Biomechanics of Running
Summary
TLDRThis video delves into the biomechanics of running, contrasting it with walking gait. It highlights increased velocity and ground reaction forces in running, along with a double float phase where both legs are off the ground. The video discusses pelvic, hip, knee, and ankle movements, emphasizing the kinematic, kinetic, and energetic differences between walking and running. It also covers joint moments, torques, and power, illustrating how running efficiency is influenced by muscle mechanics and the spring-mass model of leg movement.
Takeaways
- 🏃 Running biomechanics involves analyzing the kinematic, kinetic, and energetic patterns of the lower body during running.
- 🔄 The running gait cycle differs from walking by having a double float phase where both legs are off the ground, eliminating the double stance phase.
- 🚶♂️ Stance phase during running is reduced to about 40% of the gait cycle compared to 60% in walking, with an increased swing phase.
- 🌟 Running involves increased velocity and ground reaction forces, with the center of gravity experiencing less vertical displacement as speed increases.
- 🦿 There's an increased range of motion at the hip, knee, and ankle joints during running, requiring greater eccentric muscle contractions.
- 👣 The foot strike pattern varies with speed, impacting how the runner lands and pushes off the ground.
- 🔼 Ground reaction forces during running show an initial impact force upon heel strike, which can be three to four times the body weight.
- 👟 Running shoes aim to cushion the impact, stabilize the foot, and support the runner's biomechanics efficiently.
- ⚖️ Leg stiffness is a key biomechanical measure in running, representing the effectiveness of the spring-like action of the legs.
- ♻️ The spring-mass model of running suggests an optimal leg stiffness and contact time for efficient energy transfer and reduced metabolic cost.
Q & A
What is the primary focus of the video?
-The video primarily focuses on biomechanics of running, comparing it with walking gait and discussing the kinematic, kinetic, and energetic patterns observed during running.
What are the key differences between running and walking gait?
-The key differences include increased velocity, higher ground reaction forces during the stance phase, and the presence of a double float phase where both legs are off the ground during running, as opposed to the double stance phase in walking.
How does the stance phase percentage differ between running and walking?
-During running, the stance phase is roughly 40 percent of the gait cycle, whereas in walking, it is around 60 percent.
What is the double float phase in running?
-The double float phase in running is when both legs are off the ground, resulting in no double stance phase as seen in walking.
What are the two main phases of the running gait cycle?
-The two main phases of the running gait cycle are the stance phase and the swing phase.
How does the biomechanics of the joints during running compare to walking?
-The biomechanics of the joints during running are similar to walking but with an increased range of motion and more exaggerated movements.
What are the two phases of the stance phase in running?
-The stance phase in running is divided into the absorption phase, where the runner lands and absorbs shock, and the propulsion phase, where the runner pushes off the ground.
What is the impact force during running and how is it measured?
-The impact force during running is the initial contact force associated with the runner landing from the double float phase. It is reported to be between three to four times the person's body weight.
How do running shoes contribute to the biomechanics of running?
-Running shoes are designed to cushion, stabilize, or control rear foot motion efficiently, helping to attenuate the initial impact of the heel strike.
What is the spring mass model in the context of running biomechanics?
-The spring mass model in running biomechanics represents the human body where the legs act as a spring and the head, arms, and trunk act as the mass. It helps to understand the energy cost of locomotion during running.
How does the role of hip extensors change from walking to sprinting?
-As running speed increases, the contributions of the hip extensors, such as the gluteus maximus and hamstrings, increase to help propel the runner at a faster rate.
Outlines
🏃♂️ Introduction to Running Biomechanics
The speaker begins by expressing enthusiasm for the topic of biomechanics, specifically focusing on running. They mention previous discussions on walking gait and explain that running is a natural progression from walking. The video will analyze the kinematic, kinetic, and energetic patterns of the lower body during running, noting similarities and differences when compared to walking. Key differences highlighted include increased velocity, ground reaction force, and the presence of a double float phase where both legs are off the ground, unlike walking which has a double stance phase. The video will also compare the gait cycles of walking and running, with a focus on stance and swing phases, and the energetic aspects of shock absorption and propulsion during running.
🔍 Detailed Analysis of Running Mechanics
This section delves deeper into the biomechanics of running, examining the increased range of motion at the hip, knee, and ankle joints, and the greater eccentric contraction of the muscles around these joints. The speaker discusses how the center of gravity and vertical displacement change with speed and how runners maintain balance on one leg at a time. They also describe the joint kinematics, including hip flexion/extension, adduction, knee flexion, and ankle movement during the stance and swing phases. The impact forces involved in running are explored, with a focus on the initial heel strike and the subsequent shock absorption and propulsion phases. The speaker also discusses their past research on the effect of shoe cushioning on ground reaction forces and impact forces.
👟 The Role of Running Shoes in Biomechanics
The speaker discusses the three main functions of running shoes: cushioning, stabilizing, and controlling rear foot motion efficiently. They explain the concept of impact attenuation and how shoes can help minimize the initial impact of the heel strike. The video also touches on how runners can minimize impact forces through their own biomechanics, such as ankle, knee, and hip movements. The speaker references a review on the biomechanics of running and mentions that the joint moments or torques about the hip, knee, and ankle during running are similar to walking but with different magnitudes. They also introduce the concept of joint power, explaining how it is calculated and its significance in understanding the efficiency of running.
🌟 Energy Efficiency in Running
This section focuses on the energy efficiency of running, comparing it to walking, which is modeled as an inverted pendulum with an exchange between potential and kinetic energy. Running, however, is modeled using a spring-mass model, where the legs act as a spring and the upper body as a mass. The speaker explains how leg stiffness is a key measure of the effectiveness of this spring-mass model and how it relates to the energy cost of locomotion. They also discuss how running does not have a velocity-dependent function in terms of energy cost, unlike walking, and how the spring-mass model with elastic recoil and optimized contact time contributes to running efficiency.
🏃♂️ Advanced Biomechanics and Efficiency in Running
The final section discusses how runners can improve their mechanical efficiency through the exchange of kinetic energy between body segments, facilitated by biarticular muscles. The speaker uses a graph to illustrate how the rectus femoris muscle can transfer energy from the hip to the knee during the stance phase. They also examine the role of hip extensors, such as the gluteus maximus and hamstrings, in propulsion and how their contribution increases with running speed. The section concludes by emphasizing the importance of understanding these biomechanics for optimizing running performance and minimizing injury risk.
Mindmap
Keywords
💡Biomechanics
💡Running Gait
💡Kinematics
💡Kinetics
💡Energetics
💡Stance Phase
💡Double Float Phase
💡Ground Reaction Force
💡Joint Kinematics
💡Eccentric Contraction
💡Spring Mass Model
Highlights
Biomechanics of running is a natural progression from walking gait analysis.
Running involves similar kinematic, kinetic, and energetic patterns to walking but with exaggerated deviations.
Key differences in running include increased velocity and ground reaction force during stance phase.
The double float phase in running occurs when both legs are off the ground, unlike walking.
Running gait cycle has a stance phase of roughly 40%, compared to 60% in walking.
Increased swing phase and overlap between left and right sides in running gait.
The first half of the stance phase in running is absorption, transitioning to propulsion.
Running involves greater eccentric contraction of muscles around the hip, knee, and ankle joints.
Foot strike in running varies with speed and impacts the biomechanics of the gait.
Vertical displacement of the center of gravity decreases with increased running speed.
Hip abductors play a crucial role in maintaining the center of gravity in the frontal plane during running.
Knee flexion increases during the stance phase for shock absorption and propulsion in running.
Ankle dorsiflexion occurs in the early stance phase, transitioning to plantar flexion as the runner pushes off.
Impact forces in running can be three to four times a person's body weight.
Running shoes are designed to cushion, stabilize, and control rear foot motion efficiently.
Joint moments or torques about the hip, knee, and ankle are calculated from kinematics and kinetics.
Power at the hip, knee, and ankle joints indicates energy flow during the stance phase of running.
Running is less efficient than walking due to the absence of potential and kinetic energy exchange.
Leg stiffness is a key measure of the spring mass model in running biomechanics.
The energy cost of running does not have a velocity-dependent function like walking.
Biarticular muscles play a significant role in the economical transfer of mechanical energy during running.
Hip extensor contribution increases with running speed, playing a larger role in propulsion.
Transcripts
so in this video i'm going to talk about
one of my favorite topics of
biomechanics which is running
i've talked a lot about walking gait in
my previous videos or if you're taking
my
undergrad or graduate courses locomotion
is one of the most fundamental human
boobs that we can biomechanically
analyze so it's a natural progression
to shift from walking gait over to
the running gate and you'll find that
the kinematic kinetic and energetic
patterns that we see in the lower body
during running it's very similar to what
we see during walking but obviously
obviously there are some exaggerated
deviations and we're going to talk about
that
in the next few minutes here so we've
got here a runner that's
on a treadmill and we can view the
runner from both
the sagittal view as well as the frontal
view and the posterior side
we can discuss the different aspects
of pelvic movement hip kinematics and
knee kinematics
as well as the ankle and describe the
differences that we see during running
as compared
to walking and the obvious difference
that we see
during runnings is increased velocity
increased ground reaction force during
the stance phase and of course the
double float phase that's the major
difference that we see
between running and walking is that the
person is literally off the ground and
there are two
periods during the running gait cycle in
which we see that double float phase
it's called double sibling because both
legs are off the ground
as a result there is no double stance
phase the way that we see in walking
right and walking we see an initial
and second double support phase the
stance
phase is decreased down to roughly 40
percent of the gait cycle whereas during
walking we see that at 60 there's
increased
swing phase and there's an overlap in
swing phase between the left
and right side so this is the running
gait cycle this is one stride from
a foot strike let's just say it's the
right side to foot strike again
of the same side at 100 percent
so as i mentioned stance phase is 40
percent of the gait cycle that's when
the right toe in this example with toe
off
it goes into the the first double float
phase
right here that's roughly 15 or the
period in time in which that occurs is
15
so both legs are obviously off the
ground
and then the contralateral leg contacts
the ground and
the right side in this case is swinging
forward and then as it approaches its
terminal swing
the contralateral leg goes into its
respective swing phase so that's why
they have that overlapping
swing phase here so to kind of give you
an idea
on the difference in the stride or the
gait cycles between walking and running
i've got here
the gait cycle for walking here on the
top and the gate cycle for running here
at the bottom so you
like i said if you viewed in my videos
on gate on the gate cycle
on walking gait cycle a lot of these
events
and phases should be familiar to you so
stance phase 60
that's when toe off occurs swing phase
is 40
initial double support represents the
loading response here then the midstance
terminal stance and of course
toe off into the swing phase now let's
take a look here at the stride for
running stance phase as i mentioned
earlier occurs right around 40
you see the double float phase here when
both legs are off the ground
goes into its initial swing and then
terminal swing
and then that overlaps with the
contralateral side going in
into its respective swing phase during
the stance phase it's pretty
straightforward
the first half of the stance phase is
absorption that's power absorption
i'm going to talk a little bit about the
energetic aspects of running so the
first part is shock absorption this is
the person the runner is now landing
and on the ground and so he or she will
be eccentrically firing the muscles in
order to absorb that shock right the
initial shock from landing on the ground
to minimize what's called the impact
force
and then that transition over to the
propulsion phase of the stance phase
in which the person now pushing off
toeing off into
the swing phase or specifically the
double float phase here
so here stance phase and swing phase for
walking
for the walking gait cycle and this is
the running gate
cycle as i mentioned earlier the initial
contact
say the right side to initial contact on
the same side
0 to 100 and the phases stance and swing
phases
are represented here along with this
sandwich
or the swing face is sandwiched between
the early and
late float phases when both legs are off
the ground and so you all
again a number of these events are very
similar
to what we see during walking but it's a
lot more exaggerated
major difference is the excuse me the
double flip faces
so what we see from a kinematic and
temporal aspect is that
during running there are increased range
of motion at the hip
knee and ankle joints the muscles around
these joints
typically have greater eccentric
contraction right there's muscle
contraction while it's lengthening
initial contact a foot strike will vary
depending on speed
as i'll show you here in a sec the
center of gravity the vertical
displacement of the center of gravity
decreases with
increased speed and because the runner
is always on one leg at a time
there's a decreased basis support so if
again
if you're familiar with joint kinematics
um you're walking
you will see that these patterns are
very similar
um what we see here this is running they
are very similar to what we see during
walking so for example hip flexion
extension
the only difference is is the increased
range of motion increase of dynamic
range of motion
hip adduction this is very important
because now as i mentioned
the runner is always on one leg at a
time so
the runner has to maintain
that kind of the center of gravity and
the frontal point closer to
that base of support on the one leg so
obviously they're firing their
hip abductors right their gluteus medius
lymph glucose medius
muscles as well as their tensor fasciae
latae
in order to maintain that that nice
centered position in the frontal plane
looking at knee flexion you can see the
loading response that initial absorption
that's the
increased flexion during the stance
phase here as it goes from absorption
through
propulsion phase periods during the
stance phase
and then during the swing phase here you
have increased
knee flexion in order to swing the toe
forward
at the ankle depending again on the
running speed what we observe initially
is dorsiflexion
in the early part of stance phase and as
the person begins to toe off or push off
you can obviously the plantar flex
position of the ankle and then back to
dorsiflexion
in the late swing as a person prepares
for
a initial heel strike in terms of ground
reaction forces
i mentioned earlier that there are
impact forces involved with running
because the person is
literally landing from a double flow
phase so something has to make do
so what we observe over um many many
research studies and that involve forced
platforms
is that the impact force the impact
force is an
initial contact force that's associated
with all the segmental mass and
acceleration as the person contacts the
ground
and the magnitude of that impact force
has been
reported to be somewhere between three
to four times the person's body weight
that initial impact force is all
otherwise known as a heel strike transit
it's passive it's not anything that
the runner does in terms from a muscle
contraction that's just
you know momentum that sudden change in
momentum in a
very small window right a small duration
we'll talk here a few milliseconds here
that's why is that that impact
it's just landing on it's like landing
from a jump very similar to that
and so the initial uh part of that
stance phase
as i mentioned earlier is that
deceleration that eccentric contraction
that would
allow some absorption of the
initial impact shock and then the second
half
again is generation the person is now
propelling into the swing phase
so the running force the ground reaction
force during running
obviously is analyzed only during the
stance phase
and one of the key differences that we
see during
running as compared to walking is that
in walking you don't see that butterfly
that that little double bump that you
see in the vertical ground reaction for
you kind of see it here but this is that
heel strike transient i was talking
about
this is that impact force that happens
in the first few milliseconds
when the person contacts the ground now
assuming
this person or this runner is a
heel-to-toe type of runner
this is the type of ground reaction
vertical ground reaction force
that we see during running now many
years ago
i did some biomechanical study i did a
biomechanical study on cushioning issues
the effect of cushioning issues
on ground reaction force impact forces
here and
the three metrics that we looked at was
the impact force which is the magnitude
of that heel strike transient force here
which is
denoted here by fz1 the
loading rate or the rate at which that
impact force occurred over time as well
as the propulsive force this is the
force associated with the person or the
runner beginning to toe
off into the swing phase so here
in a separate video i'll talk about
forward biomechanics so running shoes
are designed to do a number
of three main things you need to cushion
stabilize or or control
the rear foot motion and do so in an
efficient manner
the cushioning part is what's known as
impact attenuation is how
well does the shoe on its own be able to
attenuate this
initial impact that initial heel strike
transient the second mechanism by
which a runner can minimize that load or
attenuate that impact is what they do
from a kinematic perspective what they
do at the ankle what they do with the
knee
and hip so i talk a little bit about
that here later in this
video so subsequently and once we have
ground reaction for if we've got
kinematics
we can then calculate the joint moments
or torques about the hip knee and
ankle again looks very similar to
walking
these grafts here is taken by tom
novacek's
review on the biomechanics of running
you're taking
my graduate as well as my undergrad
biomechanics class i give
a copy of this pdf so it's a very
informative
it gives you a nice introduction into
the kinemaster kinetics
and energetics of of walking here so
let's concentrate on the knee so this is
the knee moments and keep in mind these
are
internal moments or internal torque and
you can see
what's happening initially during the
gate cycle so this is a stance
phase the solid line here represents
running the dotted line the this one
right here
represents i believe the long line is
it's sprinting sorry
and then of course this dotted line
represents um walking so very similar
but obviously the magnitudes
are different in terms of the knee
extension
moment that occurs during the stance
phase so
think about what that runner is doing
during the stanza remember it's going
from absorption to propulsion so that
initial
a part of the stance phase is all shock
absorption is all proportions so
a key kinematic and kinetic
mechanisms by which that occurs is
through that eccentric contraction
of your quadriceps quadriceps are what
knee sensors so when they contract they
create a knee extensor moment
that would allow in the first half
of the stance phase for the knee to flex
eccentrically right to control that knee
flexion
that that shock absorption followed by
the concentric contraction of those same
muscles to propel the person for
the runner forward uh so that's the the
knee moment
at the ankle joint you could see here
that the
internal joint i'm sorry internal moment
at that joint is in a plat
plantar flexor moment what is a person
trying to do from the goal as they
transition
from the absorption to propulsion part
of the stance phase
they're trying to toe off trying to push
off so that's that
plantar flexion torque created by the
gastroc soleus and posterior tibialis
muscles
as you can track into the late stance
there
now joint power here i have here
three up joints hip knee and ankle
and i have the joint power for those
specific joints in the sagittal plane
power is the rate of energy flow
over time we measure that in watts and
the way that we can calculate power
is by taking the product of the joint
torque
as well as its angular velocity so when
the torque and angle velocity are moving
in the same direction
we call that positive power and that
indicates when that joint in generating
power so that is
an indicator of concentric attraction
when the torque and angle velocity are
moving in the opposite direction
like for example controlled knee flexion
knee extensors those quadriceps
eccentrically contract in order to slow
down knee flexion even though
knee joint is flexing during that early
part of the stance phase
we call that absorption so that is shock
absorption
so the energy flow that's going through
these respective
joints can move from generation to
absorption and vice versa
depending on where they're at during the
stance phase and so
through some basic mechanics um some
like equations such as showed you here
we can use the kinematics and kinetics
and ground reaction force that i showed
you here in order to calculate
joint power and joint work
mechanical energy why is that important
because it helps us
to understand the efficiency of running
so kind of give you an idea even if
you've never
you know talked about power and don't
know about power or energy you know that
it takes a lot more energy to run a mile
or two miles than it does to walk a mile
right everyone could walk a mile or two
because walking is very efficient
in fact walking and i mentioned this in
a separate video is
modeled much like an inverted pendulum
where there is a nice exchange between
potential energy and kinetic energy
potential energy
energy due to position right or in this
case height
whereas kinetic energy is energy due to
movement
and so during walking is often modeled
as an inverted pendulum
pendulum shifts from potential to
kinetic energy
and so walking we see this so you know
person doesn't
have to use a lot of metabolic energy in
order to walk
at a preferred strike frequency whereas
running on the other hand
running the potential energy waveforms
are actually in phase so there is no
exchange if you will so a lot of the
cost that's
due to running has to do with the runner
being
able to contract the muscles in order to
sustain
the efficiency of running right so this
is by the tendons
by the joints themselves and the muscles
most specifically the biatricular
muscles
so and unlike walking walking as i
mentioned is model
much like an inverted pendulum running
is modeled
with what's called a spring mass model
here
and if you can envision the body the
human body
as the the the head the arms and the
trunk what we call the hat as the
passenger
and the locomotor system is the lower
body here
the legs act as a spring and the mass or
point mass
is um is basically the head arms and
trunk
and so all that mass has been suspended
or being
supported by this spring here which
represented here by your legs and then
during the running gait cycle that
spring
compresses and then it releases what we
call an elastic coil
into the the um the swing phase here
and one of the ways that we can measure
the effectiveness of that spring of that
spring mass model
is what's known as leg stiffness and leg
stiffness is the ratio
of vertical force and what's called
deformation the change in the length
here so if it takes more force in order
to deform or change that length
that system or those limbs are 10 are
are
quote-unquote stiffer if it takes less
force then
they're less stiff right or if it
deforms
at a larger to a larger degree then the
stiffness
obviously goes down so there are a
number of different ways there's
um a number of research studies that use
like stiffness
in order to measure the performance and
injury risk of runners or the
effectiveness of training interventions
or running shoes but the biomechanical
model
most used to
illustrate what's happening here um in
terms of the energetics you're running
is what's known as the spring mass model
so
spring here your legs and that's
measured with leg stiffness
mass again is the passenger your head
arms and trunk so
you might have seen this you've taken
exercise physiology
this represents the energy cost of
locomotion
for both walking and running this u
shape here is is what's known as the
the energy costs of during walking and
that is dependent on walking speed
so there is a preferred walking speed in
which a
an individual is most efficient in
walking be able to get that nice
exchange between potential and kinetic
energy and as a person speeds up
you use a more injury if this person
slows down you would try walking slowly
on a track
um it actually takes up more energy than
it was
than it would if you were to walk at
your preferred stride frequency
running on the other hand we really
don't see that
that time dependent or velocity
dependent
function in terms of the energy cost
during running
what we believe is happening is that
because of that spring mass
model you get that elastic recoil and
there
there's an optimized point in which that
recoil occurs where the leg stiffness
can't be too high
or too low in addition to that there's
also contact time
optimized contact time so this is a
runner on a treadmill
the legs here as i mentioned act as the
spring that spring compresses in the
early part of the stance phase and then
releases if you will that elastic recoil
during the propulsive phase in addition
to what your muscles do
from an active perspective you might
have heard of the stress shortening
cycle we talk about that
ssc phenomenon specifically
during jumping well that can also be
used to explain what we're
viewing here in the spring mass model
during running
from an ideal perspective we would like
to see a nice
exchange between that spring absorbing
energy and then releasing all his energy
during the propulsive phase but in
reality that very rarely happens it
depends on what the runner does
and also what the speed is at which that
runner is
moving now one of the ways a runner can
be
more economical or efficient in terms of
their mechanics
is by this exchange of kinetic energy
from one segment to the next
so this is a graph that was published in
tom novacek's systematic review on the
biomechanics of running
and what he wanted to illustrate here is
the role that muscles specifically the
biarticular muscles play
in having these joints move in an
economical pattern here
and what we believe is occurring is that
while
a segment let's just take the femur for
example is moving into
an extended position into the latter
half of the stance phase remember this
is uh propulsion so this is triple
extension
uh at the hip knee and ankle the femur
is moving in this direction
the rectus acts as a conduit it acts as
an
energy strap through which mechanical
energy that's being absorbed at the hip
can be transferred over
to the knee joint so this is the later
half of the stance phase the solid line
represents
the power generated at the knee while
this dotted line represents
the power absorbed at the hip and
that energy exchange that energy
transferred is manifested by that rectus
femoris that biarticular muscle that
controls
knee extension as well as hip flexion so
that is one of the ways that a runner
at at least on the joint level can be
more
efficient or more economical in terms of
their movement
um so looking at the hip and specific
look at the hip extensor
the role that the gluteus maximus
and the gluteus minimus and hamstrings
play
in terms of propulsion increases as you
go
as you go from walking to running into
sprint because
of running speed so as running speed
increases
the contributions of the hip extensor
subsequently increase it goes from 7
to 14 to 24 so you think of someone
who is sprinting the hippic sensors the
the glutes
and hamstrings play a larger role in
making sure that the person can propel
at a
faster rate
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