Webtoon Advanced Structural Understanding of the Chest and Back
GCC Academy
Hello, I am Webtoon artist Uksoo
The topic we will be discussing today is the anatomy of the torso
There is a saying I like
The background speaks as well
A background scene alone can convey various emotions
So, what about body movements?
Gestures themselves convey a great deal of information
Take a look at this illustration
This comes from a scene in TOON by artist Boichi
In the scene, a great artist
quickly sketches this line and asks
the aspiring comic artist protagonist what it looks like
What do you think it looks like?
Yes, that's correct
It is the silhouette of an arm
Given the delicate lines,
it is likely a woman's arm
Now, here is how it looks internally
Even when drawing just the outline of an arm,
knowledge of anatomy makes a significant difference
Before we dive into the lesson,
let’s briefly go over the names of bones and muscles
In the past, anatomical terms were often written in Chinese characters
A well-known example is the trapezius muscle
It is the muscle that gives prominence to the neck
However, the official term has now changed to triangular back muscle in Korean
As the name suggests, it describes a triangular shape on the back
I will try to use both names where appropriate
But I will primarily use Korean terms whenever possible
That said, familiar names like trapezius
might occasionally slip out
The Bones and Muscles of the Torso
Now, let’s first
divide the body into different skeletal regions
The human body consists of a total of 206 bones
That’s quite an impressive number
First, we categorize the skull,
spine,
and ribcage as part of the torso
Then, the shoulders, collarbone,
upper arms, and forearms are the arm bones
The pelvis, thighs, and shins are leg bones
But the shoulders, collarbone,
and pelvis are technically part of the limbs
We will discuss them today
because they are
key connection points to the torso
Now, let’s examine the bones of the torso
The primary components include the spine, ribcage, and pelvis
The collarbone and shoulder blades are secondary but significant elements
We will explore how these bones affect the body's outline and muscle movement
Then, we will move on to the muscles of the torso,
examining how they attach and function
Finally,
we go to the torso
We will look at practical examples of torso poses
and analyze how muscle lines appear in different positions
Let’s begin with the spine
The term spine actually refers to an individual vertebra
The proper term for the structure as a whole is vertebral column
However, since spine is more commonly used,
we will stick with that term
As the saying goes, all roads lead to Seoul
The spine acts as a bridge connecting the head to the torso
and serves as a pillar that supports the body's internal organs
It is divided into three main sections
The first seven vertebrae make up the cervical spine
The next 12 vertebrae, from the eighth
to the 19th, form the thoracic spine
This section is where the ribcage is attached
Finally, the last
five vertebrae, from the 19th to the 24th, make up the lumbar spine
Considering that the lumbar spine bears the most weight while maintaining flexibility,
it is surprising that it consists of only five vertebrae
It has even fewer bones than the neck
One key characteristic of the spine is its S-curve
See here
The neck,
the upper back,
and the lower back, each forming a slight C-shape
So we have three parts
that create a smooth S-curve as a whole
Here’s something to note about the ribcage
Its inward curve causes
the thoracic spine to arch backward
Then, the rest compensates by bending in the opposite direction
From the thoracic to the lumbar spine, the dominant structure is the fascia
Remember?
The fascia and tendons
They do not grow larger with training
Because of this, the contours of the bones are clearly visible in this region
This creates key anatomical landmarks along the back
Next is the ribcage
The ribcage protects internal organs,
is closely linked to the chest muscles,
and connects to the collarbone and upper arm bones
So arm movement also influences the shape of the chest
The basic shape of the ribcage resembles an upright egg
The inside of the ribcage
cannot simply isolate the organs
It also needs to allow for forward and backward bending
Because of this, the interior is hollow
From the side, its egg-like shape becomes even more apparent
A hollow ribcage alone would not be sufficient to contain the internal organs
For this reason,
the rectus abdominis,
or abdominal straight muscle, provides a firm layer of protection for the internal organs
The sternum, or breastbone, is also an essential structure
It is the tie-shaped bone in the center of the ribcage
This bone connects to the clavicle,
serving as a crucial link between the torso and the arms
You may have heard the expression, my chest is about to burst with frustration
We tend to beat their chests when feeling overwhelmed,
which makes this an accurate description, given the sternum’s location
Earlier, I mentioned featured bones, right?
Those are the clavicle and scapula
We will cover these in more detail in the next session,
but for now, focus on how the clavicle
is attached to the sternum
This breastbone
The clavicle clicks into place right at this central connection point
Beneath it, the large pectoralis major muscle
extends along the clavicle
and continues along the sternum
Understanding this attachment will help you with proportions
One key characteristic of the clavicle
is its role as a reference point for the torso,
just as we used cross guidelines when drawing faces
The clavicle serves as a structural guideline
for proportioning the chest in various angles
That will make it easier to draw it
Its shape is somewhat like bicycle handlebars
Now, let’s briefly look at the scapula,
the next featured bone
The scapula is positioned on the back of the torso
It connects with the trapezius muscle,
also known as the triangular back muscle
This muscle is anchored to this part of the scapula
This ridge on the scapula is known as the scapular spine
It serves as a firm attachment point for the trapezius muscle
The trapezius extends along this ridge,
connecting securely to the scapula
For now, just keeping this in mind should be enough
The pelvis connects the legs to the upper body
while also providing crucial support
to prevent internal organs from collapsing
It is one of the trickiest
bones to visualize in the mind, in my opinion
There is also a distinct difference in shape between male and female pelvises
Fundamentally, the pelvis serves as a structural support for the internal organs
It is tilted at a particular angle,
giving it a basin-like shape
However, this basin must not be completely sealed off
The body must expel waste,
and various muscles, nerves, and blood vessels must also pass through
For this reason, the bottom of the pelvis is open
The pelvis is connected to the lower end of the spine by the sacrum,
which is also called the sacral bone
Structurally, the pelvis can be divided into three main sections
The ilium, the broad, wing-like part of the pelvis
The pubis is at the front
And the ischium is positioned at the back
And the hip bones,
the pubic and sitting bone, respectively
Those are the two
You can see how the ilium supports the internal organs
So what role do the pubis and ischium serve?
In quadrupedal animals like dogs and cats,
when they sit, their abdomen rests on the ground
Because of this, their internal organs are supported by the surface beneath them
Since their upper body weight is spread over a broad area, the pressure isn’t as significant
However, humans sit with only their buttocks touching the ground
This means that all upper body weight is concentrated in this area,
requiring additional structural support
That’s where the pubis and ischium come in
The pubis is the attachment point for the inguinal ligament, connecting the abdomen to the legs
This line extends from the ilium
to the pubic bone
It will appear frequently in future discussions
The inguinal ligament is a key structural landmark when drawing the lower body
We will cover it in more detail later
Now, let’s take another look at the entire skeletal structure
How is it?
Does it look a bit different now?
Let's summarize
The spine follows an S-curve
The ribcage has an upright egg shape
The sternum
resembles a tie in both shape and position
Above it, the clavicle
is securely connected
The clavicle serves as a reference line for the torso
The pelvis has a basin-like structure
And the inguinal ligament forms a key dividing line
between the torso and the legs
That’s all for bones
Now, let’s move on to muscles
Wow, this is getting complicated
But actually, what you see here
is just the surface layer of muscles
Muscles are layered, at least two, sometimes up to four or five layers deep
This intricate layering evolved
to allow for complex movement
But we’re not going to dive into every detail
To understand why the body's contours appear as they do,
you don’t need to memorize every single muscle
So, let’s break it down step by step
Neck muscles first
The neck is the closest connection between the face and torso,
so it’s one of the most commonly drawn areas
A key landmark here is
the sternocleidomastoid muscle (SCM)
This muscle runs along the side of the neck
It plays a crucial role in bending and rotating the neck
You're familiar with cylinders, right?
Think of two cylinders moving organically together,
creating three-dimensional motion
At a glance, you might think
the SCM muscle starts from the transition between the face and neck,
but it actually originates behind the ear,
extending down toward the clavicle
Rather than being a single rope-like structure,
it's more like a broad, slightly twisted sheet, like fen haozi noodles
Take a look here
See how it's not a simple line?
It flattens and fans out, attaching along the clavicle
Rather than just a contour,
it's a layered, three-dimensional shape
If you want to add more detail to your depiction of the SCM,
notice how
these additional lines
are there, aside from the main line,
creating a subtle sunken effect
At the bottom, the edges of the muscle also form visible ridges
Now, let’s talk about another key feature, the Adam’s apple
The thyroid cartilage acts as the gatekeeper of the throat, forming a protective structure around the larynx
This cartilage extends forward to create the laryngeal prominence,
commonly known as the Adam’s apple
appearing as a noticeable bump below the jaw
This feature is much more pronounced in men,
creating a distinct protrusion just below the jawline
In contrast, in women, the prominence is much less visible,
resulting in a smoother, uninterrupted neck contour
When drawing the Adam’s apple, keep in mind
that it isn’t just a random bump on the neck
It aligns directly under the jaw
At the back of the neck,
the trapezius plays a crucial role in shaping the upper body
This broad, triangular muscle
extends from the base of the skull,
runs down along the spine,
and spreads out over the shoulders
It is more commonly emphasized in depictions of masculine physiques
As this muscle develops,
it creates a thick and sturdy neck,
reinforcing the impression of strength and power
For a delicate or slender look
minimizing the prominence of the trapezius is key
Now, let’s move on to the chest
The pectoralis major
is the most noticeable muscle in this region,
but it contributes more to arm movement than to torso structure
There are two key muscles here
Serratus anterior
And pectoralis major
as the next one
These are the two types
The serratus anterior is located beneath the pectoral muscles,
attaching along the ribs
in a saw-like pattern
Notice how it is attached along the ribs here too
When we do push-ups, it plays a key role
in pulling the shoulder blades forward
Although it’s often hidden beneath the pectoralis major,
understanding its placement
is important because
it interacts closely with the external oblique muscles
I will delve into it later
Now, the alpha and omega of the upper body,
the chest muscles
Let's take a look at the pectoralis major
It originates from the clavicle and the sternum
Remember the tie-shaped bone?
It extends from there,
moving downward
and on
Here,
it spreads in three sections before attaching to the humerus
Isn't this surprising?
When I first learned this, I thought,
Why does the chest muscle attach to the arm?
Even though this muscle connects to the arm bone,
it doesn't make the arm look shorter
That was my impression
But the pectoralis major
is responsible for pushing movements,
like in push-ups
So, naturally, it needs to be connected to the arm bone
Pay attention to how the pectoralis major shifts when the arm is raised
When the arm lifts,
the muscle twists
and tucks in at the end of the bone,
following the contours of the raised arm
Observing these shape changes
will help deepen your understanding of chest muscles
Now, let's take a look at the abdominal muscles
You all like six-pack abs, right?
Has anyone here successfully uncovered theirs?
I really envy you if you have
Personally, I've never managed to reveal mine
Instead, I've packed my belly with plenty of warmth
The abdominal muscles play a crucial role in moving the upper body forward
and side to side while also supporting respiration
Rectus abdominis,
is also known as the six-pack muscle
External oblique
is also called the outer abdominal muscle
These are the key muscles
Here, you can see the rectus abdominis
and the external oblique
First, the rectus abdominis
This is the muscle responsible for that six-pack look
When developed, it makes the front of the torso stand out
and is activated in intense abdominal contractions like sit-ups
It starts from the sternum, the chest bone
and extends downward, connecting to the pelvis and pubic bone
Earlier, when I talked about the chest bone,
I mentioned how this muscle prevents the internal organs from spilling out
The reason the rectus abdominis has this distinct bulging, segmented appearance
is to efficiently distribute muscle mass over a broad area
Remember this from last session?
If it were structured like arm muscles,
with fibers running continuously in a single direction,
it would be too long and inefficient for movement,
if not the sit-ups at all
That's why tendinous intersections divide it into segments,
creating the six-pack shape
Now, let’s look at the external oblique muscle
This muscle is responsible for the rotation and lateral bending of the torso
It starts at the lower ribs and, similar to the rectus abdominis,
follows a boundary as it moves downward
It attaches near the abdomen and continues to the fascia
As mentioned earlier, this area is important
because it works with the serratus anterio to define the muscle structure of the upper body
The external oblique
overlaps with the serratus anterior,
like this,
creating a layered effect
Behind them, we have the latissimus dorsi,
and in front of that, the pectoralis major
These are some details you can have
with these overlapping layers of muscle
And behind it, there is always the latissimus dorsi
And then behind that, there is the large back muscle
And in front of that,
there is the rectus abdominis
When you draw the front part, try drawing this section as well
Once you draw it, you’ll likely find it enjoyable
This was the muscle of the torso for the front view
Now, let’s look at the back muscles
What does it mean when we show the back in a scene?
Depending on the situation, it can convey various nuances
It could be the image of someone coldly leaving, showing their back
It could also show the developed back muscles,
symbolizing a strong, protective guardian
Or it might give off a mysterious or sexy vibe
Actually, I haven’t shown the back much in my works either
When it does appear, it’s usually with clothing
But when necessary, impactful scenes often require
detailed depictions of the human body
What am I trying to say?
It’s something you still need to know
Now, let’s move on to the back muscles
The primary muscles include the latissimus dorsi and the teres major
Also mentioned earlier, we have the trapezius
or the triangular back muscle
Let’s start with the latissimus dorsi
You might be more familiar with the term lat
This muscle is the widest in the back
and is responsible for moving the arms and shoulders
Are you familiar with pull-ups?
Many people think that pull-ups are done by arm strength,
but in reality, you can’t do them without developing this latissimus dorsi
The latissimus dorsi starts around the middle of the spine
and stretches down to the sacral bone
It continues upward and forms
a wing-like shape connecting to the upper arm bone,
specifically the humerus
When depicting male figures, this wide triangular shape is often used to express masculinity
This triangular shape forms the major silhouette of the back
It’s the same for the front view too
You might think that the large chest muscles define the silhouette,
but that’s not true
Right behind them,
the latissimus dorsi has to make its presence known
to truly complete the wide chest of a man
Similar to the chest muscles,
this muscle is also attached to the upper arm bone in a crosswise fashion
It attaches to the front part of the upper arm bone
So, the line from the latissimus dorsi, which starts from the bottom, attaches to the upper arm bone
And conversely, the line of the latissimus dorsi that attaches from the top connects like this
It’s the crossing point
When viewed from the side,
the latissimus dorsi aligns with the position of the serratus anterior
It overlaps with the upper layer at that location
If we draw the line, it would look like this
And above that, the pectoralis major covers it
Now, let’s look at the trapezius
The trapezius
This is the muscle we already discussed when talking about the neck
But here, we will examine its overall silhouette
As I mentioned before,
the upper part of the trapezius starts from the back of the skull,
extending to the shoulder blade
The spine of the scapula
And it connects all the way to the scapular spine
And it attaches along the ridge of the clavicle
Then, it continues in this direction
It forms a shape that drops from the shoulder blade area towards the spine
f you look again, here’s the scapula
This structure shows the clavicle connecting forward from the neck
It connects like this
As you can see, the structure of the trapezius muscle is,
simply put,
a structure where two triangles attach symmetrically
What you should focus on in the trapezius muscle is the muscle part and the fascia part
For the efficiency of movement,
like the rectus abdominis muscle, this muscle is also divided by fascia,
dividing the muscle into two parts
The fascia also forms a diamond shape
As you can see, the fascia forms a diamond shape
Therefore, the more you develop the trapezius muscle,
the more prominent the gap between the muscle and fascia will become
If you understand and describe this part, you’ll be able to better emphasize
the presence of the back muscles in your drawing
Oh, and earlier I mentioned that this part is fascia
Tendons
The protruding part of the seventh cervical vertebra appears here
Looking from the neck, the back of the head looks like this
And the part that drops is located here
Please also refer to this part
Now, we’ve finished with the bones and muscles of the torso
Now, let’s look at a few more details
Understanding the Other Torso Structures and Describing Poses
First, we’ve only focused on the muscles among the body’s outline
It feels incomplete
What might be missing?
Yes, that’s right
Our friend, fat
Most importantly, we haven’t covered the breasts in women
Let’s take a look
Women’s breasts are mainly made up of fat
While the shape and size vary from person to person,
let’s first go over the basic shape
The breast starts at the center of the large pectoral muscle,
like this
It attaches all over in a circular shape
o easily understand the outline of the breast,
think of a water pouch
And the opening of the pouch is like this,
it’s closely attached to the large pectoral muscle
The liquid inside, being a fluid, is affected by gravity
Therefore, depending on its position or interference, the shape changes freely
Let’s look at the breasts when standing
This is the breast
This position does not change
What about when lying down?
It’s the same
First, we establish the fixed position of the breast
It will be the pectoralis major
The breast starts from the pectoralis major
And the water pouch of the breast,
imagine that it stays in that position
If that’s the case,
The breasts will spread out like this,
retaining that shape from the spread
In this way, a woman’s breast
is, first of all,
a suspended water pouch
And second,
that water pouch is affected by gravity
If you understand these two points as the focus,
I think you won’t have much difficulty in drawing
Next, we move on to the pelvic bone
We covered this earlier, so why bring it up again?
The pelvic bone has a significant difference between males and females
Therefore, the key landmarks are different as well
Take a look
Here are the pelvic bones of males and females
What stands out the most?
Yes, the sizes are different relative to the torso
In men, the pelvic bones are more narrow compared to women
On the other hand, women have the last bone, the sacrum, that drops from the spine
Unlike men, women’s pelvic bones are wider and more expansive
Therefore, the femur of the thigh,
which is the femur,
the length of its neck in that area also differs
The reason for this difference is because women have a uterus
Not only the internal organs, but also the need to create space for a growing babㅛ
impacts the pelvic bones
The part in front of the pelvis is called the anterior superior iliac spine
This part is definitely pushed forward,
for the women
On the other hand, in men, it is slightly inward compared to a woman’s pelvis
It feels as though it rotates inward
While the iliac crest retreats further in men than in women,
the pubic bones,
which is this area,
extends more forward
So, when drawing the female pelvis,
the line that starts from the iliac crest
and drops towards the inguinal ligament is the key point
This is how it looks
To summarize, in the case of the female pelvis,
it is much wider and expands more horizontally than the male pelvis
And as you can see here,
to reiterate, the iliac crest is much more prominent than in men
When you draw the female pelvis, if you depict this bone part,
you can achieve a more accurate depiction of the pelvic area
Now, let’s examine the muscles of the torso based on different poses
First, let’s look at a pose with the arms raised, seen from the front
Let’s start with the neck
Here, we see the SCM muscle descending
Normally, the SCM falls in a straight line like this
Shall we add some details?
As mentioned, it bends and enters here
If we connect it to the collarbone like this,
the SCM muscle is complete
Behind it, the trapezius muscle is positioned like this
Next, focusing on the collarbone muscle,
and along the breastbone,
the pectoralis major muscle connects like this
Do you remember the T-shape I mentioned earlier?
Now, if you think of the raised arm on this side,
as I mentioned earlier,
the pectoralis muscles intersect and attach to the upper arm bone
That’s why the pectoral muscles extend like this
And the wide back muscles that came from behind
occupy the back like this
And the serratus anterior and external obliques
depict the crossing points of these muscles
Next,
the rectus abdominis is present like this
Finally, let’s look at the pelvic area
In males, due to the difference in muscle mass,
the side of the torso can protrude like this
Along that line, the pelvic crest protrudes like this
This is different compared to female pelvis
For women, it feels like the bone is protruding,
whereas for men, it feels like the muscle is folded
By doing this, you can depict this area
With that, the front view depiction is complete
Now, let’s move on to drawing the back view of the previous pose
First, let’s take a look at the trapezius muscle
The trapezius muscle, which runs from the back of the head downwards
Here, you can see the shoulder blade spine
Following the spine of the shoulder blade,
as I mentioned earlier, it wraps around like this
It follows and connects to the spine
And this is the trapezius muscle
You should already know this
When divided, the trapezius muscle
has a diamond-shaped fascia at the center, as I mentioned
This is the fascia
And in the center, there’s the protrusion of the seventh cervical vertebra
Below that, what do we have?
Yes, we have the latissimus dorsi
It pushes upwards like this
Everyone,
as you saw in the previous pose,
in this pose, one arm is raised
That’s why, as mentioned earlier, the large pectoral muscle
changes shape to follow the arm
And the wide back muscles are also attached to the arm,
which is why they curve and attach like this
They follow this upward curve
Draw the line of the latissimus dorsi for this part
And finally,
the line of the back
The back is mostly
made with tendon and fascia
As I mentioned, that’s why the line is more visible
This is how you depict the line
By doing so, ultimately,
you will be able to draw the outer contour
This is the final example
This pose is a mix of contrapposto
and twist
The arm is covering the torso
But this doesn't mean
that we can't draw it
because we can't see it
Let’s use our imagination
to figure out what goes where
First, let’s draw the torso
Let’s start with the parts covered by the arm
You’ll see the sternocleidomastoid muscle descending here
And the trapezius muscle will be going backwards
It will descend like this
However, because she is female, the size of the muscles
is being depicted a little smaller compared to the previous model
The pectoralis major muscle
does not show at all here
Because the collarbone and arm joints are not visible,
the starting point of the chest muscle is not visible
But we can still see that the chest muscles continue like this
And below that, there are shoulder blade muscles,
but we haven’t addressed them yet
Below that, we have
the latissimus dorsi, which rises from the back
that dives toward the armpit like this
At the same time, in the middle here,
is the rectus abdominis
It's the straight abdominal muscle
And now,
there is the navel at about the third joint
Please depict the navel
And finally,
tthe serratus anterior and external oblique
can be depicted like this
However, be gentle
Don't make it too intense
Just depict its existence, but don't overdo it
With that,
the twist pose for women is complete
There is one thing I missed
It is important
It's the pelvis
As I mentioned earlier, there is the iliac crest
We can’t leave out the iliac crest
From here,
the crest protrudes and reveals its presence
And as I mentioned before, the inguinal ligament,
this ligament crosses over,
and that line is visible on the skin
In this direction as well,
the iliac crest is visible,
and it connects with the inguinal ligament like this
With that, the depiction is complete
We have now covered the anatomy of the torso
It feels like we’ve been powering through it
I’m a bit exhausted too
Great job today, everyone
Thank you
Understanding the Bones and Muscles The Structure of the Human Body A total of 206 bones The shoulder, clavicle, and pelvis each belong to the limbs
Vertebral bones: Connect the head and torso, support the torso with the organs Rib bones: Protect the organs, connected to chest muscles
Xiphoid process: Connects the clavicle, between torso and the arms Scapula: Securely attaching the trapezius to the spine
Pelvic bone: Connects the legs and torso, supports the organs Pubic bone: Connects the inguinal ligament, separating the abdomen and legs
Clavicle: Baseline for the torso Sternocleidomastoid (SCM) muscle: Extends the side of neck to the shoulder, or bending or turning the neck
Serratus anterior: Attached in a serrated pattern along the upper chest bones Abdominal muscles: Forward and lateral movements of the torso
Rectus abdominis: When developed, visible and performs strong contraction movements External oblique: Rotating and bending the torso
Latssimus dorsi: Broadest muscle in the back, for moving arms and shoulders Trapezius: Two triangular muscles symmetrically attached
Other Torso Structures and Pose Depiction The breasts: Attached to the central part of the pectoral's major in a circle pattern
The pelvic bone differs in size The femur also differs in length Female pelvis: From the lilac crest and to the inguinal ligament
Depicting Various Poses SCM muscle: connect the form from the clavicle The chest muscles: Three strands on the upper arm Men: protruding sides
The latissimus dorsi is also attached to the arms, rising along the arm The back, with fascia, has its lines highlighted
When the arms are covering the torso, the SCM muscle should fall away, while the trapezius is descending along