LESSON - General Anatomy Primer (Part 2)

Part 1 - Basics and Neck: https://www.patreon.com/posts/lesson-general-125387198
Part 2 - Torso: You are Here
Part 3 - Arms and Legs: www.patreon.com/posts/134309486

FRONT TORSO

1. Pectorals
Aka pecs, tiddies, honkers, you name it; the pectorals are the star of the front torso. Being attached to the arm at its insertion, the pecs’ shape changes greatly depending on the position of the arms. See examples below.

The exact shapes in each position can vary between individuals, so make sure to do your studies!

Aside from that, because the pecs are resting on top of the ribcage, whenever the ribcage moves (such as when leaning or bending), the pecs move along with it.

All this to say, be careful not to mistakenly draw the pecs in its neutral shape when it’s supposed to be changing shape according to the pose.

2. Deltoids
The deltoids are a big muscle that covers the shoulder joint. It can be considered part of the torso, but also part of the arm muscle group.

It consists of three heads, the anterior/front head, medial/middle head, and posterior/rear head. They work together, but each head is more active during certain motions than others.

As can be seen above, the shape of the Deltoids changes dramatically depending on the position of the arms. In certain positions and angles, like when the arms are lifted, a part of it may even peek from under the armpit.

Since the Deltoids are located on the shoulder (and indeed is the shoulder), it moves along when the shoulder is rotated or raised in a shrug, as you can see below. Note how the rotation affects which heads of the deltoids are visible from a given angle.

Lastly, the Deltoids are usually key in making a character look “buff”. If your character is lacking a certain oomph, you might want to try making the delts bigger.

3. Trapezius
The Trapezius, aka Traps, are actually a part of the back muscle group. This muscle shows up above the pecs and deltoids.

For simplicity, I’ll include the minor neck muscles as part of the mass of the traps for the diagrams below.

The visibility of this muscle highly depends on the size of the muscle, and the angle of the torso relative to the camera. See the diagrams below for some examples.

The posture or bending of the torso can also affect how much of the traps is visible to the camera.

Lastly, note how the traps are connected to the top of the deltoids. Be careful not to draw them too narrow or too wide!

More about this muscle will be covered in the Back muscle section below.

4. Latissimus Dorsi
Like the Trapezius, the Latissimus Dorsi aka the Lats are part of the back muscle group, but unlike the traps, the Lats are very prominently visible, especially in poses where the arms are raised.

The lats are also prominently visible in poses where the shoulder is extended outwards, such as in the lat spread or double biceps pose in bodybuilding.

Bigger lats tend to be key in making a character look “wide”. If your character is lacking a certain oomph, enlarging the lats might do the trick! Keep in mind that you may need to adjust the surrounding muscles to keep things proportional.

More about this muscle will be covered in the Back muscle section below.

5. Abdominals
The Abdominals or abs, aka the six-pack, is the other star of the front torso. Its primary function is to flex the torso, bending it forwards, and to stabilize the torso, working together with the other muscles around it.

Despite being called the “six pack”, there’s actually eight sections in the abs, with the lowest sections going all the way to the crotch. The belly button is usually right above the lowest sections, but it may be a bit higher or lower depending on the individual.

The size and shape of the overall muscle also differs between individuals. Here are some examples.

The abs can get crunched/squished or stretched/extended based on the twist and rotation of the torso and hips, as well as the position of the legs. Though this motion is pretty limited, since the body's midsection doesn't typically bend all that dramatically (without hurting or being uncomfortable).

The Abs are actually pretty thin and flat. Even when a character gets really muscular, the abs don’t usually get as huge and juicy as the other muscles like the pecs or delts. Usually, they instead gain definition.

Of course, you absolutely can make them extra big and bulky if you want. This usually results in a roided or roidgut kind of look. Just be careful not to make them look like bread or dinner rolls.

Note, I’ve noticed a common quirk among artists is putting a gap between the pecs and the abs. This is a mistake! 

It may seem like there’s an area of Only Ribs right below the pecs, especially when the stomach is sucked in; but in reality, the abs still exist on top of the ribs, and they’re just overshadowed by the more prominent shape of the ribs.

The first few seconds of this video shows this in action: https://www.youtube.com/watch?v=Y9yF7Ih49K8 

Another note, be careful about overdoing the definition, especially using lines, as it may have the opposite effect and make the abs look drawn-on with a marker. Personally when drawing a defined set of abs, I do the lines sparingly, but carve out the shapes using shading and highlights instead.

6. Serratus and Obliques
The serratus and the obliques are groups of muscles that make up the sides of the midsection. They're most visible at the area where they intersect, right below the lats.

This criss-cross pattern happens because both the serratus and the obliques are made up of smaller muscles, and the obliques thread through the gaps between the serratus muscles.

Note, be mindful that it’s easy to overdefine this area, especially with lines. I personally do it similar to the abs, where I do the lines sparingly and use shading and highlights to define the shapes.

If you’ve ever heard the term “Adonis belt”, or sometimes more vulgarly, the “cum gutters”, this refers to the External obliques. Specifically, the lowermost obliques which sit on the hipbone, creating the V-shaped line that goes from the sides of the body into the crotch.

This line may be subtle or defined depending on how well-developed the character’s obliques are.

BACK TORSO

Before going into the muscles itself, I’d like to touch on the nature of the Scapula/shoulder blade.

The scapula/shoulder blade is a floating bone, that is to say, it isn’t anchored to the spine by another bone, and is instead anchored only by muscles. This means that it is very mobile, and can move much more freely compared to other bones in the torso. See animations below:

I made a little youtube playlist with some real life examples of these motions (plus a 3D animation of just the bones): https://www.youtube.com/playlist?list=PL0BwTEHHmBudN7Cpj0zbpGDIh1VBVZTRp

Because of the Scapula's mobility and its connection with the shoulders and the arms, the back muscles changes shape a lot based on the arm's position. Don't default to drawing the back in the neutral position! Make sure to pay attention to how they would change in each pose! See examples below:

1. Trapezius

The Trapezius is a large muscle that dominates the upper back region. The muscle originates along the spine, and mostly inserts onto the upper ridge of the scapula, with some of the uppermost fibers wrapping around the shoulder and attaching to the clavicle. 

Because this muscle’s function is mainly to do with the scapula, whenever the scapula moves (such as when moving your shoulder or arms), this muscle would flex accordingly. 

The upper, middle, and lower fibers have specific functions, as shown below.

Be mindful that because this muscle is attached to the spine, its shape may also change based on the current posture of the torso, even if otherwise they’re in a neutral state. This is true for the lats as well.

2. Latissimus Dorsi

The largest muscle in the body in terms of surface area, the Lats dominate the lower back region. This muscle originates in the spine, but then wraps around from under the arms, and inserts into the humerus around the armpit area. 

Due to its sheer size, the lats are usually visible in most angles, even if only partially. Though it can be obscured by the arms, as shown below.

When the arms are raised, the lats make up the huge, wing-like silhouette under the arm. This is most prominently visible from a frontal or back angle, but even from the sides it can still look pretty striking, as shown below:

3. Scapular Group

Not a scientific term, but the scapular group consists of the muscles that exist on the scapula; the most visible of which are the Teres Major and Infraspinatus. These muscles have their own function, primarily to stabilize or rotate the shoulder, but for the purposes of art, they are simply an indicator of the scapula’s position and rotation.

Note: The scapula and the deltoids (and the arms) are directly connected, so make sure you don’t separate them!

4. Hidden Muscles

There are many back muscles that are not visible due to the Traps, Lats, and Scapulae obscuring them. For the purposes of art, I’m only going to talk about two of them: the Rhomboids and the Spinal Erectors.

The Rhomboids are located under the traps, connected to the scapula. They’re only visible from a small triangular window between the lower traps, scapulae, and the lats, as shown below. For the purposes of art, it’s not super important to remember their function.

As for the Spinal Erectors, they are actually a group of several muscles (the spinalis, longissimus dorsi, and the iliocostalis), that run all along the middle of your back, from the back of the skull to the base of the tail bone.

This muscle is functionally the opposite of the abs, where the abs flex to crunch the body forward, the spinal erectors flex to straighten or arch the body backwards.

Despite being mostly covered by the traps and lats, this muscle is thick enough to be somewhat visible in the lower back, where the lats are thinnest, especially in certain poses as shown below.

5. Deltoids

As already explained in the front torso section, the Deltoids can be considered a part of the torso, but also part of the arm muscle group.

From the back, the rear head is usually the most visible, but the middle and front heads may be visible based on the angle and the position of the arm.

6. External Obliques

Though not strictly a part of the back muscle group, the external obliques make up the sides of the lower back. When viewing a character from the side, you can actually draw the obliques wrapping from the back, all the way to the front where it meets with the abs.

7. Glutes

The butt, the booty, the dumpy, etc; the Glutes are not strictly a part of the back muscle group, moreso a part of the leg muscle system. Even so, this muscle is often the highlight of back angles.

Since the glutes connect the torso with the legs, its shape changes based on the position of the two.

More information about this muscle will be covered in the Legs section in Part 3.

Next Part

Part 3 - Arms and Legs: https://www.patreon.com/posts/134309486

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As always, if you have any questions, feel free to hit me up in the Art Labs channels in the AA Labs discord!