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 toward 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 pinky 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 your curves 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, pop
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 rare 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 a 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 simple 'find 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
focussed 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
towards 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 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 harm out in front of you,

palm side up, this is the least twisted view of your forearem.

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 are just 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 things 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,
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 it 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 normally 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 focussed 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

or at least giving this video a chance,

I'm not a frequent uploader, so be sure to subecribe

if you don't want to miss out on the

handful of videos I put out each year.

Of course, if you want some fun, specialised content

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and its definitely worth your time and money

if you haven't tried them out yet.

Info is down in the description.

I also, of course, do want to give an earnest thank you

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money to keep these videos coming.

You guys are wondeful.

Seeya everyone.

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