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Joint action and muscles

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This content explains the roles of different muscles (agonist, antagonist, fixator) in producing specific joint movements, detailing the primary muscles responsible for actions at the shoulder, hip, elbow, wrist, knee, and ankle joints.

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hi folks welcome to this video on joint

actions and muscles so this video is now

the time to look at um the individual

joints and see which muscles are

Contracting to create which movements so

there's also a video in this playlist to

do with the movements that you can get

at which joint so if you need to recap

that please watch that video first this

is dealing with the muscles that are

Contracting uh and the movements that

are taking place as a result right joint

actions and muscles then there are a few

key terms that just need to make sure

we're happy with first these are Agonist

antagonist fixator and this thing about

antagonistic muscle action so let's

quickly Define each of

these so The Agonist is a muscle that

contracts to produce the movement and

he's also known as the prime mover you

might have heard it as either one of

those so as an an example there very

basic example during a biceps K the

biceps is The Agonist or the prime mover

that is the muscle that is contracted to

create the major movement at the elbow

joint which we're going to have a look

at in a few

minutes the antagonist in contrast Works

in opposition to The Agonist and as it

says there relaxes or lengthens as The

Agonist contracts now just to clarify

when we say Works in opposition it

doesn't mean it's trying to oppose it's

trying to stop The Agonist from doing

its job it's happy for The Agonist to do

its job if we come back to the example

that I've mentioned biceps K the biceps

will be The Agonist

in order for that biceps to contract the

triceps on the back of the arm must be

the antagonist it must relax in order

for The Agonist to do its job so they

are a partnership they work together

equally if we was to turn that bicep

kale into a tricep you know extension a

dip something like that the tricep would

then become The Agonist and the biceps

would become the antagonist so they work

in opposition in terms of as one's doing

one one thing I Contracting the other

relaxing the fixator that might be a new

bit of terminology to you the fixators

contract to stabilize or fix the joint

and or body in position now what do we

mean by that think about that there's

this big thing about you know when you

go to the gym try and use free weights

try and use dumbbells try and use bars

as opposed to the fix weight machines

where you're sitting in a seat the

reason is when you are standing doing

weights exercises you are Contracting on

a lot more muscles because you're having

to fix your body in position think about

the bicep K again when you do a bicep

you're in a standing position when you

do the bicep kale the bicep contracts to

flex the elbow the biceps is The Agonist

at the same time the triceps is going to

relax and that's going to be the

antagonist but at the same time you are

Contracting a lot of muscles around the

shoulder joint around your spine around

your hips and your knees to fix your

body in a nice stable position so they

are still contracted and we call those

muscle actions and those muscles

fixators they are fixing your body in

position in order to allow the required

or desired movement to take place so if

you to if you to get a question

specifically about a bicep kale for

example the fixators you'd be interested

in would be those around the elb the

shoulder joint and the wrist joint

fixing the wrist and shielder RM

position so the only movement you are

getting is that that is wanted at the

elbow joint but it leads me on to a key

thing that can sometimes come up a key

fixator in the

body there's a key fixated muscle group

we have in our bodies we all have it we

all need it called the transverse

abdominis so as you can see here's your

rib cage here there's your pelvis the

ilen part of your elv H Elvis of your

pelvis sorry and there's your transverse

abdominis you've got one on this side

and you've got one on the other side and

it wraps underneath so your sixpack you

know is on top there your abdomin is on

top there but this one wraps around you

it's basically like a corset every time

you want to lock your core nice and

tight you think it's the ABS that are

doing it it's not it's your transverse

abdominis that are Contracting nice and

tight um to uh keep your core nice and

and and fixed and we call it a core

stabilizer any of you that do core

stability training you are specifically

trying to strengthen this stabilizing

muscle group now you might get questions

on core stability of the spine or how do

you increase core stability or how do

you generate or what's a key fixator in

the body transverse abdominis this

muscle here this muscle here is the key

term there that's the muscle that we

associate with high levels of core

stability one of the big fixators of the

body but like I said any muscle that is

Contracting to fix a body position is

classified as a fixator during the

action so finally for this slide what is

this term here this antagonist muscle

action is basically what we've just said

in terms of when one muscle becomes The

Agonist it's opposite it's opposite

muscle its partner is probably a better

way to do it becomes the antagonist so

when I do my bicep K my biceps is The

Agonist the triceps is going to become

the antagonist if I then decide to

extend the elbow joint and now do a

tricep extension the tricep would then

switch and become The Agonist and the

biceps would become the antagonist so

the fact that these muscles switch from

Agonist to antagonist depending on the

action we call that an antagonistic

muscle action so that's just the Key T

there to describe the fact that The

Agonist does its job and at the same

time the antagonist does its job and

then they can switch over if you decide

to do the opposite action that will

hopefully make more sense as we go

through these what we're going to do now

is look at the actions the muscles at

each of the key joints that we need to

know let's start with with the Biggie or

you know one of the biggies the the

shoulder and the hip joint because they

have ball and socket joints they have

the most amount of movements therefore

the most number of agonists and things

like that to remember so let's deal with

this one first the shoulder joint has

got a lot of movements as we mentioned

therefore we need to know which muscles

create those movements like I said if

you're unfamiliar with the movements you

need to watch the video on movement

analysis cuz I'm just going to say the

terms and expect that you know them or

presume that you know them

so there are all the muscle actions

sorry the The Joint actions we can get

at the shoulder joint we can Flex

remember that is where you swing I swing

this entire arm forward so like an

underarm throw is an easy example of

that extension is where this arm moves

backwards behind my body abduction is

where this arm comes out to the side

there adduction is bringing it back

towards the middle of the body these are

two that can cause confusion medial and

lateral rotation look at this humorous

that bone in the upper arm there if I

was to rotate that arm away from my body

so like twist the arm away from the body

that would be lateral rotation if I was

to rotate the arm so it is pointing

towards the middle of my body that is medial

medial

rotation horizontal adduction or flexion

are the same that is where my arm comes

up to the side and I move it behind

me horizontal adduction or flexion is

where I bring this arm up in front of me

and across my body that way and

horizontal abduction or extension is

where I bring this arm up to the side so

I abduct it and then I move it behind me

rotate behind the back of my body like I

said I'm not dealing with the movements

in this video that's in the other video

so you need to look at those let's look

at the muscles that create these actions

then so these are all the agonists right

now Panic automatically kicks in because

a lot of times you're not familiar with

a lot of muscles you've not heard of

just calm down let's look for the um

look for the easy things to get our

heads around well first of all look at

this deltoid deltoid deltoid deltoid so

deltoid is I am I've put couple there by

mistake but you can easily put them

there don't worry it's not a different

muscle deltoid is very very useful

muscle to know however don't just put

deltoid anterior means front posterior

means back and middle means middle so

what do we mean by that well let's just

have a look here if I was to just very

crudely turn this deltoid here into a

circle okay what we're saying

is here is the front of the athlete so

this third of it at the front is called

the anterior deltoid the third at the

back is called the posterior deltoid and

the third in the middle is called the

middle deltoid so if I contract my

anterior deltoid is going to pull this

entire arm forwards and I'm going to get

flexion if I contract my posterior

deltoid at the back here okay is going

to pull my entire arm backwards and I'm

going to get shoulder extension if I

contract the middle thired of my deltoid

is going to abduct as it says their

middle deltoid abduct and bring the arm

out to the side so one muscle group does

three of the key muscle movements at the shoulder

shoulder

joint where it gets a little bit

different is if you see here your

latissimus doorsa your lats are these

big muscles here now yes they're

attached on your back but look at that

point there it just goes up in fact let

me just change this you'll see here a

little bit better it just goes up there

into the back of the humorous joint so

when you contract your lats it pulls

this arm back down towards your side so

it addu it brings the arm back to the

side of the body the shoulder back uh to

the side these are some of the little

weird ones now okay what you can see

here is Terrace minor Terrace major

don't worry about it Terrace minor is

that one there this is called um or one

of your rotate cuff muscle so if you've

ever heard of anyone with a rotate cuff

injury terce Miner and

subscapularis are two of your rotates

cuff muscles you're just going to have

to memorize these The terce Miner

laterally rotates so when you contract

your Terrace Miner you are rotating your

entire arm outwards away from your body

when you you contract your

subscapularis sub meaning below is in

submarine and scapularis as in scapula

so you can't actually see on this

diagram your scapula is somewhere here

underneath the muscles and the

subscapularis is below the scapula

underneath it when you contract your

subscapularis it will immediately rotate

so that is rotating your entire arm

towards the middle of your

body finally horizontal adduction and

flexion bringing the arm across cross

the body in a horizontal manner that is

your pectoralis major your big pec

muscle groups on the front of your chest

and finally the posterior deltoid gets

repeated again in terms of it is

involved in horizontal abduction so as

well as this posterior deltoid ear as

well as extending the arm bringing it

behind the body it will also abduct it

and horizontally abduct it sorry back at

the horizontal abduction one think of

like someone like Andy Murray's arm

position on the back swing of a forearm

the arm is up out round the out to the

side and also behind his body slightly

as he's about to strike through that's a

horizontally abducted position so in

order to get the arm in that position

that is the posterior

deltoid right they are not all as

complicated as the shoulder joints so

don't be getting put off but you're

going to have to remember these agonists

these muscles that contracted create these

these movements

movements

much easier than is the elbow joint why

well because the type of joint is it's a

hinge joint so it can only do two

movements the elbow joint can only Flex

or extend and just to recap that what

are we talking about remember flexion is

the um the elbow joint doing that you

are flexing extending is the arm doing

that straightening your elbow joint and

as you can see by the diagram you've got

the names of the two Agonist

there now my advice I know it's going

that a little bit of extra M but don't

give them reason to dock you a mark

don't put bicep and tricep you're a

level students now you're better than

that biceps brachi ey or brachi ey or

brai whatever you want to pronounce it

that is the muscle that contracts to

flex um the elbow joint triceps brachi

is the muscle that contracts to extend

the elbow joint and as we' said you know

these are examples you know the example

that I gave you at the start in terms of

Agonist and antagonistic muscle pairs so

just to quickly recap that while we're

here as that elbow flexes from there to

there the bicep contracts and becomes

The Agonist the tricep even though it's

not on this pitch obviously he's still

there it's going to relax to become the

antagonist if this person then decides

to extend their elbow joint the tricep

will contract to become The Agonist and

the bicep will relax to become the

antagonist and that's that antagonistic

relationship if it didn't get any easier

it's just about to I think the examiners

feel guilty about uh the whole shoulder

situation the wrist joint there are lots

and lots of muscles

inside your wrist inside your forearm

however at a level we group those muscles

muscles

together even though some of you know

that the wrist pronates and uh

supernates and all this kind of stuff we

are just interested in flexion extension

at the wrist joint so flexion extension

and if life didn't get any easy than

that it's just about

to the muscles that contract to flex the

wrist are called wrist flexors and the

muscles that contract to extend the

wrist are called wrist extensors so

flexing the wrist is bending so the the

the palm of your hand coming closer to

your forearm and the wrist extension is

the back of your hand uh moving close to

the opposite side of your forand so

wrist flexion uh is you know bending the

wrist forwards wrist extension is

bending the wrist backwards and it's the

wrist flexors and the wrist extensors

that the agonists for each of those

actions so that's really

straightforward so the hip joint then

again it gets a little bit trickier here

because again it's a ball and socket

joint we have lots of different

movements therefore lots of different

agonists so the hip you know we are

talking about that thing there the that

ball of the FEMA fit into that socket of

the pelvis um in the ilium so there's

the ilium there's the isum there's the

pubis and the head of the femur just

fits into the socket

there so there are the muscles that

we're interested in as you'd expect a

lot of them very similar to or exactly

the same as the shoulder joint because

it is the same type of joint ball and

socket so we got flexion extension

abduction adduction lateral rotation and

medial rotation the only ones we haven't

got those horizontal ab and adductions

so so flexion remember FEMA forwards is

flexion every time you see the FEMA this

bone up sorry this bone swing forwards

as if you were kicking something or

raising your entire H feema up in front

of you that would be flexion activity

extension is moving the FEMA behind your

body abduction raising out to the side

adduction bringing it back down to the

middle lateral rotation I maybe I didn't

explain it I never do explain these

things too well but lateral rotation

like I said in one of my other videos If

you draw a line not the best line in the

world down the middle of that leg there

if you then twist your leg so that line

is pointing this way out away from your

body that would be lateral rotation if

you then twist or rotate your leg so

that line is now pointing towards the

middle of your body that would be medial

rotation so just in case you're

struggling with those ideas that's what

it means

Here We Go Again loads of weird words

calm down don't panic at all right

flexion you'd think that because you

obviously swing your leg every time you

take a step forwards and you know every

time you kick or run you swing your your

entire hip joint forward there must be a

big very well-known muscle that does

that it's not it's actually quite a

small it's called ilos soos Silent P so

your ilos soos is the most musle that

swings uh the hip joint forwards when

you're running now what you can see here

it's actually not a small why is it

called ilas soos you don't need to know

this but it's just in case you're

struggling look here it says SE major

psos major and

iliacus now these two muscles even

though there's a line here actually join

together so they've taken the Ilia bit

from that one and the SE bit for that

one and they call them ILO soos so the

muscle that flexes your hip swings it

forwards is an ILO seus right a it fun

this in terms of extending the hip so

now we're looking at you from your front

here so if your ilos s contracts this

FEMA swings forwards now we're looking

at you from behind here and as you can

see it is the you know the biggest

muscle in the body the gluteus maximus

when you contract your gluteus maximus

that extends the hip that pulls the hip

joint backwards it pulls the femur

behind your body the biggest most

powerful muscle in the body because

every time you jump every time you drive

off the ground your uh FEMA moves behind

you to drive the rest of your body

forwards so that's a big powerful

movement therefore it needs a big

powerful muscle in order to do that the

gluteus maximus because you've got a

gluteus maximus you must also have a

gluteus medius and there it is there you

don't have a glutitis Maximus on one

side and medius on the other you've got

a glutitis Maximus there and a gluteus

maximus there you've got a gluteus

medius there and a glutitis medius there

obviously two sexs you know you know one

for each hip joint when you contract

your gluteus medius that abducts the hip

so as you can see there when this muscle

contracts and shortens it's going to

pull this FEMA out to the side so when

you abduct your hip joint when you swing

your leg out to the side that is the gluteus

gluteus

medius when you adduct your hip you

contract your adductor longest now just

think of this in common terms it's an

adductor because it creates adduction

and it's longest because there it is

look adductor longest it runs from there

all the way down all the way down there

you've got an adductor brevis which you

don't need to know about that means it's

a short adductor we're interested in the

adductor longus the long adductor that

is your prime mover the adductor brev

isn't a prime mover that's why we only

need to know the adductor longus is now

your glutes make another appearance here

lateral rotation like we said coming

back to this diagram there's that line

going down the front of your leg you

want to twist or rotate your leg so that

line is facing outwards away from your

body again that is a gluteus maximus

look that that white bit is where it

becomes a tendon if I contract this

muscle it's going to pull my leg behind

but it's also going to rotate it so that

the middle of my fem is pointing out

it's going to tug it that way equally

the gluteus medius is responsible for

medial rotation when you contract your

medius gluteus medius that line will

then rotate back towards the midline of

your body you have a gluteus Minimus I

is a really tiny gluteal but that's

mainly just involved for the stabilizing

the hip joint it's not really used for a

massive major action so they're the

muscles that you need to know for the hip

hip

joint okay two to go and it's relatively

straightforward again from here why well

we're back to a hinge joint aren't we

the knee joint is a hinge joint same as

the elbow so again there's only two

movements we can

get their flexion extension however EX

air level let's get nasty again not May

the examiners the hamstring muscle on

the back so there's the KNE capap

there's your FEMA there's your tibia so

we're looking at you know the knee H so

it's it's side onto US there's patella

there quadriceps on the front of your

thigh hamstrings on the back of your

thigh when you contract the hamstrings

that will Flex the knee joint it will

pull as you can see there look the

hamstring is attached to the top of the

tibia the top of your shin bone so when

this contracts it's going to pull the

shin or your tibia behind you so it's

going to flex the knee joint here's the

quadricep here even though it looks like

it's attaching here it's not it's

attaching into the patella which then

attaches on the front of the tibia so

when I contract my quads the force acts

through here and that's going to pull

the tiia forwards and that's what's

going to

extend my knee joint however they are

muscle groups individual muscles make

them up so let's have a

look oh dear God what fresh hell is

this they've made it complicated but we

need to know these terms I remember when

I did a levels I'm going back many years

and I'm not sure enough but I just had

to sit and memorize these and I got an A

on my air level and it's you know it is

down to that there is no easy thing here

but if the we easy to remember easy to

memorize everyone would have a grades

and that's not the point those of you

that will to graft and work hard will

remember the names of these muscles but

it's going to take time and you're not

going to get it first time don't get get

downbeat about it is what I'm trying to

say what have we got here then well as

you'd expect muscle these two big

muscles are made up of um muscle groups

sorry muscle groups are made of

individual muscles the hamstrings is

made up of three individual muscles

one's called biceps for morus I thought

biceps was in Europa body it is but

you've got a biceps up in your elbow

joint but you've also got a biceps in your

your

leg don't worry about it biceps means two

two

heads but you don't need to know worry

about what that means in essence it

means that your biceps in your upper

body attaches it as two different heads

two different attachments into the

shoulder joint and the biceps for morus

in your hamstring has two separate

attachments into the uh pelvis don't

worry about that it's just so you know

that there are it's okay to have those

two terms

you're going to get a question in the

exam that could be what is happening at

the knee joint and if you identify that

as knee flexion and write this is caused

by the hamstrings you won't get the mark

you will not get the mark you need to

put knee flexion and one of these terms

whichever one you think you have best

chance of remembering I go with biceps

for moris why because the same applies

to the

quadriceps quads there are four muscles

um rectus moris vastest lateralis

vastest medialis vastest intermedius if

you want to go and find their locations

individually please feel free want to

look at them in anatomy book please feel

free but I'm just trying to you know

condense it all down again if you see an

action in the exam and it says what

action is this and you know that it's

the extension and you put caused by the

quadriceps you will not get the mark you

need to put one of these muscles down so

I go for the two for morus muscle groups

flexion is biceps forus extension is erectus

erectus

forus okay but whichever ones you think

you will learn best or memorize

best finally then the ankle joint the

last one thank God for that and again

there are only two movements we need to

know at the ankle joint you're looking

at all these different muscles named on

these diagrams don't worry about them

dead straightforward planter flexion and

dorsy flexion then the two that you need to

know there's your gastrous muscle this

big one here the Posh name for your calf

but you can't put calf in the exam it's

got to be gastrous that planter flexes

remember planter flexion P Point your

toes every time you go up onto tip toes

every time you point your toes to strike

a ball through your laces or something

like that you are planter Flex in the

ankle joint and that is created by the

gastrus dorsy flexion is to draw the

toes back so if you look at the foot

position here imagine this person tries

to pull their toes upwards and pull

their foot back towards their Shin their

tibia as much as they can that is done

by the tibialis anterior remember

anterior means in front of tibialis the

tibia so the tibialis anterior is the

muscle in front of your tibia and that

will dorsiflex your ankle joint so

they're the key movements and the

muscles The Agonist that create those

movements that is a lot to take on board

so you need to but you know some of the

joints are dead straightforward the

shoulder and the hip are the most

complicated ones watch those as much as

you can as much as you need to there's

no hiding you're going to have to know

these if you want to get top grades in

the exam you could get asked short

answer questions on them one Mark you

could get 10 Mark questions on movement

analysis highlighting what's going on at

various points of an action at the the

knee and the hip joint you know so you

need to know what's going on at these

joints and the movements are on a

separate video I'm also going to deal

with types of contractions on a separate

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YouTube Transcript:Joint action and muscles