Levers | Skeletal System 09 | Anatomy & Physiology

[INSTRUCTOR] Hi guys,
welcome to this

video on levers.

Now this can sometimes be
a bit of a tricky subject

so let's take our time and
see if we can explain this

as clearly as we can.

So let's just define
our key terms.

These are the symbols that
I'm gonna be using in this

video, and they represent
these key terms or key

parts of the lever system.

So first off we have
this red triangle which

represents the fulcrum.

Now the fulcrum is the point
at which the lever arm pivots.

In our case as far as AMP
is concerned the fulcrum

usually just means the joint

But it might also mean a contact
point for example a contact

point with the ground where
the feet meet the ground or

where the hands meet the
ground or something like

that or some other surface

So the fulcrum is the pivot
it's a joint usually or

some contact points.

Second key term is this,
we're gonna use a red

square to represent our
second key term and that

is the idea of the load.

Again load is sometimes
just as fulcrum is

sometimes known as pivot,
the load is also sometimes

known as resistance and this is
the mass or the object that the

lever system is set up to move.

So it might be a dumbbell,
it might be a football,

it might be a cricket bat
or it might simply just be

the weight of the body.

Next we've got this red arrow.

The red arrow represents the
effort and the effort is the

force that's being applied to
the system, to the lever system.

In the case again of anatomy
and physiology it means the

muscular force so where the
muscle is contracting in

order to pull on the bone.

Which brings us to the last
piece in the puzzle and that

is the lever arm, the lever arm.

So again from an anatomy and
physiology perspective the

lever arm essentially just
means the bone or the bones

on which the contracting
muscles are exerting their

muscular force or their effort.

So the fulcrum, load,
effort and lever arm and

there are basically three
ways we could arrange these

elements in a lever system
and each one has its own

name so let's look at those.

So here's our lever arm and
we're gonna place the fulcrum

somewhere roughly centrally to
the lever arm and then either

side of the fulcrum we're going
to have our load and effort.

So whenever we have the fulcrum
in the center between the load

and the effort we have a
particular type of lever

system and that is known
as a first-order lever.

So where the fulcrum is in the
center and it doesn't have to be

in the middle of the lever arm
just have to be in the center

of the other two it has to be in
between the load and the effort.

Between the load and the effort
it's a first order lever.

The fulcrum might be slightly
closer to the effort, might be

slightly closer to the load,
whatever it doesn't really

matter if the fulcrum is in
the center between those other

two elements then we've got
ourselves a first order lever.

So how else could we
arrange these things?

So here's our lever arm
again this time instead

of having the fulcrum in
the center we're gonna have

the fulcrum at the end.

So the fulcrum is at one
end and then this time in

the center instead of the
fulcrum we've got the load,

so we put the load in the
middle and we've got

the effort at the end.

Now this arrangement is
known as a second order

lever so whereas a first
order lever has the fulcrum in

the center a second order lever
has the load in the center.

Let's do another example then
there's only one other way

we can arrange these things
let's have our fulcrum at

an end and the load at the
other end and this time we've

got the effort in the center.

Now with the effort in the
center you could probably guess

where we're going with this.

To have the effort in
the center means we've

got a third order lever.

The effort is there in the
center so if the fulcrum is

in the center it's first order,
if the load is in the center

it's second order and if the
effort is in the center

then it's third order.

Sometimes the orders are known
as classes as well so you might

read or see elsewhere first
class, second class, third class

it's exactly the same thing
just different terminology.

How do I remember this?

There's a really handy
little memory tool for this

very simply first, second,
third order levers one, two, and

three.

And then we've got fulcrum,
the load and the effort in

the center so we can say one,
two, three, F for fulcrum,

L for load, E for effort one,
two, three, FLE and that reminds

us what comes in the center of
each of the orders of lever.

So one, two, three,
FLE first order fulcrum,

second order load,

third order effort.

Let's do some examples in the
human body then where do we find

these different orders of lever?

So a good example for a
first order lever where

we have the fulcrum in
the center is in the neck.

So if you wanted to
lift up your head,

to lift up your eyes
to look to the skies

and you would use the
first order lever that

you have in your neck.

So the fulcrum is gonna
be in the center and in

this case the fulcrum is
the atlas vertebrae at the

top of the vertebral column
which inserts or articulates

with the base of the cranium.

So on either side of
the fulcrum now we have

the load and the effort.

Now in this case the load is
simply the weight of the head

and on the other side of the
fulcrum we have the effort

and the effort is produced
by the contraction of the

posterior muscles of the neck
and pulling downwards in this

example to lift up the load to
enable you to lift up your head.

So because the fulcrum's
in the center, we've got

ourselves a first order lever.

Second order levers then.

A good example here
is a calf raise or to

stand on your tiptoes.

And in this example,
as we've got on the diagram

already, we've got a fulcrum.

And the fulcrum in this
example is not so much

a joint, it's more the
contact point with the ground.

But we've got of course the
load in the center and here

the load is the entire body
weight which is placed directly

over the sort of the center of
the ankle and then behind the

body weights at the other side
of the load meaning the load

is in the center we have the
effort which of course is the

insertion of the calf muscles
by the Achilles tendon into

the back of the heel.

So the effort is behind the
load the load is in the center

and the fulcrum is on the other
side therefore a really good

example of a second order lever.

Now the third-order levers,
there's loads of these in

the body and the majority
of the body's levers are

in fact third-order levers.

So let's just do one
example and we'll use a

bicep curl as an example.

So here we have
initially the fulcrum,

the fulcrum is the joints and
in this case the elbow joints.

The load is the dumbbell itself
of course plus the weight of the

lower arm and obviously mostly
the dumbbell here and then the

effort is actually central,
which is why it's a

third order lever.

Now sometimes some students
get a little confused about

this because isn't it the case
it's the bicep does the bicep

curl and isn't the bicep on
the other side of the joint?

Yes that's true but what
we're after is where the

insertion of the muscle is.

So where does the
actual effort occur?

The effort when the
bicep contracts,

although the bicep is the
other side of the joint,

it obviously crosses the
joint by a tendon and the

tendon attaches in between
the joint and the dumbbell,

tendon attaches in between
the fulcrum and the load.

Therefore the effort produced by
the muscle is actually acting on

the lever centrally in between
the fulcrum and the load and

that is why it's a third
order lever and you'll see

that repeated again and
again throughout the body.

So I hope that's
been helpful to you.

Any questions or queries please
put them in the comments and

I'll get back to you.

Other than that please don't
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But other than that,
enjoy the rest of your day.

Take care.

See you in the next video.