are not as effective as the
5
muscles fatigue.23, 38 Therefore, the protective functions of an athletic shoe
midsole might vary, depending on the level of fatigue.38, 73
Sharkey, Ferris, Smith and Matthews also suggested that muscle fatigue
can contribute to an increase in injuries because of the muscles decreased ability
to attenuate forces. They indicated that repetitive impact forces were less
detrimental than the increase in peak strain imposed by tired and uncoordinated
muscles.73 This further reinforces the need for an external protective mechanism,
such as a sufficiently cushioned athletic shoe. An appropriately cushioned
athletic shoe midsole should provide external force attenuation that is resistant to
fatigue and may be better able to consistently reduce the transmission of impact
shocks upon landing.38
Extensive research has been conducted on the effects of constructional
changes in the midsole of running shoes.2, 15, 38, 50, 51, 53, 59, 61, 74, 86 Evaluations of
athletic shoe cushioning, however, have produced inconclusive results. Most
locomotor studies have shown improved cushioning of shod over barefoot
conditions but they fail to detect differences between athletic shoes with different
midsole properties during running trials.13, 15, 37, 38, 53, 61 Anticipated reductions in
force rate or magnitude through changes in midsole density has rarely be
demonstrated. 2, 15, 38, 50, 51, 53, 59, 61, 74, 86 Kinematic adaptations have been used as
a possible explanation of these results.15, 28, 53
Most of the research on athletic shoes and midsole cushioning has
focused on running.4 Running is a very rhythmic activity. When running, the
ground reaction forces can be changed or maintained through kinematic
6
adjustments made by the runner because the runner knows the next step should
be similar to the last step.26 In running, shock induced acceleration at the level of
the tibia is between 5 g and 15 g. In contrast, a basketball player landing from a
jump may experience up to 20 g’s, generating shock waves at a level that has
been implicated in athletic injuries.4 Landing after a dynamic activity that is nonrhythmic produces tibial shock accelerations up to four times those seen when
running. The role of the athletic shoe midsole cushioning may be crucial in
athletic activities that are not rhythmic, but rather are practiced sequenced
activities. There is limited data on the role of athletic shoe midsoles in jump
landing sequences which are practiced but non-rhythmic skills.
When landing from a vertical jump, athletes rely primarily on the
lengthening of active muscle during joint flexion to attenuate the forces
experienced during initial contact with the ground.45, 49 If the midsole of an athletic
shoe is appropriately cushioned, it should help delay the onset of peak impact
force, increase impact duration, attenuate shock induced acceleration and
redistribute pressure beneath the feet.
The present study is designed to explore the effect of variations in athletic
shoe midsole density on attenuating impact forces while athletes perform a jump
landing sequence. Volleyball jump landing sequences were selected for study
because of the continuous non-repetitive landing forces that occur during
volleyball play. Volleyball players also frequently experience lower extremity
injuries as a result of repetitive high impact peak landing forces experienced
during play.9, 16
7
Statement of the Problem
Running is a repetitive activity that allows athletes to get into a rhythm.
When the midsole density of an athletic shoe is altered, a runner subconsciously
responds to these differences by making kinematic adaptations after a series of
repetitive and rhythmic gait cycles. As a result research has indicated that impact
forces during running remain constant regardless of the density of the midsole.
There is limited research determining what effect variations in midsole density
will have on impact forces during a non-rhythmic jump landing sequence that
involves an approach. Further, there is limited evidence in the literature
demonstrating that athletes performing non-rhythmic jump landings will adapt
kinematically to differences in athletic shoe midsole density.
Purpose of the Study
¾ To determine the influence of variations in athletic shoe midsole
density on impact forces, loading rates, and peak joint moments after
landing from a volleyball spike approach jump.
¾ To determine what specific kinematic variables are affected when
landing after a jump with athletic shoes of varying midsole densities
Hypotheses
H1: It is hypothesized that vertical ground reaction forces will be
significantly different when landing in athletic shoes with different
midsole densities.
H2: It is hypothesized that loading rates will be significantly different
when landing in athletic shoes with different midsole densities.
8
H3: It is hypothesized that peak joint moments will be significantly
different when landing in athletic shoes with different midsole
densities.
H4: It is hypothesized that specific kinematic variables will be
significantly different when landing in athletic shoes with different
midsole densities.
Chapter Two
REVIEW OF THE LITERATURE
The following review of literature is divided into 4 sections: athletic shoe
anatomy; impact forces; landing mechanics; and midsole cushioning. A review of
the basic construction of athletic shoes is provided, followed by a discussion of
the purpose and function of the athletic shoe midsole. The various components
of an athletic shoe that provide comfort and protection are discussed with specific
attention to the cushioning effects of the athletic shoe midsole. The midsole’s
effect on performance and gender differences are also briefly discussed.
To understand the effect athletic shoes can have on impact force, it is
important, first, to understand impact forces and attenuation of these forces. A
general description of the components of impact forces are provided, followed by
methods of attenuating impact forces. The effect athletic shoes have on
attenuating impact forces enlarges on this basic discussion.
The third section of this review will examine landing forces. It is important
to fully understand the biomechanical principals related to landing forces and the
possible strategies for dissipating impact upon landing. Landing mechanics and
their specificity to volleyball athletes enlarge on this basic discussion. Current
research on landing mechanics, athletic shoe midsoles, and volleyball are also
examined.
9
10
The final section of this literature review focuses on midsole cushioning in
an athletic shoe. There is a controversy in the literature regarding the potential
positive or negative effects of midsole cushioning in athletic shoes. Some studies
demonstrate the benefits of midsole cushioning, while others have shown a
negative association between midsole cushioning, performance and safety. The
controversy surrounding the benefits and drawbacks of cushioning the midsole of
athletic shoes is currently unresolved and reviewed in detail. There are, however,
aspects of this controversy that have yet to be examined. This review of the
literature will examine some of these areas more fully and open a discussion
regarding the effect of midsole cushioning in volleyball, where the athlete is
subjected to repetitive, non-rhythmic landing forces.
11
Anatomy of an Athletic Shoe
Shoe Construction
Athletic shoes are constructed with different features and made of various
materials that are commonly assumed to improve comfort and performance and
to reduce the frequency of overuse injuries.25, 58, 61 Typical construction of an
athletic shoe consists on an insole, midsole and outsole (Figure 1). The foot shoe
complex forms the dynamic base upon which an athlete functions. What happens
at the foot shoe interface affects the total functional mechanism of the athletic
shoe.6
Figure 1. Typical Shoe Construction
The upper is the part of an athletic shoe that holds the foot to the sole of
the shoe and is generally the most aesthetic part of the shoe. It typically is very
12
colorful and contains the company logo. The upper is designed to enclose and
help stabilize the foot on the sole. In traditional shoe production terms the part of
the upper covering the forefoot is called the vamp.12 The vamp is the area on the
shoe where the laces are found. The lacing pattern can affect how the shoe fits.
A good lacing system allows the upper to apply uniform pressure over the entire
forefoot. Many athletes experience impingement of nerves and tendons on the
top of their foot if the laces are not in the proper place. There are many ways to
lace up an athletic shoe to relieve pressure points and still prevent heel slipping
during activity. The tongue is another method of relieving impingement from
laces. It is designed to protect the top of the foot from the pressure of the laces.
The insole is the bottom inside portion of the shoe that is in direct contact
with the foot. The first insole was developed out of cork in the 18th century in
Germany.52 Throughout the evolution of insoles various materials have been
used such as leather, cork, wood, metals and plastics. In athletic shoes today,
plastics, in different combinations, are primarily used to create the athletic shoe
insole. Most shoes have removable insoles. Good insoles are made from
compressible foam that will mold to the contours of an athlete’s foot. The insole is
constructed to improve comfort and provide a minimal amount of shock
absorption. It is important to realize that insoles tend to wear out faster then
many other parts of an athletic shoe and should be replaced often to maintain
their effect.12, 25, 52
The midsole is the layer between the insole and outsole. Most of the
recent advances in athletic shoe production have been made in midsole design
13
and materials. Support and cushioning, two of the most important elements found
in athletic shoes, are based on the construct of the midsole.25
The outsole is the treaded layer of the shoe which is in direct contact with
the ground; it provides traction and resists wear. The amount of friction
generated between the shoe and the athletic surface can influence injuries and
the rate at which they occur.21, 56 The traction pattern and materials of the outsole
are usually developed specific to the playing surface. For example, a court shoe
will usually be flat and flexible with a lot of traction, while a trail or hiking shoe will
have a more rigid outsole with a more aggressive traction pattern. Outsole
materials, however, have been found to have more influence on traction than the
pattern on the bottom of the shoe.21 The correct use of the term sole actually
refers to the combination of the insole, midsole, and outsole.
Figure 2. Anatomy of an Athletic Shoe
The toebox or toe wrap is located in the front of the shoe and encloses the
toes (Figure 2). It is important to have adequate room in the toebox to prevent
14
friction and irritation related injuries. Some toeboxes are made especially wide or
narrow to accommodate various foot types.12
The heel counter surrounds the back of the heel and prevents excessive
rearfoot motion. It stabilizes the heel and aids in motion control. It is usually a
reinforced plastic cup within the upper portion of the athletic shoe.3, 52, 75
An important aspect of shoe design is the last of the shoe (type of last)
and how the shoe is lasted (how the upper of the shoe is attached to the sole).
The word last originates from the Old English laesk, meaning sole, footprint, or
track; it refers to the shape of the shoe.52 The first lasts were chiseled out of
stone and later whittled out of wood. In 1969, the plastic last was developed by
the Sterling Last Corporation, U.S.A., and today the shoe industry primarily uses
plastic lasts.52 The last is the mold or form on which the shoes are built, either a
straight, curved, or semi-curved last. Shoe manufacturers construct shoes over a
last, or model, that resembles a generic or average foot. Unfortunately, each
person’s foot is slightly different and the generic last may not exactly reflect the
shape of all feet.
It is possible to determine how a shoe is lasted by removing the insole to
reveal the type of lasting used in the construction. There are three general
methods of lasting, slip, board, and combination. In a slip lasted shoe the upper
is sewn together at the bottom and then glued to the sole. This allows the shoe to
be light and flexible. In a board lasted shoe the upper is sewn to a board, similar
to cardboard and then attached to the sole. This creates a more rigid shoe with
more support. A combination lasted shoe has a slip lasted front and a board
15
lasted back; this combination allows good flexion and cushioning while
maintaining rearfoot control.12
Athletic Shoe Midsole
As mentioned previously the primary purpose of an athletic shoe midsole
is to provide cushioning and support. Cushioning provides an interface for shock
absorption, by spreading out the force of impact so it is not transferred directly to
the feet and legs of the athlete. The midsole additionally provides support and
stability to help control excessive foot movements.25
Support is an important element in the athletic shoe midsole; it directly
affects the health and comfort of the feet. Athletic shoes may contain different
densities of foam or more rigid devices in specific areas of the midsole to aid in
controlling the motion of the foot.4 The midsoles affect on motion is brought about
by a change in the effective lever arm of the ground reaction forces. Softer and
more flexible shoes have a smaller lever arm resulting from different deformation
of the midsole causing less pronation than shoes that are harder.26, 30 The shoe
hits at an angle to the ground, and the lateral edge of the shoe can either bend or
compress so the effective lever arm of the ground reaction force is shifted
medially. A smaller lever arm results in a smaller moment; this causes the
subtalar joint to pronate more slowly than in an athletic shoe with a harder
midsole. The lever arm affects the speed of pronation more then the total amount
of pronation. Shoe manufacturers have addressed this problem by making shoes
with dual density midsoles.26 One example of this is the medial post, where a
firmer density of midsole material is added to the inner side of the midsole of an
16
athletic shoe. This medial post is designed to reduce overpronation. The medial
post has also been called the Footbridge (Nike), Support Bridge (Reebok),
Diagonal Rollbar (Brooks) and Graphite Rollbar (New Balance). Although the
shoe is considered a powerful manipulator of human movement, an extreme
overpronator will always force the weakest material to yield. Therefore, footwear
design may not solve overpronation or correct bad running styles.4, 56, 74
The construction of the athletic shoe midsole is very important and
requires a delicate balance between cushioning and support. A conflict of
requirements exists when considering midsole material. A soft shoe designed for
maximum cushioning may deform when loaded, resulting in increased rearfoot
motion, whereas a thin firm midsole may minimize rearfoot motion but transmit
high impact forces.4, 15, 22
The primary purpose of cushioning in an athletic shoe midsole is to protect
the body from the consequences of repeated impacts between the foot and the
ground by providing an interface. The shock absorbing and attenuating
properties of an athletic shoe are mainly determined by the type of material that
is inserted into the midsole.25 The density or hardness of a midsole is measured
in durometers. A durometer is the international standard for measuring the
hardness of rubber, foam rubber, plastic and most nonmetallic materials.
Durometer hardness can be measured on different scales, typically the lower the
number the softer the material, the higher the number the harder or more rigid
the material.26 Inserting any type of cushioning in an athletic shoe represents an
17
attempt to attenuate impact forces by inserting a material at the foot ground
interface.38
Athletic shoe midsoles function to reduce impact force by delaying the
timing of the impact force peak through the use of cushioning.59 By inserting a
soft material at the foot-ground interface the additional deformation of the
midsole should act to reduce the impacting system.28, 38 In theory, a thicker sole
will deform more than a thinner one causing more attenuation of impact forces.4
The additional deformation of the midsole acts to reduce the stiffness of the
impacting system, upon contact of the shoe to the ground.38 In simpler terms, the
midsole cushioning is compressed causing a delay in landing force or vertical
impact force peak at footstrike. When all other factors are equal, collisions that
involve greater deformations are generally characterized by lower peak forces
and slower rates of loading.2 According to this theory, the more cushioning, the
more impact is attenuated.
A number of different adaptations have been made to athletic shoes to
improve midsole cushioning.59 As a result, the midsole of athletic shoes have
evolved over the past 25 years from relatively flat (for example, Converse All
Stars) to the current designs that utilize a significantly increased heel thickness.
This increased heel thickness is created by increased cushioning in the midsole
which is believed to provide better shock absorption and cushioning, especially
during jumping and pounding activities.40, 50 59
Shoe manufacturers must carefully consider the type and thickness of
cushioning placed in an athletic shoe. In order for the midsole to assist in force
18
attenuation, shoe midsole materials need to be sufficiently stiff and retain their
spring characteristics to prevent the midsole from bottoming out during impact.4,
21, 52
When midsole cushioning is too soft it leads to maximum compression of the
material, which can result in less support and loss of attenuation.52, 59
Athletic shoe midsoles are usually manufactured from a combination of
two basic materials, ethyl vinyl acetate (EVA) and polyurethane. These two
materials have very different characteristics; EVA is light, has excellent
cushioning properties, and can be manufactured at different densities.
Polyurethane is denser and heavier but is more durable than EVA. Both of these
materials have also been used to encapsulate other cushioning materials such
as air (Nike), gel (Asics), silicone (Brooks), honeycomb pads (Reebok and Puma)
and EVA (New Balance).25, 61
One of the most well known forms of cushioning is the air midsole. Nike
first introduced this concept in 1979, using encapsulated air pockets in the
midsole to enhance cushioning.25 Other companies have further implemented the
concept of using air to cushion the midsole with some variations in types of air
and placement within the shoe. Ambient air has been used by Etonic and freon
was used by Nike.25
In today’s athletic shoes various types of midsole cushioning can be found
in the heel, forefoot, or both, depending on the demands of the activity or the
athlete.25 This allows manufacturers to produce athletic shoes that can
accommodate the different characteristics of various athletic movement patterns.
19
In the early 1960’s, several sports medicine clinics and research centers
started projects to study the connection between sports activities, the occurrence
of sports injuries, and the influence of footwear on movement and load
characteristics.72 Many of the changes in shoe construction over the last 30
years, however, have been purely cosmetic and simply a response to everchanging fashion trends with little concern for athletic function.40
Performance and Athletic Shoes
From an orthopedic point of view, with no regard to performance related
criteria, athletic shoes should be constructed to: 1) support the function of the
foot, 2) adapt to the physiological ranges of the foot, 3) avoid excessive rotational
movements due to excessive moment arms, and 4) attenuate excessive forces.54,
61
Shoes constructed according to these criteria are assumed to restrict motion
and to avoid excessive movements in the joints. Consequently, the internal
structures should be less strained and stressed, and the frequency injury should
be reduced.54, 61 These theoretical considerations, however, ignore athletic
performance related criteria such as improvement in performance. Stacoff,
Steger, Stussi and Reinschmidt78 found that ignoring performance related
variables in athletic shoes can be detrimental to athletic performance. They found
that higher cut athletic shoes can reduce the risk of ankle sprain injuries but only
at the expense of full ankle mobility and overall athletic performance.78 Athletes
may choose to wear lower cut athletic shoes, compromising protection for
improved athletic performance.78 Injury prevention in athletic shoe design is an
20
important criteria but success on the playing field is what is most important to the
athlete.
Many concepts have been studied with regard to increasing athletic
performance and athletic shoes. Two specific concepts presented by
Stefanyshun and Nigg79 are return of energy and reduction of loss of energy. For
each joint, there are phases where energy is absorbed and phases where energy
is produced. If the absorbed energy is dissipated and not stored for later re-use,
it could be speculated that a reduction of such energy absorption might lead to
an increase in performance.80 Return of energy to improve athletic performance
has been studied for both sport surfaces and athletic shoes.61 In theory, a system
must be able to return the energy at the right time, location, and frequency. Sport
surfaces can be appropriately tuned to return energy; surfaces for track and field
gymnastics and are successful examples of energy return by sport surfaces.61, 79
Return of energy by athletic shoes has been attempted several times, but has
never been completed successfully.82
The main reasons that these attempts were unsuccessful are that the
materials associated with cushioning are not good energy return materials and
the location of maximal possible energy storage (the rear foot) is not the location
where effective use can be made of returned energy.79 Possible shoe-related
factors affecting energy conservation or reduction in loss of energy include: a)
work against gravity (weight of shoe); b) work for acceleration; c) work due to
cushioning; and d) work to stabilize joints.61 The concept of reducing the loss of
21
energy has been unsuccessful and theoretical attempts to use this approach are
limited in the literature.79
Gender Differences in Shoe Design
A very important factor in athletic shoe design is the anatomical
differences between the male and female foot. The foot of the female tends to
have a narrower heel in relation to the forefoot, a smaller Achilles tendon, and is
narrower overall than a man’s foot relative to length. Athletic shoes are currently
being designed for men and women through research studies involving only
men.24 Females have different needs from athletic shoes than males. In many
cases, athletic shoes are built on a scaled down version of a man’s shoe rather
than based on the specific anatomy of the female foot. The result is an athletic
shoe that improperly supports the foot of a female.61
Another gender difference is that the female athlete completes the heel-totoe gait cycle faster than the male athlete, and females almost always have a
shorter leg length.24 Therefore, female athletes take more steps to cover the
same distance causing the female athlete’s foot to strike the ground more often
than male athletes. These increased impacts for the female athlete may require
increased cushioning in a female athletic shoe.
Another problem in athletic shoes design for women is that most of the
studies on impact forces and performance are being performed with male
subjects. These results cannot simply be translated and applied to women
because the foot and ankle in females are structurally and biomechanically
22
different from males.24 More research with female athletes is needed in the area
of athletic shoe design.
Impact Forces
One of the first things to understand about impact forces is how force is
transmitted from the ground to the foot. Newton’s third law, “For every action
there is an equal and opposite reaction,” is essential to understand forces acting
on the body. In static stance, ground reaction forces are equal and opposite to
the pull of gravity acting on the body and the shoes. The force from the shoe
acting on the foot is equal and opposite to the weight of the body.26 The force
from the femur acting on the tibia is equal and opposite to the weight of the femur
plus the rest of the body above the femur. Therefore, force acting on any
particular body part in static stance can be determined by the weight of the rest
of the body above it.26
Forces are not as easily explained when they involve a fall from a height.
Running and landing activities have been compared to falls from a height.26
When an object is moving, it has momentum, equal to mass times velocity. An
impulse, equal to force times time, is required to reduce the speed and the
momentum of a body part to zero. A high amount of force, times a short amount
of time, can produce an impulse equal to a lower amount of force, times a longer
amount of time. In running and landing activities not all body parts stop their
vertical motion at the same time. When the trunk takes a longer time to stop, the
force required to stop it is less, lowering the effect of impact on the feet.26
23
The previous explanation of impact forces mentioned the effect of ground
reaction forces on different joints of the body. There are also forces at the joints
generated by the muscles. When the soleus fires, it pulls the calcaneus upward
and, at the same time, pulls the tibia downward, increasing the compressive
forces at the subtalar and ankle joints. These types of forces are known as
internal forces; they are usually calculated and cannot be measured directly like
ground reaction forces. The compressive force at the knee from the quadriceps
has been calculated as high as four times body weight at footstrike during
running.26, 61
Research indicates that there is a range of possible impact force
accommodation strategies.5, 34 Bates5 suggested three specific categories of
responses to impact forces: Newtonian, biomechanical, and neuromuscular. In a
Newtonian response an increase in impact force is linearly related to the increase
in the applied stressor and occurs at an equal rate. The impact force is
determined by mechanical events and no biological accommodation occurs.5, 34 A
biomechanical response results when an increase in impact force occurs at a
rate less than the rate of increase of the applied stressor. Partial biological
accommodation occurs, but the response is mechanically driven.5, 34 In a
neuromuscular response, total biological accommodation occurs and an increase
in the magnitude of the stressor does not change the magnitude of the impact
force. 5, 34
Impact forces during human locomotion are the forces that result from the
foot colliding with the ground.55 A recent review article by Whittle,85 indicated that
24
upon landing, ground reaction forces produce internal loading to the lower
extremities and cause transient stress waves to travel up throughout the skeletal
structures of the body.85 Research suggests that stress waves (high frequency
contacts) are major factors in the development of degenerative osteoarthritis, and
cartilage breakdown.29, 48 These high loading frequencies have been related to
cartilage injury due to the viscoelastic behavior of the cartilage. High frequency
vertical contact forces within joints prevent fluid flow within the cartilage which
leads to radial displacements and high tensile forces in the collagen fibers.63 High
impact forces or impact loading have also been related to fatigue fractures, shin
splints, Achilles tendon problems, and hematological problems. It has been
demonstrated that many of these injuries occur due to excessive forces rather
than insufficient structural properties of the human body.29, 40, 48, 61
In order to reduce impact force three materials are thought to cushion the
heel during landing: the midsole material of the shoe; the material of the running
surface; and the soft tissue of the heel.50 Cushioning is defined as any attempt to
reduce the amplitude of the vertical ground reaction force during impact.55, 61 This
definition includes any method resulting in reduced impact forces, such as
changes in shoe construction or movement.61 The midsole of the athletic shoe is
the easiest to change, by altering the cushioning properties of the shoe, but this
is not the only method of reducing vertical impact force during footstrikes or
landing.
One of the goals of athletic shoes is to attenuate impact forces and
accelerations that cause overloading of the musculoskeletal system and injury. It
25
has been suggested that injuries can be reduced by reducing the transmission of
impact force upon landing through the use of cushioning.29 An athletic shoe’s
cushioning or shock absorbing system, protects the body from potentially
injurious repeated impact, by modifying the properties of the material used in the
midsole. The effect of the midsole is to delay the onset of the peak impact force,
increase impact duration, attenuate higher frequencies of the shock, and
redistribute pressure beneath the foot. Improved shock absorption by athletic
shoe midsoles should reduce the incidence of overuse injuries associated with
loading (excessive forces and repetitive forces) but not alter the incidence of
acute injuries or injuries where excessive shock wave transmission is not
implicated.71
Schwellnus, Jordan and Noakes71 found a reduced incidence of tibial
stress syndrome, and stress fractures, in a group of military recruits wearing
shock absorbing insoles. This study demonstrates that with increased cushioning
it is possible to reduce impact force and reduce the incidence of injury. It is the
job of the athletic shoe to reduce impact force for the athlete without interfering
with performance.40, 61
The only interface between the ground and soft tissues of the foot are
athletic shoes.86 Many research studies have focused on the cushioning of
athletic shoes to decrease this impact force.15, 25, 38-40, 46, 50, 59-61, 71, 77 The midsole
is one characteristic of athletic shoes that can be easily modified to control the
amount of impact force absorbed.25 The amount of shock absorption found in an
26
athletic shoe is determined by the material characteristics and construction of the
midsole.
A basketball player landing after a jump may experience shock induced
acceleration at the level of the tibia up to 20 g, generating shock waves that have
been implicated in athletic injuries.4 Basketball players landing after jumping for a
rebound experience a landing force that can exceed five times their body
weight.69
Landing Mechanics
Newtonian mechanics dictates that increases in jump height must be
accompanied by a proportional increase in the kinetic energy that must be
properly absorbed to avoid injury.19 These landings often result in the creation of
ground reaction forces that can be five times bodyweight.1 The effects of these
forces may be compounded in athletes involved in jumping sports, like volleyball
or basketball, who jump and land repeatedly during a game.81
Jump sports can be broadly classified as activities containing an airborne
phase which results in a subsequent need for landing.18 Individuals perform
jumps in numerous sport activities such as volleyball, basketball, gymnastics,
aerobic dance, and running. As a result of the downward force of gravity, a
performer who jumps and becomes airborne must eventually return to the ground
and land.18
It has been shown that there are typically two strategies for landing from a
jump. Some athletes land toe first and then let the heel hit the ground; other
athletes land flat footed. Valiant and Cavanagh83 found that subjects landing from
27
a rebound created ground reaction force peaks averaging 6 bodyweights when
using a flat footed landing and only 4.1 bodyweights when using a toe-heel
landing strategy. Athletes that land toe first can use the ankle joint motion to
absorb some of the impact force. The attenuating properties of the ankle can
cause a reduction in peak impact forces. Athletes that land flat footed cannot,
subjecting themselves to higher impact forces.26
The role of the quadriceps seems to be critical to the distribution and
absorption of the impact forces resulting from landing. Subsequent to impact, the
quadriceps muscle eccentrically contracts to control knee flexion and decelerate
the landing.41 Without sufficient strength available to decelerate the body by the
eccentric quadriceps mechanism, athletes would land in a more extended knee
position and tend to maintain this extended knee position after ground contact
rather than absorbing the impact with controlled knee flexion. This knee extended
position is more commonly seen in females than males and is directly related to
weak leg musculature.41
During landings the effectiveness of the lower extremity to dissipate forces
is particularly important. If the impact force is applied to the knee over a short
amount of time, the body has less of an opportunity to attenuate forces. If the
amount of time to maximum angular displacement is maximal, and the maximum
angular displacement is large, then impact forces will be attenuated.41
Lephart, Ferris, Riemann, Myers and Fu41 revealed that female athletes
took significantly less time to reach maximum knee flexion then males following
impact, causing a more abrupt absorption of the impact forces upon landing.
28
Their results also indicated that female athletes have significantly less knee
flexion after impact upon landing than males.41 The lack of knee flexion found in
this research is consistent with the results from previous studies which showed
gender differences when landing from a jump.32, 41
Hewett, Stroupe, Nance and Noyes32 also reported that female athletes
tend to land with the knee in a more extended position and therefore subject
themselves to higher forces per body weight during the impact of landing. They
also found that after a training program on landing mechanics designed to
decrease landing forces, female athletes demonstrated lower impact forces than
the male athletes. Their research reported that female athletes were able to
decrease their landing forces 22% after training, suggesting that teaching proper
landing technique could reduce serious injuries among athletes.32
The literature indicates that training experience of the athlete will affect the
characteristics of the athletes landing.9, 19, 45, 62 Prapavessis and McNair62 found
that feedback from instruction in jumping technique helped athletes to land more
softly. They reported that subjects significantly reduced their peak ground
reaction forces from pre to post training by approximately one bodyweight. Their
findings supported the theory that teaching landing technique strategy can help
to reduce landing forces.62 In general, skilled, well trained, or experienced
athletes have been reported to have increased ankle plantarflexion, knee flexion,
and lowered vertical ground reaction forces during landing.19, 45, 62 Theoretically,
this would permit more time to distribute the impact forces and allow the
opportunity for the musculature to absorb these forces.45
29
Maximizing joint angles, specifically knee flexion, prior to impact will aid in
attenuating potentially harmful impact forces and ensure protective
biomechanical patterns. Additionally, awkward or poor landing strategies may
identify a specific muscle weakness in athletes requiring external methods to
attenuate harmful impact forces.41 Cushioning placed in the heel and forefoot of
athletic shoes to help absorb impact is a possible external solution.
Landing Mechanics and Volleyball Players
Volleyball athletes regularly perform landings and are exposed to large
impact forces during play. More than 40% of high level volleyball players suffer
overuse injuries such as stress fractures, and patellar tendonitis during volleyball
activity. These particularly painful overuse injuries are caused by the amount of
jumping, and more specifically the impact related landings, involved in games
and practices.9, 20
Over 70% of volleyball injuries that occur during play are associated with
blocking or spiking.84 A commonality between these two skills is the jump and
land sequence.18, 20 The jump portion of the movement is a force producing
phase which is typically used to propel the body maximally in a vertical direction.
The direct consequence of the jump is the necessity to land and therefore
dissipate all of the kinetic energy generated during the jump.81 As dictated by
Newtonian mechanics, an increase in jump height is accompanied with a
proportional increase in the magnitude of kinetic energy which must be safely
dissipated at landing to avoid injury.19
30
Stacoff, Kaelin and Steussi76 evaluated the landing technique of 12
subjects performing a volleyball block. Their research indicated an initial vertical
impact force of approximately 1 to 2 bodyweights at forefoot contact for males
performing a block jump landing. Heel contact resulted in a much larger second
impact force that ranged between 1 to 7 bodyweights.76 Adrian and Laughlin1
also evaluated the block by comparing a stationary and a moving block in
volleyball. They found the average peak vertical ground reaction force values
across 15 female subjects were 3.0 and 3.7 bodyweights, respectively.1
Volleyball players must attenuate these large impact forces that can be up to 7
times their bodyweight in order to prevent impact related injury.
Preventing injuries in volleyball is difficult because it is a high risk sport,
relative to the lower extremity, due to the repeated high impact forces. Volleyball
athletes usually train on a variety of surfaces and may use footwear especially
designed or adapted for their sport.33 Iwamoto and Takeda33 reviewed 196 cases
of stress fractures in athletes over 10 years and found the distribution of stress
fractures of the tibia, metatarsal and tarsal bones confirmed the association of
these fractures with sports performed on hard floors. Since it is usually difficult or
expensive to modify or change athletic surfaces, the high ground reaction forces
during landing skills may only be reduced by cushioned athletic shoes and
improved landing technique.33
The lower extremity injuries seen in volleyball athletes can also be
attributed to frequent jumps with a loss of balance and common single leg
landings.20 Tillman, Hass, Brunt and Bennett81 videotaped four NCAA Division I
31
female volleyball teams and carefully observed the landing technique utilized by
all players in two matches (8 games, two games were analyzed per team).
During the matches, 1087 jumps and landings were observed. On average each
player executed 45 jumps and landings for the two games analyzed. For one
particular athlete a maximum of 73 jump and landing sequences was observed
over a two game period. During volleyball spike landings they observed that
nearly half of all landings in elite women players utilize a unilateral landing
technique.81 This observed trend is especially important when it is considered
that the most frequent mechanism of knee injury in volleyball is a unilateral
landing from a jump.36 The relatively high number of unilateral landings reported
by Tillman et al.81 could result in a loss of balance and subsequent injury.
Mechanically, these unilateral landings also jeopardize the landing limb because
the landing limb must dissipate the energy created by two limbs during the jump
phase.81
Another interesting characteristic of landings in female volleyball players is
the tendency to land on the left foot during a unilateral landing. This may be
related to the fact that most volleyball players are right hand dominant. When a
right handed player spikes the ball, their goal is to reach as high as possible with
the right hand in order to hit the ball downward. As a result the trunk is flexed to
the left.82 This lateral flexion raises the right side of the body potentially causing a
left foot first contact upon landing.81
Strengthening the entire lower extremity is a possible intervention that
would allow the jumper to dissipate the energy of landing through the muscles
32
instead of the bones and ligaments.70 Another preventative strategy was
proposed by Briner and Kacmar9 suggesting that athletes be advised of the
importance of landing techniques and the significance of landing with a slightly
flexed knee and a plantarflexed foot. This position at contact would provide a
large range of motion for the lower extremity joints to utilize in order to dissipate
the impact forces.8, 9, 23, 26, 38, 76, 81
DeVita and Skelly17 compared soft and stiff landing techniques for female
volleyball and basketball players while performing a step-off movement from a
height of 0.59 cm. They reported soft and stiff landings averaging 117 and 77
degrees of knee flexion respectively. The stiff landing condition produced a more
erect body posture and a more extended knee position at impact. The stiff
landing also had larger ground reaction forces at impact, but only the ankle
plantarflexors produced a larger moment in this condition.17 The hip and knee
muscles absorbed more energy in the soft landing, while the ankle muscles
absorbed more energy in the stiff landing. This research indicates that landing
with a more extended knee could cause the ankle to absorb more of the impact
forces during landing.17 Over time this increase stress at the ankle joint could
potentially cause an overuse injury. DeVita and Skelly17 conclude when landing
from a jump an athlete should implement a landing strategy involving increased
knee flexion in order to more effectively attenuate impact forces during landing.
Many studies have come to similar conclusions regarding the mechanics
of a safe landing strategy. 9, 76, 81, 87 Zhang, Bates and Dufek87 suggested that the
knee joint extensors and plantar flexors function as the primary energy
33
dissipaters during landing. Their research compared three landing techniques
(soft, normal, and stiff), in nine active males, while performing a step-off
movement from three different heights (0.32 m, 0.62 m, and 1.03 m). Their
results demonstrated general increases in peak ground reaction forces, and peak
joint moments with increases in landing height and stiffness. They concluded that
the knee joint extensors were consistent contributors to energy dissipation and
that the ankle plantarflexors contributed more during the stiff landings, whereas
the hip extensors were greater contributors during the soft landings.87 The results
of Zhang, Bates and Dufek87 are consistent with the findings of DeVita and
Skelly17 suggesting that a landing strategy that uses increased knee, hip and
ankle flexion can potentially decrease impact forces upon landing.
Whenever possible, volleyball athletes should implement a toe-heel
landing strategy with a large amount of knee flexion to help attenuate some of
the high impact forces. Although this technique requires greater muscular
strength, it may be more advantageous relative to injury prevention.81
Strategically this landing strategy may present a problem because landing with a
more flexed knee may prevent the athlete from executing their next movement in
a rapid sucession.81 Another problem exists as fatigue sets in and athletes are
less able to attenuate high impact forces due to muscle fatigue.23, 26, 38 It is
possible that increased cushioning in the midsole of athletic shoes may help to
dissipate some of these forces.
In the aforementioned volleyball research, most of the landings were
observed during a volleyball block. There is limited research available, however,
34
that specifically evaluates landing after a volleyball spike. It is important to
consider that a volleyball spike also involves not only a jump but an approachjump-landing sequence.81 It is also possible that the accelerations involved with
the volleyball approach to the spike may increase the impact forces upon
landing. Therefore, even more cushioning may be needed in the athletic shoe
midsoles of volleyball players, especially during fatigue when the force
attenuating characteristics of the lower extremity muscles have been
diminished.23, 26, 38
In the literature, there are very few studies that address changing the
midsole of athletic shoes for volleyball players. One reason for this is the
controversy that exists over the benefit of changing the cushioning properties of
an athletic shoe. The controversy that exists in the literature regarding cushioning
has mainly focused on runners, not volleyball athletes. Therefore, further
research is needed on changes in midsole density for volleyball players to
determine if these changes are needed or warranted.
Midsole Cushioning: A Research Controversy
Positive Effects of Cushioning
The cushioning properties of athletic shoes have been linked to the
prevention of injuries and comfort.15, 25, 38-40, 46, 50, 59-61, 71, 77 Excessive rearfoot
motion, shock, and high impact forces have been discussed as some of the main
causative factors for athletic injuries. It has been assumed that these different
factors can be influenced by different athletic shoe constructions.46
35
Cushioning in an athletic shoe affects more than just landing properties, a
fact which must be considered when constructing the shoe. Sports related
injuries and especially overuse injuries could be reduced by wearing athletic
shoes with appropriate cushioning.60 Schwellnus, Jordon and Noakes71 indicated
that improved shock absorption in athletic footwear could reduce the incidence of
injury. They investigated the influence of neoprene insoles, which have a
cushioning effect, on the frequency of overuse injuries during nine weeks of
military training. The results documented that the incidence of overuse injuries
and tibial stress syndrome was significantly reduced (from 31.9% to 22.8%) by
wearing cushioned insoles. Conversely, lack of shock absorption or cushioning in
shoes was implicated as a cause of injuries71.
Stacoff, Nigg, Reinschmidt, van den Bogert and Lundberg77 found a
substantial decrease of impact force peaks with decreasing shoe sole hardness.
LaFortune, Hennig and Lake38 indicated similar results, they used a mechanical
model to show that the use of EVA materials as impacting surfaces substantially
reduced impact force and shock experienced by the shank. They also found that
time and frequency variables indicated that the soft EVA provided greater
cushioning than hard foam.38
Surprisingly, Aerts and De Clercq2 found no significant difference in the
peak landing force at footstrike when running over a force platform with either
soft of hard soled shoes. Their research indicated, however, that the heel pad of
the foot is not able to withstand the impact force during running in hard soled
36
shoes. These findings suggest that decreasing cushioning in an athletic shoe
midsole could cause damage to the heel pad.2
There is general consensus among the researchers that cushioning is
needed in athletic shoes for shock absorption and comfort.15, 25, 38-40, 46, 50, 59-61, 71,
77
More research is needed, however, to determine exactly how much cushioning
is enough for optimum performance and safety.
Cushioning as a Negative Factor
Athletes who perform sports involving impulsive contact between the
plantar aspect of the foot and a support surface are frequently injured. The
injuries are thought to be caused by the cumulative effect of repeated trauma
from excessive impact forces.67 Support surface interfaces such as athletic shoes
and mats composed of soft expanded polymer foam materials are used to protect
against these injuries by providing cushioning. These cushioned surfaces have
reduced vertical impact peaks from inanimate dropped objects, but the same
materials have caused increases in impact forces when used by humans.15
In the literature, much of the research on cushioning does not consider
human behavior; humans are viewed as inanimate objects that behave
identically.67 Humans, however, are able to vary the amplitude of flexion at the
knee and hip upon landing and this can either amplify or reduce vertical impact.45
McNitt-Gray45 found that vertical impact is 20% higher when gymnasts land on 10
cm thick soft mats compared to a rigid surface. It was suggested that the
gymnasts flexed less at the ankle, knee and hip joint upon impact when landing
on soft mats causing an increase in impact force.45
37
Robbins and Waked67 have suggested that too much cushioning in an
athletic shoe could be detrimental. During drop jump testing, when a subject
landed barefoot, intense stimulation of the plantar mechanoreceptors was
perceived as uncomfortable, and the subjects naturally used flexion to lower the
impact force. They found that barefoot subjects actually landed softer (with less
force) on hard platforms than on cushioned mats as a result of this protective
mechanism in the plantar region of the foot.67 This protective mechanism is
neutralized by interfaces such as athletic shoes because the landing force is
absorbed by the cushioning properties of the shoes and not perceived by the
foot. Robbins and Waked67 indicate that without this protective sensation, people
wearing very cushioned athletic shoes reach higher levels of impact when
landing than individuals that are barefoot. From this research it could be
speculated that less cushioning, and not more, is needed in athletic shoe design.
This is a very different view from that of shoe manufacturers.67 This study,
however, only investigated landing without shoes and did not investigate how an
athlete would land on various surfaces when wearing an athletic shoe and how
various landing forces might be affected.
Robbins and Gouw69 also suggest that increased cushioning can actually
lead to injury by reducing the body’s own sensory feedback mechanism coming
from the plantar surface of the foot. In a study where subjects were asked to walk
on a 4 inch wide beam, there were fewer falls in firmer shoes. They suggested
the reason for better balance could be that the harder midsoles transmit force
more effectively. When the weight of the person on the beam shifts, the pressure
38
on the bottom of the foot has to shift or the individual will fall. As the muscles
attempt to shift the pressure on the foot, they spend time deforming the midsole
before there is a change in location of force on the foot. This time lag may be
enough to cause the person to loose their balance.69 In other words, it takes
longer to compress the soft midsole and gain proprioceptive feedback. This
increased time causes the individual to fall, whereas the harder midsole deforms
more quickly speeding up the proprioceptive feedback and balance is regained.
Their research indicated that increased cushioning in the midsole of an athletic
shoe while walking was shown to decrease medial and lateral stability effecting
overall balance.69
Another study by Robbins, Gouw and McClaran66 found that softer
midsoles were associated with poor stability. They indicated that when softer
materials are heavily loaded, such as when humans land on them impulsively,
they compress momentarily to become thinner and stiffer. They concluded that
for optimal stability, shoes with thin harder soles were preferable.66, 68 Robbins
and Waked67 indicated that subjects sense relative stability when they first land
on support surfaces impulsively. They suggested that athletes develop a strategy
when landing on a compliant surface. Consequently they plan their landing
strategy to optimize stability. More specifically, when athletes land impulsively
wearing soft athletic shoes, they increase impact through reduced flexion at the
hip and knee so as to momentarily achieve improved stability by compressing the
soft midsole material.67
39
Although moderate amounts of cushioning may be needed to reduce high
impact forces during landing, placing excessive amounts of cushioning in the
athletic shoe midsole may be detrimental.45, 52, 67, 69 Nigg52 found that in studies of
shoes that were identical except for the midsole durometer, the softest shoes had
some of the highest impact peaks. This result was attributed to the fact that the
shoe may have “bottomed out”. The force for the soft midsole was initially low,
but once the material was compressed maximally, forces were more effectively
transferred to the foot. The harder midsoles, in this research, had much lower
impact forces then softer midsoles.52
It has been suggested that too much cushioning in athletic shoes may
actually be responsible for athletic injuries, due to increased landing forces, and
changes in balance.45, 46, 52, 67, 69 Increased cushioning in athletic shoes could
create a perceptual underestimation of actual impact severity.69 In the
development of sports injuries the perception of cushioning is an important issue.
Hennig, Valient and Liu31 reported high correlations between cushioning
perception and biomechanical variables related to the quantification of impact
loading magnitude. Their research was performed with three pairs of shoes that
featured large differences in midsole hardness. The cushioning properties of the
shoes were perceived very differently. They found a reduction in impact force
with increasing shoe stiffness, these authors attributed these results to locomotor
adaptation to protect the body from high heel impacts.31 Locomotor adaptation
requires the perception of differences in shoe midsole density (hardness). The
40
tendency to lower impact forces with harder shoes in this study indicates that
subjects may adapt their running style to avoid high heel impacts.31, 46
Increased cushioning may also cause a decrease in performance.
Stefanyshyn and Nigg79 collected kinematic data using a force platform and a
four-camera motion analysis system while subjects performed a vertical jump test
in shoes with varying midsole durometers (stiffness). They found a significant
difference in the jump height of the subjects wearing athletic shoes with hard
midsoles. The average increase in jump height was 1.4 cm when wearing hard
midsoles. The results of this study are very unique and raise many questions
regarding athletic shoe design.79 Shoe manufacturers are making athletic shoes
more and more cushioned to prevent injury, however, increased cushioning in
athletic shoes could actually lead to decreased performance. Athletic shoes with
hard midsoles need to be researched further to determine whether this gain in
performance is offset by increases in injury.79
Stefanyshyn and Nigg79 did not measure the impact force upon landing in
the stiff midsoles, which were very rigid and had very few cushioning properties.
It is possible that performance may increase with a stiffer or hard midsole, but it
is unclear how an athlete would absorb the impact force without adequate
cushioning.79
Another issue related to cushioning is heel height. Increasing the amount
of cushioning in an athletic shoe has a tendency to increase the heel height of
the shoe. As shoes become softer they also have an increased heel height.
Mandato and Nester43 suggested that increasing heel height increases pressure
41
to the forefoot and shifts the pressure location to the hallux during locomotion.
Higher heeled shoes have a tendency to force the foot into a position that could
cause injury to foot.43
Along with this controversy on cushioning and reducing impact there is
another theory suggesting positive benefits of impact forces during running.35, 61
Kersting and Bruggemann35 found that impact force at heelstrike during running
can actually cause positive changes in the bone mass of the calcaneus, if these
changes are experienced over a period of time. High impact loading has been
related to increased collagen structure and subchondral bone density in
humans.35 These changes in calcaneal bone density cause an increase in bone
density, and can protect the foot which is considered to be a positive
adaptation.35 These changes can only occur when the foot experiences the
repetitive impact forces that researchers are constantly trying to attenuate.
Therefore, if changing the midsole properties of athletic shoes has only a small
effect on impact force, less cushioning may be needed in running shoes then
originally believed.
Cushioning: An Unresolved Controversy
The effect of variation in midsole density of athletic shoes on vertical
impact forces has been surprising. Impact forces did not differ significantly when
running in shoes with varying midsole density.2, 15, 38, 53, 59 Peak vertical impact
forces have been found to have no correlation or a negative correlation with
athletic shoe midsole hardness.15, 16 Most locomotor studies during running have
shown positive correlations between improved cushioning of shod over barefoot
42
conditions, but few have shown differences between footwear with different
midsole properties.15, 38 These results indicate that there must be some
mechanism by which the body regulates the magnitude of external impact force
during running.86
There are at least two possibilities to explain the surprising result that the
external forces remained constant for different material properties of the shoe
midsole: 1) the changes in midsole density were too small to have an effect; or 2)
there must be an adjustment in the kinematics of the leg. A change in kinematics,
however, would have an effect on internal loading and may increase or decrease
internal forces and stresses.8, 53, 86 The mechanism behind these observations
are not understood clearly and there is a lack of conclusive evidence due to
varying speculations.53, 86 The lack of effect seen when changing the midsole
stiffness may be due to runners adapting kinematically to different cushioning
systems and surfaces in a manner that compensates for the effect of the
cushion.25
Gerritsen et al.28 found that more extended knee angles at footstrike
resulted in higher peak forces. During running the knee undergoes 30 degrees of
flexion following footstrike. This flexion at the knee is thought to attenuate part of
the impact of the body at the ground contact and has been referred to as
cushioning flexion. The link between stiffness and injury protection, however, is
not confirmed.38 Stiffness of the body affects the transmission of potentially
harmful impact shocks.38 Decreasing stiffness seems to initially decrease impact
shock.
43
Nigg and Liu59 also found that subjects preactivate (tune) their muscles
differently when midsole hardness changed and that these changes may have
been part of the reason that the impact force peaks in running experiments did
not change with changing midsole hardness. Evidence to support this finding
relates to the force-length relationship of human muscles. The force-length
relationship of human muscles results in a spring like behavior with the stiffness,
depending on muscle activation level.86 Therefore, the change in muscle activity
may alter the stiffness and damping of the human body, leading to a
corresponding change in impact force peaks. The results of this study indicated
that muscle tuning is a possible strategy that influences impact forces when
running.59 Muscle tuning could account for the minimal differences found in
impact forces with varying midsole density.
Gerritsen, van den Bogert and Nigg28 suggested that when shoe
properties are changed, runners may adapt their gait pattern and therefore mask
any changes in impact peak forces. Frey25 indicated that runners have
significantly greater knee flexion velocities immediately following impact at heel
contact when wearing harder shoes. When the knee is flexed more rapidly during
an impact, the leg behaves as a more compliant spring, thus reducing the peak
force at impact.25 Therefore, lower extremity impacts that involve greater knee
flexion amplitude should result in lower initial leg stiffness and better cushioning
of the body.8
Fuller26 also suggests that the more the knees are flexed, the softer the
impact will be upon landing. As the knees flex they increase the amount of time
44
that a force can be applied to stop downward momentum. Runners wearing
harder shoes could alter the impact forces by increasing knee flexion. Fuller
indicates that this phenomenon shows that in running, a rhythmic activity, people
can adapt to characteristics of shoes.26
The results of LaFortune et al.38 follow the results of previous studies that
found that lower limb kinematic adaptations were responsible for the lack of
midsole effects on impact force. They also found, however, that EVA interfaces
produced impact force changes that they speculated reduce the risks of
musculoskeletal damage. The potential benefit of increased knee flexion at
footstrike is similar to the benefits of an EVA midsole. The differences are that
running with increased knee flexion results in greater O2 consumption. The higher
energy requirement suggests that running with increased knee flexion may be
effective in reducing running peak ground reaction forces, but it is only a
temporary solution. Therefore, they suggested that the protective functions of a
shoe midsole might play a greater role with fatigue.38
Further evidence that knee activity changes with the hardness of the
midsole of an athletic shoe comes from relating oxygen consumption to knee
activity in runners. Frederick, Clarke and Larsen23 found a correlation between
knee flexion velocity, caused by midsole hardness, and oxygen consumption.
They suggest that when the knee was more flexed (bent), muscles have to work
harder to keep the body from collapsing.23, 26 Therefore, similar to the results of
LaFortune et al.,38 increased knee flexion may be a temporary solution to
attenuate impact forces, however, muscle fatigue may gradually reduce the
45
protective mechanism of knee flexion upon impact. Research suggests that when
muscle fatigue reduces the dampening and shock absorbing effect of muscles
there is an increase in the transmission of impact shock to the lower extremity.47
McMahon, Valient and Frederick44 found that using increased knee flexion
to attenuate impact forces has some negative affects. They collected data on
three subjects who attempted to run with exaggerated knee flexion, Groucho
running.44 They found that initial peak force remained unchanged with increases
in knee flexion upon impact but that axial stiffness was reduced when compared
to normal running. They also indicated that shank shock increased as knee
flexion became more exaggerated during running.44 The results of this study
further indicate that increases in knee flexion may not be enough to protect the
body against increased impact forces upon landing.23, 38, 44
Knee flexion initially appears to reduce impact peaks when running but
these increased knee flexion angles are not as effective as the muscles
fatigue.23, 38 Increased knee flexion angles also appear to increase the
transmission of impact shocks as the knee flexion angles increase during
running.44 This further indicates the need for an external protective mechanism,
such as a sufficiently cushioned athletic shoe. A cushioned midsole provides
external force attenuation that is resistant to fatigue and may be better able to
consistently reduce the transmission of impact shocks upon landing.38
LaFortune, Hennig and Lake38 concluded that if musculoskeletal damages
are solely dependant upon the magnitude of the external impact force, the
protection provided by increased knee flexion would be similar to that provided
46
by soft EVA cushioned midsoles. They found that softer EVA interfaces in the
midsole of athletic shoes produced foot loading and shank shock changes that
have been speculated to reduce the risk of musculoskeletal damages.38
Another theory on athletic shoe construction by Stacoff, Denoth, Kaelin
and Steussi74 proposed that future athletic shoe designs should aim to reduce
the length of the lever at touchdown rather than focus on pure shock absorption.
Their research indicated that during the touchdown phase, initial pronation
occurs when the line of action of the impact force does not pass through the
subtalar joint. Forces that cross beyond this point produce a moment and
therefore the length of the lever is important to the loading of structures
surrounding the joint. Initial pronation tends to increase with an increase in
leverage, which is affected by the shoe construction. A change from soft to hard
midsoles produces an increase in the length of the lever. The lever length affects
initial pronation, which in turn affects the magnitude of the initial impact force. 51,
74
Another consideration, which adds to the controversy, is the type of
cushioning being placed in athletic shoe midsoles to provide shock absorption.
Schwellnus et al.,71 found that by adding neoprene insoles to the boots of military
recruits for 9 weeks there was a decreased incidence of overuse injuries and
stress fractures. Conversely, Gardner et al.,27 failed to demonstrate a reduction in
overuse injuries and stress fractures after adding viscoelastic insoles to the boots
of US Marine recruits for 12 weeks. The reason for this is not clear but it has
been speculated that it may be the type of insole that was used for the study.27
47
Viscoelastic insoles have not been shown to significantly reduce vertical impact
forces as compared to conventional running shoe insoles.57 Furthermore,
studies comparing the material properties of viscoelastic and neoprene insoles
found neoprene insoles to be less rigid, more resistant to shear compression
forces, and better able to reduce transmitted force than viscoelastic insoles.71
These studies reinforce that the material that is placed in an athletic shoe to
provide cushioning must be selected very carefully. There are many materials
available that attempt to attenuate impact forces and all of these materials do not
perform the same during dynamic testing.
Summary
There is a great deal of controversy in the shoe and running literature.
Evaluations of footwear and the effectiveness of cushioning have produced
inconclusive results. Athletic shoes continue to be produced with increased
cushioning even though research indicates that impact force is not significantly
attenuated by cushioning. It is possible that the benefits of cushioning are more
evident during fatigue or on unfamiliar surfaces.
It is apparent, throughout the literature, that each runner modifies their
running gait to reduce impact force at footstrike, and that kinematic adaptations,
as well as the cushioning properties of the shoe, give runners added protection
from impact forces at footstrike. In running, there is a complex interaction among
the runner, the shoe, and the ground. Impact forces can be changed by
adjustments made by the runner because the runner knows the next step should
48
be similar to the last step. These adjustments can be in knee angle or touchdown
velocity.26
The study of the effects of shoes is complicated by the wide range of
responses seen in individuals wearing the shoes. Most of the research that has
been discussed was mainly concerned with the effect of midsole density during
running activities. Through this running research, it is well documented that
proper amounts of cushioning can reduce impact forces.15, 25, 38-40, 46, 50, 59-61, 71, 77
There is controversy, however, in determining exactly how much cushioning
should be in the midsole of an athletic shoe for runners and little research has
been conducted to examine cushioning in the athletic shoes for athletes who
perform jumping sports.
Athletic shoe design is an important area of research and the literature
indicates that specific modifications to a shoe can affect an athlete’s comfort,
safety, and performance. The research, however, has yet to clearly define which
materials or how much should be placed in the midsole of an athletic shoe.
Cushioning materials are necessary for protection from hard impact landing force
to prevent injury but the exact amount and type of cushioning is yet to be
determined. A midsole that is hard or stiff seems to improve jumping
performance but increased midsole stiffness may increase the impact force upon
landing after a jump. Therefore, a hard midsole in an athletic shoe may increase
performance, but without cushioning properties may also increase the injury rate.
A soft midsole in an athletic shoe may improve shock absorption and reduce the
incidence of injury, but excessive cushioning may actually lead to injury by
49
reducing the body’s own sensory feedback mechanism possibly causing peak
impact forces to increase.
A balance of these factors needs to be achieved to develop an optimal
shoe for athletes. Further, more research is needed in the area of female athletic
shoes, taking into consideration the anatomical difference between the male and
female foot. Research is also needed to determine how an athletic shoe should
be constructed for female athletes who routinely perform landing activities.
Additional research is needed on changing the midsole properties of an athletic
shoe to determine the effect these changes will have on impact forces during
landing in a repetitive, non-rhythmic sport.59
Chapter Three
METHODOLOGY
Subject Description
Twenty female subjects (mean ± S.D., age = 21.1 ± 2.84 years, height =
178.59 ± 3.81 cm, weight = 72.82 ± 6.65 kgs) were recruited to participate in this
study. All subjects were elite volleyball players still currently competing in
volleyball competition at least 3 times a week. Elite volleyball players were
considered any volleyball athlete that was currently competing, or had previously
competed, in NCAA Division I intercollegiate athletics. Of the twenty participants,
9 were middle blockers, 8 were outside hitters and 3 were right side hitters.
Informed written consent was obtained from every subject who
volunteered for the study according to the policy of the Human Research Review
Committee at The University of Toledo, Toledo, OH (Appendix A). All participants
were considered to be healthy and in excellent physical condition. This was
determined by a medical health questionnaire, completed by all subjects, before
starting the study (Appendix B). Subjects were excluded if they had any history of
lower extremity surgery. Subjects were also excluded if they had any lower
extremity injury within the last six months, which caused them to miss a game or
a practice. Additionally, all of the participants completed a volleyball history form
providing a detailed account of their volleyball playing
50
51
history (Appendix C). This information ensured that all subjects fit into our
operational definition of elite volleyball athlete.
Volleyball athletes were selected as subjects because of their familiarity
with constrained vertical jumping. This skill is specific to volleyball athletes and
athletes from other sports are usually not trained in this type of jump. The design
of the data collection protocol required the subjects to perform an approach and
jump, in a defined area, with a two footed landing on two force plates. This task
was similar to the spike approach which is routinely performed by volleyball
athletes. The consistency of the spike approach ensured consistency in the
approach and jump needed in this investigation. Volleyball athletes were also
selected because they routinely experience continuous non-repetitive landing
forces during play. Female athletes were selected because limited research has
been conducted in the area of women’s athletic shoes and therefore, female
shoe sizes were selected for testing and data collection. All subjects had a shoe
size in the range of 8.5 to 11 US women’s.
Instrumentation
Shoes
The shoes used in this investigation were commercially available athletic
shoes manufactured by Fila USA (FILA USA, Peabody, MA) style number
51T275LX-120, last 2-7996-1, and mold FL-780-3. Each shoe contained one
molded ethylene vinyl acetate (EVA) foam layer in the midsole. Fila USA
provided the investigator with shoes representing three versions of this midsole
(Figure 3). Each midsole condition used in this investigation had the same
52
density measurement throughout the entire midsole layer. All shoes were the
same in appearance and varied only in the density (durometer measurement) of
the midsole. Durometer hardness can be measured on different scales; the
measurement scale used in this investigation was Asker C.
A total of eighteen pairs of shoes were used during data collection, with
the three different midsole densities represented for each size (8.5 to 11): a
control shoe; a shoe with a soft midsole; and a shoe with a hard midsole. The
control shoe had a midsole durometer measurement that is similar to
commercially available volleyball shoes, 55 Asker C. The soft shoe had a
midsole durometer measurement of 45 Asker C, and the hard shoe midsole
measured 65 Asker C.
The durometer measurements selected for this research were all within
the normal range of density that could safely be placed in the midsole of an
athletic shoe. The midsole durometer measurement of volleyball shoes typically
ranges from 53 to 58 Asker C. This typical volleyball durometer is represented by
the control shoe with a durometer of 55 Asker C. The soft and hard midsole
durometers were chosen to be 45 and 65 Asker C respectively in order to
represent a range of midsole above and below that which found in a typical
volleyball shoe. The durometer of 45 Asker C is more cushioned and the
durometer of 65 Asker C is slightly harder than the typical midsole in an athletic
shoe.
53
A. Control Shoe
B. Soft Shoe
C. Hard Shoe
Figure 3. Fila Athletic Shoes used for data collection
Kinematic Data
Kinematic data was collected simultaneously with the kinetic data using a
six camera Motion Analysis EVa Hi-Res system (Motion Analysis Corporation,
Santa Rosa, CA). The EVa Hi-Res system is a fully integrated hardware-software
system for video and analog data acquisition and processing. The EVa software
allowed for calibration, data collection and marker tracking. All kinematic data
was sampled at 120 Hz and low pass filtered at 10 Hz.
Six electronically synchronized Falcon High Resolution cameras (Motion
Analysis Corporation, Santa Rosa, CA) were used to collect the motion of the
retroflective markers. Each camera had a ring of lights placed around the lens
that produced a red strobed light. The strobes were used to illuminate the
retroflective markers and produce a clear video image of each marker. The
cameras transmitted the images of the markers directly to the video
processor/computer (MiDAS). MiDAS accepts the input from the cameras and
produces the coordinates of the retroflective markers. A Dell Dual Pentium PC
received the data from the MiDAS system and the EVa Hi-Res software (version
6.15) was used to process the video data. All video data were tracked, rectified,
54
interpolated, and smoothed using the EVa Hi-Res software. All processed video
data was saved as binary .trb files for further analysis. All tracked kinematic data
(.trb files) were transferred to KinTrak (version 6.2.2) (Motion Analysis, Santa
Rosa, CA) for data analysis.
Kinetic data
Ground reaction forces were collected using two AMTI force platforms
(Advanced Medical Technology Inc. Model #’s OR6-3 & SGA6-4, Watertown,
MA). Force platform data was collected at 1500 Hz. The gains on the force
platform were set at 1000 and the data was low pass filtered at 1050 Hz. To
provide a means of standardizing, all force measurements were converted into
body weights (BW). All kinetic data was time matched with kinematic data and
was transferred through the MiDAS system to the Dell Dual Pentium PC. The
kinetic data was saved with video data as a binary (.trb and .anb) files and was
transferred to KinTrak (Motion Analysis, Santa Rosa, CA) for analysis.
Experimental Set Up
The six cameras and two force plates were arranged in the University of
Toledo Applied Biomechanics Lab (UTABL), Toledo, OH. The cameras were
positioned so the subjects could be visualized during the entire event (Figure 4).
This ensured that the subjects’ entire movement could be collected by at least
two cameras at all times to ensure accurate data collection. Two AMTI force
plates were placed parallel to each other to allow each of the subjects’ feet to
land completely on their respective force plates (Figure 5). A volleyball was
suspended directly over the force platforms using the Crush It (Excel Sports,
55
Huntington Beach, CA). The ball was positioned to naturally allow the subjects to
land directly onto the force platforms (Figure 6). This allowed players to easily
land on the force plates without modification to their natural landing. Each subject
landed with one foot on each force platform.
The testing area had to be calibrated prior to each testing session in order
for the marker images from all cameras to be translated into 3D coordinate
values. Calibration involved the use of a calibration cube (Motion Analysis, Santa
Rosa, CA) with 8 markers in a known configuration. The cube was positioned in
the center of the testing area and data was collected for 1 second. In order to
expand the calibrated space a wand calibration was performed. The calibration
wand has three linear markers in a known configuration; data was collected at 5
Hz for 190 seconds. The wand calibration ensures that a direct measurement of
an object of a known size has been made by all cameras throughout the entire
capture volume. The software uses the wand calibration to locate the position of
each camera and account for any optical distortion of the camera lenses. A
calibration was performed prior to each data collection session.
56
Camera
A. Frontal view
C. Transverse view
Figure 4. Position of 6 cameras
A. Sagittal view
Force
Plate
Force
Plate
Figure 5. Alignment of force plates
57
Camera
Crush It
(suspended volleyball)
Force Plate 1
Force Plate 2
Figure 6. Frontal View of Experimental Set Up, testing
area, position of 6 cameras and force pates
Data Collection Procedure
Subjects attended one 2 hour laboratory session at The University of
Toledo’s Applied Biomechanics Laboratory (UTABL) where all data was
collected. During data collection, all subjects were filmed while landing after
performing a volleyball approach jump and spike. Subjects performed in three
different shoe conditions: control midsole, soft midsole, and hard midsole. All
shoes were randomly assigned (Appendix G). All activities were performed at a
self selected pace and subjects were permitted to rest or take breaks at any time
during testing, to minimize the effects of fatigue.
All data collection procedures were explained to the subject upon arrival at
the UTABL. Subjects were asked to read and sign the Informed Consent Form
(Appendix A) before data collection began. After the informed consent was
58
signed subjects were asked to fill out a Medical Health Questionnaire (Appendix
B) and a Volleyball History Form (Appendix C). Volleyball History Data are
presented in Appendix D.
Measurements of each subject were taken bilaterally in bare feet of foot
width, ankle width, knee width and foot length. Subjects were also measured
barefoot for height, weight, standing reach (flat feet to the fingertips of their
dominant hand), and wing span (fingertip to fingertip of horizontal outstretched
arms) (Appendix E). Anthropometric data was obtained from each subject prior to
data collection (Appendix F). A summary of Anthropometric Data is presented in
Table 1.
Table 1. Summary of Anthropometric Data
Measurement
Mean ± SD
Age
Shoe Size
Weight
Height
Standing Reach
Wing Span
Right Foot Length
Left Foot Length
21.1 ± 2.84 years
10.05 ± 0.81 US Women's
72.82 ± 6.65 kg
178.59 ± 3.81 cm
231.14 ± 6.89 cm
181.45 ± 6.25 cm
25.42 ± 1.82 cm
25.58 ± 1.59 cm
After all measurements were complete subjects were given an identical
pair of new socks to wear for all testing procedures. It was necessary to
standardize the type of socks that subjects wore to prevent any differences in the
midsoles being attributed to possible differences in socks. Subjects were then
fitted for the shoes that would be used for testing. Subjects were instructed to
select the size that felt the most comfortable. It was important for subjects to
59
select their own shoe size because some athletes prefer tighter or looser fitting
athletic shoes when participating in athletic competition. Therefore, subjects were
instructed to select the shoe size they would feel most comfortable wearing while
participating in volleyball. Subjects were told to notify the investigator at any time
if the shoes were causing discomfort. None of the subjects indicated any
discomfort and none of the subjects changed shoe sizes after data collection
began.
After a comfortable shoe size was selected retroflective markers were
placed on specified anatomical landmarks. Markers were composed of ¾ inch
dyelite Styrofoam and completely covered in retroflective tape (Figure 7).
Styrofoam Markers were attached to a flat base and a Velcro loop coin with
adhesive was affixed to the bottom of the base. Small ¾ inch Velcro hook coins
with adhesive were attached to the skin and clothing. The hook and loop Velcro
connected to hold the markers securely in place on the skin and clothing. On all
marker locations located directly on the skin, the skin was prepared by spraying
Quick-Drying Tape Adherent (QDA) (Cramer Products, Inc., Gardener, KS) to
prevent markers from dislodging during data collection procedures. Retroflective
markers were placed on the sacrum and bilaterally on the: wrist, elbow,
acromion process, ASIS, greater trochanter, mid anterior thigh, lateral femoral
condyle, tibial tuberosity, lateral mid shank, medial low shank, calcaneus, 5th
metatarsal, and superior navicular. A total of 27 retroflective markers were placed
on each subject for all dynamic data collection trials. Four additional markers
were placed bilaterally on the patella, and lateral malleolus for one static trial,
60
prior to data collection (Figure 8). Subjects we required to wear spandex shorts
and a tank top during all testing procedures. Form fitting clothing allowed the
markers to be tightly secured to bony landmarks when it was necessary to place
markers on top of clothing. Tighter clothing was also less likely to shift and
potentially block or cover a marker during data collection.
A one second static trial was collected as soon as all of the markers were
placed on the subject. Subjects were required to face forward with their feet
shoulder width apart and their arms out to the side. Subjects were instructed to
stand as still as possible for a one second static trial. Upon completion of the
static trial, the 4 static markers were removed for the remainder of data
collection.
Figure 7. Retroflective Marker and
Sacral wand
61
A. Frontal view
B. Sagittal view
C. Transverse view
Figure 8. Position of 31 retroflective markers during static trial
Subjects were now permitted to warm up their shoulder by throwing and
hitting a volleyball against the gymnasium wall. All subjects performed a self
selected warm up and were provided with as much time as necessary to
adequately prepare for data collection. After this warm up subjects were
permitted 10 practice trials to become familiar with the data collection procedure.
Testing Procedures
All subjects performed approximately 30 volleyball approaches and
spikes. All jumps were performed using a three step hitting approach, common to
volleyball players. All left handed subjects started the approach with their right
62
foot and all right handed subjects started their approach with their left foot. All
subjects left the ground by planting both feet and springing upward using their
arms and legs according to the technique involved in the hitting approach.
As the subjects hit the peak of their jump they performed a spike by
swinging in mid air at the Crush It suspended volleyball, they then landed
downward onto the force platform to measure landing force. Prior to data
collection, during the warm up trials, the Crush It was individually adjusted for
subjects at their comfortable hitting height.
Volleyball players are trained to land directly downward and stop their
forward momentum to avoid hitting the net. The ball was positioned to naturally
allow the subjects to land directly onto the force platforms. This allowed players
to easily land on the force plates without modification to their natural landing.
Each subject landed with one foot completely on each force platform.
The order of shoe assignment was determined through random
assignment. A chart indicating the order of random assignment is presented in
Appendix G.
For each shoe condition, 10 successful trials were collected for kinetic and
kinematic data. A successful trial counted as a jump where both of the subject’s
feet landed completely on the respective force platforms.
Condition I Testing
Subjects were given the first pair of randomly assigned athletic shoes.
While wearing the first pair of assigned athletic shoes the subjects were required
to perform a 1 lap warm up jog around the inside lane of an indoor track
63
(approximately 170.85 meters). After the warm up jog, data was collected on the
subjects while wearing the first pair of athletic shoes and performing a volleyball
approach jump. Kinetic and Kinematic data were collected for a total of 5
seconds. When data collection is initiated by the investigator the video system
provides an audio tone to designate the start of data collection. The subjects
were instructed to begin their approach from a self selected mark, determined
during the practice trials, upon hearing the tone. This procedure was repeated
until 10 successful trials were collected. For most subjects a total of 12 to15
volleyball approach jumps were attempted during each condition. All activities
were performed at a self selected pace and subjects were permitted to rest or
take breaks at any time during testing, to prevent a fatigue effect. There was a
30 second mandatory rest between each volleyball approach jump trial.
Kinetics and kinematics were measured for each subject in shoe condition
one, for a total of 10 successful trials.
Condition II Testing
After the first shoe testing session and data collection, the athletic shoes
were given back to the investigator. The subjects were then required to jog
around the indoor track without shoes (sock-only) for 1 lap (approximately 170.85
meters) before putting on the next pair of shoes. This sock-only jog was used to
wash out the previous shoe condition.
Shoes were traded without the subject’s knowledge, while the subjects
performed the sock-only jog outside the UTABL on the indoor track. Shoes were
arranged exactly as the subjects had left the previous pair in order to prevent the
64
subject from knowing the shoes had been changed.
After the one minute sock-only jog, subjects were required to jog around
the gym again for 1 lap (approximately 173.98 meters), to warm up in the second
shoe condition. Kinetics and kinematics were measured for each subject in shoe
condition two, for a total of 10 successful trials.
Condition III Testing
After the second shoe testing session and data collection, the athletic
shoes were given back to the investigator. Again the subjects were required to
jog sock-only around the indoor track for 1 lap. This sock-only jog was again
used to wash out the previous shoe condition. The shoes were again traded
while the subjects were performing the sock-only jog and the subjects had no
knowledge that the shoes had been changed. After the 1 lap sock-only jog,
subjects were required to jog around the indoor track again, for 1 lap, to warm up
in the last shoe condition. Landing force and kinematics were measured for each
subject in shoe condition three, for a total of 10 successful trials.
Upon completion of the last trial, all markers were removed from the
subject. The Crush It volleyball height was measured, from the bottom of the ball
to the floor and subjects were asked to fill out a Post Participation Questionnaire
(Appendix H).
Statistical Analyses
The independent variable for this investigation was midsole density with
three levels (control midsole, soft midsole and hard midsole). The dependent
variables of interest can be found in Appendix I. A total of 30 landing trials (10
65
trials × 3 shoe conditions) were collected and analyzed for each subject. At least
8 trials for each subject, for each condition, were averaged for each dependent
variable and used for statistical analysis.
A one-way repeated measures analysis of variance (ANOVA) was used to
compare how the within subjects experimental group performed in the three
midsole conditions. The ANOVA was used to determine whether the mean of any
of the individual experimental conditions differ significantly from the aggregate
mean across the three experimental conditions. A separate repeated measures
ANOVA was performed using SPSS 12.0 software for each of the dependent
variables.
Within subject contrasts were performed with the repeated measures
ANOVA. The within subject contrasts does not affect the results of the univariate
analysis, they are used to determine significant contrasts between the levels of
the within subject factors (control midsole, soft midsole and hard midsole). The
level of significance was at p ≤ 0.05.
Chapter Four
RESULTS
The kinetic data collected from the two force platforms, during the three
athletic shoe midsole conditions, are presented as vertical forces, internal
moments and loading rates. These values represent vertical ground reaction
force values, vertical ground reaction force loading rates, and ankle, knee and
hip joint moments during landing from a volleyball approach and spike.
The three dimensional kinematic data for the lower extremity, during the
three athletic shoe midsole conditions, are presented as position angles, angular
displacements, and temporal parameters. These values represent specific points
in the range of motion of the ankle, knee and hip joint bilaterally during the jump
landing event.
Objective identification was used to identify initial foot contact with the
ground, at beginning of the jump landing event and was indicated by a
measurement on each force platform of 0.02 bodyweights. Subjective
identification was used to designate the end of the jump landing event. The end
of the jump landing sequence was indicated by a balanced static stance position
of 0.5 bodyweights on each force platform; this was manually set at 0.75
seconds, after initial foot contact on each force platform, for all subjects.
Objective data points were used to identify peak vertical ground reaction
66
67
force, peak ankle, knee and hip joint moments, joint positions angles of the ankle
knee and hip, and maximum angular displacements at the ankle, knee and hip.
The complete range of motion of the ankle, knee and hip from initial contact to
the end of the jump landing sequence is also presented.
The results of the Post Participation Questionnaire were collected from
each subject at the conclusion of all testing procedures. The results of this
questionnaire are presented in Table 48.
Kinetic Measurements
Peak vertical ground reaction force was the measurement of interest upon
landing after the volleyball approach and spike. Left peak vertical ground reaction
force was defined as the numerically highest vertical force after initial foot contact
with the left foot on the left platform. Right peak vertical ground reaction force
was defined as the numerically highest vertical force after initial foot contact with
the right foot on the force platform. Total peak vertical ground reaction force was
defined as the mathematical addition of left and right peak vertical ground
reaction forces.
Loading rates were calculated bilaterally for each peak vertical ground
reaction force. The value for loading rate was calculated bilaterally using the
amount of time, in seconds, it took to reach peak vertical ground reaction force.
Loading rate was defined as the peak vertical ground reaction force divided by
the time in seconds it took to reach peak vertical ground reaction force on the left
and right side.
68
Peak joint moments were analyzed bilaterally for the ankle, knee and hip.
Peak joint moments were defined as the numerically highest joint moment after
initial foot contact on each force platform.
evaluate the effect of variations in athletic shoe midsole density on peak vertical
ground reaction force, and peak joint moments at the ankle, knee and hip.
Variations in athletic shoe midsole density revealed no significant difference for
left or right peak vertical ground reaction forces. Within-Subjects Contrasts were
used to identify specific differences between the soft, control and hard midsole
athletic shoes. The Within-Subjects Contrasts identified no significant differences
were found between athletic shoe midsole density and left or right peak vertical
ground reaction forces. Means and standard deviations for bilateral peak vertical
ground reaction forces are shown in Figure 9 and Table 2. A Statistical summary
table for the effect of athletic shoe midsole density on left and right peak vertical
ground reaction forces is presented in Table 3. The complete range of vertical
forces for the entire jump landing event was evaluated bilaterally and is
presented in Figure 11 and 13. The means and standard deviations for left and
right vertical ground reaction forces are found in Table 6.
The repeated measures analysis of variance indicated no significant
differences in athletic shoe midsole densities for total peak vertical ground
reaction force. Within-Subjects Contrasts also revealed no significant differences
between the athletic shoe midsole densities for total peak vertical ground
reaction force. Means and standard deviations for total peak vertical ground
69
reaction force are shown in Figure 10 and Table 4. A Statistical summary table
for the effect of athletic shoe midsole density on total peak vertical ground
reaction force is presented in Table 5. The complete range of total vertical
ground reaction forces for the entire jump landing sequence is presented in
Figure 13. Means and standard deviations for total vertical ground reaction forces
are found in Tables 7.
There were no significant differences found between athletic shoe midsole
densities for right or left loading rates. Within-Subjects Contrasts also revealed
no significant differences between midsole density and left or right knee loading
rates. Means and standard deviations for bilateral loading rates are presented in
Figure 14 and Table 8. A Statistical summary table for the effect of athletic shoe
midsole density on left and right loading rates is found in Table 9.
The repeated measures analysis of variance determined that there were
no significant differences between athletic shoe midsole densities for left or right
peak ankle joint moments. Within-Subjects Contrasts also revealed no significant
differences between midsole densities. Means and standard deviations for
bilateral peak ankle joint moments are shown in Figure 15 and Table 10. A
Statistical summary table for the effect of athletic shoe midsole density on left
and right peak ankle joint moments is found in Table 11.
Variations in athletic shoe midsole density had a significant effect (p ≤
0.05; p = 0.042) on the left peak knee moment. Within-Subjects Contrasts used
to assess individual differences determined that the peak knee moment was
significantly different between the hard and the soft midsole (p = 0.024), and
70
between the hard and control midsole (p = 0.045). There were no significant
differences found between athletic shoe midsole densities for peak knee
moments on the right side. Within-Subjects Contrasts also revealed no significant
differences for right peak knee moments. Means and standard deviations for
bilateral peak knee moments are shown in Figure 16 and Table 12. A Statistical
summary table for the effect of athletic shoe midsole density on left and right
peak knee moments is found in Table 13.
densities for left or right peak hip joint moments. Within-Subjects Contrasts also
revealed no significant differences between midsole densities. Means and
standard deviations for left and right peak hip joint moments are shown in Figure
17 and Table 14. A Statistical summary table for the effect of athletic shoe
midsole density on left and right peak hip joint moments is shown in Table 15.
71
Figure 9.
Peak Vertical Ground Reaction Forces:
After Initial Contact with the Ground
Soft Midsole
Control Midsole
Hard Midsole
Force (bodyweights)
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Left
Right
Means and Standard Deviations
Table 2. Means and Standard Deviations:
Peak Vertical Ground Reaction Forces
Midsole n
Means ± Standard Deviations (bodyweights)
Soft
Control
Hard
20
20
20
Left
Right
2.394 ± .527
2.343 ± .356
2.335 ± .394
2.327 ± .568
2.341 ± .596
2.309 ± .519
Table 3. Statistical Summary of Athletic Shoe Midsole Density on Left and
Univariate Comparisons: Greenhouse-Geisser
F-value
p-value
Left
.537
.550
Right
.181
.773
Within-Subjects Contrasts: Left
Midsole vs. Midsole
Soft vs. Control
Control vs. Hard
Soft vs. Hard
F-value
.616
.034
.662
Power
.123
.073
p-value
.442
.856
.426
Power
.116
.054
.121
Within-Subjects Contrasts: Right
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
.043
.839
Control vs. Hard
.411
.529
Soft vs. Hard
.202
.658
* indicates significance at the 0.05 level
Power
.054
.094
.071
72
Figure 10.
Total Peak Vertical Ground Reaction Force:
After Initial Contact with the Ground
Soft midsole
Control midsole
Hard midsole
Force (bodyweights)
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Total Peak Vertical Ground Reaction Forces
Midsole n Means ± Standard Deviations (bodyweights)
Soft
Control
Hard
20
20
20
4.720 ± .867
4.684 ± .823
4.644 ± .779
Table 5. Statistical Summary of Athletic Shoe Midsole Density on Total
Peak Vertical Ground Reaction Force
F-value
p-value
Total:
.586
.526
Within-Subjects Contrasts: Total
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.180
.676
Control vs. Hard
0.353
.559
Soft vs. Hard
1.894
.185
Power
.130
Power
.069
.087
.257
73
Figure 11.
Left Peak Vertical Ground Reaction Force
Soft Midsole
Control Midsole
Hard Midsole
2.6
2.2
Bodyweights
1.8
1.4
1
0.6
0.2
-0.2 0
50
150
200
250
300
Samples
% of the Jump
Landing Sequence
Impact
Figure 12.
100
Soft Midsole
Hard Midsole
Control Midsole
2.6
2.2
Bodyweights
1.8
1.4
1
0.6
0.2
-0.2 0
50
Impact
100
150
200
250
Samples
% of the Jump
Landing Sequence
Left and Right Peak Vertical Ground Reaction Forces
Midsole n
Soft
Control
Hard
20
20
20
Left Peak GRF
Right Peak GRF
2.394 ± .527
2.343 ± .356
2.335 ± .394
2.327 ± .568
2.341 ± .596
2.309 ± .519
Peak GRF = Peak Ground Reaction Force
300
74
Figure 13.
Total Peak Vertical Ground Reaction Force
Soft Midsole
Control Midsole
Hard Midsole
4.8
Bodyweights
3.8
2.8
1.8
0.8
-0.2
0
50
Impact
100
150
200
250
Samples
% of the Jump
Landing Sequence
Total Peak Vertical Ground Reaction Forces
Midsole n
Soft
Control
Hard
20
20
20
Peak GRF
0.75 sec Post
4.720 ± .867
4.684 ± .823
4.644 ± .779
1.003 ± .031
1.045 ± .026
1.062 ± .015
Peak GRF = Peak Ground Reaction Force
0.75 sec Post = 0.75 seconds after impact
300
75
Figure 14.
Loading Rate:
Time to Peak Vertical Ground Reaction Force
Soft Midsole
Control Midsole
Hard Midsole
Loading Rate
(bodyweight/seconds)
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Left
Right
Loading Rate
Midsole n
Means ± Standard Deviations (bodyweight/seconds)
Soft
Control
Hard
20
20
20
Left
Right
36.208 ± 14.852
35.241 ± 12.057
34.932 ± 11.078
29.622 ± 9.890
30.122 ± 11.735
29.569 ± 10.097
Right Loading Rate
F-value
p-value
Left
.331
.690
Right
.110
.865
Midsole vs. Midsole
Soft vs. Control
Control vs. Hard
Soft vs. Hard
F-value
.424
.045
.437
Power
.096
.064
p-value
.523
.834
.516
Power
.095
.055
.096
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
.124
.729
Control vs. Hard
.146
.706
Soft vs. Hard
.003
.957
Power
.063
.065
.050
76
Figure 15.
Soft Midsole
Control Midsole
Hard Midsole
Bodyweight
Meters
Bodyweight •Meters
0.00
-0.05
-0.10
-0.15
-0.20
-0.25
-0.30
-0.35
-0.40
-0.45
-0.50
Left
Right
Midsole n
Means ± Standard Deviations (Bodyweight • Meters)
Soft
Control
Hard
20
20
20
Left
Right
-.334 ± .119
-.353 ± .104
-.321 ± .079
-.268 ± .075
-.251 ± .053
-.254 ± .049
Right Peak Ankle Joint Moments
Ankle:
F-value
p-value
Left
0.644
.509
Right
1.953
.173
Midsole vs. Midsole
Soft vs. Control
Control vs. Hard
Soft vs. Hard
F-value
0.355
2.023
0.186
Power
.142
.298
p-value
.559
.171
.671
Power
.087
.272
.069
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
2.664
.119
Control vs. Hard
0.423
.523
Soft vs. Hard
1.592
.222
Power
.341
.095
.224
77
Figure 16.
Soft Midsole
Control Midsole
Hard Midsole
Bodyweight • Meters
0.70
0.60
*
0.50
0.40
0.30
0.20
0.10
0.00
Left
Right
Midsole n
Soft
Control
Hard
20
20
20
Left
Right
.479 ± .109
.499 ± .153
.408 ± .100
.385 ± .099
.387 ± .087
.377 ± .083
Right Peak Knee Joint Moments
Knee:
F-value
p-value
Left
3.838
.042*
Right
0.430
.627
Midsole vs. Midsole
Soft vs. Control
Control vs. Hard
Soft vs. Hard
F-value
0.420
4.597
5.996
Power
.588
.110
p-value
.525
.045*
.024*
Power
.094
.530
.642
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.051
.825
Control vs. Hard
1.038
.321
Soft vs. Hard
0.334
.570
Power
.055
.162
.085
78
Figure 17.
Soft Midsole
Control Midsole
Hard Midsole
0.00
Bodyweight • Meters
-0.05
-0.10
-0.15
-0.20
-0.25
-0.30
-0.35
Left
Right
Midsole n
Soft
Control
Hard
20
20
20
Left
Right
-.210 ± .107
-.179 ± .095
-.186 ± .086
-.162 ± .082
-.156 ± .079
-145 ± .108
Right Peak Hip Joint Moments
Hip:
F-value
p-value
Left
.751
.444
Right
.838
.410
Midsole vs. Midsole
Soft vs. Control
Control vs. Hard
Soft vs. Hard
F-value
.871
.117
.970
Power
.150
.161
p-value
.362
.736
.337
Power
.144
.062
.155
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.435
.517
Control vs. Hard
0.560
.463
Soft vs. Hard
1.238
.280
Power
.096
.110
.185
79
Angular Displacements
The angular displacement of interest at the left and right ankle joint was
dorsiflexion and plantarflexion. The angle at initial foot contact and peak vertical
ground reaction force, and the maximum angular displacement were analyzed
during the jump landing. The dorsiflexion/plantarflexion angle was defined as the
sagittal plane angle formed between the foot and the lower leg. The maximum
angular displacement was measured as the largest angle in degrees after initial
foot contact. The complete range of motion at the ankle for the entire jump
landing sequence was evaluated bilaterally between the three athletic shoe
midsole densities for parallels.
The angular displacement of interest at the left and right knee was flexion.
The flexion angle at initial foot contact and peak vertical ground reaction force,
and the maximum angular displacement were analyzed. The knee angle was
defined as the sagittal plane angle formed between the thigh and lower leg. The
complete range of motion at the knee was assessed bilaterally for the entire jump
landing sequence between the three athletic shoe midsole densities.
The angular displacement of interest at the hip was flexion. The flexion
angle at initial foot contact and peak vertical ground reaction force, and the
maximum angular displacement were analyzed. The hip angle was defined as
the sagittal plane angle formed between the vertical axis of the pelvis and the
thigh. The complete range of motion at the hip was evaluated bilaterally for the
entire jump landing sequence between the three athletic shoe midsole densities.
80
The ability of an athlete to dissipate forces with joint flexion upon landing
after a vertical jump is essential to prevent injury. Therefore, the angle position
data represents two time points during the jump landing sequence: 1) at initial
contact were the athlete is preparing to dissipate forces, and 2) at peak vertical
ground reaction force were the athlete is effectively dissipating forces. The
maximum angular displacement is also a measure of the attenuation of forces
and therefore, the amount of maximum flexion at the ankle, knee and hip joint
was also analyzed.
evaluate the effect of variations in athletic shoe midsole density on the angle
position and the maximum angular displacements at the ankle, knee and hip.
Variations in athletic shoe midsole density had a significant effect (p ≤
0.05; p = 0.047) on the right ankle position at peak vertical ground reaction force.
condition at right ankle position at initial foot contact, and maximum angular
displacement. Within-Subjects Contrasts were used to identify specific
differences between the soft, control and hard midsole athletic shoes. The
Within-Subject Contrasts revealed significant differences between the soft and
hard midsole (p = 0.014) for right ankle position at initial contact. The WithinSubject Contrasts revealed significant differences between the soft and control
midsole (p = 0.010), and the soft and hard midsole (p = 0.049) for right ankle
position at peak ground reaction force. Within-Subjects Contrasts also
determined that maximum angular displacement was significantly different
81
between the soft midsole and the control midsole athletic shoe (p = 0.050). No
significant differences were found between athletic shoe midsole density and left
ankle positions and maximum angular displacement. Within-Subject contrasts
also revealed no significant differences for left ankle position. Means and
standard deviations for bilateral ankle positions and maximum angular
displacements are shown in Figures 18, 19, and 20 and Tables 16, 18, and 20.
Statistical summary tables for the effect of athletic shoe midsole density on ankle
positions and maximum angular displacements are found in Tables 17, 19, and
21. The complete range of motion at the ankle for the entire jump landing
sequence was evaluated bilaterally and is presented in Figure 21 and 22. The
complete tables for means and standard deviations for left and right ankle range
of motion angles are found in Tables 22 and 23.
The repeated measures analysis revealed there were no significant
differences between athletic shoe midsole densities for left or right knee positions
and maximum angular displacements. Within-Subjects Contrasts also revealed
no significant differences between midsole densities. Means and standard
deviations for bilateral knee positions and maximum angular displacements are
shown in Figures 23, 24, and 25 and Tables 24, 26, and 28. Statistical summary
tables for the effect of athletic shoe midsole density on knee positions and
maximum angular displacements are found in Tables 25, 27, and 29. The
complete range of motion at the knee for the entire jump landing sequence was
observed bilaterally and is presented in Figure 26 and 27. The complete tables
82
for means and standard deviations for left and right knee range of motion angles
are found in Tables 30, and 31.
The repeated measures analysis determined that there were no
significant differences in athletic shoe midsole densities for position or maximum
angular displacement at the hip. Within-Subjects Contrasts also revealed no
significant differences between midsole densities. Means and standard
deviations for hip angles and maximum angular displacements are shown in
Figures 28, 29, and 30 and Tables 32, 34, and 36. Statistical summary tables for
the effect of athletic shoe midsole density on hip positions and maximum angular
displacement are found in Tables 33, 35, and 37. The complete range of motion
at the hip joint for the entire jump landing was evaluated and is presented in
Figure 31. The complete table for means and standard deviations for hip range of
motion angles are found in table 38.
Measurements of vertical ground reaction force during landing are
affected by the height of the jump. Therefore, it was important to measure the
maximum displacement of the hip joint as an indicator of jump height. The
displacement of the hip was defined as the difference between the right ASIS
retroflective marker in the vertical plane during static stance and the maximum
ASIS position in the vertical plane during the volleyball approach and spike. This
measurement was used as an indicator of jump height.
Variations in athletic shoe midsole density did not show significant
differences in vertical hip displacement (jump height) during the jumping phase of
the volleyball jump and spike. Within-Subjects Contrasts also indicated no
83
significant differences between midsole densities. Means and standard
deviations for vertical hip displacement are shown in Figure 32 and Table 39. A
Statistical summary table for the effect of athletic shoe midsole density on vertical
hip displacement is found in Table 40. The complete range of motion for vertical
hip position indicating maximum vertical hip position during the jumping phase is
compared to hip position in static stance in Figure 33. Means and standard
deviations for hip position during dynamic and static trials are presented in Table
41.
84
Figure 18.
Soft Midsole
Control Midsole
Hard Midsole
0.0
Angle (degrees)
-5.0
-10.0
-15.0
-20.0
-25.0
-30.0
Left
Right*
Midsole n
Means ± Standard Deviations (degrees)
Soft
Control
Hard
20
20
20
Left
Right
-21.230 ± 4.67
-20.992 ± 5.34
-21.786 ± 5.19
-15.624 ± 5.91
-15.999 ± 4.92
-17.110 ± 6.17
Table 17. Statistical Summary of Athletic Shoe Midsole Density on Ankle
Ankle:
F-value
p-value
Left
0.802
.429
Right
2.843
.078
Within-Subjects Contrasts: Left Ankle
Midsole vs. Midsole
F-value
Soft vs. Control
0.293
Control vs. Hard
0.299
Soft vs. Hard
0.548
Power
.159
.493
p-value
.594
.268
.468
Power
.081
.191
.108
Within-Subjects Contrasts: Right Ankle
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.343
.565
Control vs. Hard
2.238
.151
Soft vs. Hard
7.389
.014*
Power
.086
.295
.732
85
Figure 19.
Soft Midsole
Control Midsole
Hard Midsole
40.0
*
Angle (degrees)
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
Left
Right*
Midsole n
Soft
Control
Hard
20
20
20
Left
Right
28.229 ± 6.54
28.029 ± 7.37
27.818 ± 7.00
27.505 ± 6.95
25.731 ± 7.05
25.731 ± 5.56
Table 19. Statistical Summary of Athletic Shoe Midsole Density on Ankle
Ankle:
F-value
p-value
Left
0.076
.867
Right
1.725
.047*
Midsole vs. Midsole
F-value
Soft vs. Control
.070
Control vs. Hard
.045
Soft vs. Hard
.095
Power
.061
.548
p-value
.795
.833
.761
Power
.057
.055
.060
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
8.154
.010*
Control vs. Hard
0.000
1.000
Soft vs. Hard
4.406
.049*
Power
.773
.050
.513
86
Figure 20.
Soft Midsole
Control Midsole
Hard Midsole
50.0
Angle (degrees)
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
Left
Right*
Midsole n
Soft
Control
Hard
20
20
20
Left
Right
38.519 ± 4.41
39.130 ± 5.79
38.821 ± 6.23
42.210 ± 4.97
41.180 ± 5.19
41.382 ± 4.17
Table 21. Statistical Summary of Athletic Shoe Midsole Density on
Ankle:
F-value
p-value
Left
0.265
.690
Right
1.696
.200
Midsole vs. Midsole
F-value
Soft vs. Control
1.275
Control vs. Hard
0.000
Soft vs. Hard
0.083
Power
.083
.318
p-value
.273
.996
.776
Power
.189
.050
.059
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
4.310
.050*
Control vs. Hard
0.097
.759
Soft vs. Hard
1.783
.198
Power
.504
.060
.245
87
Figure 21.
Left Ankle Range of Motion:
From Initial Foot Contact to 0.75 sec Post Impact
Soft Midsole
Control Midsole
Hard Midsole
50
Angle (degrees)
DF
40
30
20
10
0
-10
-10
0
10
20
30
40
50
60
70
80
90
100
-20
PF
-30
Samples
% of the Jump
Landing Sequence
Impact
Left Ankle Range of Motion
Midsole n
Impact
Peak GRF
Max Ang Disp
0.75 sec Post
28.229
38.518
18.862
Soft
20
-21.230
± 4.67
± 6.54
± 4.41
± 5.72
Control
20
-20.992
28.030
39.131
19.998
± 5.34
± 7.37
± 5.79
± 5.67
20
-21.786
27.818
38.821
18.981
± 5.19
± 7.00
± 6.23
± 5.89
Hard
Impact = initial foot contact
Peak GRF = Angle at Peak Ground Reaction Force
Max Ang Disp = Maximum Angular Displacement
Note: Negative angles represent plantarflexion
Positive angles represent dorsiflexion
110
88
Figure 22.
Right Ankle Range of Motion:
From Initial Foot Contact to .75 sec post impact
Soft Midsole
Control Midsole
Hard Midsole
50
DF
40
Angle (degrees)
30
20
10
0
-10
-10
0
10
20
30
40
50
60
70
80
90
100
-20
PF
-30
Samples
% of the Jump
Landing Sequence
Impact
Right Ankle Range of Motion
Midsole n
Impact
Peak GRF
Max Ang Disp
0.75 sec Post
27.505
42.210
20.304
Soft
20
-15.624
± 5.91
± 6.95
± 4.97
± 5.28
Control
20
-15.999
25.731
41.180
20.969
± 4.92
± 7.05
± 5.19
± 4.60
20
-17.110
25.731
41.382
20.307
± 6.17
± 5.56
± 4.17
± 4.66
Hard
Note: Negative angles represent plantarflexion
Positive angles represent dorsiflexion
110
89
Figure 23.
Soft Midsole
Control Midsole
Hard Midsole
45.0
Angle (degrees)
40.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
Left
Right
Midsole n
Soft
Control
Hard
20
20
20
Left
Right
36.442 ± 3.79
36.167 ± 3.46
35.964 ± 3.71
31.656 ± 6.44
31.829 ± 5.18
31.262 ± 6.28
Table 25. Statistical Summary of Athletic Shoe Midsole Density on Knee
Knee:
F-value
p-value
Left
.355
.692
Right
.407
.664
Within-Subjects Contrasts: Left Knee
Midsole vs. Midsole
F-value
Soft vs. Control
.201
Control vs. Hard
.119
Soft vs. Hard
.918
Power
.101
.110
p-value
.659
.734
.350
Power
.071
.062
.149
Within-Subjects Contrasts: Right Knee
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
.083
.777
Control vs. Hard
.681
.420
Soft vs. Hard
.377
.546
Power
.059
.123
.090
90
Figure 24.
Soft Midsole
Control Midsole
Hard Midsole
90.0
Angle (degrees)
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Left
Right
Midsole n
Soft
Control
Hard
20
20
20
Left
Right
74.161 ± 8.43
74.426 ± 8.37
73.681 ± 6.30
66.651 ± 7.82
67.423 ± 7.78
66.201 ± 6.20
Table 27. Statistical Summary of Athletic Shoe Midsole Density on Knee
Knee:
F-value
p-value
Left
.295
.726
Right
.839
.433
Midsole vs. Midsole
F-value
Soft vs. Control
.100
Control vs. Hard
.581
Soft vs. Hard
.186
Power
.091
.177
p-value
.756
.455
.671
Power
.060
.112
.069
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.905
.353
Control vs. Hard
1.416
.249
Soft vs. Hard
0.199
.661
Power
.148
.204
.071
91
Figure 25.
Soft Midsole
Control Midsole
Hard Midsole
120.0
Angle (degrees)
100.0
80.0
60.0
40.0
20.0
0.0
Left
Right
Midsole n
Soft
Control
Hard
20
20
20
Left
Right
101.233 ± 7.59
101.849 ± 8.25
100.930 ± 6.19
97.683 ± 7.49
98.491 ± 6.86
97.393 ± 5.65
Knee:
F-value
p-value
Left
.379
.663
Right
.516
.590
Midsole vs. Midsole
F-value
Soft vs. Control
.250
Control vs. Hard
.745
Soft vs. Hard
.112
Power
.103
.126
p-value
.623
.399
.741
Power
.076
.130
.062
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.428
.521
Control vs. Hard
1.223
.283
Soft vs. Hard
0.067
.798
Power
.095
.183
.057
92
Figure 26.
Left Knee Range of Motion:
Soft Midsole
Control Midsole
Hard Midsole
120
Flex
Angle (degrees)
100
80
60
40
20
Ext
0
-10
0
10
20
30
40
50
60
70
80
90
100
Samples
% of the Jump
Landing Sequence
Impact
Left Knee Range of Motion
Midsole n
Impact
Peak GRF
Max Ang Disp
0.75 sec Post
20
36.442
74.161
101.233
39.800
± 3.79
± 8.43
± 7.59
± 10.63
Control
20
36.167
74.426
101.849
38.648
± 3.46
± 8.37
± 8.25
± 8.59
Hard
20
35.964
73.681
100.930
39.673
± 3.71
± 6.30
± 6.19
± 7.35
Soft
Note: Positive angles represent knee flexion
110
93
Figure 27.
Right Knee Range of Motion:
Soft Midsole
Control Midsole
Hard Midsole
120
Flex
Angle (degrees)
100
80
60
40
20
Ext
0
-10
0
10
20
30
40
50
60
70
80
90
100
Samples
% of the Jump
Landing Sequence
Impact
Right Knee Range of Motion
Midsole n
Impact
Peak GRF
Max Ang Disp
0.75 sec Post
20
31.656
66.651
97.683
38.958
± 6.44
± 7.82
± 7.49
± 8.61
Control
20
31.829
67.423
98.491
38.188
± 5.18
± 7.78
± 6.86
± 9.81
Hard
20
31.262
66.201
97.393
38.650
± 6.28
± 6.20
± 5.65
± 7.55
Soft
Note: Positive angles represent knee flexion
110
94
Figure 28.
Hip position at Initial Contact with the Ground
Soft Midsole
Control Midsole
Hard Midsole
35.0
Angle (degrees)
30.0
25.0
20.0
15.0
10.0
5.0
0.0
Hip Position at Initial Contact with the Ground
Midsole n
Soft
20
23.618 ± 9.25
Control 20
24.334 ± 7.26
Hard
20
22.837 ± 7.63
Table 33. Statistical Summary of Athletic Shoe Midsole Density on Hip
F-value
p-value
Hip:
.907
.396
Within-Subjects Contrasts: Hip
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.288
.598
Control vs. Hard
1.939
.180
Soft vs. Hard
0.786
.386
Power
.179
Power
.080
.263
.134
95
Figure 29.
Soft Midsole
Control Midsole
Hard Midsole
40.0
Angle (degrees)
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
Midsole n
Soft
20
29.772 ± 7.99
Control 20
29.988 ± 7.87
Hard
20
29.025 ± 7.78
Table 35. Statistical Summary of Athletic Shoe Midsole Density on Hip
F-value
p-value
Hip:
.467
.614
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
.033
.858
Control vs. Hard
.998
.330
Soft vs. Hard
.601
.448
Power
.118
Power
.053
.158
.114
96
Figure 30.
Soft Midsole
Control Midsole
Hard Midsole
70.0
Angle (degrees)
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Midsole n
Soft
20
47.647 ± 9.92
Control 20
48.294 ± 9.75
Hard
20
47.180 ± 9.76
F-value
p-value
Hip:
.252
.748
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
.125
.728
Control vs. Hard
.735
.402
Soft vs. Hard
.090
.767
Power
.084
Power
.063
.129
.059
97
Figure 31.
Hip Range of Motion:
Soft Midsole
Control Midsole
Hard Midsole
50
Flex
45
40
Angle (degrees)
35
30
25
20
15
10
5
Ext
0
-10
0
10
20
30
40
50
60
70
80
90
100
Samples
% of the Jump
Landing Sequence
Impact
Hip Range of Motion
Midsole n
Impact
Peak GRF
Max Ang Disp
0.75 sec Post
29.772
47.647
13.723
Soft
20
23.618
± 9.25
± 8.00
± 9.92
± 6.69
Control
20
24.334
29.998
48.294
14.283
± 7.26
± 7.87
± 9.75
± 6.38
20
22.837
29.025
47.180
14.616
± 7.63
± 7.78
± 9.76
± 7.56
Hard
Note: Positive angles represent hip flexion
110
98
Figure 32.
Vertical Hip Displacement:
A measurement of jump height
Soft Midsole
Control Midsole
Hard Midsole
60.0
Hip Height (cm)
50.0
40.0
30.0
20.0
10.0
0.0
Vertical Hip Displacement
Midsole n
Means ± Standard Deviations (cm)
Soft
20
49.780 ± 6.33
Control 20
49.486 ± 6.75
Hard
20
49.322 ± 6.20
Table 40. Statistical Summary of Athletic Shoe Midsole Density on Vertical
Hip Displacement
F-value
p-value
Hip:
.786
.461
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.706
.411
Control vs. Hard
0.177
.678
Soft vs. Hard
1.536
.230
Power
.173
Power
.126
.069
.218
99
Figure 33.
Vertical Hip Position:
Maximum Vertical Hip Position during the
Jumping Phase and Hip Position in Static Stance
Soft Midsole
Control Midsole
Hard Midsole
Static
160.0
Vertical Height (cm)
150.0
140.0
130.0
120.0
110.0
100.0
90.0
80.0
0
50
100
150
200
250
300
Samples
% of the Jump Landing
Sequence
Vertical Hip Position
Midsole n
Means ± Standard Deviations (cm)
Soft
20
153.844 ± 7.03
Control 20
153.551 ± 7.33
Hard
20
153.386 ± 7.17
Static
20
104.095 ± 0.37
Note: The dynamic phase, where the subject performed a volleyball approach
jump and spike is represented by the soft, control and hard midsole. The Static
position represents a trial where each subject was required to stand with feet
shoulder width apart, and arms out to the side.
100
Temporal Parameters
Time to maximum flexion angle at the ankle, knee and hip, after initial foot
contact, were the temporal variables of interest during each trial. The value for
time to maximum flexion was calculated for the hip, and bilaterally, for the ankle
and knee, using the amount of time in seconds it took to reach maximum flexion
angle at the ankle, knee and hip joints. Time to maximum flexion angle was
analyzed for the hip, and bilaterally, for the ankle and knee.
evaluate the effect of variations in athletic shoe midsole density on peak vertical
ground reaction force, and peak joint moments at the ankle, knee and hip.
Variations in athletic shoe midsole density did not differ significantly for left
or right time to maximum flexion angle at the ankle and knee joints. There were
also no significant differences found for time to maximum flexion angle of the hip.
Within-Subjects Contrasts were used to identify specific differences between the
soft, control and hard midsole athletic shoes. No significant differences were
found between athletic shoe midsole density and time to maximum angular
displacement. Means and standard deviations for time to maximum angular
displacements for the ankle, knee and hip are shown in Figures 34, 35, and 36,
and Tables 42, 44, and 46. A Statistical summary table for the effect of athletic
shoe midsole density for time to maximum angular displacements at the ankle,
knee and hip are found in Tables 43, 45 and 47.
101
Figure 34.
Soft Midsole
Control Midsole
Hard Midsole
0.300
Time (seconds)
0.250
0.200
0.150
0.100
0.050
0.000
Left
Right
Midsole n
Means ± Standard Deviations (seconds)
Soft
Control
Hard
20
20
20
Left
Right
.202 ± .048
.200 ± .044
.197 ± .034
.207 ± .046
.217 ± .030
.209 ± .044
Table 43. Statistical Summary of Athletic Shoe Midsole Density on Time to
Maximum Flexion Angle of the Ankle
Ankle:
F-value
p-value
Left
.189
.829
Right
.780
.464
Within-Subjects Contrasts: Left Ankle:
Midsole vs. Midsole
F-value
Soft vs. Control
.070
Control vs. Hard
.100
Soft vs. Hard
.488
Power
.077
.172
p-value
.795
.755
.493
Power
.057
.060
.102
Within-Subjects Contrasts: Right Ankle:
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
1.622
.218
Control vs. Hard
0.697
.414
Soft vs. Hard
0.111
.743
Power
.227
.125
.062
102
Figure 35.
Soft Midsole
Control Midsole
Hard Midsole
0.250
Time (seconds)
0.200
0.150
0.100
0.050
0.000
Left
Right
Midsole n
Means ± Standard Deviations (seconds)
Soft
Control
Hard
20
20
20
Left
Right
.181 ± .040
.175 ± .033
.173 ± .030
.198 ± .027
.200 ± .022
.194 ± .024
Maximum Flexion Angle of the Knee
Knee:
F-value
p-value
Left
1.211
.299
Right
0.785
.424
Within-Subjects Contrasts: Left Knee:
Midsole vs. Midsole
F-value
Soft vs. Control
1.505
Control vs. Hard
0.257
Soft vs. Hard
1.367
Power
.209
.151
p-value
.235
.618
.257
Power
.214
.077
.199
Within-Subjects Contrasts: Right Knee:
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.312
.583
Control vs. Hard
2.190
.155
Soft vs. Hard
0.376
.547
Power
.083
.290
.090
103
Figure 36.
Soft Midsole
Control Midsole
Hard Midsole
0.250
Time (seconds)
0.200
0.150
0.100
0.050
0.000
Midsole n
Soft
Control
Hard
20
20
20
.198 ± .036
.198 ± .039
.190 ± .041
Maximum Flexion Angle of the Hip
F-value
p-value
Hip:
.851
.428
Midsole vs. Midsole
F-value
p-value
Soft vs. Control
0.000
.983
Control vs. Hard
1.612
.220
Soft vs. Hard
1.027
.324
Power
.179
Power
.050
.226
.161
104
Post Participation Questionnaire
Upon completion of data collection, all subjects were asked to complete a
Post Participation Questionnaire. The results of the questionnaire indicated that
all subjects: 1) did not notice a difference between the shoe conditions; 2)
performed their regular volleyball approach during all trials; and 3) indicated that
the shoes were comfortable to perform in for the trials of the study. The complete
results of the Post Participation Questionnaire are presented in Table 48.
Table 48.
Post Participation Questionnaire Results
RESPONSE
QUESTION:
YES
NO
20
0
I performed my regular volleyball
approach during all trials.
19
1
I landed naturally during all trials.
19
1
I landed representative of how I
normally land during play.
19
1
The shoes fit my feet properly.
20
0
The shoes were comfortable to
perform in for all trials of the study.
4
16
I would wear these shoes to play
indoor volleyball.
0
20
I did notice a difference between
the shoe conditions
Chapter Five
DISCUSSION
The current investigation compared variations in athletic shoe midsole
densities. Three conditions were studied: soft, control and hard midsole. Both
kinetic and kinematic data were collected for all subjects. The investigation was
designed as a blind study to control for threats to internal validity. A blind study is
a study in which the subjects do now know they are receiving any treatment. In
this investigation the subjects were not aware they were wearing different shoe
conditions. All subjects were led to believe they wore the same pair of shoes for
the entire data testing session.
To ensure that the subjects were not aware of the differences of midsole
conditions, all subjects completed a Post Participation Questionnaire (Appendix
H). The results of the Post Participation Questionnaire indicated that none of the
subjects had a preference for any of the different midsole conditions. This was
determined by the answer on the questionnaire stating that none of the subjects
noticed a difference between the shoes. All subjects actually asked the
investigator to further explain this question because they were not aware the
shoes had been changed during testing.
105
106
Kinetics
The principle finding in this study was that variations in athletic shoe
midsole density do not significantly affect vertical ground reaction forces upon
landing after a volleyball approach jump and spike. The results of this study,
however, did indicate that the ground reaction forces during landing after a
volleyball approach jump and spike are larger then in normal walking and are
comparable with the maximal vertical forces measured during running, 2 to 3
times bodyweight.13, 14
When running, an athlete lands on one foot at a time. When landing after
a volleyball approach jump and spike an athlete lands on both feet. In the present
investigation the total (left and right) vertical ground reaction forces in elite female
NCAA volleyball players were on average 5 times bodyweight. The total peak
ground reaction forces found in this study were similar to other findings.
Richards, Ajemian, Wiley and Zernicke,65 studying the Canadian Men’s National
Team found maximum ground reaction forces during landing from a volleyball
spike were 5.6 to 6 times body weight. Adrian and Laughlin,1 studying
intercollegiate volleyball athletes, also reported vertical ground reaction forces
during landing to be on average 5 times bodyweight.
The effect of athletic shoe midsole density on vertical ground reaction
forces follows a response pattern suggested by Caster and Bates11. They
suggested that when landing there are three different possible response
strategies implemented subconsciously by the athlete: 1. Newtonian: proportional
increases in vertical ground reaction forces with increases in jump height and
107
mass; 2. Neuromuscular: no significant changes in vertical ground reaction
forces relative to experimental manipulations; 3. Differential: increases in vertical
ground reaction forces with decreases in jump height or mass.11
The results of the present investigation follows the Neuromuscular
response strategy, as midsole density increased vertical ground reaction forces
did not significantly change. Although the differences in vertical ground reaction
forces in the present study were not statistically significant, there was a potential
trend indicating that the hard midsole produced the smallest vertical ground
reaction forces bilaterally when numerically inspecting the means.
Vertical hip displacement was also not significantly affected by changes in
midsole density. Vertical hip displacement was used as an indicator of jump
height. This was an important finding because increases in jump height have
been associated with corresponding increases in vertical ground reaction forces
upon landing. These results indicate that subjects vertical jump height did not
significantly change when the athletic shoe midsole density changed. All of the
subjects in the present study landed after a volleyball approach jump and spike
from a height of approximately 50 cm. To put these results in another context,
drop jumps from 60 cm have been demonstrated to produce 5.9 times
bodyweight for peak vertical ground reaction forces when landing, and drop
jumps of more than 1 meter have produced forces up to 11.6 times bodyweight.7,
65
The landings in this study from an approximate height of 50 cm were similar to
those found in other studies.
108
Although not significantly different, when numerically inspecting the
means, jump height was the highest in the soft shoe condition. Conversely, the
hardest shoe condition was associated with the lowest jump height. This trend in
jump height is directly parallel to the trend in vertical ground reaction forces
which indicated that the hard midsole was associated with the lowest vertical
ground reaction forces and the soft midsole was associated with the highest
vertical ground reaction forces. This relationship has been previously
documented by Dufek and Zhang.19 They indicated that Newtonian mechanics
dictate that increases in jump height are accompanied by a proportional increase
in vertical ground reaction forces during landing.19 Therefore, in this investigation
higher jump heights were associated with higher ground reaction forces and
lower jump heights were associated with lower vertical ground reaction forces. It
can be concluded that the small decrease seen in vertical ground reaction forces
with the harder midsole was probably due to the proportional decreases in
vertical jump height in the harder midsole.
Loading Rates
Variations in athletic shoe midsole density did not significantly affect
loading rates upon landing after a volleyball approach jump and spike. Although
the loading rates in the present study were not statistically significantly different,
there was a potential trend indicating that the hard midsole produced the smallest
loading rate bilaterally when numerically inspecting the means. In contrast the
soft and control midsole produced higher loading rates during landing. These
results agree with the current literature indicating that the hard midsole is less
109
dense and therefore takes less time to deform then the softer midsole, as a result
the hard shoe reaches peak ground reaction forces or loads the system more
quickly than the soft or control midsole.69 The present investigation agrees with
the current literature that soft midsoles may increase loading rates causing the
impact forces to be applied to the impacting system at a slower rate. It is
important to note, however, that there is still a controversy as to whether softer
midsole will cause decreased proprioception and increase landing forces, or will
slow down the loading rate and decrease impact forces. This further emphasizes
that more research is needed to determine the effect of midsole density on
loading rates during non-rhythmic athletic activities.
Tillman, Hass, Brunt and Bennett81 indicated that 45% of the time
volleyball athletes do not land symmetrically. They also indicated that when
volleyball athletes land asymmetrically they usually contact the ground with their
left foot first.81 The loading rates in the present study seemed to agree with the
findings of Tillman et al.81 The loading rates were much higher on the left side as
compared to the right side. Although bilateral evaluations were not the focus of
this study, differences were observed on the left and right sides for loading rates
upon landing. These findings deserve further investigation.
Peak Joint Moments
Variations in athletic shoe midsole did not significantly affect peak ankle
joint moments during landing. The peak ankle joint moments found in this
investigation were equivalent to those measured in similar research involving
elite volleyball athletes performing an approach jump spike and landing. The
110
largest peak ankle joint moment during landing in this investigation was in the left
ankle at 0.353 bodyweight•meters. Richards, Ajemian, Wiley, Brunet and
Zernicke64 found that the peak ankle joint moment measured during landing in
male volleyball players was also in the left limb at 0.373 bodyweight•meters. The
right side peak ankle joint moments in this investigation were 0.268
bodyweight•meters which was also similar to those found by Richards et al.,64 at
0.353 bodyweight•meters. The present investigation was studying variations in
athletic shoe midsole density and found that peak ankle joint moments were not
affected by differences in athletic shoe conditions.
Variations in athletic shoe midsole density had a significant effect on the
left peak knee joint moment. The left peak knee joint moments were significantly
lower in the hard midsole as compared to the soft and control midsole. There
were, however, no significant differences found between athletic shoe midsole
densities for peak knee moments on the right side.
The peak knee joint moments of the present study were different then the
results of Richards et al.65 for elite volleyball athletes during landing from a
volleyball spike. The results of this investigation indicated higher peak knee joint
moments on the left side during landing from a volleyball spike. Richards et al.,65
reported higher peak knee joint moments on the right side. One possible
explanation for the discrepancy in the two studies may be the gender of the
subjects. The present study involved female collegiate volleyball athletes and
Richards et al.,65 used male Canadian National Team athletes. Tillman et al.,81
found that female volleyball athletes usually experience an asymmetrical landing
111
and usually land on their left foot first. It is possible that there is a gender
difference as to which foot contacts the ground first in an asymmetrical landing.
The present study investigating female volleyball athletes agrees with Tillman et
al. Further study is needed to evaluate these gender differences that appear to
exist in volleyball athletes during asymmetrical landings.
Bobbert, Huijung and van Ingen Schenau7 calculated peak knee joint
moments as high as 0.66 bodyweight•meters during drop jump testing from 60
cm. The present study found peak knee joint moments between 0.385 and 0.387
on the right and 0.408 and 0.499 on the left when landing from 50 cm. This
reinforces the need to evaluate peak joint moments during specific dynamic skills
because not all landings are the same even when landing from a similar height.
In this investigation, when wearing athletic shoes with the hard midsole
athletes decreased peak joint moments upon landing as compared to the soft
and control midsoles. The mean loading rates for all midsole conditions suggests
that there were differences in loading bilaterally. The higher left side loading rates
suggest that the left limb was responsible for attenuating more of the landing
forces than the right side. The vertical ground reaction forces were almost
identical on the left side but the loading rate was much higher. It is possible that
this increase in loading rate was attenuated by the left knee, as evidenced by the
left knee moment, to reduce impact force.
Variations in athletic shoe midsole did not significantly affect peak hip joint
moments during landing. The present investigation found that peak hip joint
moments were not affected by differences in athletic shoe conditions.
112
Kinematics
In order to describe the effect that variations in midsole stiffness has on
loading rates and impact force, it is necessary to analyze joint movements with
the corresponding forces to properly identify differences.42
Variations in midsole density did not significantly affect the left or right
ankle, knee or hip position at initial contact with the ground upon landing after a
volleyball approach jump and spike. There was a significant difference found
between the soft and hard midsole on the right side at initial contact with the
ground at the ankle. At the right ankle, at initial contact, there was more
plantarflexion seen when wearing the hard midsole athletic shoe as compared to
the soft or control midsole. Previous research by Luethi and Stacoff42 indicate
that impact force is a combination of the material properties of the midsole and
ankle joint motion during landing. They found that harder midsoles showed an
increase in joint motion, therefore changing the internal loading and reducing
ground reaction forces.42 This is one possible explanation for the significant
differences found at the right ankle between the athletic shoe midsole conditions.
When numerically inspecting the means, the same relationship exists for the left
ankle, although this relationship is not statistically significant.
In the hard midsole, at initial contact with the ground upon landing, there is
less hip flexion and knee flexion bilaterally when numerically inspecting the
means. Although not statistically significant this trend has been previously
indicated in the literature.25, 26, 28
113
Upon landing after a volleyball approach jump and spike, variations in
midsole density significantly affected right side ankle position at peak vertical
ground reaction force. The soft athletic shoe midsole was significantly different
than the hard and control athletic shoe midsole.
Changes in athletic shoe midsole density did not significantly affect the
position of the hip, left ankle, or bilaterally the knee at peak ground reaction force
upon landing after a volleyball approach jump and spike. It appears that at peak
ground reaction force in the hard midsole at the hip, left ankle and bilaterally at
the knee the subjects landed in a stiffer position, or with less flexion when
numerically inspecting the means. This would indicate that when landing in the
hard midsole, as the subjects experienced peak vertical ground reaction force
they were in a less flexed position and had less of an ability to attenuate impact.
This stiffer position should have caused an increase in vertical impact forces in
Newtonian response landings.19
In the present investigation there was no significant increase in vertical
ground reaction forces when landing in the hard midsole, however, when
numerically inspecting means there is a trend indicating a small increase in
vertical ground reaction forces in the hard midsole. Although, this trend was
previously attributed to similar changes in jump height it is possible that the trend
in vertical ground reaction forces is due to joint positions at peak vertical ground
reaction forces. The slightly lower vertical ground reaction forces measured in the
hard midsole athletic shoe may indicate a strategy where the subjects
114
subconsciously anticipated a harder impact and subsequently made kinematic
adjustments.
Variations in midsole density did not significantly affect the maximum
angular displacement at the hip, or bilaterally at the ankle and knee upon landing
after a volleyball approach jump and spike. There was however a significant
difference found in the between the soft and control midsole on the right side at
initial contact with the ground at the ankle.
The maximum knee flexion angles seen in this study between 97 and 101
degrees can be compared to the results of Richards et al.,65 who reported an
average knee flexion angle of 94 degrees in elite male volleyball athletes. Adrian
et al.,1 found knee flexion angles of 104 degrees during spike jump landings in
intercollegiate athletes.
One trend indicated when numerically inspecting the means is that
subjects produced the greatest amount of knee and hip flexion in the soft midsole
athletic shoe. Although not statistically significant this is contrary to the literature
that indicates that the cushioning found in a softer midsole requires less flexion to
absorb impact.25, 26, 28, 67 Robbins and Waked67 indicated that when athletes land
when wearing soft athletic shoes, they increase impact through reduced flexion
at the hip and knee so as to momentarily achieve improved stability by
compressing the soft midsole material.67 In the present study with the harder
midsole there was a decrease in maximum flexion seen at all joints except the
left ankle.
115
The landing techniques used in volleyball can potentially be related to
lower extremity energy absorption and likelihood of injury.19 Stacoff, Kaelin and
Steussi76 indicated that knee angle was a significant predictor of vertical ground
reaction force during landing. They found that landing from a vertical jump with a
more extended knee position caused an increase in forces during landing.76 In
the present study although not significantly different the knee flexion angle was
the smallest in the hard athletic shoe midsole bilaterally. As the subjects landed
with a stiffer knee position, ground reaction forces actually decreased; this is
contrary to the research of Stacoff et al.76 A possible explanation of these
conflicting results is offered by Fuller26 who indicated that changes in midsole
density result in changes in the motions and positions chosen subconsciously by
the athlete, but result in little change in ground reaction force. The changes in
body position as a result of changes in midsole density may change the internal
forces acting on internal structures.26 The results of the present study agree with
the results of Fuller26, they indicated that the changes in joint angles and joint
moments collectively were able to attenuate any changes in impact forces due to
variations in midsole density. The human body has many methods of attenuating
impact forces and when used in combination it is difficult to indicate how
variations in midsole density specifically affect kinematics during landing.
Temporal Parameters
Variations in midsole density did not significantly affect the time to
maximum flexion at the hip, or bilaterally at the ankle or knee upon landing after
a volleyball approach jump and spike. Although not statistically different when
116
numerically inspecting the means, time to maximum flexion was the fastest in the
hard condition at all joints except the right ankle. This result agrees with the
previous literature that indicates that the hard athletic shoe midsole would cause
the body to load faster due to the lack of cushioning.8, 31, 53, 86 Therefore, time to
maximum flexion would decrease in an attempt to dissipate that forces that are
being transferred at a faster rate.
It is possible that the right ankle did not respond to this relationship
because the forces at the right ankle were dissipated by changes in ankle
position at initial contact with the ground and peak ground reaction force. At initial
contact with the ground the right ankle had the largest knee flexion in the hard
athletic shoe midsole. At peak ground reaction force the right ankle in the soft
condition was significantly different then the control and hard midsole.
Volleyball athletes are trained in landing techniques and are coached to
land with a slightly flexed knee and a plantarflexed foot. This positioning at
contact provides a wide range of motion for the lower extremity joints to utilize to
dissipate ground reaction forces.9 Although this landing technique requires
greater muscular strength and therefore athletic shoe midsole cushioning may
play become more important as an athlete fatigues. More research is needed to
determine if changes in muscle activity are used as a possible strategy during
landing to affect impact forces.
Conclusions
The data presented in this investigation was used to determine the
influence of variations in athletic shoe midsole density on vertical ground reaction
117
forces, loading rates and peak joint moments upon landing from a volleyball
approach jump and spike. The kinematic data was used to determine what
specific variables are affected when landing after a volleyball approach jump and
spike with athletic shoes of varying midsole densities.
The only kinetic parameter to exhibit significance was the left peak knee
joint moment. All of the remaining kinetic variables for the three athletic shoe
midsole conditions indicated no significant difference, however, some definitive
trends did emerge from the data. In the kinematic variables, the right ankle
position at peak ground reaction force was significantly different for all three
athletic shoe midsole conditions. Significance was also noted between the soft
and hard shoe on the left side at initial contact with the ground and between the
soft and control shoe for maximum angular displacement on the right side.
In this investigation, during non-rhythmic athletic activities similarities in
ground reaction forces could not be explained kinematically. It is possible that
athletes adapt differently each time they land during a non-rhythmic skill masking
any changes in ground reaction forces due to changes midsole density.
There are many more sports where the basic repeated movements are
non-rhythmic activities as compared to the number of sports where the basic
repeated movements are rhythmic activities. Studying the consequences of
ground reaction forces in non-rhythmic sports activities would encompass more
athletes then the current literature available. More research is needed to
sufficiently explain the role of athletic shoe midsole densities during athletic
activities that are non-rhythmic.
118
Further research is needed on the effects of athletic shoe midsole density
and landings from non-rhythmic athletic activities. Future research should
evaluate the effects of pronation and supination of the foot upon impact. Although
the present investigation did not evaluate frontal and transverse plane variables it
is possible that they may play a role in the dissipation of forces upon landing.
Future research should also attempt to measure the internal pressures or forces
inside the athletic shoe to record accurate impacts of the foot to the shoe. In the
present investigation only the impact forces between the foot and the ground
could be measured. It is possible that the forces experienced inside the athletic
shoe may be different. Lastly, future research should include electromyography
to accurately determine if changes in athletic shoe midsole density affect muscle
activity during a non-rhythmic landing.
The nature of the system being studied and the multiplicity of variables
involved means that exact measurements of forces, loading rates, moments and
joint angles are generally hard to make.4 As a consequence, firm conclusions
based on such results are not always easy to justify.4 A complete understanding
of the role of the athletic shoe midsole during athletic events that involve
continuous non-repetitive landing forces has not been fully achieved. More
research is needed in athletic shoe midsole design to achieve a decrease in
injuries during non-rhythmic activities while maintaining athletic performance.
119
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APPENDIX A
Informed Consent Form
127
Informed Consent for Research Involving Human Subjects
INFORMED CONSENT
FOR
The influence of variations in shoe midsole density on the impact force and
kinematics of landing in female volleyball players
Investigator: Karen J. Nolan
Phone: 419-841-6558
You have been invited to participate in a volleyball study. You have been selected as a
possible participant because you are a female volleyball athlete (18-30 years) actively competing
in intercollegiate athletics or have previously competed in intercollegiate athletics.
Explanation of the study:
If you decide to participate, you will be asked to come to the University of Toledo
Biomechanics Laboratory for one laboratory visit. The one testing session will last approximately
2 hours. During the laboratory visit all methods and testing procedures will be explained. You
will be asked to 1) fill out a medical history and volleyball history questionnaire, 2) have
reflective markers placed on specific anatomical landmarks using adhesive tape and elastic bands,
3) have a small device attached to your lower leg with a cable running back to the computer, and
4) have pictures taken of any an all movements performed during the study. You will be given a
new pair socks to wear during all testing procedures. You will be randomly given one of three
pairs of athletic shoes. You will be asked to perform a 2 minute warm up jog around the gym.
After a warm up you will be asked to perform 10 successful volleyball spikes while wearing the
given athletic shoes. A successful spike is determined by having both of your feet land on a
designated area of the floor. After data collection you will remove the first pair of athletic shoes
and perform a 1 minute jog in socks. After the sock-only jog you will be randomly given a second
pair of athletic shoes (condition 2) and will again perform a 2 minute jog to warm up. After the
warm up you will again complete 10 successful volleyball spikes. The testing process repeats for
the third and final shoe condition. You will perform a 1 minute sock-only jog followed by a 2
minute shoe (condition 3) warm up. After the warm up you will again complete 10 successful
volleyball spikes for the third and final time.
Confidentiality:
Any information that is obtained in connection with this study will remain confidential
and the results will be used for scientific publication. Your name will not be identified in any way
as part of the publication.
Inquiries:
Your decision to participate or not will not prejudice your future with the University of
Toledo, the Department of Kinesiology, or the Department of Intercollegiate Athletics. If you
decide to participate, you are free to withdraw your consent and discontinue participation at any
time.
Benefits:
By participating in this study you will benefit by gaining knowledge about landing
forces. As an athlete you may be able to prevent injury by knowing how hard you land after a
volleyball spike. If it is determined that you land very hard you may be able to correct your
technique and prevent future injury. You will also be able to learn about your specific kinematics
while performing a volleyball spike. This may help to improve your performance during a
volleyball spike.
Participants Initials: ________Date:
Witness Initials: _________ Date:_____
_____
Investigators Initials: ________Date: _____
Page 1 of 2
128
Risks and discomforts associated with the study:
There is a small risk of injury associated with involvement in any type of physical
activity. It is possible that injury may occur during testing. Every effort will be made to minimize
risk of injury. Should any injury result from your participation in this study you will be
financially responsible to provide your own medical care.
If you have any questions before, during, or after the study, please feel free to contact
Karen J. Nolan (419) 841-6558 or Dr Charles Armstrong (419) 530-5369.
For more information regarding your rights as a participant you may contact the Human
Subjects Research and Review Committee Chair, Gerald Sherman, WO 2243.
YOU ARE MAKING A DECISION WHETHER TO PARTICIPATE OR NOT. YOUR
SIGNATURE INDICATES THAT YOU HAVE DECIDED TO PARTICIPATE HAVING
READ THE INFORMATION PROVIDED ABOVE.
_______________________________
Participants Signature
Date
_______________________________
Investigators Signature
Date
_________________________________________
Witness
Date
Page 2 of 2
APPENDIX B
Medical Health Questionnaire
130
Date___________
Subject # ____
University of Toledo
Applied Biomechanics Laboratory
Health Appraisal Questionnaire
** Confidential**
Name:
_______ Sex: F M Date of Birth: ____________
Address_______________________________________________________________________
Phone:________________________________ Email:__________________________________
Medical History: Check if Applicable, give further explanation if necessary:
_____ Heart Disease/Heart Attack/Heart Surgery
_____
_____ Heart Murmur
_____
_____ Pacemaker
_____
_____ High Blood Pressure
_____
_____ Diabetes
_____
_____ Varicose Veins
_____
_____ Muscle Disease
_____
_____ Asthma
_____
_____ Back Problems
_____
_____ Brain Injury
_____
_____ Fractures (indicate location)
Upper Extremity Injury
Lower Extremity Injury
Back Problems
Arthritis
Stroke
Rheumatic Fever
Cancer
Lung Disease
Neurological Disease
Surgery (indicate type
○ YES ○ NO ............. I have never had surgery for volleyball or other related injury
○ YES ○ NO ...............I have no lower extremity injury and have not for the past six months
Explain any above that have been marked:
Family History: Indicate which (if any) of your blood relatives have had any of the following
conditions:
______ Asthma
_____Diabetes
______ Cancer
_____Heart Attack
______ Heart Operation
Your Current Health Status: Indicate if you have any of the following symptoms
______ Chest Pain/Pressure
______ Pregnant or recent childbirth
______ Dizziness with exercise/exertion
______ Skipped or irregular heart beats
______ Shortness of breath
______ Joint Pain during exercise
Other:
Medications:
○ YES ○ NO ............. I am currently taking medication
Type of Medication: Prescription_____ Non-prescription_____
Name of Medication(s): _______________________
Purpose of Medication:_ ______________________
Health Habits:
○ YES ○ NO ............. I currently smoke cigarettes
○ YES ○
○ YES ○
○ YES ○
Amount smoked per day_______
If you used to smoke, how long ago did you quit? ______ years.
NO ...............I am currently overweight
NO ...............I am currently on a weight reduction program
If YES, briefly describe the program____________________
NO ...............I currently engage in sports and/or fitness activities
If YES, briefly describe the types of activities______________
How frequently do you exercise? Day(s) per week__Minutes per day__
APPENDIX C
Volleyball History Form
132
Volleyball History
Primary Volleyball Position: _______________________
Dominant Hand:
○ left handed
○ right handed
Years played:
High School
○1
○ 2
○ 3
○ 4
College
○1
○ 2
○ 3
○ 4
USAV
○1
○ 2
○ 3
○ 4
College:
○5
○ 6
○ 7
○8
○ 9
_________________________
NCAA Division:
○I
○ II
○ III
Total Years played: ______
Please answer YES or NO for the following questions:
I play volleyball in college.
I play volleyball, recreationally, on leagues or teams.
¾ Days per week ______ (approx)
¾ Hour per time ______ (approx)
○ YES ○ NO
I have had surgery for a volleyball or other related injury.
○ YES ○ NO
I have had a lower extremity injury within the last six months.
○ YES ○ NO
○ YES ○ NO
APPENDIX D
Volleyball History Data
134
Volleyball History Data
Subject
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Mean
SD
Age
Shoe Size
# Years
Played
(years)
(US women’s)
(years)
(cm)
19
19
20
19
20
20
25
25
28
22
26
18
18
19
19
21
20
21
19
24
21.10
2.92
9.5
10.5
9.5
11.0
10.5
10.5
9.0
10.5
9.0
11.0
9.0
11.0
9.5
11.0
11.0
9.0
9.5
9.5
9.5
11.0
10.05
0.81
5
11
9
8
9
7
13
7
11
12
15
9
7
7
7
10
10
10
13
8
9.40
2.54
248.92
247.65
250.19
246.38
248.92
256.54
255.27
251.46
250.19
256.54
247.65
259.08
251.46
248.92
256.54
256.54
264.16
252.73
250.19
254
156.89
4.56
Volleyball Positions
MB = Middle Blocker
OH = Outside Hitter
RS = Right Side Hitter
DS = Defensive Specialist
Ball
Dominant Volleyball
Height
Hand
Position
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Right
Left
Right
Right
MB
OH
MB
RS
MB
OH
MB
MB
RS
MB
OH
MB
MB
OH
OH
OH
OH
OH/R
DS/S
MB
APPENDIX E
Volleyball Data Collection Sheet
136
Volleyball Data Collection Sheet
Name:_______________________ Date_________
Age:_______
DOB:___________Address:_______________________________________________
(Street)
(City)
(State)
(Zip)
E-mail:___________________________________ Phone #: ___________________
Shoe Size: (the size you wore for the study)
○ 8½
○ 9
○ 9½
Height:
________
Weight:
________
Standing Reach:
________
Wing Span:
________
ASIS Height:
________
Ball Height:
________
Subject #: ______________________
Folder Name: ___________________
Cube Calibration File Name: ______
Static Trial File Name: ___________
Right Foot Width ______ Left Foot Width ______
Right Ankle Width ______
Left Ankle Width ______
Right Knee Width ______
Left Knee Width ______
Right Foot Length ______
Left Foot Length ______
Trial
#
1
Shoe (G)
○
off plate
Trial
#
1
2
○
off plate
3
○
4
○ 10
Shoe (B)
○ 10 ½
○
off plate
Trial
#
1
2
○
off plate
off plate
3
○
○
off plate
4
5
○
off plate
6
○
7
○ 11
Shoe (R)
○
off plate
2
○
off plate
off plate
3
○
off plate
○
off plate
4
○
off plate
5
○
off plate
5
○
off plate
off plate
6
○
off plate
6
○
off plate
○
off plate
7
○
off plate
7
○
off plate
8
○
off plate
8
○
off plate
8
○
off plate
9
○
off plate
9
○
off plate
9
○
off plate
10
○
off plate
10
○
off plate
10
○
off plate
11
○
off plate
11
○
off plate
11
○
off plate
12
○
off plate
12
○
off plate
12
○
off plate
APPENDIX F
Complete Anthropometric Data of Subjects
21.10
2.84
19
19
20
19
20
20
25
25
28
22
26
18
18
19
19
21
20
21
19
24
1
2
3
4
5
6
7
8
9
10
11
12
14
15
16
17
18
19
20
22
Mean
SD
Age
(years)
Subject
10.05
0.81
9.5
10.5
9.5
11.0
10.5
10.5
9.0
10.5
9.0
11.0
9.0
11.0
9.5
11.0
11.0
9.0
9.5
9.5
9.5
11.0
(US Womens)
Shoe Size
72.820
6.65
79.728
72.027
67.497
77.237
67.044
71.121
65.232
77.463
73.386
86.976
67.950
69.083
66.138
62.967
78.822
64.779
70.215
79.728
81.087
77.916
Weight
(kg)
178.59
3.81
181.61
170.82
175.90
177.17
181.61
180.34
176.53
177.80
177.80
184.15
176.53
186.69
177.80
176.53
181.61
180.34
179.71
176.53
171.45
180.98
Height
(cm)
231.14
6.89
233.68
224.79
222.89
231.14
237.49
233.68
232.41
230.51
226.06
234.95
220.98
246.38
229.87
226.06
233.68
233.68
238.76
233.68
215.90
236.22
Standing
Reach
(cm)
181.45
6.25
180.34
178.44
177.80
187.96
190.50
186.69
193.04
185.42
179.07
182.88
170.18
187.96
180.34
177.80
186.69
180.34
176.53
180.34
168.91
177.80
Wing
Span
(cm)
Complete Anthropometric Data of Subjects
25.42
1.82
26.67
26
26
26.5
26.5
25.5
26
27.2
26.5
27
25.5
28
22
27.5
23
22.5
23
24
23
26
Right Foot
Length
(cm)
25.58
1.59
27.4
26
25.5
26
26.5
26
25.5
26.5
27
26
25
28
23
28
25
22.7
23.5
24.5
23
26.5
Left Foot
Length
(cm)
138
APPENDIX G
Random Assignment for Athletic Shoe Midsole Condition
140
Random Assignment for Athletic Shoe Midsole Condition
Subject
#
1
Condition
2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
control
hard
soft
soft
soft
soft
control
control
hard
soft
soft
hard
hard
hard
control
soft
soft
control
hard
control
hard
control
control
control
control
control
soft
soft
soft
hard
hard
control
soft
control
soft
control
hard
hard
control
hard
3
soft
soft
hard
hard
hard
hard
hard
hard
control
control
control
soft
control
soft
hard
hard
control
soft
soft
soft
APPENDIX H
142
○ YES
○ YES
○ YES
○ YES
○ YES
○
○
○
○
○
NO
NO
NO
NO
NO
○ YES ○ NO
○ YES ○ NO
I performed my regular volleyball approach during all trials.
I landed naturally during all trials.
I landed representative of how I normally land during play.
The shoes fit my feet properly.
The shoes were comfortable to perform in for all trials of the
study.
I would wear these shoes to play indoor volleyball.
I did notice a difference between the shoe conditions
What type of athletic shoes do you wear when you play volleyball (cross
trainers, running,
volleyball, basketball, etc.)? _________________________________
What brand of volleyball shoes do you wear when you play volleyball (Nike,
Adidas, Kaepa, Mizuno, Fila, etc.)? ___________________________________
I usually wear low top OR high top athletic shoes when playing volleyball?
______________
Which shoe condition did you prefer? _____________________
Additional Comments about the shoes (optional):
APPENDIX I
List of Kinematic and Kinetic Variables
Kinematic Variables
L Ankle ROM at Initial
L Knee ROM at Initial
R Ankle ROM Initial
R Knee ROM Initial
Hip ROM Initial
L Ankle ROM at Peak
L Knee ROM at Peak
R Ankle ROM at Peak
R Knee ROM at Peak
Hip ROM at Peak
L Ankle ROM Max
L Knee ROM Max
R Ankle ROM Max
R Knee ROM Max
Hip ROM Max
L Ankle ROM TTM
L Knee ROM TTM
R Ankle ROM TTM
R Knee ROM TTM
Hip ROM TTM
Hip Displacement
Defined
Ankle position at initial contact with the ground
Knee position at initial contact with the ground
Ankle position at initial contact with the ground
Knee position at initial contact with the ground
Hip position at initial contact with the ground
Ankle position at Peak Vertical Ground Reaction Force
Knee position at Peak Vertical Ground Reaction Force
Ankle position at Peak Vertical Ground Reaction Force
Knee position at Peak Vertical Ground Reaction Force
Hip position at Peak Vertical Ground Reaction Force
Maximum angular displacement at the Ankle
Maximum angular displacement at the Knee
Maximum angular displacement at the Ankle
Maximum angular displacement at the Knee
Maximum angular displacement at the Hip
Time to maximum flexion angle of the Ankle
Time to maximum flexion angle of the Knee
Time to maximum flexion angle of the Ankle
Time to maximum flexion angle of the Knee
Time to maximum flexion angle of the Hip
Difference between the hip during static trial and dynamic trials
List of Kinematic Variables
144
Kinetic Variables
L Peak GRF
L Loading Rate
L Ankle Mom
L Knee Mom
L Hip Mom
R Peak GRF
R Loading Rate
R Ankle Mom
R Knee Mom
R Hip Mom
Explanation
Peak Vertical Ground Reaction Force after initial contact with the ground
Peak Ankle Joint moments
Peak Knee Joint moments
Peak Hip Joint moments
Peak Vertical Ground Reaction Force after initial contact with the ground
Peak Ankle Joint moments
Peak Knee Joint moments
Peak Hip Joint moments
List of Kinetic Variables
145
APPENDIX J
Mean Data Set For All Subjects
Condition
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
soft
control
control
control
control
control
control
control
control
control
control
control
control
control
control
control
control
control
control
control
control
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
hard
Subject
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Left Peak
2.123
2.512
1.420
2.842
2.200
2.769
2.079
2.258
2.052
1.870
2.944
1.925
2.113
2.705
2.836
2.395
2.619
2.050
2.436
2.559
2.521
2.100
1.550
2.872
2.308
2.587
2.108
2.151
2.172
1.956
2.664
1.861
2.196
2.610
2.939
2.650
2.516
2.237
2.173
2.698
2.011
1.863
1.540
3.610
2.455
2.657
1.986
1.986
2.288
2.023
2.644
2.019
2.098
2.779
3.424
2.858
2.837
1.990
2.423
2.384
Right Peak
1.774
2.213
2.308
2.427
2.497
2.958
2.299
2.732
2.779
1.871
2.823
1.508
2.282
3.387
3.053
1.997
1.673
1.736
1.811
2.049
2.264
2.271
1.984
2.202
2.641
3.144
2.336
2.497
2.619
1.906
3.017
1.314
2.471
3.592
3.352
2.174
1.677
1.665
1.998
1.697
1.681
2.425
2.353
2.411
2.392
3.345
2.318
2.835
2.479
2.047
3.082
1.558
2.315
3.444
2.818
1.719
1.481
1.684
1.955
2.202
Total Peak
3.897
4.725
3.728
5.269
4.697
5.727
4.378
4.990
4.831
3.741
5.767
3.433
4.395
6.092
5.889
4.392
4.292
3.786
4.248
4.608
4.785
4.371
3.534
5.074
4.949
5.731
4.444
4.648
4.791
3.861
5.681
3.175
4.667
6.202
6.291
4.824
4.193
3.902
4.171
4.394
3.692
4.288
3.893
6.021
4.847
6.002
4.305
4.821
4.767
4.070
5.726
3.577
4.413
6.223
6.242
4.577
4.318
3.674
4.378
4.587
Left Loading Rate
32.249
30.151
16.851
49.214
32.271
46.611
29.624
28.750
29.664
27.625
56.843
23.779
22.803
50.719
48.039
31.564
39.060
26.992
27.967
47.860
41.898
24.082
19.607
48.655
37.484
30.338
27.887
28.829
30.906
25.747
48.321
21.680
25.266
58.418
55.703
39.574
41.394
30.907
19.108
49.015
30.112
21.680
18.314
58.836
33.790
35.755
26.792
23.601
34.085
32.024
46.877
25.377
26.222
65.764
72.890
38.027
42.426
27.113
24.214
40.261
Right Loading Rate
26.822
19.888
19.297
34.125
30.590
44.704
29.753
28.000
32.973
24.214
36.760
15.475
20.971
56.450
41.512
25.875
30.214
23.102
16.511
34.140
37.497
21.116
17.328
36.709
31.945
32.427
22.926
24.698
27.951
21.370
52.595
16.675
23.249
56.540
50.758
29.969
32.782
19.863
18.967
27.079
23.701
22.441
22.082
41.121
28.254
40.854
23.334
25.559
27.939
30.530
45.867
18.803
22.607
51.632
41.628
21.419
27.787
21.245
18.101
37.543
Left Ankle Moment
-0.230
-0.529
-0.206
-0.410
-0.291
-0.320
-0.329
-0.283
-0.230
-0.214
-0.342
-0.258
-0.313
-0.359
-0.416
-0.328
-0.380
-0.282
-0.353
-0.357
-0.263
-0.493
-0.207
-0.433
-0.276
-0.295
-0.292
-0.288
-0.270
-0.478
-0.361
-0.223
-0.538
-0.366
-0.327
-0.286
-0.328
-0.421
-0.573
-0.346
-0.204
-0.318
-0.274
-0.464
-0.401
-0.670
-0.317
-0.342
-0.299
-0.323
-0.393
-0.212
-0.255
-0.406
-0.351
-0.332
-0.103
-0.240
-0.474
-0.299
Right Ankle Moment
-0.195
-0.272
-0.283
-0.286
-0.270
-0.291
-0.286
-0.324
-0.323
-0.178
-0.293
-0.199
-0.230
-0.325
-0.273
-0.214
-0.203
-0.219
-0.233
-0.178
-0.200
-0.296
-0.330
-0.245
-0.247
-0.302
-0.286
-0.320
-0.303
-0.178
-0.325
-0.189
-0.210
-0.289
-0.258
-0.208
-0.208
-0.208
-0.245
-0.166
-0.194
-0.310
-0.314
-0.275
-0.413
-0.434
-0.284
-0.339
-0.305
-0.182
-0.340
-0.196
-0.190
-0.276
-0.227
-0.225
-0.198
-0.194
-0.270
-0.199
Left Knee Moment
0.373
0.472
0.290
0.371
0.457
0.410
0.403
0.376
0.413
0.333
0.534
0.368
0.475
0.649
0.135
0.396
0.388
0.392
0.451
0.467
0.419
0.661
0.259
0.368
0.507
0.560
0.422
0.395
0.418
0.544
0.461
0.336
0.568
0.703
0.970
0.540
0.418
0.481
0.504
0.448
0.360
0.363
0.464
0.520
0.499
0.673
0.353
0.389
0.435
0.426
0.508
0.376
0.485
0.768
0.609
0.482
0.557
0.396
0.493
0.429
Right Knee Moment
0.275
0.327
0.467
0.384
0.381
0.420
0.416
0.374
0.474
0.299
0.504
0.224
0.438
0.439
0.516
0.328
0.290
0.371
0.360
0.261
0.345
0.353
0.428
0.329
0.418
0.509
0.477
0.392
0.440
0.308
0.463
0.214
0.489
0.484
0.485
0.350
0.306
0.347
0.383
0.219
0.249
0.349
0.451
0.303
0.393
0.597
0.442
0.437
0.400
0.327
0.537
0.242
0.485
0.473
0.443
0.308
0.260
0.348
0.379
0.271
Left Hip Moment
-0.136
-0.356
-0.066
-0.355
-0.135
-0.193
-0.160
-0.176
-0.109
-0.060
-0.214
-0.146
-0.124
-0.331
-0.239
-0.204
-0.155
-0.117
-0.181
-0.263
-0.121
-0.251
-0.114
-0.394
-0.150
-0.085
-0.078
-0.198
-0.083
-0.182
-0.261
-0.094
-0.212
-0.229
0.030
-0.212
-0.188
-0.223
-0.231
-0.300
-0.146
-0.119
-0.164
-0.228
-0.197
-0.414
-0.120
-0.251
-0.225
-0.146
-0.254
-0.074
-0.039
-0.409
-0.343
-0.212
-0.343
-0.077
-0.253
-0.190
Right Hip Moment
-0.137
0.132
-0.111
-0.138
-0.147
-0.248
-0.099
-0.168
-0.127
-0.114
-0.190
-0.127
-0.102
-0.478
-0.228
-0.113
-0.175
-0.074
-0.104
-0.143
-0.163
-0.139
-0.182
-0.141
-0.140
-0.171
-0.092
-0.163
-0.112
-0.112
-0.195
-0.129
-0.105
-0.423
-0.303
-0.132
-0.130
-0.071
-0.103
-0.120
-0.138
-0.159
-0.124
-0.198
-0.147
-0.301
-0.080
-0.167
-0.112
-0.105
-0.212
-0.116
-0.100
-0.418
-0.249
-0.145
-0.133
-0.072
-0.135
-0.130
Right Ankle Max
47.347
42.589
39.592
31.142
40.206
37.226
45.962
41.936
37.914
38.852
41.894
37.939
44.936
37.648
39.149
44.490
43.451
47.586
46.946
40.843
42.920
46.183
37.156
32.328
41.252
38.049
45.092
49.601
36.843
37.922
41.147
36.988
42.910
35.781
34.848
43.259
40.395
49.988
50.708
40.220
48.110
46.160
40.078
33.695
38.641
39.327
45.957
50.738
34.802
39.578
42.390
40.773
45.020
35.059
39.776
42.968
39.656
49.790
48.439
43.239
Left Anke Max
31.310
41.732
36.073
25.079
39.380
37.039
42.704
34.420
37.770
42.864
28.789
37.829
48.282
41.809
43.016
47.851
34.295
45.441
45.493
35.236
34.001
42.916
32.646
25.537
40.418
35.992
48.683
40.236
42.283
45.886
32.360
36.334
43.677
38.968
35.601
41.380
38.330
46.472
45.976
34.922
33.723
41.780
31.636
33.205
39.344
34.991
45.800
37.756
41.444
44.096
35.449
36.313
43.453
39.234
33.700
37.467
37.562
43.709
45.298
34.412
Right Knee Max
100.701
96.014
98.812
101.149
97.893
98.792
107.200
88.007
86.508
98.643
89.225
101.856
92.793
100.568
92.868
92.063
98.087
101.333
98.665
106.681
92.575
101.802
102.702
110.357
97.607
94.986
112.408
97.181
84.432
97.512
94.664
103.656
94.033
99.313
91.571
89.407
95.824
104.825
100.205
104.766
103.383
105.408
98.938
93.745
96.074
95.668
112.669
96.350
87.388
95.707
89.935
97.108
93.644
100.269
89.057
87.745
91.752
111.380
98.232
109.206
Left Knee Max
101.193
108.889
92.940
109.013
103.010
99.276
103.923
94.228
92.010
103.172
93.610
102.742
94.655
98.644
99.178
97.517
97.123
112.799
103.026
111.657
92.109
113.339
93.838
120.845
101.329
94.556
108.266
102.626
91.234
103.941
96.418
105.572
95.824
97.194
99.748
94.629
94.900
112.928
109.571
108.104
103.663
115.324
95.055
103.425
100.053
97.166
106.975
102.420
89.839
99.546
95.090
98.836
97.394
98.591
98.865
91.316
93.432
117.495
107.645
112.526
Hip Max
147
53.861
58.929
50.002
52.501
35.459
41.324
53.747
41.001
40.142
57.831
47.184
56.597
33.752
71.209
40.263
35.712
45.372
38.992
39.028
50.691
48.804
54.391
59.441
63.483
35.631
32.355
60.048
48.050
39.506
50.173
49.855
54.022
37.041
65.649
45.850
35.076
52.664
45.380
38.036
50.426
57.040
65.229
48.164
42.070
41.257
35.856
57.572
44.886
46.704
47.596
42.852
49.797
36.173
71.677
44.864
33.247
43.969
58.747
39.896
45.342
Right Ankle at Peak
27.870
31.474
32.969
19.590
22.464
21.215
36.294
30.757
24.431
19.758
24.857
28.660
28.714
15.195
21.541
23.519
23.032
31.625
30.819
19.835
23.727
32.694
28.606
20.732
21.778
23.718
33.714
41.601
26.998
18.077
19.598
25.704
27.349
12.436
16.416
23.013
24.485
35.571
33.077
25.320
27.808
32.380
31.319
22.823
24.604
27.426
34.045
42.135
23.555
21.870
25.986
32.291
25.903
10.736
21.580
24.745
22.733
38.811
33.715
25.644
Left Ankle at Peak
19.026
32.444
27.547
17.517
31.165
25.447
35.888
27.711
30.031
28.454
14.775
31.723
40.305
22.655
29.489
32.373
20.660
36.876
33.534
18.741
21.117
33.261
24.255
16.689
29.100
31.728
42.349
33.949
33.577
29.498
16.947
30.049
34.899
18.143
20.711
25.734
25.493
35.216
37.241
20.642
20.746
37.376
24.909
24.655
29.001
28.995
37.493
34.835
31.950
31.788
21.560
29.978
33.848
20.465
13.599
23.375
26.893
33.623
36.115
23.383
Right Knee at Peak
61.900
74.031
74.143
64.459
65.998
62.862
79.927
62.415
64.337
59.490
65.292
61.556
67.493
61.630
62.464
61.305
66.475
75.430
75.163
57.645
59.951
75.288
76.511
64.668
65.091
65.817
81.701
75.701
66.260
60.978
60.701
70.147
69.727
55.252
56.576
58.773
69.533
79.079
74.590
62.119
61.468
73.258
71.668
55.122
65.320
65.917
81.436
72.306
66.568
60.318
63.962
68.713
65.679
57.953
59.358
62.097
67.699
85.033
72.634
56.504
66.689
83.972
70.404
70.122
78.881
71.478
79.140
74.380
76.592
69.637
67.701
72.341
80.020
65.941
72.002
72.519
66.565
85.723
83.408
66.105
59.505
85.679
72.869
71.904
76.446
77.855
84.682
84.573
73.821
70.582
67.065
76.816
78.746
62.477
69.516
67.834
67.140
83.283
90.588
67.147
67.466
90.799
65.193
69.114
73.963
76.555
82.214
86.231
71.217
71.443
70.115
72.063
79.729
63.606
64.918
66.278
66.651
84.794
88.587
72.277
Left Knee at Peak
Mean Data Set For All Subjects
Hip at Peak
33.100
38.082
26.829
32.382
18.462
28.195
34.126
28.218
28.293
31.170
30.524
33.451
20.495
52.544
25.856
23.137
30.536
17.500
25.971
21.627
31.816
38.231
36.323
38.714
17.468
21.515
37.497
31.552
25.188
26.494
34.406
38.395
23.378
46.649
30.895
21.705
32.633
21.373
22.895
22.627
35.689
43.473
30.631
25.389
25.060
22.378
37.245
29.514
31.042
25.504
29.345
31.687
20.133
53.047
28.612
20.417
31.011
28.291
25.798
21.179
Left Ankle at Initial
-24.689
-12.418
-17.974
-30.340
-26.428
-24.663
-16.452
-27.888
-27.841
-21.509
-21.030
-23.915
-18.582
-18.233
-18.688
-13.415
-29.160
-24.239
-21.761
-16.489
-19.789
-11.768
-19.948
-26.481
-24.954
-25.390
-16.528
-28.786
-26.116
-22.451
-17.781
-26.917
-16.884
-10.543
-24.104
-17.042
-26.172
-24.745
-18.525
-14.918
-21.362
-11.235
-18.839
-25.028
-26.654
-24.674
-18.495
-26.892
-23.786
-19.372
-19.222
-25.863
-22.221
-11.799
-24.831
-19.204
-25.343
-24.582
-20.456
-14.751
Right Ankle at Initial
-11.939
-16.209
-13.374
-24.328
-27.961
-17.112
-16.573
-15.887
-27.002
-19.622
-15.309
-22.637
-14.893
-14.615
-15.028
-15.470
-0.015
-23.901
-13.191
-17.140
-14.480
-12.723
-12.860
-17.602
-23.655
-13.944
31.694
43.474
32.411
34.539
32.956
35.570
33.872
32.156
38.305
35.815
42.513
34.240
37.934
38.834
39.687
34.272
28.963
38.331
38.780
34.938
29.550
41.947
30.846
34.028
36.211
41.300
37.435
34.825
-14.684
34.995
34.230
39.262
36.094
41.320
37.812
39.188
34.773
30.979
36.097
37.851
34.604
34.068
42.493
30.841
36.110
30.992
35.166
35.528
35.810
32.124
36.718
43.796
35.847
41.258
38.634
40.879
33.103
31.721
37.851
39.719
36.179
Left Knee at Initial
-21.048
-25.693
-19.716
-15.766
-20.526
-11.805
-9.403
-18.743
-14.691
-6.334
-20.463
-10.364
-15.494
-10.275
-14.224
-13.109
-21.566
-24.618
-13.939
-20.452
-11.569
-25.260
-16.944
-16.401
-21.179
-14.893
-12.079
-17.778
-16.278
1.151
-19.247
-12.773
-11.062
Right Knee at Initial
30.253
31.297
30.753
30.181
26.201
35.777
41.724
26.310
24.118
21.713
36.266
29.397
31.252
37.382
31.648
22.634
47.777
29.357
32.374
28.825
31.707
30.033
32.833
32.781
28.257
32.034
39.543
30.890
26.516
24.848
37.811
28.966
34.269
29.657
31.243
22.584
45.746
35.371
32.452
29.046
29.690
29.269
32.718
27.869
26.389
34.780
41.824
29.500
27.341
26.989
36.107
26.793
29.574
33.888
30.895
22.444
51.361
36.936
31.759
26.994
Hip at Initial
24.011
25.803
21.432
25.551
13.124
19.963
18.177
25.065
21.505
19.913
28.480
21.367
16.633
46.943
21.250
17.455
34.906
23.705
18.381
13.069
25.683
25.093
36.457
32.351
12.304
19.245
19.225
29.241
22.965
18.679
33.894
23.057
18.750
37.373
23.202
16.586
30.980
28.266
16.615
16.713
25.722
30.305
22.259
22.733
14.802
16.898
19.379
27.385
27.222
14.940
28.012
18.739
16.026
46.120
25.344
16.213
40.781
34.460
14.249
10.774
Left Ankle TTM
0.201
0.207
0.190
0.151
0.186
0.158
0.169
0.154
0.169
0.234
0.177
0.200
0.254
0.177
0.168
0.263
0.243
0.210
0.209
0.233
0.190
0.208
0.219
0.182
0.173
0.110
0.174
0.170
0.167
0.204
0.192
0.268
0.209
0.184
0.179
0.244
0.166
0.215
0.231
0.318
0.222
0.174
0.203
0.103
0.176
0.142
0.179
0.167
0.155
0.270
0.163
0.210
0.226
0.219
0.202
0.289
0.190
0.238
0.229
0.289
Right Ankle TTM
0.281
0.268
0.229
0.113
0.223
0.187
0.164
0.143
0.194
0.235
0.188
0.159
0.250
0.187
0.204
0.267
0.225
0.211
0.221
0.239
0.198
0.213
0.268
0.152
0.222
0.207
0.214
0.172
0.204
0.230
0.252
0.224
0.235
0.224
0.224
0.263
0.176
0.193
0.245
0.219
0.239
0.206
0.241
0.097
0.200
0.176
0.215
0.169
0.175
0.175
0.190
0.174
0.314
0.257
0.196
0.247
0.170
0.218
0.243
0.231
Left Knee TTM
0.214
0.152
0.171
0.181
0.156
0.148
0.161
0.132
0.149
0.215
0.123
0.235
0.167
0.168
0.142
0.165
0.185
0.187
0.208
0.201
0.183
0.176
0.166
0.220
0.154
0.140
0.177
0.132
0.140
0.190
0.139
0.246
0.165
0.168
0.148
0.140
0.172
0.216
0.216
0.214
0.214
0.173
0.206
0.298
0.157
0.146
0.184
0.150
0.129
0.173
0.137
0.218
0.151
0.172
0.144
0.155
0.174
0.225
0.205
0.218
Right Knee TTM
0.224
0.193
0.204
0.172
0.186
0.167
0.178
0.220
0.182
0.239
0.158
0.232
0.214
0.167
0.167
0.183
0.180
0.197
0.200
0.222
0.197
0.203
0.212
0.209
0.181
0.168
0.221
0.199
0.175
0.222
0.179
0.238
0.222
0.185
0.183
0.176
0.172
0.226
0.214
0.226
0.232
0.224
0.200
0.244
0.172
0.166
0.223
0.185
0.162
0.203
0.159
0.207
0.220
0.190
0.181
0.179
0.148
0.240
0.205
0.223
Hip TTM
0.260
0.231
0.204
0.160
0.176
0.153
0.211
0.147
0.153
0.211
0.192
0.277
0.172
0.146
0.151
0.141
0.198
0.167
0.191
0.249
0.221
0.188
0.185
0.187
0.191
0.160
0.239
0.168
0.146
0.204
0.195
0.246
0.196
0.148
0.175
0.132
0.208
0.254
0.245
0.279
0.235
0.218
0.216
0.285
0.176
0.168
0.223
0.167
0.160
0.214
0.153
0.222
0.189
0.174
0.178
0.154
0.161
0.243
0.199
0.236
471.251
520.203
522.824
595.012
518.347
563.117
565.612
460.565
491.676
438.005
489.990
344.011
462.604
545.956
536.391
469.841
373.582
454.788
523.550
517.032
488.792
524.286
487.888
586.501
528.307
576.596
612.741
467.562
470.168
441.923
485.220
352.862
466.038
552.087
551.773
467.189
356.052
449.183
534.274
497.838
471.476
513.609
508.973
597.753
514.513
585.470
600.705
472.551
459.163
453.304
513.239
366.638
479.395
527.799
545.777
481.893
360.847
460.416
517.716
524.787
Hip Displacement

The influence of variations in shoe midsole density on the impact

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