Webtoon Advanced Structural Understanding of Arms and Legs
GCC Academy
Hello, I am Webtoon artist Uksoo
As we explored in the previous lecture, the arm, unlike the torso, has a significantly wider range of motion
and consists of multiple muscle layers
This results in highly dynamic silhouette changes depending on the movement direction and angles
In this session, we will examine
how muscles change through wrist rotation, specifically pronation and supination of the forearm
We will also look into shoulder changes when the arm is raised
and muscle transformations during arm flexion and extension
These aspects will be analyzed through various poses
It's like the practical application of arm anatomy for drawing
Let’s get started
Arm Muscles
Before diving in, let’s do a quick review
The arm performs not only flexion and extension but also wrist rotation,
known as pronation and supination
The default position is when the palms face forward, which is called supination
We previously learned that wrist rotation follows the radius
and that the radius follows the thumb
Please keep that in mind
However, when we studied muscles last time,
we only looked at the muscles in the supinated state,
that is, we only observed them in their default position
What happens when we rotate the wrist while keeping the same muscles?
The forearm muscles, for wrist and hand movements, will undergo significant shape transformations
Here’s an arm in supination,
the default
Looking at the side view,
the brachioradialis and wrist extensor muscles extend toward the thumb side
For the purpose of this session, when I refer to the brachioradialis,
please understand that I am including
both the brachioradialis and wrist extensors as a single unit
In general, many forearm muscles are relatively aligned horizontally in this neutral state
Meanwhile, in the upper arm,
the biceps brachii is prominent,
while the triceps brachii
at the back is barely visible
The deltoid, as its name suggests, maintains a clear triangular shape
Now, let’s rotate the forearm into pronation, with the back of the hand facing forward
Many things change
Let's look at the forearm
The brachioradialis, which was straight in supination,
now curves inward, following the thumb’s movement
The proximal part of the brachioradialis, which was previously hidden, becomes more visible
From a side view, this shape transformation is even more noticeable
Additionally, muscles that were barely visible before, such as the triceps brachii at the back of the upper arm
and hand extensors, become more pronounced
The deltoid also thickens, creating a more rounded shape
The interaction between the biceps and triceps becomes more distinct
When drawing pronation, the brachioradialis line
is one of the most noticeable aspects to depict
In supination, this line drops straight down
In pronation, it curves inward, creating a more dynamic appearance
Other muscles in the forearm follow a similar rotational arc
In reality, we rarely hold our palms or backs
of the hands completely forward for long
That’s because it requires muscle effort and feels unnatural
When the arm is relaxed,
the brachioradialis follows the thumb’s inward curve,
creating a triangle shape
Below that, hand and wrist muscles extend horizontally
Now it's the upper arm
Unlike before, where only the biceps or triceps were visible,
both now appear equally from this perspective
The deltoid follows the arm’s contours, blending into the silhouette
If we were to define the most natural arm pose, this neutral position would be a strong candidate
So far, I have explained pronation and supination using the brachioradialis as the reference point
So, how do we handle the rest of the forearm muscles when drawing?
Here’s a shortcut I often use
Draw two straight lines
to define the brachioradialis and wrist extensor bundle
These two muscle groups undergo dramatic changes during rotation,
making their outlines more pronounced
In contrast, other forearm muscles have weaker outlines
and less noticeable transformations
Trying to master every single muscle detail here is extremely difficult
So I simply treat them
as two main lines for clarity
This isn’t a perfect anatomical approach,
but it’s practical when dealing with the complexity of forearm anatomy,
which I cannot pull myself to master
That's about it
If you do manage to fully master all forearm and hand muscles, I sincerely respect you
You deserve a double thumbs-up
Now, let’s briefly explore how shoulder muscles
Imagine you’re stretching with one arm raised high
Like this
How does this affect the deltoid and surrounding muscles?
The deltoid previously fit between the biceps and triceps,
so in between them?
That's not true
The deltoid now moves back
The visible front muscles now include the pectoralis major
and coracobrachialis or the small shoulder muscle
The arm girdle bones we previously examined,
that is, the scapula and clavicle, do you remember how they functioned?
In order to lift the arm, the scapula must fully expand,
and the clavicle follows this movement upward
As a result, the muscles attached to these bones also shift accordingly
This is why the deltoid muscle, which was originally visible, is no longer in view
This is really fascinating
I remember when I first saw this,
I thought, wow, it changes like this? So cool!
The deltoid muscle, which is clearly visible when the arm is down,
tilts backward when raising the arms
I doubt you’ll easily forget this either
Now, let’s take a look at the upper arm
Focusing so much on pronation and supination,
I feel like we’ve neglected the key muscles of the upper arm
As I mentioned before,
muscles can only actively contract
They cannot actively relax
This is why we have flexor and extensor muscles,
which usually exist in pairs
For the arm, the brachialis and biceps brachii handle flexion,
while the triceps brachii is responsible for extension
Now, let’s flex the arm with some force
Like this
The biceps, our familiar biceps brachii,
swells up as if it’s flexing in anger
What happens when we extend the arm?
At this moment, the triceps brachii,
finally getting its turn, expands and makes its presence known
While this may seem obvious,
breaking it down by principle
makes it feel like a new discovery
The elbow is the protruding part at the head of the ulna, forming the joint
You’re all familiar with this part
This section is covered by fascia,
leaving the bone directly exposed under the skin
If you follow the elbow line down, it connects to the ulna
Remember how we said that the radius follows the thumb side?
The ulna, on the other hand, extends toward the protruding area of the pinky finger
That's right
WThe ulna, on the other hand, extends toward
the protruding area of the pinky finger
It creates a natural arm boundary
Next, let’s draw an outstretched arm pose
From the front, the arm won’t be very visible
since it’s overlapping
Just like with the torso, we tend to assume the cross-section of the arm is a perfect circle
However, as you can see, it often takes an elongated oval shape,
more like a flattened baguette
In other words, avoid drawing it as a perfect circle
For the upper arm, since the muscle layers stack more vertically than horizontally,
it takes on a taller oval shape
Conversely, the forearm connects to the hand,
where the palm is wider horizontally,
so the forearm also follows this shape
Keeping these muscle shapes in mind is crucial when depicting overlapping arms
That said, there’s no need to be overly precise
In many cases, exaggerated proportions are used in such scenes,
and bold exaggeration is often more effective than strict accuracy
If you understand the basic form
and can adapt it to your desired composition,
that alone is enough
Exaggeration is more about energy than precision
The same goes for the armpit
It’s a familiar area,
yet when trying to draw it after studying
arm and torso anatomy, it can be confusing
At least, that was my experience
Take a look
The armpit is essentially a meeting point for the upper arm and torso muscles
The pectoralis major, coracobrachialis, latissimus dorsi,
biceps brachii, and triceps brachii
all converge here on the armpit
The most influential lines in shaping this area are the pectoralis major,
biceps brachii, and latissimus dorsi
These three form the primary intersections
For added detail, the coracobrachialis runs through the middle,
and the triceps at the back also influences the contour
Many artists simplify this area
into the intersection of the biceps and chest muscles
But if you need to depict a muscle-bound character,
adding detail becomes important
Now, we’ve examined the various muscle lines and details of the arm
How do you feel?
Personally, I now feel much more confident in drawing arms
Teaching is truly one of the best ways to learn
Now, let’s move on to the grand finale, the hands
Muscles and Bones of the Hand
Here’s the hand
Yes, the hand
Since I specialize in romance illustrations,
I consider the hand to be a second face
Of course, in action genres, hand details are also important
However, in romance, conversations often drive the story rather than action
This results in many close-ups and bust shots
As I mentioned earlier,
such compositions limit expressive movement in the upper body
If two characters are conversing,
they can’t suddenly twist their torsos
into unnatural poses
At most, changes in the neck and shoulders are possible
This is where hands play a crucial role in setting the mood
Hands can also express a wide range of emotions in close-ups, just like the face
A clenched fist,
trembling fingers,
grasping a cup,
pointing a finger
All of these gestures carry specific connotations
How was it?
A close-up that might seem plain or dull
can gain a sense of presence and action when a hand is added,
In drama and romance genres, with many dialogues,
the ability to draw hands becomes especially important
However, hands are incredibly difficult to draw
Even as an artist with 15 years of experience, I still struggle with them at times
So I can only imagine how challenging it must be for you
Just drawing a single finger is difficult,
but there are five of them, one of them slightly different in size and shape
The palm that connects them isn’t flat
It’s thick in some areas, thin in others,
and has irregular contours, making it hard to grasp
You know there are five fingers on a palm,
but when you actually try to draw them, you often get stuck
This is a drawing of a hand I made when I was in first or second grade
If only we could get away with this, life would be so much easier
But we can't
If readers are admiring a beautifully drawn face,
they might lose immersion in an instant with the hand
You need to be able to draw hands at least somewhat convincingly
This is even more important if you’re aspiring to work in the romance genre
It’s tough,
but let’s tackle it together
Before diving into anatomy, let’s first get an overview of the hand
To start, let’s separate the thumb from the other four fingers and examine them individually
Starting with the four fingers
The most fundamental function of the hand is grasping objects
This involves flexion and extension movements
Flexion occurs toward the palm,
while extension is controlled on the back of the hand
Try raising your hand and observing its movement
Although drawing hands is incredibly difficult,
the advantage is that visual references are always readily available
Each of the four fingers is divided into three sections, the proximal, the middle, and the distal phalanx
If the hand were just one large, single finger,
it would still be able to grasp objects,
but its versatility would be greatly limited
Instead, having four separate fingers allows for more diverse
and adaptable grips, making it evolutionarily advantageous
Given that hands evolved from feet,
it makes sense that fingers developed as multiple segments
Another notable characteristic is that because grasping is so important,
the palm side is much thicker compared to the back of the hand
Even just comparing the palm and the back of the hand, you can see a significant difference in muscle mass,
especially around the thumb
So why do we have a thumb?
Picture yourself hanging onto something with only four fingers
You’re managing for now,
but your grip is weakening, and the fingers begin to slip
Oh no!
his is where the thumb comes in
It locks in place, securing the grip
The thumb is like the biggest brother of all fingers
It's amazing
The thumb serves as a crucial stabilizer, dramatically increasing grip strength
Try imagining gripping something without your thumb
You’ll immediately realize how essential it is
That said, the thumb is just one against four
It needs enough strength to counterbalance the weight of the other four fingers
Unlike the other fingers, the thumb only has two joints,
while others have three
This means it has a more limited range of motion,
but in return, it can focus its strength more effectively
Additionally, the muscles around the base of the thumb
are significantly larger compared to other areas of the hand
With the emergence of the thumb, the hand became capable of opposition
Think of a LEGO minifigure’s hand
The opposition between the thumb and the four fingers
That's what the opposition means
This ability is the foundation of how we grasp objects
Now that we’ve covered the basics of the hand,
let’s move on to the bones
The bones of the hand can be divided into three major groups: Carpal bones, metacarpal bones, and phalanges
The carpal bones connect the hand to the forearm
They are arranged in a compact, clustered formation, like a collection of small pebbles
You don’t need to memorize all their individual names,
but keep in mind
that the curved shape of the palm
is largely determined by the structure of these wrist bones
Please remember that
The metacarpal bones form the boundary between the wrist and the palm,
as well as between the palm and the fingers
Here’s an interesting detail
The point where the metacarpal bones connect to the phalanges
is not the same as where our fingers visually appear to begin
The actual joint between
the palm and the fingers is lower than it seems
So when you bend your fingers,
they don’t fold exactly at the point where they appear to separate,
but rather at a lower point in the hand
I actually discovered this while preparing for this lecture
It makes drawing hands both
more fascinating and more challenging
Rather than bending precisely here, the fingers fold at a slightly recessed area lower down
I had been unconsciously drawing it this way,
but now that I understand the structural reason behind it,
I can finally see why hands form those distinctive lines
That was my revelation
But anyhow, we now know
The boundary between the bone joints and the visible finger segments is different
Please take note of it
One of the most prominent landmarks of the hand
is the protruding metacarpophalangeal (MCP) joints
When drawing the back of the hand or a clenched fist, you often depict these knuckle ridges as small hills
These hills correspond to the MCP joints located at the end of the metacarpal bones
When making a fist, the fingers fold at this point,
and the MCP joints become visibly prominent
Properly depicting this part can emphasize either the delicate nature of a hand
or the strength of a clenched fist
Each finger consists of three phalanges,
the proximal, middle, and distal phalanx
The proximal phalanx connects to the metacarpal bone,
the middle phalanx links the first and second joints,
and the distal phalanx forms the tip of the finger, where the fingernail is located
Many people simplify fingers as long, straight cylinders,
but the distal phalanx actually
has a subtle curve that follows the shape of the fingernail
In contrast, the thumb has only two segments,
which, as mentioned earlier,
allows it to oppose and support the four fingers
As a result, the fingertip appears to have a slight additional bend
Since the fingernail is halfway down the distal phalanx, it creates a small inward dip
Although fingers technically have three joints,
think of the fingertip as having an extra unbending segment
to better capture the natural curve
There are also differences in how the knuckles and fingers are depicted between male and female hands
Generally, men’s knuckles tend to
be more pronounced than women’s
On the other hand, female fingers are usually thinner
and longer,
with less emphasis on the knuckles
To emphasize the roughness of a male hand, artists often exaggerate the prominence of the knuckles
and depict fingers as thick with minimal spacing
Conversely, elegant or beautiful hands
are typically drawn with long, slender fingers and greater spacing between them
Now that we’ve examined these hand characteristics,
let’s take a look at the muscles of the hand and wrist, which we briefly covered in the previous session
It may seem complex, but we’ll break it down simply
The muscles of the hand can be broadly categorized into two types
Flexor muscles and extensor muscles
The flexor muscles include the flexor digitorum profundus and the flexor pollicis longus,
both located on the palm side of the hand
to contribute to finger flexion
Previously, I mentioned the knuckle ridges
that become prominent when making a fist
In contrast, when the fingers are extended upward,
the tendons of the extensor muscles become visible
By emphasizing these lines, you can add detail to the back of the hand
Additionally, the thumb has the extensor pollicis longus and extensor pollicis brevis,
which cross over each other and form a noticeable groove known as the anatomical snuffbox
These details are particularly useful for depicting slender or bony hands
So far, we’ve covered the basic anatomy of the hand
However, when drawing hands,
understanding the overall flow of movement is more effective than focusing solely on muscle details
Unlike other parts of the body, the hand’s muscle structure is not as prominently visible
Instead, its shape follows a defined structure,
which is guided by opposition,
extension, and flexion movements,
which prioritizes that flow of movement
In other words, drawing hands is less about anatomy and more about capturing dynamic motion
With that in mind, let’s move on to practical examples of drawing hands
Before drawing fingers, let’s divide the palm into different regions
This is similar to how we first analyze the torso
before drawing body movements
Since fingers branch out like tree limbs,
it’s best to start with the foundation
We can divide the palm into four key regions
This division can also be understood as following the crease lines of the palm
First, there is the thenar eminence,
something we're familiar with palm reading
Next, there is the broad palm area next to the thumb
As mentioned earlier when discussing the back of the hand, this section,
along with the thenar eminence, contributes significantly to the overall volume
Then, we have the junction where the four fingers connect to the palm
Again, the fingers and the palm do not align exactly with the points where the fingers bend
nstead, the fingers slightly overlap the palm, forming curved junctions
When the fingers curl inward, this section folds along with them, completely covering the palm,
which is why a clenched fist has no visible gaps
Finally, there is the central hollow of the palm,
the deepest point of opposition between the fingers and the thumb
This section isn’t something you need to draw explicitly
Rather, like the supraclavicular fossa, it forms as a result of depicting the surrounding areas
Not necessarily, though
One particularly important aspect to note
is the curved boundary where the four fingers meet the palm
As you can see, fingers do not attach to the palm in a straight line but rather form a gentle arc
If you fail to account for this curve when drawing,
the hand will appear stiff and unnatural, like a robotic hand
So be sure to keep it in mind
It's a critical factor in drawing natural-looking hands
Looking back, I realize that even the crude hands I drew as a child
contained an unexpected level of insight
Of course, I wasn’t inventing anything
I was simply copying the work of professional artists
Perhaps it's something obvious
Now, let’s move on to some practical hand-drawing exercises
First, stretch out your hand
as wide as you can
Notice how, when fully extended, all the fingertips
and knuckles fan out in a radial pattern from the wrist
Let’s begin by defining the palm’s basic shape and confidently sketching out the primary structures
When the fingers are fully extended,
the indentations between them straighten out,
forming smooth, linear separations
The line extending from the palm to the thumb should also be drawn as a continuous straight line
Similarly, all other fingers should be fully stretched out,
and their forms should be carefully sketched in a natural arc
That's it
Now, let’s flip it over and examine the back of the hand
The fundamental structure remains the same
However, there’s something interesting to note
The boundaries between fingers on the palm side and the back of the hand do not align perfectly
If you spread your fingers wide open, you’ll notice
a web-like membrane between them,
somewhat resembling the webbing on a frog’s feet
This webbed section marks the finger boundaries on the palm side
Now, if you close your fingers while looking at the back of your hand
the webbing becomes hidden,
making the boundaries between fingers appear longer on the back than on the palm
See that?
That's right
The separation between fingers is more pronounced on the back than on the palm
his was something I had not consciously realized before,
but preparing for this lecture made me aware of it
Now, returning to the drawing,
let’s refine some details by highlighting key tendon structures:
Extensor digitorum, extensor pollicis longus,
and extensor pollicis brevis
These tendons will add depth and realism to the drawing
Now, let’s relax the fully extended hand
If you gradually release tension,
the hand will naturally curve into a shape that resembles gripping a small ball
That's right
Opposition again
You may have noticed that in 3D modeling or animation,
characters often start in a stiff T-pose,
which, at first glance, looks unnatural and uncomfortable
Earlier, we discussed how the most natural resting position
for the arms is slightly bent rather than fully extended
The same applies to the hand
Instead of staying stiff and flat,
a slightly curved, C-shaped opposition stance
feels much more natural
When drawing an opposed hand position, note that
the thumb and index finger form a C shape
and the middle, ring, and pinky fingers
follow a gradually increasing curve towards the palm
There's anther crucial detail for hands
Earlier, I mentioned that the finger boundaries on the palm curve naturally
Many assume that
the palm itself is a flat surface, but that’s not entirely true
In reality, the cross-section of the palm is subtly curved
Even in a relaxed state, the metacarpal bones
are arranged in a gentle arc rather than a completely flat plane
Of course, you can force the palm into a flat shape,
but that would be similar to the unnatural T-pose for arms
A natural palm shape should always retain a slight curve
It's essential point to remember when drawing hands
Next is a fist
A common approach is to simply sketch it as a boxy shape
with visible knuckles
So good!
You may end with this
But we just learned that the palm has a natural curvature
So we know that the fingers do not fold inward in a perfectly straight line when forming a fist
Instead, the fingers gradually curl inward,
with the pinky finger tucking in more deeply than the others
One, two, three, four
Notice how the fingers disappear in that order
Let’s now examine a side view of a clenched fist
The knuckles serve as the pivot points for the fingers
The palm itself also folds slightly,
as the first finger joint curls into the palm
The second finger joint bends inward,
and the third joint disappears completely inside the fist,
not leaving any space inside
The thumb presses firmly against the index and middle fingers,
This, too, happens because the first metacarpal bone moves the palm
to cover a larger portion of the four fingers
From this angle, only the first segment of the thumb is visible
Looking at the fist from the pinky’s side,
the pinky is the most visible finger of the four
Like so
Also, the thumb firmly secures the grip over the front of the fist
Now, let’s integrate what we’ve learned into a full arm movement analysis
It shows how the arm bends and extends through coordinated muscle contractions
And how the wrist naturally rotates between supination and pronation
Also, how key forearm muscles, like the brachioradialis and wrist extensors,
shift dynamically with movement is important here
With this, we’ve now completed
our two-part study on arms and hands
For those of you who have followed along this far,
I want to say: great job! You’ve put in a lot of effort
In Webtoon and comic art, dialogue-heavy scenes make up about 60% of most stories
During these scenes,
close-up shots of shoulders,
upper bodies, and hands are frequently used
Since facial expressions are crucial,
understanding the upper body is also crucial
You have now conquered about 80% of the anatomy knowledge essential for Webtoon illustrations
In our next lesson, we will focus on the anatomy of the legs and feet
Legs and feet are key elements in defining
a character’s posture, movement, and balance
We will explore the anatomical structure of the legs
and the foot movement and its impact on silhouette and posture
Great job everyone
Thank you
Arm Muscles Supination Brachioradialis + wrist extensors extend toward the thumb Biceps prominent, triceps barely visible
Pronation: Brachioradialis wraps inward along the thumb Triceps and wrist extensors more visible
Neutral: Brachioradialis curves around the thumb (triangular shape) Biceps + triceps visible together
Elbow Ulna head protrudes Follow pinky direction for arm contour
Armpit Major muscle convergence: Pectoralis major, coracobrachialis, latissimus dorsi, biceps, triceps
Hand Muscles and Bones Flexor muscles: Palm side; deep finger flexor, long thumb flexor
Extensor muscles: Dorsal side; finger extensors, long & short thumb extensors
Bones Wrist bones connect hand & arm Metacarpal bones form palm structure
Phalanges (finger bones): Three segments, proximal, middle, distal