Biomechanics of Running

Summary

This 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

00:00

🏃‍♂️ 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.

05:02

🔍 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.

10:03

👟 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.

15:04

🌟 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.

20:05

🏃‍♂️ 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.

Keywords

💡Biomechanics

Biomechanics is the study of the mechanical laws relating to the movement and structure of living organisms. In the context of the video, biomechanics is used to analyze human locomotion, specifically focusing on the mechanics of walking and running gait. The script discusses how biomechanical analysis can reveal the kinematic, kinetic, and energetic patterns of the lower body during these activities.

💡Running Gait

Running gait refers to the manner in which a person runs, including the sequence of movements and postures involved in the act of running. The video script uses the term to contrast with walking gait, highlighting the increased velocity, ground reaction force, and the presence of a double float phase where both feet are off the ground, which is a key difference from walking.

💡Kinematics

Kinematics is a branch of classical mechanics that describes the motion of points, bodies (objects), and systems of bodies without considering the forces that cause them to move. In the video, kinematics is applied to analyze the movement of the lower body, including the骨盆 movement, hip, knee, and ankle during running, and how these differ from walking.

💡Kinetics

Kinetics is the branch of physics that is concerned with the action of forces on matter, resulting in motion. The script mentions kinetics in relation to the ground reaction forces experienced during running, especially the impact forces that occur when a runner's foot strikes the ground.

💡Energetics

Energetics is the study of energy transformations and energy flow. In the video, energetics is discussed in terms of the energy cost of running versus walking, and how running is less energy efficient due to the lack of an exchange between potential and kinetic energy like in walking.

💡Stance Phase

The stance phase is the period during the gait cycle when one foot is in contact with the ground. The script explains that in running, the stance phase is reduced to about 40% of the gait cycle, compared to 60% in walking, indicating a quicker transition from one step to the next.

💡Double Float Phase

The double float phase is a period in the running gait cycle when neither foot is in contact with the ground. The script describes this as a major difference between running and walking, where the runner is literally off the ground during this phase, contrasting with the continuous contact in walking.

💡Ground Reaction Force

Ground reaction force is the force exerted by the ground on a body in response to the force exerted by the body on the ground. The script discusses how this force is increased during running, particularly during the stance phase, and is associated with the impact forces experienced upon landing.

💡Joint Kinematics

Joint kinematics refers to the study of the motion of joints during movement. The video script uses joint kinematics to describe the movement of the hip, knee, and ankle joints during running, noting the increased range of motion compared to walking.

💡Eccentric Contraction

Eccentric contraction is a type of muscle contraction where the muscle lengthens while it is generating force. The script mentions eccentric contraction in the context of shock absorption during running, where muscles lengthen as they work to control the impact of landing.

💡Spring Mass Model

The spring mass model is a simplified approach to understanding the mechanics of running, where the legs act as springs and the body acts as a mass. The script explains how this model helps to understand the energy cost of running, with the legs compressing and releasing energy during each stride.

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