Biomechanics Lab 2: Kinetics of Walking and Running
Gavin Angoh, Natasha Doroodian & Marcus Hardy
Lakehead University
KINE-4015-FDE
Dr. Carlos Zerpa
November 5, 2021
Introduction
Humans are one of few species that have evolved to enable bipedal locomotion
(Franklin et al., 2014). The human foot is made up of 26 bones, 33 joints, and 19 muscles
that form an arch which serves to distribute the forces that occur at the foot during tasks like
standing and locomotion. (Franklin et al., 2014) Mechanoreceptors found in the foot are large
in number and provide feedback that aids in balance and movement control (Ramanathan et
al., 2011). Foot problems have become increasingly more common as footwear has evolved.
Closed, pointed to shoes with a narrow toe-box and elevated heel has become a fashion
statement that has been shown to detriment the shape and function of the natural foot and
leads to issues that were not seen previously such as the development of bunions in the first
metatarsal, or shortening in the Achilles tendon which can contribute to an increased risk in
falling in aging populations (Menz et al., 2005). Moreover, common athletic shoes that tout
features to help minimize harmful impacts that occur during locomotion have been shown to
interfere with ankle stability, decrease proprioceptive feedback from the sole as well as
decrease awareness of foot position and functionality of the foot as it is intended to be used.
(Sekizawa et al., 2001; Ramanathan et al., 2011; Franklin et al., 2014) Wearing shoes has
also been shown to place higher demands on the lower limb muscles and increase the
likelihood of foot inversion. (Ramanathan et al., 2011) Shoes, therefore, may lead to
differences in gait pattern and force distribution compared to barefoot walking. (Franklin et
al., 2014)
Newton’s Third Law of Motion can be used to determine the forces that are
experienced during normal locomotive walking and running patterns. Newton’s Third Law of
Motion states that “to every action, there is always an opposed equal reaction; or the mutual
actions of two bodies upon each other are always equal and directed to contrary parts”
(Newton [1729] 1934, p13). (as cited by Watkins, 1997) Force plates and force transducers
are commonly used to record the Ground Reaction Forces (GRFs) in three dimensions Fz,
Fx, and Fy that occur as a result of jumping, landing, running, and walking. (Johnson et al.,
2018) The vertical component, Fz, is the largest of the three GRFs. It measures the vertical
acceleration of the center of mass (COM) that occurs during gait. The forwards and
backward GRF is represented by Fy. Fy begins with a negative value that represents the
breaking force of gait that occurs to decelerate the COM until midstance is reached. Fx
represents the medial-lateral GRF which takes into consideration medial-lateral shear forces.
These forces increase as step width increases due to an increased angle between the lower
extremities and contact points. (Johnson et al., 2018). Therefore, the purpose of this lab will
investigate the impact of shoes on the GRFs and gluteus medius activity during gait.
Experimental Method
Participants
The participant criteria involve the professor asking who wants to participate in the lab
process after demonstrations of the procedures. One individual from KINE4015 has given
consent to participate in the lab by raising their hand. The body-weight of the participant is
1232.66N.
Instruments
An application called ZOOM is used for the computer to deliver the experiment by the
school. This enables the online students to observe the experiment from home and follow how
the instruments are used. This experiment takes place in a classroom that demonstrates how to
use a foot scanner, force platform, wireless EMG Delsy Electrodes, LabChart Reader, Microsoft
Excel, and SPSS Statistics. A foot scanner is used on the participant to measure foot posture, and
the shape of the foot arch. A force platform measures the ground reaction forces of Fz, Fy, and
Fx of the feet when the participant walks over it. Wireless EMG Delsy Electrodes are placed on
the participant’s gluteus medius to measure the amount of force that is produced from one of the
muscle activations required to walk. LabChart Reader is a software program that calculates the
Spectrum Frequency Analysis with a low pass frequency filter, Maximum Power Frequency, and
Linear Envelope of the force and EMG data. These procedures create a graph that can be copied
and transferred to Microsoft Excel as data in a table in the form of numbers of force and time.
This Excel software then also implements another graph alongside the numerical data in the
cells. The software then incorporates an impulse function to the force. Then the total sum
function is used to calculate the total force in two separate groups between the braking (negative
values) and propulsion (positive values) forces in Table 5.
Procedures
Foot Posture Procedures. Foot posture will be analyzed first using the scanner to
determine level of pronation or supination. For this, the individual will stand on the scanner
without shoes while a photo is taken of their footprint to view how much arch of their foot makes
contact with the scanner.
Walking Procedures. To analyze the GRF during gait, the individual will then walk, as
normally as possible, over the force platform stepping one foot onto the platform with shoes on.
The participant will be given sufficient practice attempts to ensure they are walking normally.
This test will be repeated three times. After three trials, the participant will repeat the three trials
without shoes.
EMG Procedures. Once the participant has completed three trials with shoes and
without shoes, the experimenter will palpate the iliac crest to locate the gluteus medius. The
proximal third of the distance between the iliac crest and greater trochanter will be sanitized and
two Delsy electrodes will be placed parallel to the muscle fibers to examine muscle activation of
the gluteus medius during walking with and without shoes. A ground electrode will be placed on
the iliac crest on the opposite side.
Data Analysis Procedures. The raw EMG signals from both feet on the LabChart
Reader will be analyzed with Spectrum Analysis Frequency to show a proper representation of
the signal. The mean of the maximum and minimum peak curve values in the EMG data for the
(Fz), (Fy), and (Fx) ground reaction forces of the feet will be computed and normalized as a
Percent Body Weight (%BW). The stance time for each peak will be calculated and expressed as
a percentage of total time in Table 5, Table 6, and Table 7. These variables in the data collection
process will be analyzed to show similarities and differences between both feet involved in a gait
cycle.
The variables that have been produced into a graph will undergo an analysis process on
the LabChart Reader and Microsoft Excel to evaluate the level of symmetry in the participants'
gait cycle. This symmetry will examine the braking and propulsive area total forces. The analysis
process first involves highlighting the wave that shows the best minimum and maximum peak
curves on the EMG graph. Then utilize the LabChart Reader function called the Spectrum
Analysis Frequency with a low pass frequency filter. This enables stronger frequencies to have
proper representation. A calculation called Maximum Power Frequency is then implemented as a
calculation in the software to rectify the EMG data into a linear envelope. This linear envelope
produced from the EMG signal develops a scale in the amount of frequency (Hz) that is required
to output the braking and propulsive forces on the feet with or without shoes. The linear
envelope also creates absolute values that are then transferred to Microsoft Excel. The Excel
software allows the gait to be shown as a scatter plot graph through force and time. The Excel
software then uses the impulse formula to calculate the negative and positive areas forces on the
curve. In this case, it involves force multiplied by the sampling time (i.e. 1k/s) that is retrieved
from the LabChart Reader. This calculation computes a table that represents the amount of force
that occurs for every second in the walking gait. This is referred to as stance time. The negative
values represent the braking forces while the positive values show the propulsive forces in the
form of stance times in Table 5. The total sum function is then used between the negative and
positive values in the table. The total sum of the negative and positive forces are calculated
separately to measure the differences between the two group values. This evaluates numerical
evidence of the forces involved that show whether or not the participant has symmetry in their
gait. Finally, SPSS software is for the analysis of statistical differences between data collected in
the lab. Various comparison methods can be used to determine significance at various P-levels of
significance to account for random variables. This P-Value is commonly seen as 95% or p = 0.05
for statistical significance.
Results
Figure 1
Average Fz vs. Time Scatter plot for the no-shoes condition
Figure 2
Average Fz vs. Time Scatter plot for the shoes condition
Figure 3
Normalized Fy vs. Time Scatter Plot for the no-shoes condition.
Figure 4
Normalized Fy vs. Time Scatter Plot for the shoes condition.
Figure 5
Average Fx vs. Time Scatterplot for the no-shoes condition
Figure 6
Average Fx vs. Time Scatter Plot for the shoes condition
Table 1
Max IEMG values for three trials with no shoes and with shoes
Table 2
Descriptive statistics for the max Integrated EMG values for shoes vs. no shoes
Table 3
Homogeneity of Variances test for integrated EMG values for shoes vs. no shoes
Table 4
One-way ANOVA for integrated EMG values for shoes vs. no shoes
Table 5
Anterior-posterior forces for walking
Table 6
Vertical forces for walking
Table 7
Medial-lateral forces for walking
Discussion
The gluteus medius muscle plays an important role in stabilizing the hip during walking.
It serves as the prime mover in hip abduction during locomotion and acts to stabilize the frontal
plane of the pelvis during the single-leg support phase of gait. During the swing phase of gait,
the entirety of body weight is supported on one leg and the leg that is off the ground will
naturally cause the hip to drop due to loss of support. While the hip is unsupported on one side, it
is the role of the gluteus medius of the weight-bearing leg to counter this falling movement
known as Trendelenburg gait, an abnormal gait that is characterized by a dropping contralateral
hip during the midstance phase of walking. It can be seen in subjects who have poor muscular
strength, or poor nerve innervation (McGee, 2012).
The results showed small differences between IEMG conditions with and without shoes,
however, because the significance is not within 0.05, more data collection samples would need to
be analyzed before a conclusive statement can be made about the significant differences between
the two conditions. Max IEMG demonstrated in Table 1 showed slightly higher readings
compared to when no shoes were worn throughout all three trials. This shows that there was
higher recruitment in all trials when the subject wore shoes. IEMG results from the lab coincide
with literature stating that running shoes can potentially place a higher demand on the lower limb
muscles (Sekizawa et al., 2001; Ramanathan et al., 2011; Franklin et al., 2014).
This general data shows the total sum of the negative and positive impulse forces from
each point on the scatter plot graphs from Microsoft Excel to separately calculate the total area
braking and propulsive forces. (See Appendices B & C) For each of the three trials performed on
a force platform, an average formula was used on the three trials for the braking and propulsive
forces to normalize the data into one absolute value. Braking forces were shown to be higher in
the trials where shoes were worn, however, the duration of braking forces was longer compared
to when the subject was barefoot. (Refer to Appendices B & C) Figure 2 shows slightly higher
peak braking forces on heel-strike, spread over a shorter duration while walking in shoes, thus
increasing the stress that the bones, joints, and connective tissue experience. These results are
incongruent with the intended purpose of cushioned shoes. Assessment of the vertical forces
shows that slightly more vertical forces are present at heel-strike in the tests where shoes were
worn and showed longer time durations where the subject was transmitting vertical forces. After
analyzing symmetry of the gait among the participants, there has been a significant finding of the
total area braking and propulsive forces for the Fy aspect in the walk. The no shoes trials produce
an average of -22.79 N of total area braking force on the force platform throughout the gait
cycle. (See Appendices B & C) While the total area propulsion force produces an average of
19.18 N as well. The braking and propulsive forces are not equal on a numerical scale, which
concludes the individual may walk with asymmetry. Additional trials with shoes on show a
similar relationship between the braking and propulsive forces in the Fy variable. The three trials
with shoes produce an average total area of -27.55 N for braking force and 22 N with propulsion
force. (Refer to Appendix B) The two results between both conditions of the shoe for the
individual can be inferred that this participant walks with asymmetry. In reflection of this data,
the participant walks with no shoes on the force platform on the third trial with near symmetry of
-18.12 N for braking forces and 19.16 N for the propulsive force (Refer to Appendix C).
Although asymmetry has been shown, this trial can reflect that the individual actually walks with
symmetry on one of the trials. This trial issues a point to possible systematic error for the overall
data because the participant may be unfamiliar with the test. An example of test unfamiliarity is
the participants' task to step on the force platform with accuracy. This timing may affect the way
the participant walks leading up to the force platform. The participants' gait may not be at their
normal walking speed which can create hesitation on the steps with the feet. The hesitation may
change the way the knee extends or how the foot plants on the ground. After completion of the
first and second trial, the participant has seemed to acclimate to the gross motor skill to walk and
time the foot on the force platform with no shoes on.
1. Considering the differences in the stance times with respect to walking and running,
why is there a change?, how does impulse play a role in this case?
Impulse is the force and time that is required to move the object in motion.
Acceleration of each stride during bipedal locomotion can be an example to infer why there is
a difference in stance times between walking and running. Impulse has a positive relationship
with speed because it can increase as well as the ground reaction forces when the bipedal
locomotion speed increases. Impulse can also decrease when the individual slows down the
bipedal movement. EMG measurements on bipedal locomotion can show how impulse
impacts the human body when the individual transitions from a walk to a run. As the
individual increases speed, then the stance time decreases because the gait is performed
quicker which results in smaller durations of the activity overall. Peterson et al. (2011)
explains that walking speed is regulated by anterior-posterior GRF impulses. This study also
mentions how impulse in the form of acceleration for each stride decreases or increases based
on stride length and frequency. Upon examination of five male participants who walk and run
on a treadmill, the study mentions that impulse decreases in the anterior-posterior ground
reaction force when the participant starts the gait cycle with a walk. Then the impulse as well
as the braking and propulsive impulses increases when the individual starts to increase speed
(p. 562). It seems that stance time increases because the walking strides take a longer time to
complete. As locomotion speed increases, eventually the movement pattern associated with
running takes over and a different motor pattern from walking is used for motor efficiency
(Diedrich & Warren, 1995). Stance time decreases when the individual runs because it takes a
shorter amount of time to complete the gait based on impulse. Braking and propulsive
impulses is important because it contributes to the braking and propulsive forces required to
walk or run so that the body moves.
2. It has been demonstrated that following the initial 22% of stance time in seconds,
the point of application of the resultant GRF is located in the mid forefoot region. How
might this be considered in the design of running shoes?
The consideration with the construction of a running shoe for the mid forefoot region is
the forefoot and midsole of the shoe. These areas within the shoe have shown to reduce pressure
on the foot when the individual runs. Less pressure placed on the foot is important to reduce the
injury risk for muscle or bone injuries that may include strains or fractures in the mid forefoot
region. Fu et al. (2021) has demonstrated a reduction in maximum pressure on the midfoot when
the individual has worn the new shoe design. This new design in the study involved a new
cushion in the forefoot and midsole of the shoe. The forefoot design of this shoe uses a 1
millimetre thick carbon fiber plate with a segmented forefoot plate. An additional 1 millimetre
thick carbon fiber plate with a full forefoot plate is used in the midsole. These construction
design variables of the shoe have shown biomechanical changes in the body. This change
includes more metatarsophalangeal joint (MTPJ) plantarflexion velocity and positive work at the
knee joint (p. 2, 3, 10-1). These changes can benefit the body in a way to not compromise the
forefoot or midsole of the foot with an injury when the individual wants to go for a run. This high
intensity physical activity can be minimized with proper footwear that focuses on the forefoot
and midsole areas of the shoe. Focuses on these areas can be addressed to minimize the concerns
of ground reaction forces on the midsole of the foot when it undergoes the gait cycle.
3. In which major planes are most of the forces generated during running? At what
points during stance might you require greater prosthetic support in running?
Most of the forces generated during running occur in the vertical Fz plane. As shown
in Table 5, Table 6 and Table 7, Fz forces are substantially higher compared to Fx, and Fy
planes. Korpelianen et al. (2001) from the article called “Risk Factors for Recurrent Stress
Fractures in Athletes” undergoes a process to identify predisposed risk factors among
individuals on a biomechanical level. This study mentions previous limitations from methods
performed in the past. The limitation shows participants being observed on a non-weight
bearing exercise. This decision to inadequately measure the frequency of the pes planus
suggests that a functional task such as a walk must be implemented. This new method
localizes the pes planus to measure with more accuracy of the frequency. Since vertical
ground-reaction forces increase from 70-80% of body weight in walking to 275-300% during
running (p. 308). The consideration of this statistic shows how much of the major plane, being
the vertical component of the ground reaction force, shows to produce a large amount of force
in a percentage during a run.
4. What might you suggest for the heel construction in a walking shoe and a running
shoe? Why not prescribe a sturdy running shoe for a geriatric patient for walking?
Research has shown the use of a heeled shoe had a small effect on the forces produced
on the platform. Shoes with this design actually generate a higher Fz, Fx, and Fy force when
the individual wears them. The use of this shoe may change how the individual walks. This
suggests the design of the shoe is important to consider based on the individual's walk style and
foot loads on the ground. A shoe design that revolves around a personalized shoe insert and
midsole construction is recommended. Footwear that involves an elevated heel design helps
reduce the velocity produced by the achilles tendon rather than a shoe featuring a non heeled
design. This approach helps to reduce achilles tendon loading when the individual uses walking
shoes (Brauner et al., 2018). When the individual starts to run, then the heel construction of the
shoe design is considered in another study.
This additional study mentions the importance of the aspect of the heel-to-toe drop in a
shoe. Malisoux et al., (2016) mentions in this additional study the heel-to-toe drop of a standard
running shoe reduces the risk of injury differently among occasional versus regular runners. A
low drop shoe favours the occasional runner while the high drop shoe helps reduce the risk of
injury among regular runners (p. 2939). The reduction of injury among individuals is important
for people who want to buy shoes to run on occasional or regular levels based on the heel-to-toe
drop design.
Geriatric patients are not prescribed a sturdy running shoe for walking because the
running shoe may not be designed and individualized to the person's feet. An older patient
needs to have a shoe that is individualized and specialized for walking that reduces the amount
of pressure on the feet. The study from Bonannno et al. (2010) has shown the foot orthoses and
heel inserts contribute to the reduction of heel plantar pressure. The prefabricated foot orthosis
redistributes the plantar ground reaction forces with the ground (p. 388). This method aims
toward a specialization of walking shoes for geriatric patients that provide more comfort in the
heel and ensure the force distributes throughout the foot to prevent an injury on a localized area
on the foot.
5. How might stress fractures and shin splint problems be related to the force time
relationships in running?
Stress fractures are the result of repetitive loading of the skeletal system past it’s limits.
Over time, the muscle that is protecting the bone fatigues, and places more stress on the bone.
The impact acceleration on the shank increases as fatigue increases. (Edwards et al., 2008;
Mizrahi et al., 2000) As the time duration of running increases, muscle fatigue increases as
well. When muscles fatigue, greater amounts of force will be transferred to the bones of the
lower leg/foot rather than being absorbed by musculature. With the repetitive impact that
occurs in running, when the bone is absorbing forces, this can lead to stress fractures and shin
splints over prolonged exposure to running forces. Andrish et al (1974) suggests that the most
effective treatment for shin splints is adequate acclimation and a reduction in stressors,
primarily through reduced running distance.
6. What do you think should be the primary concerns in the construction of
marathon running shoes, jogging shoes, and court shoes?
Individualization of a shoe that benefits the client who has a specific foot type
is the primary concern. Purpose or athletic goal is also a key concern in shoe
construction. Everyone will not have the same benefit of stability from the same shoe
during a run because everyone's feet are not the same. Fatigue plays a key role in the
way someone performs a run activity. It can lead to repetitive strain injury that can
occur with aerobic exercise because the individual performs the gait cycle consistently
for a long duration of time. Over pronation or supination of the ankle is also possible
with fatigue for basketball because the weakened muscles in the foot and ligaments in
the ankle do not provide stability for the weight and ground reaction forces of the
bipedal stride in a lateral movement. On a personal note, primary concerns for
marathon, jogging, and court shoes is to measure the foot posture and the ground
reaction forces activated in the foot because it allows someone to determine what type
of shoe is most appropriate for that individual. It allows us to examine the areas on the
foot that produce a lot of pressure. This individualizes the intervention for people who
need to find the right shoe to reduce pressure for those affected areas on the foot based
on the activity. A cushion can support the disadvantaged area on the foot to reduce the
risk of hyper ankle inversion or eversion when someone runs either long distances or
performs sagittal or lateral movements up and down the basketball court. A
performance test of the shoe intervention with the individual in the desired activities is
important because it allows the client to see possible improvements from the last pair
of shoes that were not fitted properly. Improvements of the shoe can be judged by the
individual's personal comfort, performance, and reduction of pressure with a test that
relates to their physical activity.
7. How do braking and propulsion forces play a role during walking and
running?
The braking and propulsion forces play a role in a way different muscles activate in
higher levels than others based on exercise intensity. Ellis et al. (2014) provides insight into what
muscles contribute the most when an individual walks or runs on a treadmill. The gastrocnemius,
gluteus maximus, gluteus medius, semitendinosus, semimembranosus, and biceps femoris, vastus
medialis, and soleus are key muscles that are activated in different ways to perform the braking
and propulsion forces in both walking and running. The walk activity has shown the braking
force to correlate to the muscle activations of the vastus medialis, gluteals, and hamstrings while
the propulsion force depends on the gastrocnemius and gluteus maximus muscle activations. The
run activity has shown the propulsion force uses the most muscle activation in the gluteus
maximus, gluteus medius, vastus lateralis, gastrocnemius, and soleus muscles (p. 599). This
makes sense because the propulsion forces for the gluteus medius in the lab gait analysis activity
has shown to be one of the peak absolute values of force in the EMG data when the individual
walks over the force platform.
Conclusion
The lab results demonstrate that shoes can influence gait symmetry, impulse forces,
muscle activation during gait and foot posture, at least to some degree. This is especially
important to consider in populations where walking and gait are difficult, such as elderly, in
populations that are at high risk of lower extremity injury such as soccer players, or those who
have had a lower extremity injury such as an ACL tear. Shoe structure and design should be a
topic of future research to improve foot health, gait and to minimize risk of injuries upstream that
may occur as a result of altered mechanics at the foot and ankle.
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Appendix A
Foot posture scan
Appendix B
Braking and propulsive forces with shoes
(referenced from here:
https://onedrive.live.com/View.aspx?resid=9E1D26621EA2350E!957&wdEmbedFS=1&
authkey=!ALAM2ADIjMsBG5Y)
Appendix C
Braking and propulsive forces without shoes