Contract Research Project Report 2007
Title | The Comparative Analysis of Biomechanical Variables Between the Normal shoes and Tunnel shoes in Middle School Male Students |
Research Director | Eui-Whan Kim(Yongin University) |
Co-researcher | Jae-Wook Chung(Yongin University) Tae-Wan Kim(Yongin University) Sung-Seop Kim(Yongin University) Hyo-Jin Lee(Yongin University) Woong-Ryang Wi(Yongin University) |
Client | RYN KOREA Inc. |
International Institute of Sports Science
Yongin University
Contract Research Project Report
• Title
: The Comparative Analysis of Biomechanical Variables Between the Normal shoes and Tunnel shoes in Middle School Male Students
• Research Director : Eui-Whan Kim
(Research Director of International Institute of Sports Science, Yongin University)
• Co-researcher : Jae-Wook Chung
Tae-Wan Kim
Sung-Seop Kim
Hyo-Jin Lee
Woong-Ryang Wi
(Researchers of International Institute of Sports Science, Yongin University)
International Institute of Sports Science
Yongin University
REPORT
To : CEO of RYN KOREA Inc.
The following report is a summary of Contract Research Project concerning The Comparative Analysis of Bio-mechanical Variables Between the Normal shoes and Tunnel shoes
March 30, 2008
Eui-Whan Kim
Research Director of International Institute of Sports Science
Yongin University
TABLE OF CONTENTS
I. Introduction..................................................................................................................... 1
1. Need of this study ............................................................................................................... 1
2. Purpose of this study............................................................................................................ 3
3. Limitations............................................................................................................................ 3
4. Definition of Terms............................................................................................................... 3
II. Methods .......................................................................................................................... 5
1. Subjects of Research ........................................................................................................... 5
2. Test Equipments................................................................................................................... 5
3. Experimental Procedure....................................................................................................... 8
1) Data Collection................................................................................................................... 8
2) Human Anatomical Boundary Points................................................................................. 10
3) Standardization of EMG and Global Coordinate System.................................................. 12
4. EMG Measurement............................................................................................................. 14
5. Experimental Layout............................................................................................................ 16
6. Research & Calculation Methods of Variables.................................................................... 18
7. Data Processing ................................................................................................................. 22
III. Results & Discussion ............................................................................................. 23
1. Comparison of Kinematic Variables..................................................................................... 23
2. Comparison of Foot Moment............................................................................................... 27
3. Comparing Variables of EMG ............................................................................................. 31
IV. Conclusion & Recommendation................................................................. 34
Bibliography .................................................................................................................. 36
Table Index
Table 1. Average age & Anthropometrical Features of the Subjects............................... 5
Table 2. Measurement and Experimental Equipments....................................................... 7
Table 3. Attach Points of Human Body Mark ................................................................... 11
Table 4. The change of Angle by wearing shoe 1 or 2..................................................... 23
Table 5. The change of Moment of events by wearing shoe 1 or 2................................. 28
Table 6. Average Activation of muscles by wearing shoe 1 or 2..................................... 31
Figure Index
Fig. 1. Walking Shoes with Tunnel mid-sole......................................................................... 6
Fig. 2. Walking Pattern wearing Walking Shoes................................................................... 6
Fig. 3. Calibration Procedure.................................................................................................. 8
Fig. 4. Calibration per trial....................................................................................................... 9
Fig. 5. Calibration from ROM trial......................................................................................... 9
Fig. 6. Attach Points of Human Body Surface Reflection Mark......................................... 10
Fig. 7. Global Coordinate System(GCS)............................................................................. 12
Fig. 8. Local Coordinate System(LCS)............................................................................... 13
Fig. 9. Checking the closure of Growth Plate...................................................................... 15
Fig. 10. Attach Points of EMG to Lower Extremity Muscles............................................. 16
Fig. 11. Experimental Layout............................................................................................... 18
Fig. 12. Analysis Events and Phase..................................................................................... 22
Fig. 13. Moment of Lower Extremity Joints....................................................................... 23
Fig. 14. Comparison of Subtalar Joint, Knee, Hip Angle Events by Shoes............................. 25
Fig. 15. Comparison of Foot Joint Angles by Shoes......................................................... 25
Fig. 16. Comparison of Body Joint Angles by Shoes........................................................ 25
Fig. 17. Comparison of Foot Joint Momental Events by Shoes....................................... 29
Fig. 18. Comparison of Knee Joint Momental Events by Shoes...................................... 29
Fig. 19. Comparison of Hip Joint Momental Events by Shoes......................................... 29
Fig. 20. Comparison of Average Activity of each Muscles by Shoes.............................. 32
I. Introduction
1. Need of this study
The basic form of walking is to walk on two legs with the feature that one foot of the two is on the ground. In addition, walking is also a complicated pattern of exercise which is completed through human growth, development, change and harmonization of neuromuscular systems, bio-mechanic functions, and motor skills(Inman, Ralston & Todd, 1981; Beck et al., 1981).
To modern man living one's everyday life in a situation of extremely developed transportation and as a result, lack of exercise, walking could not only be means of transportation, but also provide exercises to improve one's health, performing a pivotal role in maintaining human health.
Recently, in addition to walking, there is an increasing interest about footwear. Mechanical approaches related with foot and footwear, are used as important data to protect one's foot from ligaments, muscle and skeletal injuries, to minimize the impulse from the ground during one's walking, and to correct wrong way of walking. Therefore, the impact of footwear to walking seems to be a very important factor.
In particular, the walking pattern of youth performs a pivotal role on developing the child's walking pattern to the adult's, and the pattern formed on one's youth would affect the walking pattern of adulthood and later adulthood(Sutherland et al., 1988; Scott & Winter, 1990).
In Korea, there are only few results of previous research(Chun, 1984; Cho et al., 1998) about the walking pattern of youth, and most research are limited to the results about their physique, body type, nutrition and growth plate.
More results are published in other countries(Beck, 1981; Kazai et al, 1976; Noguchi, 1985; Okamoto, 1993, Phillips & Clark, 1987; Sandra, 1987; Sojka et al, 1995; Todd et al, 1989), and quantitative study about the walking pattern of youth in Korea, who has different emotions, lifestyle, culture, and physical characteristics is needed.
To consider several previous studies about walking and footwear of youth, Rao & Joseph(1992) had investigated 2300 flat-footed children from 4 to 13 years old, about the change of foot-arch related with the type of footwear, and Jerosch & Mamsch(1998) had published that, among teens from 10 to 13 years old, 36.5% are normal-footed and others have deformity to some degree, which of 39.4% has pes valgus, 19.1% is flat-footed, and 17.7% is clubfooted.
These reports implies that footwear do affect, directly or indirectly, the foot shape of youth who are in the period of growth. Besides, studies about the relation between the foot shape and footwear of youth, and the effect of footwear to walking are recently going on(Donna Oeffinger et al., 1999; Stansfield et al., 2003; Macwilliams etal., 2003; Sebastian Wolf et al., 2008; Wong et al., 2008).
Recently, the recognition about the importance of footwear has been growing, and new products are being launched, specialized and are getting diversified.
Professionalism, diversity, functionality, aesthetics, and economical characteristics are the points that has to be considered importantly about footwear. However, it is the situation that the recently launched products are being sold almost without quantitative research or clinical trials because of the commercial objectives. This situation could seriously affect the person who wears it, and it also should be changed by the fact that who is going to wear it. There are many results of study about adult footwear(Gwak, 1993; Kim, 1987; Kim et al., 2006; Choi, 2003; Cho, 1990; Mann, 1980; Cavanagh et al., 1985, Nigg , 1986), but less about the youth's, so the research is requested urgently.
The period of youth just before the closure of growth plate is called '2nd growth period', while the child not only rapidly grows, but also shows lots of physical changes(Lee, 1999; Lee, 1996, 2001; Anderson et al., 1963; Green & Anderson, 1957; Eynde et al., 1988; Carter & Health, 1990).
Recently, various walking shoes emphasizing the basic function of shoes are developed, and research of footwear is going on vigorously. Most of the research about walking shoes are emphasizing the functionality by the change of out-sole and mid-sole, analyzing and evaluating the kinematic, motor mechanical, and physiological variables by focusing its safety and accident preventing function. However, most of these studies are targeting disabled persons or professional athletes and ordinary adults.
Therefore, we confronted the need to analyze and assess the kinematic and kinetic variables between normal shoes or tunnel mid-sole walking shoes in rapidly growing youth, and also, to investigate the mutual relevance of gate and shoes, also with the effect of shoes to the gait of youth showing maximum development of strength and physique, and whose gait is developing to adult.
2. Purpose of this study
The purpose of following study is to comparatively analyze the bio-mechanical variables during walking, between the normal shoes and tunnel mid-sole walking shoes in students of youth age, whose walking patterns are developing to adult. The research variables for this purpose are set as followings.
1) We comparatively analyzed the kinematic variables(subtalar joint angle, knee angle, hip angle, ankle angle, spine angle)during gait, between normal shoes and tunnel mid-sole walking shoes.
2) We comparatively analyzed the moment of lower extremity joints(ankles, knees, hips) during gait, between normal shoes and tunnel mid-sole walking shoes.
3) We comparatively analyzed the activity of lower extremity muscle during gait, between normal shoes and tunnel mid-sole walking shoes.
3. Limitations
This study was proceeded depending on the following points.
1) Body joint was assumed as pin joint, and the segment of body was considered as rigid body which the center of mass does not change.
2) Subjects were limited as 24 adolescent male students whose growth plates are opened.
3) The footpath area for measurement was limited within 6m ground of the laboratory.
4) Physical characters of subjects are not considered.
4. Definition of Terms
Terms related with this study could be defined as followings.
1) Normal shoes: Normal footwear made by mid-sole and out-sole(Shoe 1).
2) Tunnel mid-sole walking shoes: Walking shoes developed to have 'tunnel' type mid-sole and curved out-sole(Shoe 2).
3) Gait cycle: Consists of stance phase and swing phase, from the time that the standard foot touches the ground until the next subsequent touch. Generally, one gait cycle is analyzed for gait analysis.
4) Stance phase: The period of gait cycle while one's foot lies on the ground. It means the time from 'initial contact' to 'toe-off'.
5) Swing phase: The period of gait cycle while one's foot detaches the ground until it contacts again.
6) Stride length: During gait, the straight distance from the point where the supporting foot detaches the ground until it contacts again.
7) Step length: During double support, the horizontal distance from the heel of the front foot, to the heel of the foot behind.
8) Support: Also called as 'contact phase'. It means from the time that one foot promotes one's body until the other foot supports it, also from the heel contact until the toe off.
9) Double support: The moment which two feet is on the ground.
10) Single support: The moment which one foot is on the ground.
11) Walking base: Width between each feet, also called as stride width.
12) Heel contact: Also called as 'heel strike' or 'initial contact'. The moment that the foot which was in the air attaches the ground
13) Toe off: The moment which the foot detaches from the ground.
14) Growth plate: Specific areas on arms, legs, fingers, toes, wrists, elbows, shoulders, ankles, knees, femur, spine, where bone grows. It is located at the end of long bones which are connected directly to the body joints, and a person is able to grow taller by the growth of this area.
II. Methods
Subject selection, usage of test equipments, research, experiments, data output and processing methods of this study were proceeded as followings.
1. Subjects of Research
In this study, 24 middle school male students(14~16 years old) with heel strike-typed normal foot, no medical history of lower extremity for 1 year, and with opened growth plates are selected for the subjects. Physical characteristics of the subjects are listed on Table 1.
Table 1. Average age & Anthropometrical Features of the Subjects
Subjects
Subjects(year)(cm)(kg)
(cm) (%)° , ×
Subjects | Age | Height | Weight | Length of Lowerextremity | Growth by one year | Amount of muscle | Growth Plate Closure |
| (year) | (cm) | (kg) | right | left | (cm) | (%) | ° , × |
| (cm) |
| M±SD |
15.5±0.6 | 168.6±3.3 | 57.8±8.4 | 85.2±2.9 | 82.4±15.3 | 4.8±2.8 | 44.9±5.0 | ° |
2. Test Equipments
Two types of shoes were selected for the analysis of gait pattern different by shoes type. One is the normal shoes(Shoe 1), and the other is the tunnul mid-sole walking shoes(Shoe 2, Fig.1.) which is engineered recently in the form of out-sole on the basis of African Masaian walking, of which the middle bottom angle is about 30~35° different from normal shoes, and also different from other walking shoes: 45° for company R, and 25~28° for company M.
Fig. 1. Walking shoes with tunnel mid-sole
The weight of tunnel mid-sole walking shoes is 260~520g, which the 'tunnel-like' mid-sole part is designed to minimize the stress.
Fig. 2. Walking Pattern wearing Walking Shoes
To obtain video records for the study, we used a real-time video capture device (Vicon Motion System: Oxford, UK) for the movement analysis. It could be separated largely into camera equipment, data acquisition equipment, and analysis software, and the detailed features of the devices are also described (Table 2).
Table 2. Experimental Equipments for Measurement
Data Acquisition Equipment
Software for Analysis
Software for Analysis
Type | Model | Image | Features |
Measurement device | BGM-6 | | Informs whether the growth plate has been closed or not |
EMG measurement device | Telemyo2400GT | | Measures muscle activity of body. |
Camera Equipment | The MX13 1.3 Million pixels Motion capture Camera | | MX13 provides a combination of speed, accuracy, and resolution. |
Data Acquisition Equipment | MX Control | | Connects various interface devices with Vicon device, and makes into one system. |
| MX Net | | Communicates mutually with connected devices, transporting and receiving data informations of the system. |
Software for Analysis | Workstation | | Execution core of Vicon Software |
| Bodybuilder | | Programs by reducing complex 3D vector operation into simple language. |
| Polygon | | Provides systematic management of many data to upgrade the efficiency of analysis. |
3. Experimental Procedure
1) Data Collection
To obtain more accurate data, we followed this process of switching informations of space and time into quantitative digital data(Fig. 3).
Fig. 3. Calibration Procedure
Basic algorithms of Vicon system used for quantitative data collection of this study are as followings :
(1) Conventional gait model(CGM) used for static trial, provides exact center of the joint of initially estimated CGM, center of segment, and local coordinate system of segment. In other words, body markers provided to find the initially measured joint midpoint of the body, are combined with human body model(Davis et al., 199), applied by Vicon.
(2) Dynamic trial calibrates the important movement of joints. Calibration means the real-time optimizing process of joint midpoint, coordinate system, and the segment. During these studies, initial position of captured movement based on the statistical background and informations about coordinate system do not change.
(3) Calibrated model finds out the optimized angle of the joint based on the captured movement time (fame by frame). Also, these data doesn't affect the raw data, while calculating the data using Kalman kinematic filter, which is processed by the smoothing procedure(Kalman, 1960).
Using this algorithms, we selected 'plug-in-gait', provided by Vicon Co. to calculate the variables(angle of joints, moment, power, etc.) of movement exactly. The calibration process of the research is as followings(Fig.4, 5).
Fig. 4. Calibration per trial Fig. 5. Calibration from ROM trial
2) Human Anatomical Boundary Points
In this study, 'plug-in-gait' marks (Vicon Co.) are used for attach points of human body mark, and the detailed location and descriptions are described on Fig. 6. and Table 3.
Fig. 6. Attach Points of Human Body Surface Reflection Mark(plug-in-gait model marker set, Vicon)
Table 3. Attach Points of Human Body Mark
Located on 1/3 point of Left and Right upper arms
Located on Left and Right lateral view articular eminence
Located on 1/3 point of Left and Right forearms
Located on Left and Right radius and Ulnar styloid process
Located on Left and Right radius and Ulnar styloid process
Located on Left and Right radius and Ulnar styloid process
Located on the top of 2nd Longitudinal bone, right on the backhand side
Side of thigh, Located on the 1/3 position from the bottom
Located on Left and Right lateral view articular eminence
Located on the 1/3 position from the bottom of leg., defines the position of ankle refraction axis
Located on the lateral malleolus following the virtual line which passes through ankle and angle
Located on calcaneus which is at the same height with the curface of the foot bottom as with the toe mark
Located on the top of 2nd metatarsals, dent area between the front and the middle of the foot
No. | Head Marker | Location | Details |
1 | LFHD | Left Forehead | Located on the top of left temple |
2 | RFHD | Right Forehead | Located on the top of right temple |
3 | LBHD | Left Rearhead | Located on hindhead straight behind the forehead sign |
4 | RBHD | Right Rearhead | Located on hindhead straight behind the forehead sign |
| Body Marker | | |
5 | C7 | 7th Cervical Vertebrae | Located on 7th Cervical Vertebrae of Vertebra |
6 | T10 | 10th Thoracic Vertebrae | Located on 10th Thoracic Vertebrae of Vertebra |
7 | CLAV | Clavicle | Located on Jegula notch, where Clavicle meets Breast Bone |
8 | STRN | Breast Bone | Located on Xiposternal Cartilage of Breast Bone |
9 | RBAK | Right Back | Located on the middle of Right Scapula |
10 | LSHO | Left Shoulder | Located on Left Acromion |
11 | RSHO | Right Shoulder | Located on Right Acromion |
| Arm Marker | | |
12 | LUPA | Left upper arm | Located on 1/3 point of Left and Right upper arms |
13 | RUPA | Right upper arm |
| 14 |
LELB | Left Elbow | Located on Left and Right lateral view articular eminence |
15 | RELB | Right Elbow |
| 16 |
LFRA | Left Forearm | Located on 1/3 point of Left and Right forearms |
17 | RFRA | Right Forearm |
| |
Hand Marker | | |
18 | LWRA | Left Wrist Outside | Located on Left and Right radius and Ulnar styloid process |
19 | LWRB | Left Wrist Inside |
| 20 |
RWRA | Right Wrist Outside |
| 21 |
RWRB | Right Wrist Outside |
| 22 |
LFIN | Left Finger | Located on the top of 2nd Longitudinal bone, right on the backhand side |
23 | RFIN | Right Finger |
| |
Pelvic Marker | | |
24 | LASIS | Left ASIS | Located on Left and Right ASIS(anterior superior iliac spine) |
25 | RASIS | Right ASIS | |
26 | LPSI | Left PSIS | Located on Left and Right PSIS(Posterior superior iliac spine) |
27 | RPSI | Right PSIS | |
| Leg Marker | | |
28 | LTHI | Left Thigh | Side of thigh, Located on the 1/3 position from the bottom |
29 | RTHI | Right Thigh |
| 30 |
LKNE | Left Knee | Located on Left and Right lateral view articular eminence |
31 | RKNE | Right Knee |
| 32 |
LTIB | Left Shin | Located on the 1/3 position from the bottom of leg., defines the position of ankle refraction axis |
33 | RTIB | Right Shin |
| |
Foot Marker | | |
34 | LANK | Left Ankle | Located on the lateral malleolus following the virtual line which passes through ankle and angle |
35 | RANK | Right Ankle |
| 36 |
LHEE | Left Heel | Located on calcaneus which is at the same height with the curface of the foot bottom as with the toe mark |
37 | RHEE | Right Heel |
| 38 |
LTOE | Left Toe | Located on the top of 2nd metatarsals, dent area between the front and the middle of the foot |
39 | RTOE | Right Toe |
| | | | | |
3) Standardization of EMG and Global Coordinate System
Global Coordinate System(GCS) and Local Coordinate System(LCS) used to yield the 3-dimensional data in this study are as followings :
(1) Global Coordinate System
Global frame used in this study is the right-handed coordinate system.
Three axis perpendicularly centered to origin were defines as vector X, Y, and Z. X-axis means the 'medial-lateral' direction of the subject, Y-axis is the 'anterior-posterior' direction, and Z-axis is the 'vertical' direction. The walking direction of the subject was set to match the positive(+) direction of the Y-axis, and the direction to the top perpendicular to the floor was set to match the Z-axis (+), while the right part of the direction the subject is walking to was defined to match the X-axis (+).
By the three orthogonal axis (X, Y, and Z), the origin of the inertial frame(0.0.0) was defined based on the origin of reference frame made by L-frame and T-Wand (Fig. 7).
Fig. 7. Global Coordinate System
2) Local Coordinate System
In this study, the local coordinate system was defined differently by foot, leg, thigh. Each of the segments was divided into linear segment connecting two points of the joint, or into the segment which is made by connecting more than three points of external mark, and the local coordinate system of each segments were set using external marks attached on body surface. Each of calculated LCS were moved to each center of joints (Fig.8).
Fig. 8. Local Coordinate System
These are the principles of hierarchical structure of the algorithm, which applies to the local coordinate system oriented by Vicon's Conventional Gait Model(CGM).
• Pelvis shall be the primary source.
• On the basis of pelvis, two femur segments were attached to pelvis using 'ball-and-socket' joint (Degree of freedom:3, hip joint centers: HJC).
• Two tibia segments were attached to femoral segment using 'ball-and-socket' joint (Degree of freedom:3, knee joint center: KJC).
• Two foot vectors were attached to leg segment using 'ball-and-socket' joint (Degree of freedom:3, ankle joint centers: AJC).
In other words, CGM such as the Kinematic skeletal model (Vicon), is related to the model form of hierarchical structure and the joint.
Detailed definitions of LCS modeling are as followings.
• The origin of pelvic is located by direct calculation of half-way method, using the markers of LASI, RASI, and SACR.
• The location of HJC decides the LCS by regression equation(Davis, R. B. et al., 1991).
• The thigh segment and the KJC are defined by HJC and external marker(LTHI/RTHI, LKNE/RKNE).
• The leg segment and the AJC are defined by KJC and external marker(LTIB/RTIB, LANK/RANK).
• The vector of foot is defined by AJC and external marker(LTOE/RTOE).
This means that segments of all origin and coordinate system is calculated by the directly measured location of marker for each frame. All the noise or errors made by the movement of bone-connected-skin was filtered by Waltering kinematic filter.
Cardan angle formula (Winter, 1990) was used to calculate the relative angle of segments, from the LCS of segment obtained by this way.
4) Growth Plate Measurement
For this study, we selected middle school male student(14~16 years old) only normal-footed, and having opened growth plate. We firstly checked whether the growth plates are opened or not. For this, the measurement was performed using BGM-6(Bone Growth Management System up to 6 feet, WEVERINSTRUMENTS, In. Co.), based on the 'TW-3 growth measurement theory (A theory investigated for 12 years by the 3 pediatric scholars(Tanner, Whitehouse & Heely) and proved by many scientists in UC, Japan, Scandinavia, and the US)', which is the pDEXA(peripheral Dual Energy X-ray Absorptiometry)-type.
For the measurement, areas of the palm, thumb, and heel were layed on BGM-6 System after calibration. Detailed images showing the opening of growth plates are exhibited (Fig. 9).
Fig. 9. Checking the closure of Growth Plate
4. EMG measurement
1) The location of EMG measurement
To measure the EMG, each surface electrode was attached to thigh rectus femoris of right lower extremity, vastus medialis, vastus laterlis, thigh biceps femoris, tibialis anterior, medial gastrocnemius, soleus femoris, while ground electrode was attached to ASIS. Electrodes were bipolar surface electrode(Dual electrode, Noraxon, USA; Distance of electrodes: 1cm)(Fig.10).
Fig. 10. Attach Points of EMG to Lower Extremity Muscles
2) EMG Standardization
To remove noise from the MVC period and also from all the EMG raw-data measured in this study, we followed the process below.
First, full wave rectification was performed for the raw-data of EMG. EMG data of each muscle was measured for three times of MVC for EMG standardization (normalization), underwent smoothing procedure using average (mean: 50ms), and finally obtained the maximum EMG(). Also, we used the electric filter(FIR filter, 10~500Hz band pass) to remove the nose of rectified data. The reason why we used the 'low-pass' filter is that using those filter to the wave rectificated sign, makes the linear envelope very similar to the graph showing the muscle tension(Winter, 1990).
This formula for the EMG standardization is always needed to compare experimental conditions and subjects.
In other words, means the standardized EMG of each muscle, having the unit of %MVC. means the EMG of each muscle, which is filtered twice during the real-time measurement, while means the maximum EMG of each muscle found during the MVC measurement. To analyze each of the muscle activity, we comparatively analyzed the average of standardized EMG data of 7 muscles. .
5. Experimental Layout
To analyze the kinematic variables, 7 real-time infrared cameras(Vicon I.R., Strobe & Pus, MX13) were installed before, after, left, right and diagonally, and digital camcorder(NV-GS300GD, Panasonic) was also installed in front, to take video records additionally of total experiment. Also, to measure the ground reaction force of gait, 2 Force Plate (AMTI Co.) were used, with the sampling rate set to 1,000Hz. All experimental devices were connected to 'Data Station' which is a device for data processing (Fig. 11).
To input global coordinates and real-space coordinates into analyzing computer, video records were taken for 10sec, using L-frame and T-wand with reflection marker, while subjects were to walk the ground of laboratory on which two AMTI ground reaction force board is installed. During this, seven MX13 cameras(120Hz, Vicon Motion System) were installed in the space of 3m height and 5m distance to record the movement, and the angle of camera was adjusted to minimize the hidden point. First of all, we repeated the experiment until we got the suitable movement for 10 times for the case wearing normal shoes, and also conducted the gait analysis for the case wearing walking shoes, by the same method. Walking speed of both case was controlled constantly(100 steps/min), using metronome.
Fig. 11. Experimental Layout
6. Research & Calculation Methods of Variables
1) Gait movement event and phase
Events and phase for the analysis of gait movement are displayed on Fig.12.
Fig. 12. Analysis Events and Phase
(1) Event
1) Right Heel Strike (RHS) : The moment which right heel detaches from the floor.
2) Right Toe-Off (RTO) : The moment which right toe detaches from the floor.
(2) Analysis Phase
1) Stance Phase: From RHS to RTO
2) Kinematic variables
These are the kinematic variables used in this study : Foot Progress Angle( FPA), Knee Joint Angle(KJA), Hip Joint Angle(HJA), Ankle Joint Angle(AJA), Spine Angle. During walking, plantar flexion and dorsiflexion occurs around the sagittal plane at ankle joint, abduction & adduction occurs around the transverse plane, and inversion & eversion occurs around the frontal plane. Each movement occurred among segments were defined as relative motion of distal segment to guard segment. For each movement of AJC, the negative(-) direction of X-axis was defined as plantar flexion, while the positive(+) direction was called dorsiflexion; the negative direction of Y-axis was defined as abduction, while the positive was called adduction; the negative direction of Z-axis was defined as eversion, while the positive was called inversion.
For the movement of KJC and HJC, the negative direction of X-axis was defined as extension, while the positive was called flexion.
Defining each unit vector as I, J, K for axis(X, Y, Z) at guard segment, while as i, j, k for axis (x, y, z) at distal segment, the formula to get the 1st, 2nd, 3rd rotation angle could be written as followings (Winter, 1990).
Using 
,
1st rotation was performed around the X axis,
2nd rotation was performed around the Y axis,
and finally, 3rd rotation was performed around the Z axis.
This is the transformation matrix of Euler model.
: (+) angle means flexion, while (-) means extension.
: (+) angle means adduction, while (-) means abduction.
: (+) angle means inversion, while (-) means eversion.
3) Moment of Lower Extremity Joints
The moment of lower extremity joints of analysis variables, was calculated by analysis software of Vicon Motion System which is using the Inverse Dynamic analysis method by the ground reaction force data and kinematic data, and the moment calculating formula of lower extremity joint was as followings(Zatsiorsky, 2002).
Where, = The force vector delivered to the joint, which is made by k and k+1 segment
= The ground reaction force data
= The mass of i-th segment
g = Gravitational acceleration vector
= Acceleration on center of mass from the i-th segment
Where,
= The moment vector from the joint made by k and k+1 segment.
= The position vector from the center of mass of distal segment, to the point of force application which is applied to the ground reaction force.
= The position vector from the center of mass of distal segment, to the joint which is made by k and k+1segment.
= The position vector from the center of mass of distal segment, to the i-th segment center of mass.
= The change of angular momentum of the i-th segment.
Fig. 13. lower extremity joints moment(Kim, 2005)
To minimize the perversion and error made by weight difference, moment values presented in this study were standardized (normalized) by dividing the obtained moment values with the weight of subjects.
7. Data Processing
For each measurement in this study, subjects were instructed to repeat the gait movement wearing 'Shoe 1' or 'Shoe 2' for 10 times, respectively.
Average and Standard deviation of each variable were calculated using Microsoft Office Excel 2007. These average values were used in the statistical test(SPSS 12.0). We selected the 'one-way ANOVA' method to compare the calculated variables, between the gait wearing 'Shoe 1' and 'Shoe 2'. Significance level was set to α=0.05.
III. Results & Discussion
The purpose of this study is to comparatively analyze the bio-mechanical variables between wearing normal shoe(Shoe 1) and tunnel mid-sole walking shoe(Shoe 2). We selected the 10 suitable movements of 24 middle school male students for the gait analysis of each shoes. Results and discussion about detailed variables as FPA(foot progress angle), knee angle, hip angle, ankle angle, spine angle, moment of lower extremity joints(ankle, knee, hip joint), and EMG variables are described.
1. Comparison of Kinematic Variables
Wearing each shoes during gait, variables of right FPA, knee angle, hip angle, ankle angle, spine angle were calculated by events, using the 'calculating method of angular variables at lower extremity joints (Winter, 1990)', and results were as followings (Table 4).
Table 4. The change of Angle of events by wearing shoe 1 or 2 (Unit : ° )
Angle
FP
Angle | Event 1 | F | P |
| Shoe 1 | Shoe 2 |
| Foot progress Angle |
-11.0±6.3 | -9.6±6.5 | 3.178 | .07 |
Knee Angle | 2.4±5.8 | 4.9±6.9 | 10.171 | .00** |
Hip Angle | 26.9±7.8 | 25.9±7.9 | 16.794 | .33 |
| X | Y | Z | X | Y | Z | | |
Ankle angle | 6.3±4.6 | -1.3±5.3 | 5.0±21.0 | 8.1±5.5 | -0.7±5.2 | 2.2±21.3 | x 7.969 y .752 z 1.149 | x .00** y .38 z .28 |
Spine angle | 0.8±5.8 | -1.4±3.4 | -0.9±6.7 | 0.7±5.9 | -1.7±3.3 | -0.9±7.6 | x .019 y .312 z .001 | x .88 y .57 z .97 |
Angle
FP
Angle | Event 2 | F | P |
| Shoe 1 | Shoe 2 |
| Foot progress Angle |
-7.5±6.5 | -9.1±6.5 | 3.822 | .05* |
Knee Angle | 44.6±7.8 | 40.5±8.2 | 16.794 | .00** |
Hip Angle | -5.2±5.4 | -6.9±5.4 | 6.714 | .01** |
| X | Y | Z | X | Y | Z | | |
Ankle angle | -6.1±4.4 | 1.1±4.3 | -5.5±17.4 | -9.2±4.8 | 1.5±4.6 | -7.1±18.0 | x 27.221 y .555 z .502 | x .00** y .45 z .47 |
Spine angle | -1.2±6.2 | 0.9±7.6 | -0.4±4.4 | 0.2±6.2 | 0.9±8.2 | -0.7±5.3 | x 3.642 y .000 z .208 | x .05* y .99 z .64 |
* p<.05, **p<.01
Foot progress Angle : The movement on frontal plane between the Y-axis of absolute coordinate and the centerline of the foot (+)adduction, (-)abduction.
X : The movement on sagital plane of ankle joint and body joint (+)flexion, (-)extension.
Y : The movement on frontal plane of ankle joint and body joint (+)adduction, (-)abduction.
z : The movement on transverse plane(horizontal plane) of ankle joint and body joint (+)lateral rotation, (-)internal rotation.
To compare Shoe 1 and 2 about FPA(Table 4), any significant difference wasn't found for Event 1, but differences for Event 2 seemed to be significant(p< .05), while about knee joint angle, both Event 1 and 2 showed significant differences(p< .00). About the hip joint angle, both shoes did not show meaningful differences for Event 1(p< .33), while the difference for Event 2 was meaningful(p< .01).
To consider the change of ankle joint angle, flexion angle was different significantly(p< .00) for both Event 1 and 2, while inversion & eversion rotation angle and medial & lateral rotation angle didn't show significant difference. Finally, to consider the change of body joint angle between Shoe 1 and 2, significant differences was not found for Event 1, while anterior & posterior flexion angle for Event 2 was statistically different(p< .05).
To consider the change of lower extremity joint angle, knee angle and dorsal & plantar flexion angle of ankle were significantly different for Event 1 , while FPA, knee angle, hip angle, dorsal & plantar flexion angle of ankle, anterior & posterior flexion angle of body were significantly different for Event 2, showing the great difference of angular change for Event 2.
Fig. 14. Comparison of Subtalar Joint, Knee, Hip Angle Events by Shoes
Fig. 15. Comparison of Foot Joint Angles by Shoes
Fig. 16. Comparison of Body Joint Angles by Shoes
To consider the change of FPA, knee angle, hip angle of events by shoes, FPA showed the variation of 3.5° for Shoe 1(Event 1 and Event 2), and 0.5° for Shoe 2(Event 1 and Event 2), respectively (Fig. 14). This result shows that during support period of gait, Shoe 2 could help to maintain more constant angle than Shoe 1, prevent excessive eversion of ankle, and show more stable pattern of gait.
The knee angle showed significant differences for both Events, with the variation of average for Event 1 to be 2.5°. This seems that bending of knee angle appeared significantly because Shoe 2 is higher than Shoe 1, which has the higher out-sole, at right RHS of initial stance phase.
Comparing with this result, another study of ‘Comparative analysis of character of lower extremity muscle with gait pattern, by different out-sole bending type shoes(Ahn, 2007)' shows the different result showing statistically significant differences: 3.87° for normal shoes and 3.90° for rear walking shoes. This seems because the out-sole angle of rear bending walking shoes are different, and also the out-sole thickness of normal shoes could be different. Also, Perry(1992) showed that Shoe 2 shows the similar result with the result that knee joint bends about 5° during initial contact. In the case of knee joint of RTO for Event 2, which is the terminal stance phase, Shoe 2(40.5°) seems to bend more than Shoe 1(44.6°) to progress the gait. This difference of angle shows that to advance the body further than foot, Shoe 2 fits more than Shoe 1 to the principle of gait, which says that the energy formed at ankle has to move and accelerate to knee, by extending one's knee and therefore by transferring energy effectively.
The change of ankle joint angle is used as an important data to explain the pronation movements during gait by shoes (Fig. 15).
For both Event 1 and 2, the angular change of Shoe 1 and 2 at front & back side and at transverse plane appears, but the change at left & right side does not appear significantly. Dorsiflexion and plantar flexion appears intersectional by gait periods of ankle joint, while the angular change of smooth dorsal & plantar bending could help reducing the body shock during initial stance phase RHS for Event 1. In this study, we found that the medial rotation became smaller because Shoe 2 showed more dorsiflexion than Shoe 1, for Event 1. Compared with previous research, though showing different calculate variables, it seems to enlarge the shock absorbing effect by maximizing dorsal & plantar bending during landing, and also reduce the pronation during landing by minimizing the medial rotation angle, and finally reduce the injury factors which could happen during gait. Therefore, considering together with the result of Mann(1980) reporting the relation of passive shock absorbance and injury, it seems to maximize the dorsiflexion angle to enlarge the heel area to absorb the shock, while minimize the medial rotation angle related with ankle injury of initial stance phase, and finally reduce the pronation, which could be the mechanism of ankle injury.
Choi(2003) reported that rear bending shoes reduce the initial pronation, by the smooth out-sole rear area or other characters of shoe structure, and finally provide stabilized rear foot controling function. Kim et al.(2006) reported that walking shoes could reduce the injury factors of ankle adduction during gait. Knutzen & Price(1994), Milani, and Schnabel & Hennig(1995) reported that pronation of feet absorbs the shock from the ground to the body.
Comparing the change of spine angle, Shoe 1 and 2 did not show significant difference for Event 1(Fig. 16), but showed significant differences for Event 2 of anterior & posterior flexion angle, for which Shoe 2 showing the change of posture much more close than Shoe 1 to erect posture.
To summarize the results of angular variables by shoes, Shoe 1 showed significant differences with knee angle and dorsal & plantar bending of ankle of RHS, also with subtalar joint angle, knee angle, hip angle, dorsal & plantar flexion angle of ankle, and anterior & posterior flexion angle of body of RTO.
Shoe 2 showed passive shock absorbance and smooth flexion movement during gait when grounded with large flexion angle of ankle, also minimized the pronation which induces the ankle injury, and induced the momentum of RTO by extending the body to go forward.
2. Comparing the Moment of Lower Extremity Joints
The moment of three lower extremity joints (ankle joint, knee joint, hip joint) between wearing shoe 1 and 2 are shown below(Table 5).
Table 5. The change of moment by events between wearing Shoe 1 and Shoe 2 (N·m/BW )
FP
Moment | Event 1 | F | P |
| Shoe 1 | Shoe 2 |
| |
X | Y | Z | X | Y | Z | | |
Ankle moment | 0.41±0.64 | 0.23±0.21 | 0.35±0.48 | -0.02±0.53 | 0.25±0.25 | 0.12±0.37 | x 37.398 y .438 z 23.636 | x .00** y .50 z .00** |
Knee moment | -2.97±3.34 | 0.28±1.45 | 0.36±0.43 | -1.53±2.26 | -0.58±1.37 | 0.16±0.39 | x 18.215 y 18.313 z 16.035 | x .00** y .00** z .00** |
Hip moment | 2.98±0.61 | -1.59±0.39 | 0.06±0.07 | 0.95±0.54 | -2.25±0.26 | 0.17±0.54 | x 6.484 y 2.757 z 1.765 | x .01** y .09 z .18 |
Moment
FP
Moment | Event 2 | F | P |
| Shoe 1 | Shoe 2 |
| |
X | Y | Z | X | Y | Z | | |
Ankle moment | -0.34±0.88 | -0.38±0.36 | 0.12±0.37 | -0.79±1.47 | -0.35±0.34 | 0.08±0.05 | x 9.269 y .368 z .312 | x .00** y .54 z .57 |
Knee moment | 2.86±0.22 | -0.82±0.13 | 0.16±0.38 | 1.81±1.28 | -0.98±0.12 | 0.15±0.50 | x 11.738 y 1.100 z .123 | x .00** y .29 z .72 |
Hip moment | -5.28±6.4 | -2.00±0.33 | 0.91±0.42 | -3.71±0.77 | -1.63±0.31 | 1.04±0.46 | x 3.372 y .903 z 1.840 | x .06 y .34 z .17 |
* p<.05, **p<.01
X : moment of lower extremity joints at sagital plane (+)flexion, (-)extension.
Y : moment of lower extremity joints at frontal plane (+)adduction, (-)abduction.
z : moment of lower extremity joints at transverse plane(horizontal plane) (+)lateral, (-)internal rotation.
To consider the change of the moment of ankle joint, plantar & dorsal flexion moment and medial & external moment showed significant differences(p< .00) for Event 1 of Shoe 1 and Shoe 2, while only plantar & dorsal flexion moment showed significant differences(p< .00) for Event 2.
To consider the change of the moment of knee joint, Event 1 showed significant differences(p< .00)with flexion & extension, adduction & abduction, medial & external rotating moment, while Event 2 significantly differed only with bending & extending moment(p<0.00 ).
hip joint moment differed significantly only with flexion & extension moment of Event 1 (p< .01).
Comparision of ankle joint moment by events are shown in Fig. 17.
Fig. 17. Comparison of Foot Joint Momental Events by Shoes
Fig. 18. Comparison of Knee Joint Momental Events by Shoes
Fig. 19. Comparison of Hip Joint Momental Events by Shoes
Comparing the ankle joint moment different by shoes, dorsal & plantar bending moment and medial & lateral rotation moment of both shoes, showed significant difference for Event 1 and 2 (Fig. 17). Specially, dorsal & plantar bending moment differed significantly.
Ankle joint moment has close relevance with pronation of ankle, which absorbs the shock from the ground to the body(Knutzen & Price, 1994;Milani, Schnabel & Hennig, 1995), and if overloaded, it gives stress to subtalar joint. Specially, distortion of leg segment on the axis of knee joint becomes excessive than the thigh joint because of the coupling behavior of feet.
In this study, we can find that Shoe 2 could avoid injury induced by excessive pronation more than Shoe 1, from the results that dorsal bending moment and medial rotation moment declines during the initial stance phase of RHS, while it absorbs shock originated from the ground. On the other hand, during RTO which is the terminal stance phase, plantar flexion moment of Shoe 2 is bigger than Shoe 1, so advances one's body more strongly.
To compare the knee joint moment by events between shoes, Shoe 2 seems to help preventing injury by reducing the knee moment, from the result that the bending & extending moment of knee was smaller with Shoe 2 than Shoe 1, also related with other results that many people receive injury ACL and meniscus injury by the shock from the ankle forwarded to knee, during jogging or gait (Moon, 1999).
Comparing with the results of McMahon and Valiant & Frederick(1987), which concluded that, during gait, the injury mechanism occurred from pronation of ankle involves with knee, we could say that common degenerative knee joint inflammations or other knee disorders could be healed by decreasing the moment to knee during gait
Comparison of the change of hip joint moment by events between shoes, shows the similar result with the change of knee joint moment (Fig. 19). Hip joints seems to closely related with coupling behavior of pelvic during gait, while it could be said that it is loaded more than ankle & knee joint from our results, and Shoe 2 seems to function less moment than Shoe 1.
3. Comparing Variables of EMG
Muscle activity during gait movement at right lower extremity (RF, VM, VL, BF, TA, MG, and SF) is compared by wearing shoe 1 or 2 (Table 6).
Table 6. Average Activation of muscles by wearing shoe 1 or 2 (Unit : %MVC)
Muscles
FP
Muscles | Stance phase | F | P |
| Shoe 1 | Shoe 2 |
| RF |
34.0±7.4 | 35.8±7.9 | 4.566 | .03* |
VM | 33.1±8.0 | 35.6±7.4 | 8.467 | .00** |
VL | 32.1±8.5 | 35.7±8.0 | 16.320 | .00** |
TA | 27.7±7.4 | 26.5±7.5 | 2.279 | .13 |
BF | 30.3±8.1 | 30.9±9.7 | .454 | .50 |
MG | 39.2±9.0 | 39.4±9.8 | .019 | .88 |
SM | 39.9±10.4 | 43.1±11.7 | 6.967 | .00** |
* p<.05, **p<.01
***Rectus femoris(RF), Vastus Medialis (VM), Vastus Lateralis(VL), Tibialis Anterior(TA), Musculus Biceps Femoris(BF), Medial gastrocnemius(MG), Soleus Muscle(SM)
Comparing average muscle activity of lower extremity muscle by wearing Shoe 1 and Shoe 2 (Table 6), RF showed significant difference wearing Shoe 1 of 34.0 %MVC, and Shoe 2 of 35.8 %MVC(p< .03). VM showed significant differences wearing Shoe 1 of 33.1 %MVC, and Shoe 2 of 35.6 %MVC (p< .00). VL showed significant differences wearing Shoe 1 of 32.1 %MVC, and Shoe 2 of 35.7 %MVC (p< .00). SM showed significant difference wearing Shoe 1 of 39.9 %MVC, and Shoe 2 of 43.1 %MVC(p< .00). However, TA(Shoe 1, 27.7 %MVC; Shoe 2, 26.5 %MVC), BF(Shoe 1, 30.3 %MVC; Shoe 2, 30.9 %MVC), MG(Shoe 1, 39.2 %MVC;Shoe 2, 39.4 %MVC) did not differ with statistical significance.
During gait phase, the average muscle activity of lower extremity muscle of stance phase is compared and described on Fig. 20.
Fig. 20. Comparison of Average Activity of each Muscles by Shoes
To consider that muscles becoming agonist during gait are Rectus femoris, Vastus medialis, Tibialis anterior, Biceps femoris, gastrocnemius, and Soleus femoris of lower extremity(Perry, 1992), Shoe 2 seems to show higher muscle activity with RF, VM, VL, MG, SM (but except with TA, BF) than Shoe 1.
RF, VM, VL, SM showed significant differences with Shoe 1 and 2. These results show that Shoe 2 would enlarge the effect of exercise for modern man who walks for exercise, and also give help to the muscle development and growth of youth, considering that subjects of this study are on the vigorous growth period.
These results suggest that Shoe 2, more than Shoe 1, could inflict more power to lower extremity muscles during gait, under the strictly controlled experimental situation only with the difference of shoes while every other conditions are set to be equal. Additionally, it also matches the recent result that rear bending shoes could help the lower extremity muscle training because, as the joint movement of ankle is restricted, the activity of tibialis anterior and medial gastrocnemius increases during stance phase (Ahn, 2007). The results of Cho et al.(2006) and Gi(2006) concluded the muscle activity of power walking to be higher, by comparing the variables of EMG between normal walking and power walking, which is the similar result about the higher muscle activity of Shoe 2 in our study. In other words, even without power walking, one could increase the muscle activity of lower extremity to the same amount of power walking, by choosing different shoes.
To summarize our results of EMG variables, compared with normal shoes(Shoe 1), tunnel mid-sole walking shoes(Shoe 2) seems to provide higher muscle activity of lower extremity muscle, showing the possibility of strenghtening the lower extremity muscle and also increasing energy consumption. In addition, if youth on growth period wears tunnel mid-sole walking shoes, it would surely help them in terms of development of lower extremity muscle, health maintenance, and diet, etc.
IV. Conclusion & Recommendation
This study was progressed to comparatively analyze the dynamic variables of gait between normal shoes(Shoe 1) and tunnel shoes(Shoe 2), in 24 middle school male students living in Yongin city, whose gait is developing to the pattern of adult, and to define the effect of shoes to the gait of youth. For this, we analyzed the angle of lower extremity joints, moment, and the variables of electromyogram, and finally obtained these conclusions.
1. Statistically significant differences of wearing normal shoes(Shoe 1) and tunnel shoes(Shoe 2) were found during the initial stance phase of the gait, about knee angle and dorsal & plantar flexion angle of ankle, and also during the terminal stance phase, about subtalar joint angle, knee angle, hip angle, dorsal & plantar flexion angle of ankle, and frontal and lateral flexion angle of body. From which, the terminal stance phase seems to be more influenced by the change of footwear than the initial phase.
2. Statistically significant differences of wearing 'Shoe 1' and 'Shoe 2' were found during the initial stance phase of the gait, about dorsal & plantar flexion moment of ankle joint, medial & lateral moment, bending moment of knee joint, adduction & abduction, medial & lateral rotating moment, and bending moment of hip joint, and also during the terminal stance phase, about dorsal & plantar flexion moment of ankle and bending moment of knee joint. From which, the initial stance phase seems to be more influenced by footwear than the terminal phase.
3. During the support phase of the gait wearing 'Shoe 1' and 'Shoe 2', the average muscle activity of 'Shoe 2' was higher than 'Shoe 1' about RF, VM, VL, and MG of lower extremity, showing statistically significant difference. On the other hand, muscle activity was high at musculus biceps femoris, tibialis anterior, and gastrocnemius, but did not show significant difference.
As a result, compared with wearing normal shoes(Shoe 1), tunnel shoes(Shoe 2) seems to absorb stress by dorsiflexing the ankle, and to prevent excessive pronation by reducing the medial rotation, during the initial stance phase of gait. This seems to reduce the moment which is conveyed to ankle joint, knee joint, and hip joint. During the terminal stance phase, while moving forward, wearing 'Shoe 2' seems to help walking more effectively than wearing 'Shoe 1', because the plantar flexion moment, which functions as momentum to move forward, gets bigger as the plantar flexion of ankle gets larger. Also, wearing 'Shoe 2' made the muscle activity of lower extremity muscle during support phase, higher than 'Shoe 1', showing the possibility to help lower extremity muscle exercise, diet, increasing exercise, and lower extremity muscle training.
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