Anatomy Quick Tips: Arms

Hey everyone, Sinix here.

It's time for another episode of
Anatomy Quick Tips,

the series that is here to give you
some useful observations

and help you feel more comfortable with
drawing people from imagination.

Today, we'll be talking about arms -
and also, don't be alarmed but

this all-arm video puts
us near the end of this series.

Only two more videos remain.

Regardless, for now let's just focus
on these upper appendages.

This probably won't be the funniest
video in this series or anything,

but it will be definitely be the
most humerus -

so roll up your sleeves
and let's get to work.

Starting out with structure,
we've already covered both shoulders

and hands in other videos,
so we just need to make sure we

can bridge these things together.

I'm sketching a quick front, side, and
back view of a shoulder to start.

Seeing a shoulder
and torso without the arm

always reminds me of a little
lamb or something, but anyway,

we're going to focus on the
skeletal breakdown of the arm first.

Of course we have a
single major bone in the upper arm

and two in the lower arm,
connected at the elbow.

But as I draw that, the first thing
I actually want to point out

is that things aren't
in a perfect straight line.

You can even take a moment
and try to see this yourself;

just hold one arm out straight
and close your opposite eye.

Now do your best to
look directly straight down

the barrel of that massive
gun you call your upper arm.

If you line up your
sight from shoulder to elbow,

you'll notice the lower arm doesn't really
line up as much as you might've thought.

To get really good at
drawing any organic forms,

it's important to try and identify
these types of subtle offsets

as much as possible.

Anyway, let's get back to these bones.

The humerus is of course
the bone of the upper arm,

meanwhile the lower arm has the ulna,

which I would consider
the primary lower arm bone-

it's the one you would
be hitting someone with

if you elbowed them-

and then the radius, which originates
on the exterior side of the elbow,

A.K.A the side that's further
away from your body,

and always connects to
the thumb-side of your hand,

so we can do a bit
of a rotational twisting

around the lower arm:

Hence the name "radius."

The last skeletal thing I want to mention

is the funny bone.

This is just an extension of the humerus

which protrudes on the
inner side of the elbow,

closest to the body.

It's called the funny bone
because of an exposed

nerve ending next to it
that will send a shock up your arm

if you hit this part of the
elbow against something.

So if you ever see a chance
to whack your friend's funny bone

with your pencil or stylus, it's,
you know, free comedy.

Alright, I added some
hands to these drawings,

and I know this isn't the hands video,

but since wrists and organic
offsets are so important,

let's do a quick look at
that connection anyway.

Now keep in mind by the time
the radius and ulna get to the wrist

they'll always be side by side,
and therefore the lower arm connects in

a much flatter and wider way
into the palm and back of hand,

and thinner from the
side view of the hand.

Basic stuff, but the fun part is
any time you're adding a hand to an arm,

make sure to give it a bit of
an offset and step over toward the

thumb/radius side of things.

Similarly, from the side view,
the hand should always

take a noticeable offsetting
step towards the palm side.

By the way when I say the word "offset,"

it usually just means not lined
up evenly with surrounding things.

Anyway, always make sure
the thumb side of the hand

feels more chunkier and substantial
than the pinkie side of the palm.

With all of these ideas in mind,
you should be able to develop a quick

shorthand for getting
from the arm into the hand.

In fact, you should be able to
quickly deduce everything about the bones

and orientation of the
wrist without ever seeing

the thumbs or fingers or
any interior information.

So, maybe see how quickly
you can determine

where the radius and the ulna are
in any of these rough sketches I'm making.

Hopefully that seems easy enough.

Let's get back to structure and
talk about the muscle side of things.

We're going to make it really
easy for our drawing purposes

and only focus on three muscle groups.

The biceps are on the front of your upper
arm and allow you to curl up your arm.

They insert under your shoulder
muscles and chest muscles on one end

and connect to the radius and
tissue around the ulna on the other end.

The triceps are on the back of your arm
and allow you to pull your arm straight.

They also come out from under your
shoulder muscles and similar back muscles

and connect to the end of the ulna.

And yes, the deltoids are
of course the shoulder muscles,

but the third muscle that we're
going to be fixating on in this video

is going to be the brachioradialis.

You must learn to
love the brachioradialis,

it will be a pivotal part of
this video in more ways than one.

These insertions points are
important, so keep them in mind.

It connects from
the lower back of the humerus

under the triceps and
it wraps around a bit

over parts of the lower biceps and
connects to the radius on the other side.

I will be exaggerating this
muscle heavily throughout this video,

so be aware of that strategic inflation.

We are going all in on the bray-ray.

I think that's enough structure though, so

let's get into some drawing practice.

A big theme in the land of arms
will be controlling our organic curves.

So I guess I will do a quick recap
on s-curves and c-curves.

Don't let the names
throw you off too much,

most of the s-curves and
c-curves you'll be drawing

are going to be extremely subtle.

Just a whisper of curvature
going on most of the time.

And it's good to practice
that level of control

but an even more
important thing to practise

is your ability to weight your curves.

Weighting a curve means
changing up the harshness of the

curvature through the line.

So, if the curve stays
consistent from start to finish,

that would be a weightless curve.

You can have the curve be
increasingly strong at the start

or the end of the line to
give it weight in a specific direction.

This is very, very important to
practise because we spend our

entire childhoods writing letters and
shapes which curve in a very balanced way;

but the more you can break away from that,
the more organic your drawings will be,

so warm up with these often.

Alright, let's get into those
simplifications and reductions.

Or, rather, maybe mention
another little side thing...?

Sorry, there's a lot of
ways to think about arms,

such as the chain:
a common trick for approaching arms

is to imagine a giant linking chain-
the idea being that since the upper arm is

wider from the side view than from
a front view, and meanwhile the forearm is

the opposite, it will generally
create a nice little back and forth

between wide and narrow, which is
definitely good for aesthetic purposes.

So, you can use that as a little
mental note when applicable.

Meanwhile, to go back to
what we've just talked about

with curve weight, the most
important mental note I fixate on

is usually just where to weight the
curve for each part of the arm.

On the bicep side of the upper arm, the
curve weight is further toward the elbow,

whereas on the back or tricep side of
things, the curve weight is

closer to the shoulder.

The brachioradialis is definitely
weighted toward the upper forearm,

but is more rounded and gradual than
the opposite side of the forearm.

All of these things relate to the
actual muscle bodies of each muscle group,

the tricep being the most
important one to always remember,

because the muscle bodies are
located in the top half of the upper arm.

Okay, so let's sum up the
straight arm simplifications

a bit more directly.

Back view of the arm, palm
forward, minimal twisting:

The upper arm might as well
just be a simple cylinder

with minimal tapering,

but the lower arm is going to feel
closer to an upside down bowling pin.

The important part is that the
exterior side, with the brachioradialis

is going to not only curve
outward more than the interior side,

but also come up a bit higher than it.

It should definitely feel like
it starts its s-curve above the elbow.

If we raise the arm up out to the side,
yes you'll get a bit of the chain concept,

but since you'll probably
not be drawing massive bodybuilders,

it can become pretty minor.

You do want to make sure that you're
thinking about weight and gravity though.

Obviously, this gets a lot more
extreme with age, but on any body type

you should still be using these
ideas to give you at least a little

bit of subtle curve weight.

Another useful reference point to think
about comes from the shoulder muscle.

The deltoid comes down to a bit
of a point on the exterior of the arm.

While not exact, this can still be used
as a good way to indicate a break

between the front bicep side of the arm
and the rear tricep side-

especially when you're dealing with
more complex poses and off angle views.

If I draw a quick arm over here
on the left from a slightly awkward angle,

adding the deltoid and letting it point
a line towards the elbow can at least

help us visualise the
tricep and bicep sides of the arm.

If this drawing looks weirdly
off to you at first, that's good!

The brachioradialis was not
coming from the correct spot.

Let's first recall that the
brachioradialis should come from

under the triceps and over the biceps,
and using that line from the deltoid

we can visualise this
insertion much more clearly.

Moving along, some of
these straight armed elbows

might be looking a bit wonky,
so let's briefly mention them.

The most important part of
simplifying the elbow will definitely come

from seeing the triceps and
humerus all come together in a mass

that leads straight down
through the elbow and into the ulna.

The funny bone and radius both
become a bit indented on a straight arm,

so you'll mostly see these little
pockets of depth off to both sides of the

triceps and ulna, with the
forearm muscles pulling the forms back out

and really solidifying those crevices.

There's definitely a lot
of skin going on in this area,

so it tends to become quite wrinkly.

There's even
a slang name for this

folded up skin - it's called the wenis.

So, everybody should draw the wenis,
the wenis is not a dance,

and I'm happy to tell you this in advance.

[laughs] Anyway, wrinkles are tricky. The
general rule is to fold the skin with

c-curves and s-curves in a way
that squishes the curves together

without ever feeling like they're
going to cross each other, or pass through

the extended implied
lines of other curves.

You can compress a bunch
of them into a small space,

or just a couple, but I recommend
wrinkling things up a bit above the elbow

with perhaps some more
drapery style folds hanging underneath.

You can definitely develop your
own stylistic approach to wrinkles,

and they should feel
similar in theory to clothing folds,

but more organic with the lines.

Just keep in mind,
like with clothing folds,

doing less is usually
better when learning.

Alright, a little bit
more drawing in this section,

because I want to also just quickly
mention some size relations.

I'm a serial offender of
making my deltoids too small in drawings,

so I'm trying to correct that. I think it
can be useful to think of the upper

arms as a length that goes from the top
of the shoulder to the elbow.

The top third of that length
can be the distance of the

deltoid going down the arm.

I barely mentioned it
before, but the triceps

really have two main visible muscle
bodies on the back of the arm.

While they both have
those high up muscle bodies,

the interior side one is a bit
longer down toward the elbow,

while the exterior one is even more
focused at the top.

The bottom of these muscle bodies
and strong separation of them

occurs roughly halfway
down the upper arm unit

that we mentioned going
from top of shoulder to elbow.

You can kind of indicate this with a
little butt shape on the back of the arm,

especially if it's being flexed.
The arm... not the butt.

Okay, moving along
to the world of movement,

the elbow is basically just a fancy hinge
joint with the funny bone on the interior,

the ulna being the king in the center,
and the radius on the exterior.

When the arm is straight, they somewhat
line up with the ulna sticking out a bit.

From the interior view though,
once we start curling the arm,

obviously the funny bone
isn't going anywhere,

but the ulna is going to hinge around it
and form a very boxy and angular

silhouette by letting your brain fixate
on the line from funny bone to ulna.

All of the tissue of the arm is going to
crease at the insertion of the bicep and

form a bit of a line that points mostly
toward the funny bone side of things.

The important take away is that interior
arm equals boxy shape and long crease.

Also, when you raise your arm
with your bicep toward the sky,

that means the deltoid is going to be
pulled to the back of the shoulder.

As it, once again, needs to be pointing
toward the exterior line between

bicep and tricep.

Anyway, the exterior elbow
view is a bit interesting.

You'll of course be seeing the
deltoid a lot more in this view

where the exterior is facing back,

but the interesting part
is that you're now seeing

both the radius and ulna
in the straightened arm view.

This means that when you
curl your arm, those two lower

arm bones are going
to be traveling together.

Even though the silhouette
will fundamentally be the same,

I find it very useful to acknowledge
this anatomy by making the elbow

feel like it just rounds up
to and around these bones,

instead of feeling boxy.

You might also remember that the
brachioradialis is on the exterior side,

so that will create a mass in form
that will squeeze from upper arm

to lower arm.

Because of this mass, the exterior
crease here becomes a lot more

chubbier and compressed.

I like to use a shorter and
splitting crease to hint at this

thicker form-

and you should try to hint
at these things in any body type.

From a different view, you can
get some idea of how all of these bones

and muscles are working,
but for now let's jump over to the

forearm movements, because
we have rotation to deal with.

If you stick your right arm out
in front of you, palm side up,

this is the least twisted
view of your forearm.

The muscles and bones just carry
forth to the hand in a linear fashion.

This represents one extreme
of your rotational movement.

As we rotate the hand,
the elbow won't be changing much,

but the radius and brachioradialis
will start twisting a bit

to line up vertically at the wrist.

The best thing you should
observe on your own arm

is how the s-curves adjust
as you rotate your hand.

I'm not in love with
the drawing on the right here,

but the interior ulna side of
things definitely changes up its

s-curve the most, whereas the
exterior side just shifts weight a little.

Once your palm is facing downwards,
the full range of motion is complete.

This is as far as things can twist.

The radius and ulna are now
on opposite sides from the elbow.

You might be thinking,
"what if I want to give a thumbs down?'"

Well, physically you can't. So be sure
to remember that and like this video.

If you do really want
to point your thumb down,

it requires you to actually
rotate your entire arm so that your

elbow is facing a different direction.

Lastly, here I'll just mention, when
your arms are at rest at your sides,

the default comfortable state
is that central, half-twisted state,

not the completely untwisted state.

Alright, let's go back to reducing
information and recap what we've learned.

Of course, it's pretty fun
to draw giant musclebound arms,

especially when you're trying to
commit all these concepts to memory,

but we also want to be
able to simplify these things down

into little anime stick arms.

When you start out in art, it's fine
to just think of the upper and lower arms

as just cylinders, and as
you get more comfortable,

you can introduce some
tapering into these forms.

Eventually, you will want to
be capable of some level

of form complexity. These cross
sections are never just round.

They have weird oblong
shapes and blobby looking contours.

I like to practice these things with what
I would call "skinny muscle forms."

Maybe it's just my Samurai
Champloo roots coming through again.

A quick example though,
starting with a deltoid and shoulder,

letting it point toward an elbow, think
I'll twist the bicep to the bottom on

this one, bicep means curve weight
closer to elbows, so we can even dive in

with some angular shapes.

With the bicep facing forward,
that means the deltoid

can be a bit further on
top instead of on the back,

and we can even hint at some
tricep form above the separating line.

That line will let us know
where to pull the brachioradialis from,

and then we can decide on the
hand rotation and make everything line up.

Design wise, it's good to play
around with the ratios of rounded

shapes and angular shapes.

We alluded earlier to the
exterior side feeling more rounded

and the interior feeling more angular,
when discussing the elbow hinge,

so let's just run with that a bit more.

What if we just always
simplified things around the elbow

by playing up rounded exteriors
and angular interiors in the forearm?

I just noticed that that letter pointing
towards the tricep is a D instead of a T.

Clearly getting a bit
delirious at this point.

Regardless, let's keep sketching.

Here's a quick side view, still mostly
practicing curve weights and that

brachioradialis. Some slightly
more exciting things we could try

would be playing around
with perspective and dynamic angles.

If we imagine a Spiderman
type arm pose, we could still

think about where we could
exaggerate our forearm muscles.

I'll be honest though,
I sort of got distracted

right after starting this one, because I
thought of some more stuff to mention.

Such as: what does it look like
if you just have your elbow

sticking up in the air with
your arm curled behind it?

A lot of tricep weight at
the bottom, but it really thins out

into a very skeletal look at the elbow.

It does give a nice look at
the radius, ulna, and funny bone.

This becomes instantly
obscured by the forearm once you

straighten the arm out a bit,
with those forearm muscles just

taking over both sides of the elbow.

But, this made me
think of another scenario:

how about when you're resting your
weight on your elbow at a desk or table?

Where do those forearm muscles go then?

Well, since the brachioradialis
connects to the humerus,

it actually sits up higher, away from
the elbow on the exterior side of things.

I guess that's obvious enough,

kind of like how it would look
if you were drinking something.

Just always be keeping track of where
the thumb is, and where the exterior

and interior of the elbow are,
and you'll be fine.

Now, we always have a common mistakes
part in these videos,

but I think I've gone over things so much
that we can try a pop quiz instead.

I'll show a quick drawing with some
weird mistake, and we'll see if

you can deduce the problem.

Like this. What's wrong with this?

Well, you have two possible answers on
this one, since we can't see the shoulder.

We seem to be looking at the front of an
arm, so either the brachioradialis

is on the wrong side, or the hand
should be mirrored.

How about this one?
Anything seem off to you?

Well, I'm messing with you a bit,
because it's the same thing,

except this time you can see the deltoid,
so there's only one answer.

The brachioradialis is
on the wrong side again.

It should be on the
exterior, not interior.

Alright, I promise this
one will be different.

What's wrong this time?

Doesn't seem too far off, the deltoid
and forearm stuff seem okayish.

This might be a subtle one, but I
reversed the weight on the

bicep and tricep curves.

Remember, the tricep should have mass
closer to the shoulder, and the bicep

curves closer to the elbow.

That's a bit better.

One last one.

What's wrong now?

Hmm, the brachioradialis is on the
exterior, so that's fine.

But it still looks a little strange.

Well, that's because it needs
to go over the bicep, not under it.

And with that, I think
we're done learning.

You have graduated to the part of the
video where we just take everything

we learned and try to draw and paint
arms from imagination.

Hopefully they wind up looking alright.

I will be using a simple flat brush for
these lines, with pressure sensitivity

mostly on size, but with a bit on opacity.

That should make it feel
pretty comfy and natural.

One big concern I had
going into this final section

is trying to make sure
it stays focused on arms.

Shoulders are a bit unavoidable,
but I tried experimenting

with ways to make
the hands get less attention.

Literal disjointed fingers and whatnot.

Unfortunately, that
actually made them stand out more,

in rules of focus
and contrast and whatnot,

so eventually I'll get rid of that idea.

What actually wound
up being the biggest issue

is just trying to come
up with a good variety of poses.

Once again, I considered crazy
foreshortening, but then the page might

feel less cohesive with the
more traditional perspectives.

I don't know. But I'm definitely
enjoying the line art quality.

There are a couple of
disjointed lines here and there,

but I tried to hit a good number of
the c-curves and s-curves

in single strokes.

That can result in a lot of putting
something down and then undoing it,

redoing it, until I figure out what
I want it to look like,

but I'm mostly okay with that method.

I can't be too chaotic with styles, but
I did try to at least vary up

the muscularity
levels a bit as it goes on.

My brain was pretty drained
from all the previous arm drawings,

so there are definitely a couple of
moments where I've made up an arm

and then moments later realised it was
almost identical to one that was

already on the page, like this last one.

But I just decided to adjust the
angle of it a bit and move on.

For colors, I don't know how
much I can really say that would be new.

The skin video, as well as the other videos,
have really covered the general stuff,

but you can see I've lightened the
line art into a lighter reddish tone,

and then threw in my normal dull
minty background.

I like to mask out everything in order
to watch transparency, which can

be a bit tedious, but usually worth
it in the long run.

A big piece of advice is to make sure
you don't instinctually start

pressing hard with
your stylus when blocking.

This is always the most dangerous time for
your hand and wrist health,

because we tend to dig in harder when
filling things in.

Pressure is bad for your tendons.

Anyway, once everything is blocked in,
we can try out a variety

of skin tones across the page.

This is also a great time to introduce
some hue variety by air brushing

in reds on areas that might catch more
sun damage, and things like that.

The next step is form rendering, and I
know some people like a more

smooth gradiation and some people like a
more chunkier chaotic painting approach,

but, I'm going to try out some
weirder ideas, and just try defining forms

with blocky, contour tracing strokes.

Honestly it's a bit weird at times for
these videos, because I don't find myself

with a strong preference.

In my mind, as long as you have some
understanding of the forms,

you can always either step up how
abstract and chunky things are,

or step it back into
hypersoft air brushing.

In any case, the important part is
just knowing where the hard edges

and soft edges should be.

Now, how do you know which
edges are hard and which are soft?

Well, it's simple. If you would be okay
with seeing an actual line at a specific

spot in your drawing, then that can be
a hard edge in your painting.

If you think a line would look bad in your
drawing, then stick to soft edges there.

I already made pretty much all of the
lines I wanted to make

in the drawing stage, so those will
be the only hard edges.

Anyway, I started out pretty experimental,
with some of the painting stuff early on,

but I wasn't that into it this time, so
I'm slowly going to be dialling that back

as we go. Almost all of these arms
are going to be out of direct light,

you know, just ambient light for the
most part, aside from the one on the right

that is reaching toward us.

Doing this somewhat makes the whole image
a bit darker and more saturated than

I wanted, so I'll be desaturating and
lightening a bit as we go.

Other than that,
I definitely kept the line art in play

for a lot longer than I normally do.

It's not until most of the form
rendering is complete that I actually

flatten things down and
start painting out the lines.

This is also when I start playing with
slightly more interesting shapes

in some of them.

The rim light is going
to be pretty subtle today;

I definitely made it more limelight than
I usually recommend to people,

but still trying to at least taper
those lines and find some

chunkier shapes with it.

To bring back some of the other fun stuff
from the skin rendering video,

I decided to put in some
body hair on the top left arm.

Just a bit of fun with desaturating colors
and pattern-based brushwork.

This was also when I decided to at least
connect the fingers that I had there,

but we're almost done, so the last
thing I want to have fun with is bringing

some of that body hair into the rim light.

It makes the rim light a lot more fun.

Definitely recommend
trying it when you can!

And, with that, this monster
of a video is finally complete.

It has been a journey, and while the
drawings and paintings might

not be perfect, hopefully you
at least feel a bit more confident

about being able to draw
some fun arms from imagination.

As always, the best way
to fully learn is to mix in equal parts

of drawing from human reference, doing
master copies of other artists you like,

and drawing from imagination.

No matter how good or bad you might
feel about one of these three parts,

do them all evenly regardless.

We only focused on
three main muscles in this video,

so if you find yourself
wanting to build up more complexity,

just go check out one of the other
amazing art YouTube channels that dives

a bit deeper.

Alright, I want to thank you all so much
for at least giving this video a chance,

I'm not a frequent uploader,
so be sure to subscribe if you don't want

to miss out on the handful
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Info is down in the description.

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You guys are wondeful.

See you, everyone.